Kinetic determinations and some kinetic aspects of ... - ACS Publications

Anal. Chem. 1980, 52, 31 R-40R (33) Honda, S.; Fukuhara, Y.; Kakehi, K. Anal. Chem. 1978, 50, 55-9. (34) Hurtubise, R. J.; Skar, G. T.; Poulson, R. E. Anal. Chim. Acta 1978,97, 13-19. (35) Hwang. T. K.; Miller, J. N.; Burns, D. T.; Bridges, J. W. Anal. Chim. Acta 1978. 99. 305-15. 136) Jordi. H. C. J . Lia. Chromatoar. 1978. 7 . 215-30. (37j Khalaf, H.;Rimpkr, M. Fresehus' 2 . Anal. Chem. 1979, 294, 286; Chem. Abstr. 1979,90, 132366s. (38) Khan, G. R.; Scheinmann, F. Prog. Chem. Fats Other Lipids 1978, 15, 343-67. (39) Khrenova, 0. N.; Krylova, L. P.; Zhukovskaya, L. N. Metody Anal. Kontrolva Kach. Prod. Kim. Prom-sti. 1978,52-4; Chem. Abstr. 1978,89, 164243~. (40) Kiba, N.; Suto, T.; Furusawa, M.; Takeuchi, T. Therm. Anal. [Proc. Int. COnf.1 5th 1977,38-41; Chem. Abstr. 1978,89,2 0 8 6 6 8 ~ . (41) Kobayashi, K.; Tanaka, M.; Kawai, S.; Ohno, T. J. Chromatogr. 1979, 176, 118-22. (42) Kornarek, K.; Ventura, K.; Smrcek, 2 . ; Churacek, J.; Janak, J. Collect. Czech. Chem. Commun. 1978, 43, 1863-6. (43) Komarek, K.; Ventura. K.; Smrcek. Z.; Churacek, J.; Janak, J. J. Chromatogr. 1978, 154, 191-6. (44) Koppe, P.; Dietz, F.; Traud, J.; Ruebelt, C. Fresenius' 2. Anal. Chem. 1977,285, 1-19; Chem. Abstr. 1977, 87,1891279. (45) Kostyla, R. J.; Mourey, T. H.; Cohen. R.; Merritt, M. E.; Simmons, K.: LaFaucia, R.; Limentani, G.; Washburn, D. N.; Siggia, S. NBS Spec. Publ. ( U . S . ) 1979, 519 (Trace Org. Anal.: New Front. Anal. Chem.), 783-7. (46) Kostyukovskii, Ya. L.; Melarned, D. G.; Pokrovskii, A. A. Zh. Anal. Kbim. 1978,33,808-11; Chem. Abstr. 1978, 89,84377b. (47) Kosugi, Y.; Takeuchi, T. Bull. Chem. SOC. Jpn. 1978, 57, 2008-11. (48) Krull, I. S.; Goff, E. U.; Hoffman, G. G.; Fine, D. H. Anal. Chem. 1979, 51, 1706-9. (49) Laird, R. M.; Strophair, A. J. flectroanal. Chem. Interfacial Electrochem. 1978, 90,283-9. (50) Lam. S.; Grushka. E. J . Chromatogr. 1978, 758,207-14. (51) Lanovaya, G. A.; Fedorova, V. A.; Beresneva, V. I. 3 .Anal. Khim. 1977, 32, 1206-9; Chem. Abstr. 1977,87, 1932922. (52) Lapshova, A. A.; Kupreeva. G. S.; Strukova, M. P.; Chechetkina, L. N. Zh. Anal. Khim. 1977. 32, 1816-19; Chem. Abstr. 1977,87,2028202. (53) Loginova, N. K.; Kuzentsova, R. A.; Fei'dblyum, E. M. Prom-st. Slnt. Kauch. 1978,89,7 3 6 6 ~ . (54) Marhevka, J. S.; Siggia, S. Anal. Chem. 1979,51, 1259-62. (55) Mattsson, M.; Peterson, G. J. Chromatogr. Sci. 1977, 15,546-54. (56) Melamed, D. B.; Kostyukovskii, Ya. L. G/g.Sanlt. 1978,67-8; Chem. Abstr. 1978,89, 152381a. (57) Monarca. S.; Causey, B. S.; Kirkbright, G. F. Water Res. 1979, 13,503-8. (58) Mutton, I. M. J. Chromatogr. 1979, 172,435-7. (59) Obtemperanskaya, S. I.; Bitar, A. Zh. Anal. Khim. 1977,32, 1856-8; Chem. Abstr. 1978, 8 8 , 1148649. (60)Ohkura, Y.; Ohtusubo, K.; Zaitsu, K.; Kohashi, K. Anal. Chlm. Acta 1978, 99,317-24. (61) Ohshima, H.; Matsui, M.; Kawabata, T. J. Chromatogr. 1979, 169, 279-86. (62) Osis, J.; Andersons, H.; Shimanskaya, M. V. Latv. PSR Zlnat. Akad. Vestis, Kim. Ser. 1978,445-51; Chem. Abstr. 1979, 90. 2 1 6 7 5 ~ .

(63) Parees, D. M. Anal. Chem. 1979,51, 1675-9. (64) Perirnutter, P.; Shtrikman, S.; Slatkine, M. Appl. Opt. 1979, 18,2267-74. (65) Pilipenko. A. T.; Kaiinichenko, E. I.; Matveeva, E. Ya. Zh. Anal. Khim. 1977,32,2014-17; Chem. Abstr. 1978,88, 130465h. (66) Pokrovskii, A. A.; Kostyukovskii, Ya. L.; Melarned, D. B.; Medvedev, F. A. Zh. Anal. Khlm. 1978,33,970-74; Chem. Abstr. 1978. 89,139989. (67) Ponomarenko; A. A.; Obukhova, E. N. Zh. Anal. Khlm. 1977,32,2233-8; Chem. Abstr. 1978, 88, 163428b. (68) Pwle, C. F.; Singhawangcha, S.; Zlatkis, A. Analyst(London)1979, 104, 82-6. (69) Qureshi, M.; Khan, I. A. Fresenius' 2. Anal. Chem. 1978,289,282-4. (70) Rawat, J. P.; Singh, J. P. Indian J. Chem.. Sect. A 1978, 16,551-2. (71) Reddy, J. V. K.; Boparai, K. S. J. Indian Chem. SOC., 1977, 54. 752-3. (72) Robinson, J. W.; Nettles, D. Spectrosc. Lett. 1978, 1 1 , 73-88. (73) Sauerhnd, H. D.; Stadeihofer, J.; Thorns, R.; Zander, M. &mpend.-Msch. Ges. Mineraloelwiss. Kohlechem. 1978, 76-77,961-7; Chem. Abstr. 1977, 87,210687b. (74) Sawicki, E.; Sawicki, C. R. "Aldehydes-Photometric Analysis, Vol 5: Formaldehyde Precursors"; Academic Press: London, 1978. (75) Schabron, J. F.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1979,57, 1426-33. (76) Schmeltz, I.; Brunnemann, K. D.; Hoffman, D. Prev. Detect. Cancer, [Proc. Int. SYmp.1, 3rd 1976,1, Nieburgs, H. E., Ed.; Dekker: New York, 1978; Volume 1, pp 1973-92. (77) Schweiahardt. F. Retcofskv. H. L.: Friedman. S.: Houah M. Anal. Chem. 1978, 50:368-71. (78) Selig, W. Fresenius' 2 . Anal. Chem. 1979,296,396-9. (79) Selig, W. Report 1977,UCRL-52393 Avail. NTIS. (80) Siggia, S.; Hanna, J. G. "Quantitative Organic Analysis Via Functional GrouDs". 4th ed.: Wilev: New York. 1977. (81) Sleevi, P.; Glass, T.-E.; Dorn, H. C. Anal. Chem. 1979,57, 1931-4. (82) Snider, B. G.; Johnson, D. C. Anal. Chim. Acta 1979, 106, 1-13. (83) Swokina, A. N.; Kuznetsova, E. Ya.; Sorokin, V. P.; Shologon, I. M. Zavod Lab. 1978. 44,406-8; Chem. Abstr. 1978, 89, 6940r. (84) Srivastava, A.; Bose, S. Talanta 1977,24, 517-18. (85) Thomas, D. W. Appl. Spectrosc. 1977,31,515-16. (86) Thorns, R.; Zander, M. Erdoel Kohle. Erdgas, Petrochem. 1977, 3 0 , 403-5. (87) Tiwari. R. D.; Srivastava, G.; Misra. J. P. Mikrochlm. Acta 1978, 7 , 459-64. (88) Trischler, F. J . Therm. Anal. 1979, 16, 119-22. (89) Tully, W. F.; Kuryia, W. C. Microchem. J . 1979, 24,62-3. (90) Underwood, A. L. Anal. Chlm. Acta. 1977,93,267-73. (91) Veiikov, B.; Doleral, J.; Zyka, J. Anal. Chim. Acta 1977,94, 149-54. (92) Voi'berg, N. Sh.; Gershkovich, E. E.; Stykan, T. P. Otkryriya. Izobret., Prom. Obraztsy, Tovarnye Znakl1978, 55,157; Chem. Abstr. 1978,89, 36222a. (93) Wiechmann. M.; Hoppe-Seyler's 2 . Physiol. Chem. 1977,358,981-4. (94) Williams, R. J.; Siggia, S. Anal. Chem. 1977, 49,2337-42. (95) Wong, M. P.; Connors, K. A. Anal. Chem. 1978,50,2051-4. (96) Yamashita, S . ; Sando, K.; Koshjiya. S. J . Appl. Poiym. Sci. 1979,23, 1951-62. (97) Yoshirnura, C.; Miyamoto, K. Bunsekl Kagaku 1979, 28, 1-4; Chem. Abstr. 1979,90,21477). .

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Kinetic Determinations and Some Kinetic Aspects of Analytical Chemistry Horacio A. Mottola Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078

Harry B. Mark, Jr. Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 4522 1

The topics discussed in this review have been selected from reports which appeared in the literature since the previous Annual Review ( 1 )through approximately November 1979. The organization of treatment is basically the same as that of the 1978 Annual Review. As usual catalytic determinations heavily outweigh other applications of kinetics in chemical analysis. Roughly ten times as many applications of catalysis have been published as applications of differential reaction rate methods or uncatalyzed systems, and this count does not include enzymatic methods. Also, as in the past, the heavy 0003-2700/80/0352-3 1R$01 .OO/O

contributors to the literature of catalytic methods are Russian chemists. The number of papers describing catalytic methods is slightly over 100 in the past 2 years, about the same output rate as observed in the past 6 years.

BOOKS AND REVIEWS An increased academic interest in kinetics in analytical chemistry is reflected in the inclusion of the topic in several textbook and miscellaneous publications. A chapter on kinetic methods is part of the most recent textbook on instrumental 0 1980 American Chemical Society

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KINETIC ASPECTS OF ANALYTICAL CHEMISTRY

analysis (2). A recent publication of the Division of Analytical Chemistry of the American Chemical Society, of historical nature ( 3 ) ,and the fourth edition of a classic on the colorimetric determination of traces of metals ( 4 ) have made room in their pages for mention of kinetic determinations. The second edition of the monumental “Treatise on Analytical Chemistry” carries a chapter on the application of kinetics and catalysis to analysis (5), and an overview of catalytic methods has found a place in a heterogeneous collection of papers edited in memory of the late Anders Ringbom (6). A review in Japanese on the determination of chemical species at trace levels by kinetic methods using photometric monitorin has been published by Fukasawa and Yamane (7). Albrecht-8ary and Schwing (8) have written an updated review on kinetic methods in analytical chemistry; this review is directed to industrial engineers. A comprehensive classification and critical evaluation of kinetic methods used in clinical analysis has been written by Pardue (9). A short review [3 pages, 8 references] by Kreingol (10) deals with the analysis of semiconductor materials, the use of complexing agents in kinetic analysis, and the determination of organic species by kinetic methods. Limits of detection for the determination of traces of elements in natural waters using kinetic procedures have been reviewed by Nabivanets and Kalabina (11). Factors affecting the selectivity of catalytic determinations have been considered a t some length by Otto, Mueller, and Werner (12). Particular attention was given to the enhancement of selectivity by combination of separation procedures and catalytic determination with special consideration to solvent extraction and catalytic reactions in mixed and pure organic solvents. An interesting review on chemical amplification including amplification by catalysis has been presented by Blaedel and Boguslaski (13). Chemical amplification results from catalytic, cycling, or multiplication mechanisms such as to generate a large amount of product.

CATALYZED REACTION RATE METHODS This continues to be the most popular approach in the literature of kinetic methods of determination. The low limits of detection affordable by simple technology are in part responsible for such wide interest; the widespread use of photometric monitoring and the almost endless availability of “indicator reactions” for single-species determination undoubtedly contribute to the popularity. As in the past redox reactions and transition metal ion catalysis dominate the applications that have appeared in the literature. Novel a n d Unconventional Catalytic Determinations a n d Applications of Catalysis. A rather simple and new method for catalytic determinations has been described by Weisz and Meinners (14). In this method, the reactants are originally dissolved, one in each of two immiscible liquid phases. The heavier phase is allowed to fall, drop by drop, through the lighter phase contained in a vertical glass tube. As drops fall, the reactants come in contact at the interface and produce changes in the drop. The length of fall required for completion of reaction (related to the time of reaction) is a measure of the catalyst concentration [e. . the decolorization of the drop in determination of &(II) by the Fe(11*)-Sz032indicator reaction]. If a gaseous product is evolved, such as Nz and Oz, it is adsorbed on the falling drop. As a result of this, the drop stops falling and rises again. The depth of fall or the time to return to the upper level is proportional to the catalyst concentration. This latter case is illustrated with the determination of thiosulfate by means of the Iz-azide reaction and the determination of Cu(I1) by its catalysis of the HzOz decomposition. Weisz et al. (15) have extended the application of simultaneous monitoring of catalyzed reactions with two independent indication systems. Accuracy and precision of the determination is said to be improved by this approach. These authors followed the iodine-azide reaction, catalyzed by sulfur-containing compounds, simultaneously by photometric and thermometric sensing in both closed and flow systems. The application of competitive reaction systems to catalytic determinations has been explored by Klockow et al. (16). The situation can be exemplified as follows: A 32R

+ B 2 PI

(reaction under study)

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kz

B + R-PZ (2) with kz >> kl, and involves coupling the slow catalyzed reaction (reaction 1) with a fast competitive reaction (reaction 2). Under selected conditions, the time for complete removal of the indicator substance (in this case species B) is dependent only on the rate of the catalyzed reaction and permits determinating the catalyst concentration. The principle of this approach, which is used in some enzyme-catalyzed determinations, has been applied by the authors to the determination of phosphate by means of the phosphate-catalyzed reduction of Mo(V1) by ascorbic acid. Ascorbic acid is the reactant B; as the fast competitive reaction the authors used its reaction with 12. The classical Sandell-Kolthoff reaction (oxidation of As(II1) by Ce(1V) catalyzed by iodide) continues to find uses and applications. Nachtmann, Knapp, and Spitzy ( 17 ) have used this reaction as a detection approach in high-performance liquid chromatography of iodine-substituted molecules. The post-column reaction system allows detection for the hormones tetra- and triiodothyronine in the subnanogram range, sufficient for their determination in human blood plasma. Biocatalyst (enzyme) electrodes containing an enzyme in an immobilized matrix in direct contact with the electrochemical sensor have received increased use in recent years. A new type of catalytic electrode for the amperometric determination of hydrogen peroxide has been introduced by Iwase et al. (19). This electrode consists of a polymeric material containing cobalt as a catalyst for the conversion of H202 The liberated oxygen is amperometrically detected by the electrochemical sensor to which the polymeric membrane is attached. The polymeric material is prepared by reactin Co(I1) acetylacetonate with electrochemically generate$ peroxide. The electrode behavior is independent of ionic strength (0.1-1.5 M) and pH changes (2.5-10.5), a definite advantage over electrodes based on enzyme immobilization. Linear relationship between current and hydrogen peroxide concentration from 0.2-2 mM was obtained in 0.1 M KCl a t 25 “C. Some metal ion catalysts have been determined by Pantel (20) by means of the pH-stat method. For the particular case of copper(II), the pH-stat method permits determinations in the 0.5-5.0 ng mL-’ range by use of the ascorbic acid-peroxydisulfate indicator reaction and addition of sodium hydroxide. This offers a distinct advantage over conventional determinations in closed systems. Each determination requires about 10 min. A determination of zinc ion with a limit of detection of 10 ng mL-’, based on restoring the catalytic activity of apocarbonic anhydrase, has been reported by Fuwa and coworkers (21). Since linear change in absorbance (at 348 nm, monitoring the product p-nitrophenol) was observed in the first 5 min after mixing reactants, the authors regarded the change in absorbance per unit time as a measure of the rate, translated this change to enzyme activity and used, as calibration plots, activity vs. amount of zinc. The paper includes some theoretical considerations. The method has been applied to the analysis of fruitjuices and water sample for zinc. Muller et al. have discussed the catalytic activity of Nbenzoylthioureas (22) and that of N-benzoylselenoureas (23) in the iodine-azide reaction. The catalytic activity of the derivatives is hindered by the oxidation of the catalyst in a side reaction with Iz. Using a competitive reaction with ascorbic acid made it possible to overcome this catalyst deactivation. Reaction with ascorbic acid maintains the I2 concentration at a very low level allowing the sulfur- or selenium-containing compound to exert its catalytic action during much of the measurement period. The use of a competitive reaction to restore the catalytic cycle permits investigating the catalytic activity and correlating it with structural features, and it also opens avenues for analytical determinations. The good sensitivity of catalytic methods have been exploited by Yatsimirskii e t al. (24) for the detection of gas or liquid leaks from pressure vessels. A catalyst is contained in the pressurized gas or liquid while an aqueous mixture of the reaction component is applied to the external surface of the vessel; the detection of the leak is based on a color change as the result of the catalytic effect. Two systems were tested: (1)the oxidation of CNS- by Fe(II1) in the presence of NOz-, the red iron-thiocyanate complex(es) being destroyed by the


Horacio A. Mottola was born in Buenos Aires, Argentina, and received undergraduate and graduate education at the University of Buenos Aires. He earned Licentiate and Doctoral degrees from the University of Buenos Aires and did predoctoral work with Professor Ernest 8 . Sandeli at tne University of Minnesota (Minneapolis). He spent two years at the University of Arizona (Tucson) as a postdoctoral research fellow in Professor Henry Freiser's research group. After teaching for two years at the University of the Pacific (Stockton, California), he joined OSU in the fall of 1967. Dr. Mottola's research interests include studies on the role of kinetics in analytical chemistry (including reaction rate determinations), analytical separatlons (solvent extraction and liquid-liquid chromatography), continuous-flow analysis, and analytical application of photochromism. More than 40 papers have resulted from this research, which is supported by NSF. Harry 6 . Mark, Jr., Professor of Chemistry and Head of the Department of Chemistry, University of Cincinnati, received his B.A. degree from the University of Virginia in 1956 and his Ph.D. degree from Duke University in 1960. He was a postdoctoral research associate at the University of North Carolina (with C. N. Reilley) from 1960 to 1962 and at the California Institute of Technology (with F. C. Anson) from 1962 to 1963. He was a member of the staff of the Department of Chemistry at the University of Michigan from 1963 to 1970, Visiting Professor of Chemistry at the Universiti, Libre de Bruxelles, 1970, and joined the staff at the University of Cincinnati in 1970. His research interests are in electrochemistry, surface chemistry, kinetic methods of analysis, environmental analytical problems, and instrumentation. I n addition to research papers, he is the co-author of the books "Kinetics in Analytical Chemistry", "Activated Carbon: Surface Chemistry and Adsorption from Solution", and "Simplified Circuit Analysis: Digital-Analog Logic". He is also a co-editor of the monograph series "Computers in Chemistry and Instrumentation", and "Water Quality Handbook", and a member of the Editorial Board of Analytical Chemistry, Analytical Letters. Chemical Instrumentation, and Talanta .

catalytic action of I,, and (2) the oxidation of o-toluidine by C103-; osmium as catalyst results in the formation of a blue color. Schurig and Muller (25)have determined iron in drinking water, a t a rate of 30 samples/h, by a catalytic automated procedure based on iron catalysis of the hydrogen peroxide oxidation of a p-phenetidine in presence of 1 , l O phenanthroline as "activator". The procedure was implemented for a segmented continuous-flow analysis system and was correlated with the manual colorimetric determination with 1,lO-phenanthroline; the correlation coefficient being 0.999 in the range of 0-2.0 mg Fe/L of water. Molybdenum in plant materials has also been determined by an automated catalytic method by Quin and Woods (26). The determination was based on the catalytic effect of molybdenum on the liberation of iodine from iodide by Hz02. The continuous-flow determination permits one to process 35 samples per hour with a detection limit (twice the standard deviation of the blank) of 0.01 ppm in plant material, using 0.25-g samples. Catalysts (enzymes or metal ions) can be determined in closed-loop systems only if, after signal detection, they are physically removed from the system or rendered inactive by an inhibitor. Successful removals of the enzyme glucose oxidase (by physical adsorption on phenoxyacetylcellulose traps) and copper ions (by controlled potential electrodeposition) have been described as examples leading to the determination of these catalysts by sample injection in closed-flow systems (27). The catalytic determination of copper combines a unique electrochemical removal of catalyst and simultaneous regeneration of the monitored species. Catalytic Determinations Based on Inhibition a n d Activation. Organic compounds containing thiol or thione groups inhibit the iron(II1) catalysis of p-phenetidine by eriodate in presence of 2,2'-dipyridyl. This inhibition has een used for the determination of thiourea, carbon disulfide, some dithiocarbamates, some pesticides, and mercaptans by

the method of tangents (28). Average detection limits are reported as 0.01 pg/mL. The catalytic effect of manganese ions on the periodate oxidation of antimony(II1) has been used for the direct determination of manganese in nonferrous alloys and for the indirect determination of nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA) (29). A variable-time procedure with an electronic double-switch network gave average errors and standard deviations of about 2%. NTA is known to act as an activator of manganese catalysis and thus can lower the limit of detection of Mn(I1). Manganese was determined in the range of 0.1-2 pug in the absence of NTA in comparison to 4-40 n in its presence. Inhibition of the catalysis by EDTA a n f D T P A as well as activation by NTA permitted determination of the ligands in the 10-7-10+ M range. The same authors have reported a series of methods of determination based on catalytic, activating, or inhibitin effects: manganese (in natural waters), osmium, and EDTX were determined using the periodate-acetylacetone reaction (30);iridium(II1) was determined on the basis of its accelerating effect on periodate hotodecomposition (31);chromium(II1) and osmium(VIIIfacce1erate the periodate-arsenite reaction and this effect was exploited for their determination (32).

a-Amino polycarboxylic acids and condensed phosphates inhibit the iron-catalyzed oxidation of p-phenetidine with HzO2. The inhibitory effect is due to complexation of the catalytic species b the inhibitor. The inhibitory effect has been used as the gasis for determination of the inhibiting ligand with a continuous-flow analyzer (33). Determination is possible in the 2.5 X M range with a relative standard deviation of about 2% in the middle concentration range. A new reaction for the catalytic determination of rhenium has been reported by Jordanov, Pavlova, and Stefanov (34). It is reported as involving the conversion of a-furil dioxime to di-cy-furildiketone in sulfuric acid medium in the presence of tin(I1) chloride as reducing agent. The reaction is presumably catalyzed by a sulfate complex of Re(1V). The authors suggest a fixed-time method which requires 20 min for reaction in the 0.05-0.5-pg range, 6 h for the 0.005-0.05-pg range, and 5 days for the 0.0005-0.01-pg range. They report that of several hydroxycarboxylic acids tested, citric acid exhibits a noticeable promoting effect, and describe the determination of rhenium in industrial copper concentrates, ores, and rocks. They also have been abie to determine molybdenum indirectly in plant materials and mineral waters because molybdenum inhibits the catalytic effect of rhenium. Suppression of a catalytic effect by complexation with an amino polycarboxylic acid such as EDTA and proportional restoration of the catalytic effect by Hg(II), which reacts with the ligand and liberates the catalyst, has been proposed for the determination of mercury in waste water (35). Two indicator reactions have been suggested for this purpose: (1) the HzOzoxidation of diphenylcarbazone catalyzed by Co(II), and (2) the IO - oxidation of o-dianisidine catalyzed by Mn(I1). The limit of detection and relative errors are reported as 2 x pg/mL and 3-lo%, respectively. No interference from other heavy metals and elements present in waste water is reported. A similar variant of the catalytic approach has been proposed by Dolmanova et al. for the determination of Hg(II), Pb, and Cd (36). The approach makes it possible to determine metal ions which normally are not catalysts (ions of nontransition elements). The indicator reaction was the oxidation of p-phenetidine by periodate catalyzed by Fe(II1) in the presence of 2,2'-dipyridyl; the inhibiting ligand was thiourea. Selenium and tellurium have been determined by use of their ability to increase significantly the catal tic activity of colloidal gold in the reduction of a cobalt-EDTI complex (37). The sensitivity and selectivity of the catalytic determination of vanadium when using as indicator reaction the oxidation of o-phenylenediamine by bromate ions is said to be improved by the presence of Tiron acting as activator (38). The inhibitory effect of lJ0-phenanthroline on the copper catalysis of autodecomposition of hydrogen peroxide has been used for the indirect determination of the inhibiting ligand (39).

Lazarou and Hadjiioannou (40) have determined citric acid in the 96-960-pg range by means of the iron(I1)-induced oxidation of the active citrate species C6H607-and C6H607*-by ANALYTICAL CHEMISTRY, VOL. 5 2 , NO. 5, APRIL 1980

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perbromate. The rate of the reaction is followed potentiometrically with a perbromate-ion-selective electrode (41). Tartaric and lactic acid interfere. The same authors (42) studied the iron(I1)-induced perbromate-iodide reaction and applied it to the determination of perbromate in microgram amounts and iron in nanogram amounts in presence of 1,lOphenanthroline as activator. Ethylenediamine-N,N,N’,N’tetraacetic acid (EDTA), diethylenetriaminepentaaceticacid (DTPA), and ethylene glycol bis(2-aminoethyl ether)-N,N,N‘,N‘-tetraacetic acid (EGTA) were determined in microgram amounts on the basis of their inhibitory effect. Analysis was accomplished by means of a variable-time procedure using potentiometric monitoring with an iodide-ion-selectiveelectrode. Avera e errors and relative standard deviations are reported as agout 1-270.

Catalytic Titrants and Catalytic End-Point Indication.

Catalytic end-point indications (also termed catalytic titrations or catalymetric titrations) involve (1)a titration reaction, in which a catalytic titrant is added to the sample and reacts rapidly and stoichiometrically with the sought-after species, and (2) an indicator reaction, which involves the monitored species and can only occur at a noticeable rate once an excess of titrant is present in the system. Although they can be viewed as applications of inhibition, because of their uniqueness, they are treated separately. The content of acids (including weak acids such as phenol) in straight-run and air-blown petroleum bitumens was determined by nonaqueous titrimetry and catalytic-thermometric end-point indication (43). The results were compared with those obtained by potentiometric titrimetry. Catalytic-thermometric end-point indication has also been used in the determination of Ag(I), Hg(II), and Pd(I1) ( 4 4 ) . Iodide was the catalytic titrant and the Mn(II1)-As(II1) reaction was the indicator reaction. Relative errors of 3% are reported for the determination of 0.5-500 pg of silver and mercury, and 0.2-500 kg of palladium. Titrations of fluoride and silicofluoride with thorium nitrate (50% ethanol, acetate buffer of pH 3.6) as titrant have been reported (45). Excess of titrant (thorium ions) triggers the indicator reaction, that of hydrogen peroxide and iodide, whose rate can be followed amperometrically, potentiometrically (at a small constant current), or spectrophotometrically. The same authors described the application of amperometric and potentiometric detection to follow the course of titrations with catalytic end-point indication (46). This was illustrated with the titration of EDTA using copper(I1)as catalytic titrant and the decomposition of hydrogen peroxide in basic medium as indicator reaction. Valcarcel et al. (47) proposed a new indicator reaction for the titrimetric determination (with catalytic end-point indication) of amino polycarboxylic acids such as ethylenediamine-N,N,N’,N’-tetraacetic acid (EDTA) and 1,2-diaminocyclohexane-N,N,N’,N’-tetraacetic acid (DCTA) and, indirectly, some metal ions [those of Ni(II), Hg(II),and Fe(III)]. The indicator reaction involves the oxidation, by iodate, of 1,4-dihydroxyphthalimide dioxime. Nickel(I1) catalyzes this oxidation and can be used as a catalytic titrant. Nitrilotriacetic acid (NTA) and ethylene glycol bis(2-aminoethyl ether)-tetraacetic acid (EGTA) cannot be titrated because they enhance the Ni(I1) catalytic action. The same approach, manganese(I1) as catalytic titrant, and the aerial oxidation of 1,4-dihydroxyphthalimidedithiosemicarbazone as indicator reaction have been also reported by Valcarcel et al. (48) for the semiautomatic titration (with catalytic end-point indication) of EDTA and manganese(I1) and nickel(I1).

Catalytic Determinations Based on Heterogeneous Catalysis in Electrode Reactions. Although the bulk of catalytic determinations involves homogeneous systems, a few based on heterogeneous, electrochemical systems have been reported. Molybdenum(VI), for instance, reduced at -0.48 vs. the SCE (pH 2.1, 0.1 mM NazMo04, and 0.1 M KC1) produces a deposit on mercury and graphite which selectively catalyzes the reduction of nitrite ions (49). Nitrate does not interfere up to a 100-fold excess. Linear potential scan voltammetry was used (70 mV s-l). The peak current at -0.88 V was measured from a base line obtained by extrapolation of the current decay of the 4.48-V molybdate reduction peak out to 4 . 8 8 V. The peak current is a linear function of nitrite concentration in the range 0.01-1 mM. 34 R

ANALYTICAL CHEMISTRY, VOL. 52, NO. 5, APRIL 1980

A highly selective determination of uranium by differential pulse polarography measuring the catalytic peak of nitrate reduction ( N 1 V vs. a Ag/AgCl electrode) has been reported by Keil (50). The detection limit is about 1 p b of uranium and the relative standard deviation for 100 pp! amounted to 2%. Polarographic determination was effected after extraction of the uranium with 1%Ph,AsO in CHC13. Adsorbed iodine at a platinum electrode acts as a catalyst for the irreversible electrochemicalreduction of chromium(V1) in acidic media. This catalytic effect has been exploited to develop a coulometric flow-through electrode which permits Cr(V1) determination in the range of 0.4 ng to 80 pg and without interference from a large number of inorganic species including dissolved oxygen (51). Titanium(1V) has been determined in high-purity red phosphorus by monitoring polarographically the catalytic current developed in the presence of 0.1 M oxalic acid and 0.08 M KCIOB(52). The limit of detection is reported as 4 X lo-’ M titanium. The presence of 100-fold excess Fe, Zn, Cu, Ni, Co, Pb, Cr, Mn, and Sn did not interfere.

Additional Determinations by Primary Catalytic Effects. Several new indicator reactions and applications of primary (direct) catalytic determinations have been reported in the past 2 years. The reaction between 2,2’-diquinoxalyl and Ti(I1) or Ti(II1) is catalyzed by Cu(I1) and Fe(II1) and has been used for the catalytic determination of these species in spectrally pure salts (53). Determination in the 104-10-5% range was accomplished by the method of tangents for copper and the fixed-time procedure for iron (measurements after 4 min of reaction). Relative errors are reported as 40%. Dickson and Svehla determined vanadium (0-0.6 ppm) by a method based on its catalysis of the reaction between bromate and bromide at a pH of about 1.8 ( 5 4 ) . The reaction was potentiometrically monitored and the reciprocal of the reaction time showed a linear dependence on vanadium concentration. Of chemical interest is the observation that no bromine is formed but, in a two-step process, hypobromite is produced. Vanni and Amico (551, after reporting on some kinetic observations on the catalytic effect of Cr(V1) on the oxidation of aniline by chlorate, suggest this system for the determination of Cr(V1) in the range 0.05-0.5 ppm. The catalytic behavior was observed to be more pronounced in chloride than in sulfate medium; chromium(II1) does not interfere but iron, vanadium, and copper do. The effect of aqueous dimethylformamide, acetone, ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol on the Cr(II1) catalysis of the H 2 0 2oxidation of o-dianisidine has been studied (56). Aqueous dimethylformamide and aqueous acetone provide the best solvent media for catalytic determination of chromium. The sensitive and selective determination of Mn(I1) based on its catalytic effect on the periodate oxidation of the triphenylmethane dye malachite green has been applied to the determination of traces of manganese in high-purity selenium (57). Selenium was separated by heating in a quartz boat (600 “C) in an air stream; the selenium, expelled as dioxide, was absorbed in a water trap. Manganese was determined in the residue after acid dissolution and adjustment of pH to 3.8 (acetate buffer). The same authors also reported the determination of traces of manganese by a method based on its catalytic effect on the oxidation of hydroxynaphthol blue by hydrogen peroxide (58). Vanadium in air-borne particulate matter (collected on Millipore membrane filter), after wetzshing and ion-exchange chromatographic separation, was determined by a catalytic procedure exploiting the vanadium catalysis of the gallic acid-bromate indicator reaction (59). Trace amounts of Mn(I1) have been determined by a method based on its catalysis of the atmospheric oxidation of 1,4-dihydroxyphthalimidedithiosemicarbazone ( 6 0 ) . Measurement of the rate of oxidation of Azorubin S by HzOzhas been proposed for the determination of Mn(II), Mo(VI), and W(VI), which catalyze the reaction (61). The oxidation of lumomagneson with HzOzis catalyzed by Mn(I1)-carbonate complexes and is proposed as a selective indicator reaction for the determination of Mn(I1) (62). The hydrogen peroxide oxidation of o-dianisidine in aqueous dimethylformamide is another indicator reaction proposed for the catalytic determination of Mn(I1) (63).


Kawashima e t al. have determined iron in nanogram amounts based on the catalysis of p-anisidine and N,N-dimethylaniline oxidation (64). A fixed-time method (the reaction was ice quenched after 60 min) was used and linear workin curves are reported in the range of 6-20-ng iron. The methof of tangents has been applied by Vasilikiotis et al. (65) to the determination of iron based on its catalysis of the H202 oxidation of p-aminophenol. Iron a t concentration levels of pg/mL have been determined with relative about 5 X errors of about f1.6%. An electrochemical sensor for oxygen consisting of a silver cathode, a lead anode, and a 0.1 M NaOH as electrolyte has been used to follow the oxidation of gallic acid in basic media which is catalyzed by cobalt(I1). This permits the determination of the catalyst in low concentrations (66). A fixed-time determination of cobalt has been proposed based on its catalytic action in the H202.0xidation of gallocyanin (67). Cobalt can be determined by this method in the 0.2-2.4-ng/mL range. Since the oxidation of 1-naphthylamine by peroxycapric acid in basic medium is catalyzed by nickel ions, a method was proposed for nickel with a limit of detection of 0.1 pg/mL (68). In the past 2 years, more catalytic applications and new reaction systems have been proposed for copper than for any other element. Kormos and Svehla (69) have determined traces of copper by a method based on the catalytic effect of copper on the reaction between peroxodisulfate and bromide ions. A catalytic method for the determination of copper has been proposed by Lopez-Cueto and Casado-Riobo (70) based on the catalysis of the hexacyanoferrate(II1)-cyanide reaction (71). A detection limit of 1.3 ng/mL is reported using the “rate constant method” which consists in recording the absorbance-time curve for about 50 min, plotting l/absorbance vs. time, and preparing calibration curves by plotting the slope of the straight-line portions of this line vs. copper concentration. Determination of copper (5 X to 4 X g Cu(II)/cm3) has been based on its catalysis of the H 2 0 2oxidation of 1-amino-2-naphthol-4-sulfonicacid (72). Under optimum conditions, relative errors are reported as 10-19%. Dolmanova et al. proposed the oxidation of hydroquinone by H202in aqueous-organic media for the determination of Cu(I1) (73). Otto, Mueller, and Werner (74) have determined copper in liver tissue by a procedure involving the following steps: (1)digestion of the liver samples with nitric acid; (2) extraction of copper as the salicylate-pyridine complex; and (3) direct catalytic determination of copper in the organic extract by addition of ethanolic solutions of sulfanilic acid, pyridine, and hydrogen peroxide (75). The absorbance of the reaction mixture was measured a t 370 nm after 30 min of reaction (fixed-time procedure) a t 45 “C. The limit of detection for copper is reported as 5 ng/mL, which allows determining as little as 10 ppm of copper in 5 mg of dried liver. A comparison with neutron activation and flameless atomic absorption determinations is also offered. The catalytic effects of copper(II), thyroxine, 5-chloro-7iodo-8-hydroxyquinoline,and the enzymes horseradish peroxidase and glucose oxidase on well established “indicator reactions”, have been used by Pantel and Weisz (39) for the direct determination of these species by a signal-stat procedure with biamperometric detection. The rate of reduction of molybdate by Sn(I1) is increased by Ge032- with the formation of molybdogermanate blue allowing its determination of as little as 3 to 8 X pg/mL of germanium (76). The catalytic effect of niobium and tantalum on the H202 oxidation of o-aminophenol, pyrogallol, or gallic acid has been proposed for the determination of niobium and tantalum with and 0.5 to 2 X limits of detection of 1 to 3 X M, respectively (77). o-Aminophenol offers, comparatively, the best sensitivity but its solutions are less stable. Kataoka and Kambara reported a catalytic determination of molybdenum(V1) by means of the peroxoborate ion oxidation of iodide ion to iodine in acidic medium (78). The rate of the reaction was followed by monitoring the decrease in iodide concentration using an iodide-ion-selective electrode. The most suitable reagent concentrations were selected by the method of experimental design of three-sided classification and the detection limit is reported as 0.09 pg/cm3. The same

monitoring approach and indicator reaction was used by Kataoka, Takahashi, and Kambara for the determination of tungsten(V1) (0-6.0 pM tungstate) and vanadium(V) (0-40 pM orthovanadate) (79). Christian and Patriarche have determined molybdenum in blood and urine by means of its catalytic effect on the reduction of selenium(1V) to the element by tin(I1) in hydrochloric acid medium (80). The method of analysis involves the dry ash of the sample, dissolution in 6 M HC1, extraction of the molybdenum into pentyl acetate, back-extraction of the molybdenum into an aqueous phase, addition of acid, and catalytic determination by the fixed-time procedure (10 min) measuring the absorbance of the red colloidal selenium a t 390 nm (gum arabic added to stabilize the colloid). Molybdenum(VI) and tungsten(VI) have been determined by a method based on their catalysis of the H 2 0 z oxidation of o-aminophenol (81). Masking of Mo(V1) by C2042-permits the determination of tungsten in the presence of molybdenum. Rhodium(II1) does not catalyze the reduction of silver(1) with iron(II), but Rh(II1) preliminarily reduced to colloidal rhodium by use of polyhydridosiloxane with poly(viny1alcohol) and UV irradiation is an active catalyst (82). A method is suggested for the determination of rhodium (limit of detection = 1x pg Rh(II1) mL). The procedure has been used to determine R h in hy rochloric, perchloric, and sulfuric acid solutions. A procedure has been developed for iridium determination based on its catalytic action in the oxidation of copper tellurate with hypobromite (83);the same system is also proposed for the determination of rhodium (84). Alekseeva e t al. reported on the reproducibility and limit of detection of Os(VII1) determination based on its catalytic action on the As03,-/Br03- indicator reaction (85). Iridium, rhodium, and palladium amounting to 10”-10-7 % in rocks have been determined by catalytic procedures in separate aliquots and without prior separation (86). Using the fixed-time procedure, limits of detection are reported as 0.002 g Ir/ton, 0.001 g Rh/ton, and 0.01 g Pd/ton. Gillet (87) has determined platinum a t the ng level by amalgamation of platinum with mercury (reduction in homogeneous medium by means of formate), volatilization of the mercury, dissolution in aqua regia, reduction of platinum (by formate) in the presence of gold forming a colloidal suspension, and determination of Pt based on its catalysis of the decolorization of methylene blue by formate. Concentrations of Ag(I), Au(III), and Hg(I1) at subpark per million (aqueous solutions) have been determined by means of the catalytic effect of these species on the ligand exchange reaction involving pentacyanoaminoferrate ion and ferrozine. Organormercuricals (methylmercury and ethylmercury) also catalyzed the ligand exchange. The metallic species have been determined by a fixed-time procedure (measurement of absorbance after 10 min of initiation of the reaction) (88). No more increase in absorbance due to the formation of the Fe(11)-ferrozine complex is observed after 10 min, probably as a result of cyanide complex formation by the catalytic species and blocking of the catalytic cycle. A catalytic determination of mercury based on its ability to accelerate the reduction of molybdo hosphoric acid by NaH2P02in the presence of colloidal golf has been proposed by Klochkovskii and Klochkovskaya (89). Even though most of the catalytic methods reported are for the determination of metallic species, a few involve catalysis by anions of the nonmetals. Sulfur-containing species such as SCN-, Sz032-,SO3:-, and Sz-catalyze the decomposition of HBrO, in acid medium. The decomposition generates Br- which further reacts according to BrO - + Br- 2H+ = HBrO + HBr02. The catalytic effect has keen used for the determination of the sulfur-containing species by either the method of tangents or the fixed-time procedure (90). Borate a t the parts per million level has been determined by following the hydrolysis of N-nitrosohydroxylamine-Nsulfonate (91). Borate in the form of boric acid catalyzes the reaction, which can be monitored spectrophotometrically a t 258 nm (sulfonate absorbance). Protons and certain metal ions also.exert catalytic action and the reaction is run in the presence of complexing agents to suppress the catalytic effect of metal ion species. Calibration curves were prepared by plotting the observed rate constant vs. borate in the reaction mixture (0-40 p g ) . The procedure was used for the determination of borate in NBS glass No. 93.

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A chloramine-T-selectiveelectrode has been used to monitor the iodide-catalyzed oxidation of chloramine-T by H 2 0 2and determine iodide (1.5-9.0 pg with mean relative errors and coefficients of variation of about 2 % ) by a variable-time procedure (92). The same system and approach was used to determine osmium in the 10-150-pg range (93). New indicator reactions have been proposed for the determination of iodide and iodate ions in mineral waters; these reactions are the HzOz oxidation of o-phenylenediamine, diphenylcarbazide, or Variamine Blue (94).

DIFFERENTIAL REACTION RATE METHODS T h e main goal of differential reaction rate methods is the simultaneous determination (not necessarily determination of low concentrations) of two or more species without prior separation. A few novel approaches have been proposed; ligand exchange reactions continue to be the most often used to utilize differences in rates of reactions of closely related species in their mixtures. Connors (95) has proposed a reaction-variable distribution curve for the treatment of data in the simultaneous determination of mixtures based on rate differences. Connors’ proposition consists in transforming the product concentration vs. time curve into a difference in product concentration (at fixed intervals) vs. ordinal intervals; this generates a curve showing a maximum and resembling an absorption spectrum. The area under the curve (resolved for a single component) is proportional to the initial reactant concentration; if rates are sufficiently different, a maximum is observed for each component and visual observation of the product distribution curve conveys qualitative information. Application of the approach is illustrated with ternary mixtures of p-nitrophenyl para-substituted benzoates and by use of their hydroxylaminolysis reaction with generation of the common product p-nitrophenolate which can be followed spectrophotometrically. Quantitative treatment of the data resembles the method of proportional equations since it is based on simultaneously solving equations with data collected a t selected ordinal intervals. In contrast with the method of proportional equations, however, in the proposed treatment of data the ratios of the coefficients of proportionality can be inverted (as is the case in the spectroscopic analysis of mixtures). This possibility of altering the rank order of coefficients in sets of simultaneous equations is an attractive feature of the approach. The greater error in calculating differences appears to be the principal disadvantage. The so-called “flow injection analysis” (a form of unsegmented continuous-flow analysis), introduced by Ruzicka and Hansen in 1975 (96), has been used for the differential determination of magnesium and strontium by Dahl, Espersen, and Jensen (97). They used the well-known acid dissociation of the trans-1,2-diaminocyclohexanetetraacetatemetal complexes in presence of Cu(I1) ions as scavengers for the free ligand anion. The instrumental set-up utilized consisted in two photometric units in tandem (Beckman DU spectrophotometers) which monitored the absorbance at 320 nm a t two different times after initiation of the reaction by injection of the sample containing the sought-for species. The same approach has been used for the determination of magnesium and calcium with [2.2.1]cryptand as ligand and sodium ion as scavenger (98). Improved techniques to acquire, to calculate, and to test data sets for simultaneous kinetic analysis have been suggested by Ridder and Margerum (99). Emphasis is given to the importance of using the entire response curve with the aid of a minicomputer, instead of the graphical approach based on the signal after all but the slowest component have reacted, or initial rate measurements for only the fastest component, or two-point methods. Simultaneous analyses of four-component mixtures [Zn(II), Cd(II), Hg(II), and Cu(II)] a t 104-10-5 M concentrations are reported. The procedure consisted in following the dissociation of metal-Zincon complexes a t 620 nm (stopped-flow mixing). Each complex has a different molar absorptivity as well as a different rate constant for dissociation. Mixtures of copper, nickel, and cobalt ions have been kinetically resolved by the monitoring of the ligand exchange reaction between their 2-(2-thiazolylazo)-4-methylphenol (TAC) complexes with EDTA (100). Aqueous solubility or a t least dispersion of TAC and its complexes is effected by 36R

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addition of Tween 20, a nonionic surfactant. The substitution reaction was followed spectrophotometrically (610 nm) after stopped-flow mixing. Determinations at the lo* M level gave errors of 4%. Several metal ions and anions do not interfere. A similar approach (stopped-flow mixing and photometric monitoring) has permitted to determining Cd(1I) by extrapolating to zero time the rate curve of the ligand substitution complexes and reaction between 1-(2-thiazolylazo)-2-naphthol EDTA (101). Binary mixtures of ions of the actinides have been analyzed as single samples by following the rate of ligand exchange and application of the method of proportional equations (absorbance measurement at 665 nm at two predetermined time) and Pu4+ (102). The exchange reactions of the Th4+ U6+, complexes with DCTA in the presence of Akenazo I11 and in 0.1-0.3 M H N 0 3 have been used for this purpose. Binary mixtures including Np4+were resolved by the same approach using DTPA as well as DCTA as primary ligands (103). Simultaneous determinations of calcium and magnesium ions by means of the exchange reaction of lead(I1) and the alkaline earth metal complexes with DCTA have been reported by Schwing and co-workers (104). Computer-controlled amperometric and potentiometric monitoring are reported to provide precision and accuracy of 5-10% in amperometric measurements and 5% in potentiometric, over the range of to 5 x This precision and accuracy is considered better than that obtained by fast mixing (stopped-flow) and spectrophotometric detection, but the time needed for measurement is 20 min for electrochemicaldetection in comparison to about up to 10 s in the stopped-flow spectrophotometric operation. Essentially the same approach to differential rate determination has been developed for the determination of vanadium(V), molybdenum(VI), and tungsten(V1) in mixtures (105). This method of determination takes advantage of the different rates of ligand exchange between the hydroxyl ion and the complexes of V(V), Mo(VI), and W(V1) with nitrilotriacetic acid (NTA). Monitoring in this case was by stopped-flow spectrophotometry. A logarithmic extrapolation method for the determination of nickel(I1) and cobalt in their binary mixtures has been proposed by Kitagawa et al. (106). The chemistry of this method involves complex formation with the ligand 2carboxy-1-pyrrolidinecarbodithioicacid. The complexes of both nickel and cobalt have almost identical absorption spectra with maximum absorption at 324 nm and comparable molar absorptivities; the reaction rate of Co(II), however, is rignificantly different ( k N i o ~ k C =” 70) , ~ because of the oxidation of Co(I1) to Co(II1) by issolved oxygen. Stopped-flow mixing enables preparation of calibration curves that are linear in the concentration range of 2 X lo4 to 8 X lo+ M. Binary mixtures of phenols in water samples were analyzed by a modification of the single-point method of Lee and Kolthoff by the oxidative coupling reaction with N,N’-diethyl-p-phenylenediamine in the presence of hexacyanoferrate(II1) using stopped-flowmixing (107). The modification consisted in taking into account the formation of two different final products. A rather unusual analytical application of kinetics is the separation of salt mixtures based on the tendency of salts to dissolve at different rates (108). The difference of solution enhanced by judicious selection of temperature, hydrodynamic conditions, and the design of the instrumental unit used for the determination. High degrees of separation can be predicted when the solubilization of one component is controlled by diffusion kinetics while the other component dissolves at a rate dictated by a chemical reaction. The proposed method was tested on a halite-langbeinite mixture with good results, particularly when the separation was effected by sodium chloride solutions. Logarithmic extrapolation has been applied by Nishikawa et al. to analysis of binary mixtures of metal complexes (aluminum, gallium, indium, magnesium, zinc, and cadmium) of 5-sulfo-8-quinolinol in a method based on differences in fluorescence lifetimes (109). The method was applied to the determination of aluminum in magnesium alloy and magnesium in aluminum alloy. When the difference between fluorescence lifetimes exceeds 4 ns, each component in the binary mixture can be determined by the logarithmic extrapolation plot resulting from analysis of the fluorescence decay curve. Nishikawa et al. (110) have also applied the same


approach to the simultaneous determination of 8-quinolinol and 5,7-dihalo-8-quinolinols. The simultaneous determination of uric and ascorbic acid in mixtures of these species has been reported by Pelizzetti and Mentasti (111). This is accomplished by means of a stopped-flow measurement of the rate of reduction of tris(2,2’-bipyridine)iron(III).Plots of ( A , - A , ) / A , (where A , and At represent the absorbance a t equilibrium and at a fixed time of 0.50 s, respectively) vs. the molar fraction of uric acid, even though not linear, give calibration curves useful for the estimation of the mixture composition. A differential-kinetic method based on the enhancement of the rate of oxidation of o-dianisidine by H 2 0 2has been proposed for the individual determination of some organophosphorus pesticides (112). Reported average errors are in the 19% range and the detection threshold is reported as 0.05 CLg. De Oliveira and Rodella used the method of proportional equations and enthalpimetric monitoring of the reaction between glucose and fructose with periodate for the simultaneous determination of these sugars (113). The largest ratio (equal to 3) for the pseudo-first-order rate constants was obtained at pH 5.2 (acetate buffer) and measurements were performed a t 1 and 3 min after starting the reaction. The precision and accuracy of analysis of mixtures containing equal amounts of glucose and fructose was found to be about 4 % , but the uncertainty increased rapidly as the ratio of concentrations departed from unity. The procedure may find application with procedures involving the hydrolysis of saccharose, which give mixtures containing comparable amounts of the two reducing sugars.

UNCATALYZED REACTION RATE METHODS Formaldehyde and hexamethylenetetramine have been determined (60-300 pg of formaldehyde and 50-250 pg of hexamethylenetetramine in 0.050-mL samples) by treating samples containing a large excess of the sought-for species with a solution of cyanide (approximately 1.6 X M), following the rate of the addition reaction potentiometrically with the aid of a cyanide-selective electrode, and application of the variable-time procedure ( 1 1 4 ) . The method was applied to the determination of hexamethylenetetramine in pharmaceutical preparation. The determination of perbromate (0.3-3 Kg) by the method of tangents and by monitoring I,- spectrophotometrically in its reaction with the perbromate has been proposed by Hadjiioannou e t al. (115). The so-called phosphomolybdenum blue reaction (reduction of molydophosphoric acid with ascorbic acid) has been implemented in an automated reaction rate method for the determination of phosphorus in agricultural materials ( I 16). Determination was performed after digestion by the block digestion procedure of the Association of Official Analytical Chemists (AOAC), and reaction progress was followed spectrophotometrically during 30 to 40 s. Relative standard deviations are reported as 0.3% and good correlation was obtained with the official AOAC spectrophotometric procedure for AAFCO check grain and feed samples. The oxidation of ethanol by Mn04- has been proposed for the determination of that alcohol (117). Monitoring the formation of Mn042-photometrically (400 nm) showed the reaction rate to be directly proportional to the concentration of ethanol; acids, higher alcohols, and methanol are oxidized a t lower rates. The method was used to determine ethanol in hydrolysis products of (EtO)4Siand (EtO)+Ti. The formation of iodoform from acetone and iodine in KOH solution has been proposed for the determination of iodine in aqueous solution by application of the method of tangents and potentiometric monitoring with an iodide-ion-selective electrode (118). Steinhart (119)has developed a kinetic-fluorometric method for the determination of tryptophan based on the reaction with formaldehyde at a p H of 10.8 (carbonate buffer). The difference in fluorescence emission (Aexcitation 289 nm; Xemission 356 nm) between 45 and 105 s, directly proportional to the tryptophan concentration, was used for the preparation of calibration curves. Indole derivatives and guanine interfere, but since these substances are rarely present in large amounts in food and feedstuffs, the method is, in most cases, suitable to determine tryptophan directly in such samples after alkaline

hydrolysis. The limit of detection is reported as 2 nmol of tryptophan/mL. Aliphatic amines such as butylamine and isobutylamine and trioctylamine have been determined in waste water by reaction with tetrachloro-p-benzoquinone in a variety of solvents (120). The kinetics of uncatalyzed peroxydisulfate oxidation of organic materials in fresh water has been examined by Goulden and Anthony (121). The kinetics of this oxidation in natural water samples and of single organic compounds can be represented by simple rate equations. This study suggests the use of the uncatalyzed peroxydisulfate oxidation as a convenient route to an automated, wet chemical system for the determination of organic carbon in some water samples. A specific method for ascorbic acid which can be applied to turbid or colored food samples has been reported by Hiromi et al. (122). The method is based on the linear relation, over a wide range, between the apparent first-order rate constant for the reduction of 2,6-dichloroindophenol by ascorbic acid and the concentration of ascorbic acid. The content of cellulose in dry pine sawdust has been determined by a kinetic approach (measurement of the rate constant of cellulose hydrolysis a t a given temperature and in the presence of 0.8% H2S04)(123). The experimental error was estimated as f3.04% and the cellulose content in -41 %. The thickness of the surface high-diffusivity layer of T i 0 2 was kinetically determined by means of the solid state reaction between TiOz and BaC0, a t different temperatures (124).

MISCELLANEOUS KINETIC ASPECTS OF ANALYTICAL INTEREST The applicability of electrokinetic detection by measuring the streaming current generated on an analytical or capillay chromatographic column has been demonstrated (125, 126). According to Holcombe et al. (127) a t the pressures encountered in flameless atomizers for atomic absorption measurements, reaction kinetics play a significant role in predicting the degree to which the analyte and an interfering substance may interact. The mixing efficienc in systems in which the force of injection is the sole modie of mixing is of interest in reaction rate-based methods. Carter and Stanbridge (128) described a method of assessing mixing efficiency when injecting one of the reactants (with a mechanically actuated syringe) into the other reactant contained in a spectrophotometric cell. The rate at which iodide is oxidized by hydrogen peroxide (as measured by the time to consume a given amount of thiosulfate) was used as a measure of mixing efficiency. Tawa and Hirose (129) described a graphical method which allows estimation of the number of reacting light-absorbing species from the plots of complementary color points obtained with the aid of simplified complementary tristimulus colorimetry. Complementary color points for a series of solutions were also used for the determination of the rate constant for a first- or pseudo-first-order reaction. The reaction between permanganate ions and oxalic acid, the catalytic decomposition of HzOzby tungstate in the presence of Cu(II), and the oxidation of some sulfonephthalein dyes by periodate are presented as systems for the application, of such tristimulus colorimetry to kinetic situations. The analytical application of solution chemiluminescence (CL)for the determination of very low concentrations of metal attention. The measurement apions IS receiving incre~~sed proaches utilized in these applications are kinetic in nature and sometimes they are classified as “catalytic determinations” despite the fact that the so-called “catalyst” is irreversibly converted into inactive products of higher oxidation states and a “catalytic cycle” is difficult to envision. The approach offers very low limits of detection, is applicable in rather large dynamic concentration ranges, and is relatively simple. As an example of this, it seems pertinent to mention the work of Montan0 and Ingle (130, 131),who after investigating the chemiluminescence reaction involving lucigenin in basic solutions containing H 02,applied it to the determination of cobalt in subpart per billion levels (limit of detection reported as 20 ppt). Calibration curves (log-lo ) are linear up to 100 ppm. The method was applied to the cfetermination of cobalt in solutions from dilution of tap water and digestion of NBS orchard leaves standards. Other recent applications of CL to chemical analysis include the observation that several inorganic species (some metal ANALYTICAL CHEMISTRY, VOL. 52, NO. 5, APRIL 1980

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cations and some anions) enhance the chemiluminescence of the lophine reaction with HzOZin basic medium (132). Detection limits are reported as l X lo4 M for OC1-, 8 X M for Co(II), and 5 X lo+ M for Cr(II1) and Cu(I1). Since several reducing agents of clinical importance produce chemiluminescence by reaction with lucigenin (in absence of H202) in basic medium, Veazey and Nieman (133) have investigated the determination of ascorbic acid, creatinine, uric acid, glutathione, glucuronic acid, lactose, and glucose by CL measurement. A kinetic approach to the estimation of the water content of solids by the Karl Fischer method has been proposed by Yap et al. (134). Analysis of only part of the experimental titration curve before the end point allows determining the water content and some kinetic parameters; the approach is particularly useful in case of slow dissolution of solids. N-Methylimidazole is reported 400 times as effective as yridine as a catalyst for analytical acylations by acetic anydride used as standard methods for the determination of amino and hydroxy groups (135). Weisz and co-workers (136) reported a modification of the spot-test, chronocolorimetric technique, proposed earlier by Weisz (137). It is a simple approach based on comparison of the speed of decolorization of colored reaction products of the test substances on filter paper. Since the sample drop and two standards are simultaneously compared, working conditions are not critical and simple comparison of the speeds of decolorization satisifies the semiquantitative application of the method. Microgram amounts of nickel in about 1-pL drops were estimated by comparing the speed of decolorizing the butanedione dioxime (dimethylglyoxime) chelate by complex displacement with cyanide. Reactions for the determination of iron(III), copper(II), iodide ion, and resorcinol are also proposed. A new approach to data treatment in first-order kinetic situations has been presented by Mieling and Pardue (138). The main attraction of this treatment is that it results in a method analysis which is insensitive to changes in variables such as pH and temperature. This is possible because firstorder reactions possess the unique property that the rate constant can be determined without knowledge of the concentration of the rate-limiting species. An alternative method of analyzing first-order kinetic data has been published by Schwartz and Gelb (139). The discussion is of interest to those involved in kinetic methods of determination since the predominant kinetic situation in these methods is either first-order or pseudo-first-order. A discussion centered on the effect of uncertainties in rate parameters on the precision of kinetic determinations by the fixed-time procedure has been presented by Carr (140). The discussion is limited to first order and Michaelis-Menten kinetics and concludes that the random uncertainties in rate constants generate effects that are strongly dependent on the extent of the reaction. For enzyme kinetics with predominantly zero-order kinetics the results can be extremely imprecise. Kelter and Carr discussed a second-order noniterative technique able to distinguish second-order data from nonsecond-order data (141). The approach is also able to verify noise simulated data as being second-order,and yields accurate estimates of input rate constants and initial absorbance. The technique is fast, requiring about 30 steps in BASIC or in a programmable pocket calculator. The same authors have described a microcomputer-compatible method of resolving rate constants in mixed first- and second-order kinetics (142) and discussed limitations in the normal variate as a statistical evaluation of kinetic data (143). Mottola and Hanna have proposed a series reaction mechanism to describe transient signals in unsegmented flow through systems (144). The paper discusses the effect of rate proportionality constants on the three fundamental parameters of the analytical signal: (1)the ratio of peak height to theoretical steady-state signal; (2) the time to reach the maximum (minimum) signal value; and (3) the time to return to base line. Application to the determination of some phenothiazines based on the transient redox effect observed in their oxidation with Ce(1V) is also illustrated. The discussion and application is limited to the case of direct injection of sample into the detection chamber.

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Davis and Pevnick (145) have examined the optimization of the coupled enzymatic measurement of substrate. Factors such as variations in the activity of the coupling enzymes affect the analyses but by proper selection of the time of the rate measurement these effects can be minimized, contrary to the case of initial rate measurement. They developed an optimization procedure for variations in activity of the primary or the coupling on both enzymes. Four methods are given for estimating the kinetic arameters used in such optimization. The same concepts sEould be applicable to any coupled catalytic system. Fox (146) has carried out a very comprehensive kinetic and mechanistic study of the Griess reaction used in nitrile analysis. This study has resulted in establishin the utility of reagent combinations to be used in this methof Similarly Goulden and Anthony (147) have studied the kinetics of the uncatalyzed peroxydisulfate oxidation of organic material in fresh water over a wide temperature and pH range. They show the conditions and times necessary for total oxidation of the material which is important in obtaining reliable total organic carbon analysis in fresh water. There have been a number of other studies of rate phenomena of processes other than simple chemical reactions that have resulted in improvement of analytical methods. For example, Zsak6 (148) has examined theoretically the effect of heating rate and other kinetic parameters on the shape and position of the analytical signal response in flameless atomic absorption spectroscopy. He has also discussed the physical significance of these kinetic parameters. Similarly, an examination of the kinetics of ion exchange processes in polydisperse systems by Bunzl (149) has shown that particle size significantly affects the time required to attain equilibrium. He showed, however, that the slow attainment of equilibrium was between adsorbed ions on the different size particles and that concentration of the ion in the solution phase is constant after just a short period of time and, thus, simulates equilibrium in the solution phase of the system. These slow kinetic exchange processes, therefore, do not negate the practical use of polydisperse ion exchangers. A very interesting and significant paper by Cammann (150) has shown that the exchange kinetics a t potassium-selective liquid membrane electrodes is analogous to the classical electron exchange currents (kinetics) between metal electrodes and solution phase redox systems. Thus, there is a high correlation of this exchange current for potassium solutions containing various interfering ions and the corresponding Nernstian behavior of the electrode response. Cox and Cheng (151) has studied the rate of attainment of the Donnan dialysis enrichment of weak acids as a function of pH and nature of receiver electrolyte. The results suggest that diffusion of the sample anion is not the rate-determining step in these enrichments but that the rate of transfer across the membrane/receiver interface is especially important.

INSTRUMENTATION AND COMPUTERS In the past 2 years, there has been a very significant decrease in published research dealing with instrumentation, automation, data handling, detectors, etc., which have been applied to kinetic measurement and/or analysis or which could be otentially applied to kinetics. 8aserta et al. (152) have devised a computer-controlled bipolar pulse conductivity system which has been developed specifically as a detector for chemical rate determination. The instrument has an extremely wide dynamic range (10-1-10-8 Q-'). They discuss in detail all the factors which affect the accuracy of the system and data rate limitations. Measurements can be made in as little as 30 ks which makes it applicable to stopped-flow studies. A unique aspect of the instrument is its ability to make numerical corrections of the data for temperature changes which occur within the conductance cell. The temperature monitoring systems employed in this system has been described by Holler et al. (153). Mieling and Pardue (154) have evaluated a computer-controlled stopped-flow system that they designed for fundamental kinetic studies. The imprecision was about 0.03 s-l for rate constants in 1.8-5 s-l range. Whiting and Carr (155) have built a simplified model of a differential scanning calorimeter (DSC) with large (40-120 pL) aqueous enzyme sample for digital simulation using a mathematic technique of orthogonal collection in order to study errors in kinetic parameter calculations due to thermal lag (temperature and


concentration gradients). Results show that, in general, random errors can be several times greater than the determinate errors related to thermal lag. A few papers have appeared which employ electrochemical detection in kinetic measurement. Lazarou and Hadjiioannou (42) has described an automated recording and measurement system employing iodide selective electrodes. Gulberg a n d Christian (156) have devised a flow cell for use with the Clark type oxygen membrane electrodes which were used for kinetic measurement, and Karweik and Huber (157) have demonstrated the application of lead dioxide electrodes for pyrophosphite hydrolysis rate studies. Ratzlaff et al. (158) have developed a computer controlled-dual wavelength spectrophotometer which has characteristics that would make it very suitable as a kinetic detector.

ACKNOWLEDGMENT Research support (to H.A.M.) by the National Science Foundation and of which this review is a by-product is acknowledged here. LITERATURE CITED (1) Greinke, R. A.; Mark, H. B., Jr. Anal. Chem., 1978. 50, 70R-76R. (2) Mark, H. B., Jr. I n "Instrumental Analysis", Bauer, H. H., Christian, G. D., O'Reilly, J. E., Ed.; Allyn and Bacon: Boston, 1978; pp 523-558. (3) Pardue, H. L. I n "A History of Analytical Chemistry". Laitinen, H. A,, Ewing, G. W., Ed.;The Maple Press Co.: York, Pa., 1977; pp 97-102. (4) Sandell, E. B.; Onishi, H. "Photometric Determination of Traces of Metals. General Aspects", 4th ed. of "Colorimetric Determination of Traces of Metals", Wiley-Interscience: New York, 1978; pp 200-206. (5) Guilbault, G. G. I n "Treatise on Analytical Chemistry", 2nd ed.; Kolthoff, I. M..Elving, P. J., Ed.; Wiley-Interscience: New York, 1978; Part I, Vol. 1. pp 663-710. (6) Yatsimirskii, K. 6.; Tikhonova, L. P. I n "Essays on Analytical Chemistry (in Memory of Professor Anders Ringbom)", Wanninen, E., Ed.; Pergamon Press: Oxford, 1977; pp 529-536 (7) Fukasawa. T., and Yamane, T., Bunseki(J. Jpn. SOC.Anal. Chem.) 1977, No. 8,491. (8) Albrecht-Gary, A. M.; Schwing, J. P. "Les Methodes Cinetiques in Chimie Analytique", Les Techniques de L'IngBnieur: Paris, 1978. (9) Pardue, H. L. Clin. Chem. 1977, 2 3 , 2189-2201. (10) Kreinml. D. S. U. Fiz. Khim. Metodv Anal. 1978. 3 , 32-35; Chem. Abstr. 1979, 91. 1505382. (11) Nabivanets, B. I.; Kalabina, L. V. Zh. Anal. Khim. 1977, 32,2018-2024; Chem. Abstr. 1978. ~ . . 88 ~ , 78834m ... (12) Otto, M-Mueller, H.; Werner, G. Talanta 1978. 25, 123-130. (13) Blaedel, W. J.; Boguslaski, R. C. Anal. Chem. 1978, 50, 1026-1032. (14) Weisz, H.; Meiners, W. Taianta 1979, 26,789-772. (15) Weisz, H.; Meiners, W.; Fritz, G. Anal. Chim. Acta 1979, 107,301-307. (16) Klockow, D.; Graf, G. F.; Auffarth, J. Talanta 1979, 26, 733-736. (17) Nachtmann, F . ; Knapp, G.; Spitzy, H. J . Chromatogr. 1978, 149, 603-702. (18) Tikhonova, L. P.; Zakrevskaya, L. N.; Yatsirnirskii, K. B. Z h , Anal. Khim. 1978, 33, 1991-1994; Chem. Abstr. 1979, 90,4 7 8 5 2 ~ . (19) Iwase, A.: Kudo, S . ; Tanaka, N. Anal. Chim. Acta 1979, 110, 157-160. (20) Pantel, S. Anal. Chim. Acta 1979, 104, 205-213. (21) Kobayashi, K.; Fujiwara, K.; Haragushi, H.; Fuwa, K. Bull. Chim. SOC.Jpn. 1979, 52. 1932-1936. (22) Muller, H.; Beyer. L.; Muller, Ch.; Schroter Ch. 2 . Anorg. Allg. Chem. 1978, 446. 216-226. (23) Muller, H.; Beyer, L. 2 . Chem. 1979, 19,295-296. (24) Yatsimirskii, K. B.; Zapunnyi, A. I.;Budarin, L. I.; Fel'dman, L. S.; Kazakevich, M. L. Zavod. Lab. 1977, 43. 920-922; Chem. Abstr. 1978, 88, 138304a. (25) Schurig, H.; Muller, H. Acta Hydrochlm. Hydrobiol. 1979, 7 ,281-288. (26) Quin, B. F.; Woods, P. H. Analyst (London) 1979, 704,552-559. (27) Ramasamy, S. M.;lob, A.; Mottola, H. A. Anal. Chem. 1979, 51, 1637-1639. (28) Dolmanova. I.F . ; Zolotova, G. A,; Mazko, T. N.; Dymshakova, G. M.; Trunov, P. P. Zh. Anal. Khim. 1977, 32,807-811; Chem. Abstr. 1977, 87. 48798q. (29) Nlkoleiis, 0. P.; Hadjiioannou, T. P. Anal. Chem. 1978, 5 0 , 205-208. (30) Nikolelis, D. P.; Hadjiioannou, T. P. Anal. Chim. Acta 1978, 97,111-120. (31) Nikolelis. D. P.; Hadjiioannou, T. P. Mikrochim. Acta 1978 I , 383-390. (32) Nikolelis, 0. P.; Hadjiioannou, T. P. Mikrochim. Acta 1978 11, 105-112. (33) Muller, H.; Schurig, H.; Werner, G. Talanta 1979, 26. 785-790. (34) Jordanov, N.; Pavlova, M.; Stefanov, S . Talanta 1978, 25, 389-393. (35) Il'icheva, I. A.; Antul'skaya, N. L.; Dolmanova, I. F.; Petrukhina, L. A,; Metcdy Anal. Kontrolya Kach. Prod. Khim. Promsii. 1979 (8),43-44; Chem. Abstr. 1979, 91. 44052b. (36) Dolmanova, I. F.; Zolotova, G. A,; Mazko, T. N. Zh. Anal. Khim. 1977, 32, 1025-1027; Chem. Abstr. 1978, 88,685384. (37) Klochkovskii, S. P.; Klochkovskaya, G. D. Zh. Anal. Khim. 1977, 32, 736-740; Chem. Abstr. 1977, 87. 1931211. (38) Kreingol'd, S. U.; Yutal, E. M.; Sosenkova, L. I. U.S.S.R. Patent 652,485; C.hem. Abstr. 1979, 90, 1 7 9 6 4 3 ~ . (39) Pantel, S.;Weisz, H. Anal. Chim. Acta 1979, 89,47-54. (40) Lazarou, L. A.; Hadjiioannou, T. P. Anal. Chlm. Acta 1979, 708,375-377. (41) Lazarou. L. A.; Hadjiioannou, T. P. Anal. Lett. 1978. All, 779-795.

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Electron Microscopy Michael Beer The Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 2 12 18

Biological electron microscopy is a vast and enormously active area of research. I have concentrated in this review on technical aspects of structure determination which may have broad impact on the field. No attempt was made to review particular areas of biology unless in those areas approaches were used which promise to have wide applicability. The period covered is 1978 to December 1979.

LOW D O S E ELECTRON MICROSCOPY Electron microscopy of biological samples is limited today not so much by the resolution of the instruments as by the damage which inevitably accompanies irradiation. In 1975 Unwin and Henderson (1) published a classic paper in which they showed how for a two-dimensional crystalline array this limitation can be circumvented by spreading the total electron dose necessary for high resolution over a large number of unit cells and then by image processing obtaining a single composite high resolution image of the unit cell. They studied the naturally crystalline membrane of the purple bacterium Halobacterium halobium. These low dose procedures are of course applicable to any material which can exist as a two-dimensional crystal. Accordingly Chiu and Glaeser ( 2 ) are studying the structure of the gene 32 protein, GP32. The attraction of the procedure has now been recognized by many workers and several systems are under investigation ( 3 ) . Unwin and Henderson ( I ) in their original paper recognized that their electron diffraction patterns indicated specimens 40 R

0003-2700/80/0352-40R$O 1.00In

ood to about 3 A, yet the images obtained had resolution no %etter than 7 A. This discrepancy is probably due to instrumental distortions and aberrations. Perhaps the most important of these is variation in magnification over the large fields generally observed, which leads to barrel or pincushion distortion. T o avoid loss of structural information manufacturers will have to design microscopes such that the magnification is constant over the field.

LOW TEMPERATURE MICROSCOPY Not all biologically interesting entities can be incorporated into two-dimensional arrays. For those which resist crystallization either prior to observation or during exposure, damage can apparently be reduced by various low temperature procedures. Low Temperature of Specimen Reduces Beam Dependent Artifacts. The studies of Unwin and Henderson ( I ) showed clearly that to avoid beam damage, dosages had to be kept below about 0.5 e A2. Hayward and Glaeser ( 4 ) , using the same membrane, s owed that if the specimens are cooled to about -120 OC the structure will tolerate some 3-7 times greater irradiation than a t room temperature. Similar results were obtained by Taylor and Glaeser (5) on frozen crystals of catalase. For this type of microscopy manufacturers do offer specimen stages with which the sample can be cooled to near the temperature of liquid nitrogen. Unfortunately the commercial ones are still unstable, whereas those modified to give better

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0 1980 American

Chemical Society

Kinetic determinations and some kinetic aspects of ... - ACS Publications

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