Teor. i. Eksperim Khim. Akad. Nauk Ukr. S S R 2 (3), 318 (1966).
5C) Collins, D. W., Mulay, L. N., Abstract. Paper presented a t Intermag. Conference (IEEE), Washington, D. C., April 1968. This paper is expected to appear in the I.E.E.E. Transactions on Magnetics in Sept. 1968. 6C) Collinson, D. W., Molyneaux, L., Stone, D. B., J . Sci. Znstr. 40, 310 (1963). 7C) Collman, J. P., Monteith, L. K., Ballard, L. F., Pitt, C. G., Proc. Inter. Symposium, on Decomposition of organometallic compounds to metals, metal alloys. Materials Research Center, Wright Patterson Air Force Base, Dayton, Ohio, 1967. (8C) Colton, R., Tomkins, I. B., Austr. J . Chem. 19,(5), 759 (1966). (9C) Cotton, F. A., Quart. Rev. 20, 389 f~ 1966). --..
(lOC) Deb-Ray, D. K., Ryba, E., Mulay, L. N., J . Appl. Phys. 38, 3459 (1967). (1lC) Dmitriveva, L. P.. Korin, M. M., Biophysics 6 , l 2 i 6 (1964). ‘ (12C) Ehrenbere. A.. Kamen. M. D.. Biochim. Biopxys. Acta 102, 333 (1965): (13C) Feinleib, J., Paul, W., Phys. Rev. 155,841 (1967). (14C) German, E. D., Dyatkina, ?*I.E., Zh. Strukt. Khim. 7 (3), 428 (1966). (132) Gersonde. A.. ‘Netter., H.., J. Mol. Si&. 10, 475 (1964). (16C) Gersonde, K., Seidel, A., Netter, H., Zbid., 14, 37 (1965). ~
~
(17C) Ginsberg, A. P., Sherwood, R. C., Martin. R. L.. Chem. Commun. 17, 856 (1967).‘ (18C) Kasiyan, A. I., Kon, L. Z., Th. Khim, Part I , No. 8, Abstr. No. 8B283, 1966. (19C) Keys, L. K., Mulay, L. N., Appl. Phys. Letters 9, 248 (1966). (20C) Keys, L. K., Mulay, L. N., Jap. J . Aaal. Phus. u - 6. 122 ~- (1967). (2i%fKeys, L. K., Mulay, L. N., Phys. Rev. 154,453 (1967). (22C) Keys, L. K., Mulay, L. N., J . Appl. Phus. 38. 1446 (1967). (23Cj Keys, L. K., Mulay, L. N., Bull. Am. Phys. SOC.XI1 (4), 503 (1967). (24C) Keys, L. K., Mulay, L. N.,Abstr. l52nd Meeting, Am. Chem. SOC.,Sept. 1966, New York. See also Phys. Letters 24A. 628 (1967). (25C) ’Kosu’ge, K., J . Phys. SOC.Japan 22,551 (1967). (26C) Lasheen, M. A., Acta Cryst. 20,926 ( 1966). (27C) Lindskog, S., Ehrenberg, A., J . Mol. Biol. 24, 133 (1967). (28C) Martin, R. L., White, A. H., Znorg. Chem., 6 , 712 (1967). (29C) Morimoto, H., Itzuka, T., Otsuka, J., Kotani, M., Biochim. Biophys. Acta 102, 624 (1965). (30C) Mulay, L. N., Collins, D. W., Abstract, Div. Phys. Chem., 155th National Meeting, Am. Chem. SOC. (San Francisco), April 1968. - I
(31C) Mulay, L. N., Collins, D. W., Fisher, W. F., Jr., Japan., J . Appl. Phys. 6 , 1342 (1967). (32C) Mulay, L. N., Danley, W., unpublished results. (33C) Mulay, L. N., Dehn, J. T., “Characterizttion of Organometallic Compounds, RI. Tsutsui, Ed., Wiley, New York, 1968. See also J . Znorg. Nucl. Chem. (1968), in press. (34C) Mulay, L. N., Hofmann, N. L., Znorg. Nucl. Chem. Letters 2, 189 (1966). (35C) Mulay, I. L., RIulay, L. N., J . Nut. Cancer Inst. 39, 735 (1967). (36C) Murthy, D. S. N., Le Fevre, R. J. W., Austr. J . Chem. 19 (8), 1321 (1966). (37C) Nortia, T., Suomen Kemistilehli B 38(9), 171 (1965). (38C) Rutzen, C., Ph.D. Thesis, Technische Hochschule Hanover (West Germany) (1966). (39C) Shinjo, T., Kosuge, K., Kachi, S., Takaki, H., Shinjo, M., Nakamura, Y., J . Phys. SOC.Japan 21, 193 (1966). (40C) Tasaki, A., Otsuka, J., Kotani, M., Biochim. Biophys. Acta. 140, 284 (1967). (41C) Umeda. J.. Kusumoto. H.. Narita. ~, K., Yamada, E., J . Chem. Phys. 42; 1458 (1965). (42C) Vasilev, Y. V., Ariya, S. &I., Soviet. Phys. (Znorg.Mat.) 1, 322 (1965). (43’2) Zeilmaker. H.. Drotschman. C..’ Rec. Trav. Chih. 85‘(6), 545 (1966). ~
Kinetic Aspects of Analytical Chemistry Garry A. Rechnifz, Departmenf o f Chemistry, State University o f N e w York, Buffalo, N . Y.
I
K THE TWO YEARS since the appear-
ance of the last review (58) on this subject, the study and use of kinetics by analytical chemists has grown to the point where kinetics is regarded as a legitimate sub-area of analytical chemistry. This maturation is attested to by frequent symposia on the subject, the publication of two monographs devoted solely t o analytical kinetics (61, 83), and the introduction of rate and mechanistic considerations in the undergraduate analytical curriculum (59, 7 5 ) . At the same time, the number and coverage of specific kinetic studies is rapidly increasing to the point where detailed data on many reactions of analytical interest are now available in the chemical literature. The number of inorganic and organic reactions studied from the kinetic viewpoint during the period covered by this review is so vast, in fact, that no effort is made here t o provide a comprehensive listing or critique. Fortunately for the overworked analytical chemist, some excellent reviews dealing with various aspects of reaction kinetics are available for reference. Noteworthy among these, from the viewpoint of thorough and critical coverage, are the reviews of Sutin (66) and Kratochvil (43) on inorganic solution reactions and redox reactions in nonaqueous solvents, respectively.
Other reviews on the hydrated electron (33, 7 7 ) , substitution reactions ( 7 4 , organic redox reactions (41, 42), and catalytic phenomena (5) will also be of interest to readers of this article. The paper by H a r t (33) is particularly interesting because it documents the first direct utilization of the hydrated electron for purposes of chemical analysis-a development predicted in the last review (58). Hart uses the hydrated electron method to determine submicromolar concentrations of oxygen, hydrogen peroxide, nitrous oxide, and other oxidants via their effect upon the spontaneous decay rate of the hydrated electron in water. The method is in its infancy but promises enormous sensitivity. ANALYSIS BY KINETIC METHODS
It is possible that the pendulum has swung too far in favor of kinetic methods of analysis. Where a few years ago there was almost total indifference to kinetic methods, there are those who now hail reaction rate methods as the answer to all difficult analytical problems. Both viewpoints are extreme and deplorable, it is time that kinetic methods be recognized as a supplement to conventional methods and as a substitute only in selected situations where
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the equilibrium chemical properties of materials are not sufficiently distinguishable or measurable for direct resolution of the desired component. Kinetic methods have three powerful advantages: great sensitivity when catalytic, inhibition, or chain reactions can be employed; the ability to resolve, in favorable cases, mixtures of components with highly similar chemical properties; and ready adaptability to automated measurement techniques. On the other hand, kinetic methods are generally not well suited for continuous analysis, usually yield results of only moderate accuracy, and are not easily applied to nonsolution samples. Thus, it is necessary that an intelligent choice be made between conventional and kinetic methods in any given analytical situation. Fortunately, such choices have been made easier by published work dealing with the successful and, sometimes, critical application of kinetic methods. Aside from the comprehensive monographs (58,83), general discussions have been provided for automatic rate measurements (48, 55) and for inorganic kinetic methods (22). The latter paper lists the sensitivity, reaction conditions, and literature citation for more than 80 inorganic analyses employing rate methods. The kind of critical evaluation VOL. 40, NO. 5, APRIL 1968
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that is needed at this point as exemplified by the work of Oglesby et al. (54) on the comparative study of the kinetics of the benzidine rearrangement by four electrochemical techniques and of Broman and Bowers (1I ) on models for the analytical application of dialysis using differential kinetics. Also noteworthy in this connection are the careful studies of Greinke and N a r k on synergistic effects and other sources of error in the rapid analysis of binary amine mixtures by differential reaction rates (23) and the effect of relative concentrations in the analysis of closely related carbonyl mixtures by differential reaction rates using the method of proportional equations (24). Both studies use conductance measurements to monitor the progress of the reaction. An important finding (23) is that synergistic effects, i.e., nonadditive rates, due to solventreactant interaction, changes in activity coefficients, and catalysis can be eliminated through the proper choice of solvents and reaction conditions; this takes much empiricism out of the use of differential rate methods. A number of useful methods, based on differential rate measurements, have been developed for the determination of organic compounds. Guilbault et nl., for example, have described a rapid method (27) for the determination of phenolic compounds using the measurement of the initial rate of the reaction of N-(benzenesulfonyl) quinonimine with phenols. The method was successfully used for the determination of phenols in the 1 to 100 pg per ml range with a relative precision of 1.201,. A competing method is that of Burgess and Latham (12) who determine phenols in aqueous solution by a kinetically controlled bromination in which the only measurement is the time required for the decoloration of an indicator under constant conditions. An interesting, although limited differential rate method is that of Benson and Fletcher (6) for the determination of two-component glycol mixtures based on the measurement of reaction rates with lead tetraacetate in acetic acid solution; the relative error of more than 10% is considerably higher than is usual for such methods, however. An improved method for the determination of the primary hydroxy content in polyols has been described by Willeboordse and Meeker (81). This method uses a differential pseudo first-order reaction rate approach with IR-spectrophotometric monitoring of the reaction of the functional group with phenyl isocyanate and requires only a fraction of the time needed for the earlier extrapolation method. Robinson (63) has demonstrated an interesting variation on kinetic methods by employing rate measurements for the identification, not the quantitative determination, of 456 R
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unknown alcohols from the rates of alkaline hydrolysis of their 3,5-dinitrobenzoate esters. This study shows that kinetic measurements can be useful in the characterization of organic compounds. Once again this year, inorganic applications of kinetic methods of analysis far exceed the number of organic examples. Of these, the largest portion involve some variation of the catalytic method. Ginzburg and Yuzko (ZO), for example, determined trace amounts of iridium by its catalytic effect on the rate of decomposition of cerium(1V) in sulfuric acid media a t elevated temperatures. The disappearance of cerium (IV), monitored spectrophotometrically, is governed by the rate law Rate = k[CeIV][Ir] Fvhich permits, a t constant cerium(1V) concentration, the determination of iridium in the 0.01 to 0.25 pg/ml range with reaction times of 2 to 13 minutes. Similarily, osmium is determined (56) via catalysis of the cerium(1V)-arsenic (111) reaction in the 1 to 60 ppb range with a relative precision and accuracy of about 1%. The determination is greatly facilitated by the use of an instrument system which automatically measures the reaction rate, converts the data into concentration units, and prints out the result. The entire operation requires only about 3 or 4 minutes per sample. Several catalytic methods for the determination of molybdenum have been devised. Wilson (82) has used the rather rapid molybdenum catalyzed perborate-iodide reaction for this purpose in conjunction with a continuous flow system and has been successful in measuring molybdenum a t the submicromolar level with a relative precision of 2 to 3%. Hadjiionannou (31) instead chose the hydrogen peroxide-iodide reaction for the same purpose and with rather comparable results. The same author (SO) also studied the catalytic microdetermination of mercury through its catalysis of the overall reaction [Fe(CN)6I4- -I- C&NO ---+. [Fe(CX)5(C6H&O)]a- -I- C N Amounts of mercury in the 0.25- to 2.5-pg range were determined with relative errors of 1 to 2y0 in less than two minutes by measuring the absorbance of the violet product after a fixed time interval. Other catalytic methods for heavy metals include the determination of germanium ( I O ) , vanadium (8),and silver (9) ; the latter method employs a catalytic titration procedure. A general summary of selected catalytic methods has also been given (78). Special attention must be given to the continuing development of coordination chain reactions as tools for trace analysis.
Margerum and his students have now extended the method with the utilization of masking agents and automated rate measurement (65) and the use of coupled reactions (60). I n the first of these papers, thiosulfate and cyanide plus chloral hydrate are used as masking agents to achieve selectivity among heavy metal ions in their catalytic effect upon the coordination reactions. I n this manner, cupric ion can be determined at the loW6to lO-*M level in the presence of interferences like silver(I), mercury(II), and iron(II1) as well as lead and cadmium in the presence of silver and mercury. The second paper describes an elegant method for the determination of traces of dissolved oxygen based upon its effect on the kinetic stoichiometry of the coordination chain reaction. The method is, in principle, sensitive to f 0.003 ppm O2 in mater. I n the 2.6-18 X mole O2 concentration range a 0.015 pmole standard deviation was achieved. Crouch and Malmstadt (17 , 18) have reported on a comprehensive analytical and mechanistic investigation of the determination of phosphate by an automatic rate method. The method is based on the measurement of the initial rate of molybdenum blue formation from phosphate, molybdate, and ascorbic acid. Phosphate concentrations in the 1-12 ppm range are determined with l-2% relative error in aqueous solution; inorganic phosphate concentrations in blood serum can also be measured with similar relative errors. The complicated reaction mechanism seems to involve the formation of 12molybdophosphoric acid, as in intermediate, and its reduction in a 2-electron step. Another fine study is that of Chen (15) involving a comprehensive investigation of the spectrophotometric determination of microquantities of chlorate, chloride, hypochlorite, and chloride in perchlorate by a kinetic method. This study includes an evaluation of the rate law, the effect of interferences, and the optimum reaction conditions; thus, it can serve as a model for future publications on rate methods. Perhaps the largest potential for the use of analytical rate methods exists in the area of biochemical and enzymatic systems. Furthermore, the use of enzyme catalyzed reactions in kinetic analysis is highly attractive because of the great sensitivity and selectivity inherent to such reactions. Kratochvil et al. (44), for example, used the enzyme-catalyzed conversion of isocitric acid to a-ketoglutarate in the presence of triphosphopyridine nucleotide for the determination of various metals. Manganese(II), magnesium(II), and cobalt (11) are activators for the reaction, while many other metals act as inhibitors. Zinc(I1) both activates and inhibits depending upon its concentra-
tion. By judicious selection of conditions, the authors were able to determine several combinations of metals in the micromolar range. The inhibition of enzyme activity is also the basis of a method for copper(II), iron(II), and cyanide (26), which can be determined with a relative precision of 2.3% in the micromolar range. The method employs hyaluronidase catalyzed hydrolysis of indoxyl acetate to highly fluorescent indigo white and can also be used for the sensitive and precise determination of the enzyme, itself. Electrochemical rate monitoring is used for the determination of the enzyme, glucosidase, or its inhibitor, mercury(II), in a kinetic method based on the enzyme catalyzed liberation of cyanide from amygdalin (65); mercury concentrations as low as lo-' JI can be measured. Epstein and Demek (19) have devised a chemical analog of the cholinesterase inhibition method for the estimation of organophosphorus compounds. Hexanehydroxamic acid is used in place of the enzyme esterase; while the sensitivity of this method is not so high as that of the enzymatic method, it has the important advantage of using stable chemical reagents. Time-resolved phosphorimetry (64) has been used to measure two-component mixtures of phosphorescent compounds like tryptophan and tyrosine. The different decay rates of the phosphors provide the necessary analytical differentiation. Recently, Updike and Hicks (76) eliminated the reagent requirement entirely by coupling an immobilized enzyme system with an electrochemical sensor for the continuous determination of glucose. The enzyme glucose oxidase is entrapped in a gel matrix by photolytic polymerization and the change in oxygen concentration is continuously monitored with a Clark-type oxygen electrode after passage of the glucose-containing sample over the enzyme gel. I n this manner, a continuous analysis method is achieved which requires only a sample solution; the principle of the method should be generally applicable. STUDIES OF ANALYTICAL REACTIONS
While most analytical chemists have come to recognize, to a greater or lesser extent, the importance of kinetic methods of analysis, few, as yet, fully appreciate the significance of fundamental rate and mechanistic studies to analytical chemistry. The real importance of such studies, putting it briefly, is that they help to take some of the empiricism out of analytical chemistry and strengthen the entire theoretical basis of the field. This process becomes apparent when empirical laboratory observations need t o be clarified and explained. The
cerium(1V)-vanadium(1V) titration reaction, for example, was found to be sluggish and otherwise unsatisfactory, when carried out with ferroin indicator or potentiometric end point detection. By trial and error, it had been found that the addition of phosphoric or acetic acids to the reaction mixture or the use of elevated temperatures is beneficial to the titration in the attainment of the end point. For nearly thirty years, it was simply assumed that these effects and difficulties arise from the sluggishness of the primary reaction between cerium(1V) and vanadium(1V) ; a recent kinetic study (62) has shown that this is not so. The primary reaction is actually quite fast even a t room temperature and the observed difficulties are the result of an unfavorable kinetic and equilibrium situation involving the vanadium(IV)/vanadium(V) couple and the potentiometric or chemical indicator systems. The effect of the additives to the medium is accounted for by their influence on the kinetics of these vanadium-indicator processes; the analytical problem can be solved by the selection of proper conditions on the basis of the kinetic information or by simply carrying out the primary reaction with spectrophotometric end point detection-an approach which circumvents the problem of indicator kinetics entirely. An admirable kinetic study of an analytical system is reported in a paper by Guilbault and McCurdy (28) on the catalyzed oxidation of mercury(1) by cerium(1V). The catalysts studied were silver(I), manganese(II), and mixtures of the two. The most interesting finding is that the double-catalyzed reaction displays an enhanced effect in perchloric acid media but only the additive effect of the two individual catalysts in sulfuric acid media. Clearly, different mechanisms are operative; some likely paths are detailed in the original paper. It would be misleading to suggest that fundamental kinetic and mechanistic studies of realistic analytical systems abound in the literature. Specific analytical cases are usually too complex and specialized to attract such fundamental and time-consuming attention. As a result, most basic kinetic studies are carried out under idealized conditions from the physical-chemical viewpoint. There is no reason, however, that the analytical chemist cannot draw on these studies for useful information. In many cases, the general guidelines suggested by a rate law and mechanism are still applicable to complex analytical systems or require only minor modification. Thus, the general kinetic literature is of immense value to analytical chemists in selecting reactions, conditions, catalysts, etc. The series of recent papers by Gordon
el al. (21, 69, 70), for example, substantially clarifies the reaction scheme for the reduction of chlorine oxidants by homogeneous reducing agents such as vanadium(I1) or chromium(I1). The reduction of chlorine by iron(I1) has been studied by Crabtree and Schaefer (16) who found no inhibition by iron (111) but pronounced catalysis by copper(I1) ; the kinetic information should be useful to analytical chemists interested in the coulometric titration of iron (11) with electrogenerated chlorine. Until the recent paper by Liu et al. (47), no kinetic data for the oxidation of chloride by permanganate had been published, even though the interference of chloride in permanganate titrations of reducing agents like iron(I1) has been recognized for decades; the reaction was found to be first order in hydrogen ion, and to have a rather high activation energy of 17.7 j= 2.3 kcal. mole-1. Knowledge of these kinetic data permits a quantitative prediction to be made concerning adjustment of reaction conditions to minimize the titration interference. I t is interesting to note that the oxidation of iodide ion by permanganate (do), in contrast, shows first order dependence on the reductant and, furthermore, has a rather low activation energy; the kinetics and mechanism of the permanganate-ferrocyanide reaction have also been elucidated (57), very recently. I n some cases, the results of kinetic studies have suggested reactions which may be of future analytical usefulness because of their desirable characteristics. The reduction of nitrate by molybdenum(V) (89), the oxidation of vanadium(I1) by thallium(II1) (4), the oxidation of europium(I1) with vanadium (111) or chromium(II1) ( I ) , the reactions between neptunium(1V) or (V) with chromium(I1) (71, 7 2 ) , several reactions of silver(I1) (35) and the cerium (1V)-manganese(I1) reaction (61) may fall into this category. The reduction of nitrate by molybdenum(V) , which yields KO and molybdenum(V) as the major products, is especially interesting because it is one-half order with respect to molybdenum(V) ; this indicates that the molybdenum(V) monomer is probably involved. Studies of other oxidation-reduction reactions of likely analytical interest include the oxidation of vanadium(I1) by iron(II1) and chromium(II1) complexes (3), the chromium(I1)-chromium (VI) reaction ( 3 4 , the electron transfer reactions of europium(I1) ( 2 ) ,the oxidation of mater coordinated to cobalt (I1I) ( B ) ,the vanadium (I1I) -uranium (VI) reaction (53),interpretation of the vanadium(II1)-chromium(I1) reaction mechanism (32),kinetics of the reaction of peroxydiphosphate with iodide (SY), the direct observation of intermediates in the chromic acid oxidation of seconVOL. 40, NO. 5, APRIL 1968
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dary alcohols (go), the kinetics and mechanism of the cerium(1V) oxidation Of hypollhosl)horous acid (’a), the iron (111)-catalyzed oxidation of cysteine by molecular oxygen (67),and the reaction betTvee11 CoEDThZ- and ferricyanide (36).
Interesting kinetic and mechanistic studies are, by no means, restricted to oxidation-reduction systems. Currently, a great deal of attent’ion is being given to coordination reactions and their mechanistic intricacy. Many of t’hese studies are of direct allalytical illterest because allalytical chemists are amo% the main users of coordination reactions for titration, masking, extraction, etc. Examples of such studies range from simple complex formation of iro11(II) (79) and iron(II1) (52), through fast indicator reactions (79,to the complicated effects of coordination on redos reactions (39)* h high level Of sol1histication is reached in the currently popular experime11tal and theoretical consideration of chelation processes involving various combinations of comples formation, exchange, and dissociation reactions ( I S , 38,45, 46,49, 60, 68)’ Hol’efullyJ the end Of these efforts will be the establishment of a general compendium of data on the kinetic aspect,s of analytical systems; proper~vused, such illformatioll could Well ne\%’areas of oPPortuI1itY to analytical chemists. LITERATURE CITED
(1) Adin, .4.,Sykes, A. G., J . Chem. Soc.,
1966, 1230. (2) Adin, A,, Sykes, A. G., Nature, 209, 804 (1966). (3) Baker, B. R., Orhanovic, hf., Sutin, N., J . Am. Chem. Soc., 89, 722 (1967). (4) Baker, F. B., Brewer, W. D., Newton, T. W., Inorg. Chem., 5 , 1294 (1966). (5) Beck, AI. T., Record Chem. Progress, 27, 37 (1966). (6) Benson D., Fletcher, K.,Talanta, 13, 1207 (1966). (7) Bewick, A., Robertson, P. &I., Trans. Faraday Soc., 63,678 (1967). (8) Bognar, J., Jellinek, O., Mikrochim. Acta, 1966, 453. (9) Bognar, J., Sarosi, S., Ibid., p. 534. (10) Bognar, J., Toth, K., Ibid., p. 526. (11) Broman, R. F., Bowers, R. C., ANAL. CHEM.,38, 1512 (1966). (12) Burgess, A. E., Latham, J. L., Analyst, 91, 343 (1966).
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(13) Cam, J. D., Libby, R. A., hfargerum, D. w*,Inor& Chem., 6, loS3(1967). (14) Carroll, R. L., Thomas, L. B., J . Am. Chem. sot., 88, 1376 (1966). (15) Chen, T., ANAL. CHEM., 39, 804 (1967). (16) Crabtree, J. H., Schaefer, w. p.7 Inorg. Chem., 5, 1348 (1966). (17) Crouch, S. R., Malmstadt, H. V., ANAL.CHEM.,39, 1090 (1967). (18) Crouch, S. R., Alalmstadt, H. V., Ibid.i P. loS4. (19) Epstein, J., Demek, hf. M,, Ibid., p. 1136, (20) Ginzburg, S. I., Yuzko, hl. I., Zh. Analit. Khim., 21, 79 (1966). (21) Gordon, G., Tewari, P. H., J . Phys. Chem., 70,200 (1966). (22) Gregorowicx, Z., Suwinska, T., Chem. Anal. (Poland),11, 3 (1966). (23) Greinke, R. A., Mark, H. B., Jr., ( 2 $ ~ ~ d ~ ~ ? lool $ ~ (1966). ~ ~ 8 ,
(25) Guilbault,, G. G., ilnai. Biochem., is, 313 (1967). (26) Gklilba~llt, G. G., Kramer, D. N., Hackely, E., Ibid., p. 241. (27) Guilbault, G. G., Kramer, D. N., Hackley, E., ANAL. CHEM.,38, 1897 (1966). (28) Guilbault, G. G., NcCurdy, W. H., Jr., J . Phys. Chem., 70,656 (1966). (29) Giiymon, E. P., Spence, J. T., Ibid., p. 1964,,, (30) Hadjiionannou, T. P., Anal. Chim. Acta, 35, 351 (1966).
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2:
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