frequency and the nieasured absorbance are given in Table 11. h comparison of coinpounds 50 to 54 \Tith 55 to 57 indicates t h a t the additional conjugation of the phenyl group lowers the frequency slightly and enhances the intensity considcrahly .
50 51 32
ACKNOWLEDGMENT
53 54 55
l'h author is grateful to the Research Cor)). for its bupport of this investigation in the form of a Frederick Gardner C'ottrcll grant.
i;
LITERATURE CITED
(1) Baran\-. H C., Braude, E. -4., Pianka, AT., J . Chem. SOC.1949, 1898. ( 2 ) Bellaniy, L. J , ('Infrared Spectra of
C=C Stretching Frequency of Type D Azomethines R-C=N-R' Frequency, R R' crn.-' -CH~CH~)LCH~ 1624 CHZCH=CH-CH,CH( CH,)2 1631 CH~CHZCH1624 CHZCH=CH-C(C&h -CHJ( CH,),CH, 1628 CHsCH=CHCH3CH=CH-CH,CsH, 1628 1620 C6HacH=CH- CHZCHzCH? CEHSCH=CH-CH,CH(CH3)2 1620 C6H4CH=CH-CH,( CH,),CH, 1620 Table II.
(5) Freeman, S.K., A r a ~C H E x . 25, 1750
Complex Molecules," 2nd ed., p. 268, Methuen and Co., London, 1958. (3) Berg, RI. -4., Bull. SOC.Chim. 37, [4] 637 (1925) ( 4 ) C:impbrll, K. N., Sommers, A. H., Campbell, B. I Ac- > C12 l\TOg-. The iodide supporting electrolyte shifts the free nickel ion reduction wave slightly positive (approximately +0.05 volt). This effect is thought t o be a typical 3 effect (8) resulting from changes in the potential difference across the electrical doublelayer caused by the specific adsorption of anions (8). This effect has been studied in detail for ?;i(HzO)e+2 polarographic reduction ( 5 ) . Both sodium and potassium ions were used as the cation of the supporting electrolyte and the prewaves were identical for either. Analysis of Pyridine. Examination of t h e curves of Figure 4 in-
Table 1. Variation of Prewave Height with Nature of Supporting Electrolyte Solutions contain 1.30 X 10-zfif 1.35 X 1 O - * X Ca+2, and 12.2 X l O - 5 J f pyridine. pH adjusted to value shown Height of prevave at -0.85 Supporting volt us. electrolyte pH S.C.E., fia. 0.10M NaAc 6.36 5.2 0.10M KI 6.35 5.6 0.1OM KCI 6.25 4.5 0.10M KX03 6.25 4.4
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Table II. Analysis for Pyridine Solutions contain 1.30 X 10-2Jf 1.35 X 10-2Jf CaL2, and 7.10 f 0.05 and the temperature = 25’ C. =t Concentration of pyridine Kumber of Taken, Found, determinations 111 x 105 M x 105 I .22 1.2- 1 . 4 3.0- 3 . 2 3.06 4.3- 4 , s 4.28 5.7- 6.2 6 11 9.17 9 . c 9.6 11.8-12.5 12.2 14.8-15,6 15.3 18.3 18.1-18.6
dicates t h a t the optimum range of nickel concentration i n t h e sample should be approvimately 0.9 X 10-2 t o 1.2 X 10-2M. A t these concentrations the free nickel reduction wave starts t o rise a t about -0.85 volt 2’s. t h e S.C.E., a n d this represents a suitable potential for the analysis. The range of pvridine concentrations which can be measured under these
Table 111.
Comparison of Catalytic Properties pH = 7.5 =t 0.05, 7’ = 25’ C., supporting electrolyte 0.10M SaAc, = 1.3 X 10-2JI, [CaA2]= 1.35 X 10-*M Catalytic Em, volts enhancement? Compound us. S.C.E. 50.0 1,2-Diaminonaph- 0 , 70 thalene 3,4-Toluenedianiine - 0 7 3 o-Phenylenediamine - 0 7.5 2.5-Toluenediamine - 0.85 3;4-Diarninobenzoic -0.85 10.0 acid 1 &Diaminonaph- 0.80 thalene Pyridine -0.81 3-Methylpyridine -0.81 2-Methylpyridine -0.82 2-Aminopyridine -0.83 2-Hydroxgpyridine -0.83 3.0 4,4-Diaminostil-0.85 bene-2,2‘-disulfonic acid p-Phenylenediamine -0.83 1,5-Diaminonaph- -0.86 thalene Aminoethylpiper-0.86 nene Aliphatic 1,2-di-0.86 amines ( u p to 4 carbons) 2,2’-Bipyridine -0.86 2-Aminoethanol -0.86 1 nz-Phenvlenedi-0.86 1(almost amine inactive) KHQ t
1
i
I
Monoamines*
complex). * All aliphatic and aromatic monoamines (primary, secondary, and tertiary) tested were inactive: Fee text.
198
ANALYTICAL CHEMISTRY
=
Deviation, M x 105 0 to 0 2
-0 1 t o +O 1 OOto+O2 -0 -2 to f O 1 -0 2 to f O 4 -0 4 to +o :3 -0 5 to +o 3 -0 2 to $0 3
conditions is 1.0 x 10-5 to 3.0 X 10-4Jf; a precision of about 1 0 . 4 x 10-5.11 was achieved. Table I1 shows the results of some typical deterniinations of pyridine in a solution containing 1.30 X 10-23f nickel ion, 1.35 X 10-25f calcium ion, and 0.1031 sodium acetate (pH 7.10 =t 0.05). Concentrations of pyridine as low as 0.5 x 10-6N can be detected by increasing the nickel ion concentration to about 3 x 10-231 although the precision is poor a t such low concentrations. Acetate was chosen as the anion for the supportiny electrolyte in this in\ estigation because large prewaves could he obtained in its 1)rescnce without shifting the nickel ion background v ave toward positi\ e potentials as did iodide. As the temperature coefficient of the catalytic current is quite large, i t is necessary to maintain the temperature to ivithin 1 0 . 3 ” C. t o obtain reproducible it values. OTHER COMPLEXING AGENTS EXHIBITING PREWAVES WITH NICKEL(I1)
d variety of organic compounds containing basic nitrogen \\-ere tested. A summary of the results is shown in Tablc I11 where the compounds are listed in order of the magnitude of the enhancement of the current due to the catalytic mechanism. Formation of 1 to 1 metal ion-ligand complexes with 100% aswciation was assumed in calculating the cnliancement. Table 111 also lists, with each compound, the approximate 1-alue of the half-wave potential, El 2 of the catalytic prewave. The term E , 2 does not, of courqe, carry here the same meaning as !\-hen applied to diffusion-controlled rj-ares. Aniinoethylpiperizene, 4,4’-dianiinostilhene-2,2’-disulfonic acid. 2-aminoethanol, ethylenediamine, 1,2- and 1.3proprlenediamine, 1,2- arid 1,3-butylenediamine, p-phenglenediamine, and trans-l,2-diaminocycloli~~ane exhibited more poorly defined prervaves than the other compounds. Their prewaves occur a t more negative potentials, and the catalytic enhancement is less. These preivares, however, are suitable for
inacre
a The factor by which it is greater than a calculated diffusion controlled current (assuming 100% association of a 1 t o 1
0.1OJI SnAc. pH
0.1
analysis of these species in the to IO-jJI concentration range. The aromatic cornpounds p,p’-diaminiodiphenvlmethane, benzidine, 2,2’-bipyridine, and 1,5-diaminonaphthalene yield well defined prewar es and also suppress the Si(H?0)6t2 background wa\ e (probably the result of their adsorption on mercury). These prewaves are also applicable for analysis in approximately 10-4 to 10-jZlf concentration range. Kater-soluble aliphatic and aromatic monoamines (primary, secondary, arid tertiary) were also investigated over a wide range of concentrations. S o prewave mas observed for any of these compounds. The presence of 10-4X or less of these monoamines (including K H 2 ) does not inkrfere with the determination of any of the above compounds which exhibit a pren ave. Because other metal ions, such as CoT2 and I n f 3 ( I @ , behave siniilarly to X i f 2 in noncomplexing media (form hexa-aquo complexes) and In+3 has been observed to reduce a t more positive potentials as does S i + 2 ( I S ) in the presence of C1-, it is believed that catalytic waves may also be found with these other metal ionq. Thus, this analytical method might bc extended to include a large number and variety of compounds. The mechanism of this process, the subject of future investigation, appears to be quite complex. Undoubtedly, several effects enter into the over-all reaction and in varying degrees. These effects are thought to be the ability of the ligand to form a complex, adsorption of the ligand on the mercury surface, ability of the ligand to act as bridge 1% hich facilitates the transfer of the electrons from the electrode t o the metal ion, and the various competitive effects of protons on certain of these proccsses. ACKNOWLEDGMENT
The authors express their appreciation to Lucien Gierst, Laboratory of hnalytical Chemistrj-, Faculty of Science, Free University of Brussels. Belgium, for his helpful discussions of and valuable suggestions for this research. LITERATURE CITED
(1) Ablov, A. V., Sazarova, C. V., Z h . S e o r g a n . Khzvi. 2, 53 (1957). (2) Bjerrum, J., Chem. Reis. 46, 381 (19?0). (3) Rjerriim, J , Schnarzenbach, G., Sillen, L. G,, “Stahility Constants, Part I, Organic Ligands,” p. 27. Chem. SOC.,
London, 1956. (4)Brdicka, R., Collection Czech. ChenL. Conlintin. 5 , 238 (1933); 8, 366 (1936). ( 5 ) Dandoy, J., Gierst, L , J . Electroanal. Chem. 2, 116 (196:). (6) Delahay, P., Sew Insfrumental Methods in Electrochemistry.’ pp. 112113. Interscience, S e x York, 1954. (7) Emelianova, N. V., Heyrovsky, J., Trans. Faraday Soc. 24, 257 (lp28). (8) Gierst, L., private communicatlon,
1962; “Trans. Sympoeium on Electrode Processes,” Chap. 5, p. 109, Wiley, Yew York, 1939. (9) Harris, IT. E., Kolthoff, I. )I., J . A m . Chem. SOC.68, llT5 (1‘146). (10) Kolthoff, I. h l . , Lingane, J. J., “PolarouaDhv.” Vol. I. 2nd ed.. Cham 13, Inteysrience, Sew York, 1952. (11) Kolthoff, I. >I., I’arrv, E. P., J . i l m . Chern. SOC. 73, .%15 (1951); Sorhnik Jfenzurad. Polarog. Sjerdu ~
Pruzc., 1st Congr., 1951, Pt. 1, Proc., p. 145. (12) Lingane, J. J., J . A m . Chem. SOC. 61, 2099 (1939). (13) Lingane, J. J., Kerlinger, H., IND. E A G CIIEV., . k A L . ED. 13, 77 (1941). (14) Mark, H. B., Jr., Reilley, C. S . , J . Electroanul. Chem. 4, 189 (1962). (15) Xleites, L., “Polarographic Techniques,’’ pp. 75-82, Interscience, X e w York, 1955. (16) Ibad., p. 56.
(17) Tur’yan, Ya. I., Serova, G. F., Zhttr Fis. Khim 31, 1956, 2200 (1967). RECEIVED for review September 26, 1962. Accepted December 14, 1962. Research sponsored in part by the U. S.Air Force, Office of Scientific Research and Development Command, under Contract KO. 49(638)-333. Presented a t the Combined Meeting of the Southeast and Southwest Sections, .4CS, New Orleans, La., December 7-9,1961.
Comparison of Spectrophotometric and Spectrophotofluorometric Methods for the Determination of Malonaldehyde EUGENE SAWICKI, THOMAS W. STANLEY, and HENRY JOHNSON Roberf A. Taft Sanitary Engineering Center, Cincinnati 26, Ohio
b Ten new methods for the determination of malonaldehyde are compared with the thiobarbituric acid method. The reagents used in the new procedures are aniline, 4-hexylresorcinol, N-methylpyrrole, indole, 4’aminoacetophenone, ethyl p-aminobenzoate, 4,4’-sulfonyldianiline, pnitroaniline, and azulene. The most sensitive spectrophotometric method i s the thiobarbituric acid method; the most highly selective is the pnitroaniline method. The spectrophotofluorometric methods are b y f a r the most sensitive; they are highly selective also. Nanogram amounts of malonaldehyde can be determined with very little interference from other compounds. All methods measuring absorbance are in compliance with Beer’s law. The spectrophotofluorometric methods measuring emission show a similar linear relation between the emission reading and the concentration. Most of the methods have a reasonable preckion and color stability.
I
a continuation of prerious research on the origination of methods of analysis for ox) genated organic fragments that could contribute to air pollution, a group of diverse procedures for the detwmination of malonaldehyde are introduced. The availability of a group of methods giveq the researcher a distinct advantage in obtaining optimum results for a specific test mixture. Also, the results of analyses by several methods may be checked against each other. Nalonaldehyde exists in aqueous acidic solution mainly as the tautomer, 8-hydroxyacrolein (14). It can be determined in aqueous acidic (A,,, = N
245 nip, E = 13,000) or alkaline (A mar = 267 mp, E = 30,000) solutions. Obviously the presence of organic compounds that absorb in the ultraviolet region would interfere seriously in this determination. Phloroglucinol has been used to determine nialonaldehyde; a red dye is formed ( 6 ) . llalonaldehyde also can be determined with barbituric or thiobarbituric acid and its I,3-diphenyl and 1,3-diethyl derivatives; the chromogens obtained absorb at 486, 530, 537, and 540 mp, respectively (21). The red phloroglucinol chromogen is about one fifth af intensely colored as the red thiobarbituric acid dye; t h r yellow barbituric acid chromogen is almost as intense as the thiobarbituric acid dye, but requires over 100 minutes of heating for quantitative condensation ( 2 2 ) . Of the published methods for the determination of malonaldehyde, the most satisfactory appears to be the thiobarbituric acid method. 4 disadvantage, however, is that the thiobarbituric acid reaction as applied t o animal tissue gives color reactions M ith various compounds and therefore ir not specific ( I S ) . Some of the interfering colors obtained are due to the decomposition of the thiobarbituric acid nhen it is heated in the presence of acids or oxidizing agents (19). If the mixture being analyzed contains hydroperoxides, the decomposition is accelerated. Many types of mixtures submitted t o the thiobarbituric acid test have yielded a n appreciable amount of absorption in the 440- to 460-mfi region (3, 4,10, 25, 26). Compounds such as glycidaldehyde and glyceraldehyde form a yellow chromogen absorbing a t 466 nip (16). d large amount of this background absorption would interfere seriously with
the determination of malonaldehyde by thiobarbituric acid. Thiobarbituric acid has been used to determine malonaldehyde and its derivatives as derived from rancid foods (do), linolenic acid ( 7 ) , 2-deoxy sugars and galactal (22), 2-aminopyrimidine and sulfadiazine (17 ) , highly unsaturated fatty acids (9), sialic acids (259, p-formylpyruvic acid (24), 2keto-3-deoxyheptonic acid (8), and 2-keto-3-deoxygluconic acid (2). p-Nitroaniline has been used for the detection of malonaldehgde ( 5 ) . Following periodate oxidation, deoxy sugars and glycals n-ere distinguished from methylpentoses by the deep yellow zone which they gave when the chromatogram was sprayed m-ith a n acidic solution of p-nitroaniline. The yellow color is due t o the neutral dianil, I, X = NO2,or its salt. The procedurrs introduced for the determination of nialonaldehyde and malonaldehyde-yielding compounds are compared with the thiobarbituric acid method. EXPERIMENTAL
Reagents and Apparatus. dzulene, 10% aqueous tetra-n-propylammonium hydroxide, and 3-niethoxyacrolein dimethyl acetal were obtained from Distillation Products, Rochester, 1;. Y.; 4’-aminoacetophenone, p nitroaniline, indole, 4-hexylresorcinol, and malonaldehyde bis(dimethy1 acetal) from Laboratory Services, Cincinnati, Ohio; S-methylpyrrole, 4.4’-sulfonyIdianiline, and S-ethylcarbazole from Aldrich Chemical Co., ,Ililwaukee, \Vis. Most of the other compounds were obtained from these sources also. All chemicals were purified by crystallization to a constant melting point or by distillation. VOL. 35, NO. 2, FEBRUARY 1963
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