Simultaneous Determination of Ferrocyanide and Ferricyanide in Aqueous Solutions Using Infrared Spectrometry D. M. Drew Research Laboratory, Kodak (Australasia) Proprietary Limited, Coburg, Victoria, 3058, Australia
A number of analytical procedures are available for the determination of ferrocyanide or ferricyanide. Redox procedures ( 2 - 4 ) , precipitation titrimetry (5, 6), spectrophotometry (7, 8 ) , and electroanalytical techniques (9-22) have been used. These methods, however, are reasonably lengthy procedures which may require several steps in order to mask or separate interfering ions. Only one of these methods (12) is applicable to the simultaneous determination of ferrocyanide and ferricyanide. Many photographic bleach solutions contain a mixture of sodium ferrocyanide and potassium ferricyanide. Some of the bleach is carried into the fixer solution during processing, and a convenient method of analysis in both the bleach and fixer is desirable. In 1949, Robert Gore (13) indicated that it was possible to obtain useful infrared spectra from aqueous solutions of certain compounds. Since then, almost every worker (14) who has reported aqueous solution spectrometry in the infrared region mentions the inherent technical difficulties such as energy losses, limited range of useable absorption frequencies, and lack of suitable window materials. The latter problem has been overcome by the availability of Kodak Irtran infrared transmitting window materials, but the relatively small number of publications on this technique is indicative of the technical difficulties involved. Even so, certain specific applications can still make use of water as a solvent. This paper describes an infrared spectrophotometric procedure for the simultaneous determination of ferricyanide and ferrocyanide. Aqueous solutions are used and for photographic bleaches no pre-treatment is required other than dilution. The method is applicable to analysis of photographic bleaches, fixers, and fixer effluents.
EXPERIMENTAL Apparatus. All the infrared spectra were recorded in the range 2200-2000 cm-1 on a Grubb-Parsons "Spectromajor" infrared spectrometer (equipped with a Vitatron log/linear recorder) a t a scan rate of 25 cm-' min-l. For all analytical work, the direct recording absorbance scale was employed. The cell used in this study incorporated Irtran 1 infrared transmitting windows and had a fixed pathlength of 50 pm, using a polyethylene spacer. A similar cell filled with distilled water was employed in the refer(1) P. s. Dubey and K . N. Tandon. Talanta, 13,765 (1966). (2) K. Bhaskaro Rao and C. V. Krishnamurthy, lndian J Appl. Chem., 31, 108 (1968).
(3) L. Erdey. G.Svehla, and 0. Weber, Fresenius' Z.Anal. Chem., 240, 91 (1968). (4) E. Ruzicka, V . Dostal, and A. Haviger, Mikrochim. Acta.. 1969, 698. (5) H. D. Drew and J . M . Fitzgerald,Anal. Chem., 38, 778 (1966). (6) M . C. Eshwar and S. G . Nagarkar, Curr. Sci., 38,410 (1969). (7) T. J . Bydalek, J. E. Poldoski, and D. Bagenda John, Anal. Chem., 42, 929 (1970). (8) D. K . Kidby, Anal. Biochem., 28, 230 (1969). (9) R. J. Merrer and J . T. Stock, A n d . Chim. Acta., 53, 233 (1971). (10) H. Berge and P. Jeroschewski, Fresenius' Z. Anal. Chem., 212, 278 (1965). (11) H. Mendezand F. LucenaConde, Talanta, 16, 1114 (1969). (12) G. Farsang and L. Tomcsanyi, J. Electroanal. Chem., 13, 73 (1967). (13) R . Gore, R . Barnes, and E. Peterson,Anal. Chem., 21, 382 (1949). (14) F. S. Parker. "Progress in Infrared Spectroscopy," H. A. Szyrnanski, Ed.. Plenum Press, New York, N . Y . , 1967, Vol. 3, pp 75-87,
ence beam. A flat base line was obtained in the region of interest. Reagents. All chemicals used were analytical reagent grade. Investigations were made with pure solutions of sodium ferrocyanide, potassium ferricyanide, and mixtures thereof. Spectra were also obtained from used fixer and bleach solutions. Effects of some other cations and anions on the determinations were investigated by additions of 1.6 X 10-1M sodium thiosulfate and 3.0 X 10-1M ammonium sulfate to 2.5 X 10-2M sodium ferrocyanide and also by the addition of 3.0 X 10-1M ammonium sulfate to 6.0 x 10-2M potassium ferricyanide. Procedure. The bleach and fixer samples analyzed required dilution by a factor of five to bring the concentrations of F e ( C N ) p into the analytical range. The spectrum was recorded in the region from 2200 to 2000 cm-l. The absorbance of ferricyanide was obtained a t 2115 cm-I and that of ferrocyanide a t 2040 cm-1 by measuring the peak height from a straight line drawn through the horizontal base line. The concentration of each species was determined by reference to calibration curves previously produced from pure solutions.
RESULTS AND DISCUSSION Figure 1 shows the spectrum obtained from an aqueous solution containing both ferrocyanide and ferricyanide. The calibration graph obtained for solutions of sodium ferrocyanide was linear up to 0.04M and had a molar absorptivity of 4.24 X l o 3 liters mole-1 cm-1. The useful analytical range for ferrocyanide was 0.00031M to 0.04M. The potassium ferricyanide calibration graph was linear and its useful analytical range was from 0.0012M to 0.1M. The molar absorptivity for ferricyanide was 1.18 X 103 liters mole-1 cm-1. Absorbance readings taken from five determinations show standard deviations of *0.01 to h0.02A for both species. All standards were analyzed by chemical methods to determine actual concentrations. Ferrocyanide was determined using a cerimetric titration with sodium diphenylaminesulfonate as indicator, and an iodometric procedure was employed for ferricyanide after addition of excess zinc ion to precipitate any ferrocyanide. The results of analyses performed on synthetic mixtures of ferrocyanide and ferricyanide are shown in Table I. The observed concentration of sodium ferrocyanide in mixture 1 is in error because a t concentrations above 4.0 X 10-2M the calibration graph curves off significantly. It is evident that the determination of either ferrocyanide or ferricyanide is independent of the other Fe(CN)Gn- species present. For the interference work, the study was restricted to the effect of anions and cations most common to the photographic solutions in question. The determination of ferrocyanide was not affected by the presence of sodium thiosulfate and ammonium sulfate either separately or together. Ammonium sulfate had no effect on the determination of ferricyanide. Sodium thiosulfate was not added to the latter solutions because of its reaction with ferricyanide. Table I1 shows the results of analyses by both the infrared and wet chemical techniques of three commercial bleach processing solutions. The solutions were sampled at different stages in the usage-regeneration cycle.
A N A L Y T I C A L C H E M I S T R Y , V O L . 45, N O . 14, D E C E M B E R 1973
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Table I. Analysis of Synthetic Mixtures of Ferrocyanide and Ferricyanide Composition Species determined
Mixture
Ferrocyanide
1 2 3 1 2 3
Ferricyanide
Taken, M
Found, M
5.0 X IO-’
2.50 X lo-’ 5.0 x 10-3 1.18 X lo-’ 2.50 X lo-’ 7.50 X lo-*
4.62 X 2.50 X
lo-’
lo-’
5.0 x 10-3 1.10 X 2 . 5 0 X lo-‘ 7 . 4 2 X lo-‘
Table II. Results of Analysis of Commercial Bleach Solution Method
0.6
~
2800
2100
~
2000
Species determined
Sampie
Ferrocyanide, M
A
B
W a v en u rn b a r
cm Figure 1. Infrared spectrum of 8.0 X 10-’M potassium ferricyanide and 9.5 X 10-3M sodium ferrocyanide in water
C’
Ferricyanide, M
A B
C
The infrared method described possessed accuracy and precision which was acceptable for the intended application. Unfortunately, the analytical range could not be extended in either direction, for if the path length was increased beyond 50 km, the available energy was decreased markedly and if more concentrated solutions were used, no further information could be obtained from the ferrocyanide calibration curve because of non-adherence to Beer’s law. Since very few compounds absorb in the region near 2100 cm-1, it is likely that other applications involving water soluble compounds containing a CN group are well suited to this technique. For example, the method may be applicable to the determination of cyanide in electroplating baths, provided the concentration is large enough to fall into the analytical range suggested above. Initially, Irtran 2 (hot pressed zinc sulfide) cell windows
Infrared
1.34 X 1.03 X 4.75 X 3.04 X 4.99 x 4.04 X
10-1 lo-’
lo-’ 10-1 10-1
IO-’
Chemical
1.31 X 1.09 X 4.88 X 3.07 X 4.99 x 3.99 X
10-1
lo-’ lo-’ 10-l 10-1 10-l
were used, and it was found that the stronger potassium ferricyanide solutions attacked the surfaces leaving a white deposit which showed an absorption band a t 2090 cm-1. Zinc ferricyanide and zinc ferrocyanide were prepared in the laboratory, and the infrared spectra showed bands a t 2185 cm-1 and 2090 cm-I, respectively. It therefore appears that the white deposit was zinc ferrocyanide. Irtran 1, which is hot pressed magnesium fluoride, did not show any evidence of attack after six months of use in the ferricyanide solutions.
ACKNOWLEDGMENT The author wishes to thank J. T. van Gemert for his helpful discussions and suggestions during the course of the work. Received for review May 14, 1973. Accepted July 9, 1973.
Determination of Water Content in Toluenesulfonic Acid by Nuclear Magnetic Resonance Kiyoshi Mashimo and Tohru Wainai Department of Industrial Chemistry, Faculty of Science and Engineering, Nihon University, Tokyo, Japan
p-Toluenesulfonic acid, which is important as an acid catalyst for esterification, dehydration, and polymerization, is formed by sulfonation of toluene. However, this reaction always produces three isomers, the ortho, meta, and para forms, and the proportion of the products differs greatly according t o the reaction conditions. Because toluenesulfonic acid is very hygroscopic, its water content must be determined. The water content of toluenesulfonic acid can be determined by Karl Fischer titration, but the values obtained vary because of the compounds very strong hygroscopic property. The nuclear magnetic resonance (NMR) 2424
ANALYTICAL CHEMISTRY, VOL.
spectrum of toluenesulfonic acid in anhydrous dioxane provides a convenient handle on the water content of toluenesulfonic acid. In this NMR spectrum, the sulfonic acid proton is shifted appreciably to a low field, but with increasing water content it shifts to a higher field. Several examples have been reported for similar quantitative analyses utilizing the NMR chemical shift. These include accurate determinations of the water content of benzenesulfonic acid ( I ) , the water content of tributyl phos(1) T. Wainai and K . Mashirno, BunsekiKagaku, 19, 1629 (1970)
45, NO. 14, D E C E M B E R 1973
