lem (7). Experiments conducted in this laboratory have shown that t r a n s mittance area measurements allow the use of a spectral band pass four to five times greater than that required for highest sensitivity when peak height measurements are used.
(2) Churchill, J. R., IND.ENQ. CHEM., ANAL.ED. 16, 653 (1944). ( 3 ) Harrington, W. L., Skogerboe, R. K., Morrison, G. H., ANAL. CHEM.37, 1480 (1965). ( 4 ) McCrea, J. M., Proc. XI1 Ann. Conf.
LITERATURE CITED
21, 1016 (1965). ( 6 ) Owens, E. B., Giardino, N. A., ANAL. CHEM.35, 1173 (1963).
( 1 ) Bourgin, D. G., Phys. Rev. 29, 794 (1927).
M a s Soectrv. and Allied ToDics, - . Paper 92; Mohtreal, 1964. ( 5 ) McCrea, J. M., Spectrochim. Acta
(7) Wilson, E. B., Jr., Wells, A. J., J . Chem. Phys. 14, 578 (1946). R. K. SKOGERBOE
W. L. HARRINGTON~ G . H. MORRISON Department of Chemistry Cornell University Ithaca, N. Y. WORK supported by National Science Foundation research grant (GB-3324). ’Present address: E. I. DuPont de Nemours and Co., Wilmington, Del.
Spectrophotometric Determination of Coordinated Pyridine SIR: The pyridinium ion is a weak acid withpK = 5.18 at 25OC. (4)and has a strong absorption peak at 255 mp with molar absorptivity, B = 5350. These two properties of the ion were first used for the quantitative determination of pyridine in air samples by Hofmann (8), and in phosphoric acid extracts of hydrocarbons by LeRosen and Wiley (3). However, the pyridine content of metal complexes has usually been obtained through the microanalysis of the nitrogen content. Here it is shown that coordinated pyridine can be quantitatively determined by a combination of steamdistillation and spectrophotometric measurement. EXPERIMENTAL
Reagents. The chemicals used were of analytical reagent grade. Pyridine was dried over potassium hydroxide and distilled immediately before use. Preparation of Compounds. The vyridine complexes of Mn, Co, Ni. Cu, Zn, and Ccl were prepared by well established methods (7). The mercury complex was prepared as described in the literature (6). Analysis. The uitrogen content was determined by the Micro Dumas method in the Microanalytical Lahoratory of the Chemistry Department. Spectral Measurements. -4bsorb&rice measurementq were made on a Beckman Model 13)u Spectrophotometer in a room niaiiitained a t 25” C. using matched 1-cm. and 10-cm. silica cells. The molar absorptivity, e, of the pyridinium ion in 0.lX sulfuric acid was determined for a series of solutions with concentration ranging from 4 X 10-6M t o 1.4 X 10-‘M and found to be 5346 f 31 in agreement with the reported value ( 5 ) . -Procedure. In the analvsis of w r i dine in a complex, 10 ml. 6f a sohiion ?oiitaining about 2.5 to 5 mg. of the complex was treated with 20 ml. of 2 N sodium hydroxide solution and steamdistilled. .ibout 150 ml. of distillate was coilected in a flask containing 25 ml. of I N sulfuric acid. The distillate was diluted to 250 rnl. in a standard flask
Table I.
Nitrogen and Pyridine Determination of Pyridine Complexes
Compoundsa MnPd(NCS)r COP~(NCS)Z NiP,(NCS)Z CUPZ( NCS)z ZnPZ(NCS)z CdPz(NCS)z HgPd CrZO,) a
P
=
Nitrogen microanalyses, % N Calcd. Found Difference, %
Pyridine analyses, yo pyridine Calcd. Found Difference, %
17.24 17.10 17.11 16.58 16.49 14.49 4.87
64.90 64.37 64.41 46.82 46.56 40.90 27.52
17.17 16.80 17.16 16.54 16.40 14.66 4.90
-0.4 -1.8 +0.3 -0.2 -0.5 $1.2 +0.6 Mean = 0 . 7
65.2 64.5 64.0 46.3 46.1 40.9 27.6
+0.5 +0.2 -0.6 -1.1 -1.0 . . .
-0.3 Mean = 0 . 5
pyridine.
and the absorbance of the solution measured in matched l-cm. silica cells a t 255 mp. For the blank solution, the same procedure of distillation was employed except that 10 ml. of water was used in place of the sample solution. Several steamdistillations of pyridine from solutions containing known amounts of pyridine were carried out under the same experimental conditions. The recovery of pyridine was found to be quantitative. RESULTS AND DISCUSSION
The results from the steamdistillation of the pyridine complexes are shown in Table I. The mean deviation of the percentage difference between the calculated and the experimental values for the pyridine determination is close to 0.5%, a value comparable to that obtained in the nitrogen analysis by the Micro Dumas method. One attractive feature which recommends the proposed method is that it can be performed rapidly with the usual laboratory facilities. Furthermore it gives the pyridine content rather than the total nitrogen content, and hence is suitable for the determination of pyridine in the presence of other nitrogen-containing compounds, provided these do not absorb in the same region of the spectrum. Should the distillate contain other species absorbing in the same region of
the spectrum as the pyridinium ion, the method would have to be slightly modified to include measurements a t more than one wavelength and the use of a set of simultaneous equations tor calculating the concentrations of the component species (I). ACKNOWLEDGMENT
The author thanks A. K. Kiang for his interest and Mrs. H. K. Tong for the microanalyses. LITERATURE CITED
(1) Bauman, R. P., “Absorption Spectroscopy,” p. 403, Wiley, New York, 1962. (2) Hofmann, E., Arch. Hyy. Bakterzol. 128, 169 (1942). (3) LeRosen, H. D., Wiley, J. T., ANAL. CHEM.21, 1175 (1949). (4) Murman, R. K., Basolo, F., J. Am. C L m . SOC.77, 3484 (1955). (5) Podall. H. E.. ANAL.CHEM.29. 1423 . (1957). ’ (6) Spacu, G., Dick, J., Z. Anal. Chem. 76, 273 (1929). (7) Vogel, A. I., “A Textbook of Quantita-
tive Inorganic Analysis,” 3rd ed., pp. 132, 493, 497, 526, 529, 533, Longmans, Green and Co., London, 1962. K. P.
..\NO
Chemistry De artment, University of gingapore, Singapore VOL 38, NO. 10, SEPTEMBER 1966
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