INDUSTRIAL A N D ENGINEERING CHEMISTRY
748
TABLE 11. BLANKSOBTAINED UNDER VARYIN0 CONDITIONS No. of Determinations
HC1
KI per 25 M1. of Solution
Time,of Standing
M1.
aroma
Min.
3
10 10
2 3
20 10
5.0 2.5 4.0 4.0
15 15 5 5 15
3
10
7.5
0.1 N NaeSnOa,
Average
MI. 0.25
0.17 0.14
0.23 0.29
Discussion Several factors must be carefully controlled. It is advisable to use samples of 0.7 to 1.00gram, as then the volume of the thio-
sulfate used is well within the desirable titration range, The ratio of the sample weight in grams to the volume of hydrochloric acid in milliliters must be kept between 1 to 7 and 1 to 15 to ensure complete solution and yet avoid too great an excess of acid. The ratio of the volumes of the hydrochloric acid and potassium iodide solution must be kept between 1 to 2 and 1 to 3 to prevent the precipitation of the ferric phytate and yet maintain as low an acid concentration as possible. There is a blank liberation of iodine which depends upon the amount of potassium iodide and hydrochloric acid and the time of standing (Table 11). Varying these three factors within the limits set up herein does not affect
Vol. 15, No. 12
the determination, provided a correction is made for a blank run under identical conditions. It is suggested that rn a routine procedure the volume of the hydrochloric acid and potassium iodide solution be accurately measured by pipet and the time of standing be recorded on a stopwatch. It will then be necessary to run only one set of blanks for each batch of hydrochloric acid and potassium iodide for different times of standing. A 1 to 50 dilution of the thiosulfate in the blank titration will give more reliable values. If the blank titration is plotted against the time of standing, the correction to be applied to any determination can be read off the graph. The results by the Zimmerman-Reinhardt method are slightly lower (0.1 to 0.2 per cent) than those by the direct titration method, which can undoubtedly be attributed to incomplete digestion and solution.
Literature Cited (1) Andrews, J. S., Evans, L. H., and Huber, L. J., U. S. Patent 2,239,543(Apr. 22, 1941). (2) Kolthoff and Furman, “Volumetric Analyses”, Volume 11, p. 422, New York, John Wiley & Sons, 1929. (3) Kolthoff and Sandell, “Textbook of Quantitative Inorganic Analysis”, p. 570,New York, Maomillan Co., 1938. (4) Morrow and Sandstrom, “Biochemical Laboratory Methods”, p. 226,New York, John Wiley & Sons. 1935. (5) Posternak, S.,Compt. rend., 168, 1216 (1919).
Quantitative Determination of Sulfanilamide and Sulfathiazole in Mixtures Spectrophotometric Method D. T. ENGLIS
AND
DOUGLAS A. SKOOG’, Noyes Chemical Laboratory, University of Illinois, Urbana, Ill.
T
H E wide use of the sulfa drugs has given rise to considerable interest in their analytical reactions. Their assay, differentiation, and identification have been the subject of a recent article by Calamari, Hubata, and Roth (5). The principal chemical reaction employed for the quantitative estimation of those substances involves the diazotization of the aryl amino group. By coupling the diazonium salt and production of an azo dye the compound may be estimated colorimetrically and the sensitivity gteatly increased (6). Anderson ( 1 ) has called attention to the fact that free sulfanilamide and acetylated sulfanilamide have different absorption characteristics in the range 310 to 360 mp and has devised a unique fluorometric method for the estimation of each. A problem which was presented to the authors was the determination of sulfanilamide and sulfathiazole when present together in a mixture. It seemed probable that these compounds would show markedly different absorption characteristics in the ultraviolet range and that the determination of each could be accomplished by a physical method without separation of the constituents. I n 1930 Barnard and MacMichael (2) demonstrated that a color system of two components may be quantitatively analyzed, even if both components show absorption a t the selected wave length, provided the degree of absorption is sufficiently different and the sample represents a definite total amount of the two constituents only. Knudson, Meloche, and Juday (4) have pointed out an extension of the general principle and have indicated how the method may be used for more than two components. It is necessary to determine the extinction coefficients of each pure component at selected wave lengths 1
Present addreas, Standard OilCo., Richmond, Calif.
which give the widest differences in absorption of one from the other components. The extinction value of the mixture is then determined at the selected wave lengths and the proportions of the various constituents are calculated from the data by the solution of a series of simultaneous equations. It was the object of this study to develop a method for the analysis of the sulfa drug mixture based upon this principle.
Experimental The instrument employed in this work was a Bausch & Lomb medium quartz s ectrograph. The slit was adjusted to a width t y e hydrogen discharge tube, which gives of 0.06 mm. A a continuous spectmm o r fairly uniform intensity over the desired wave-length range, served as the source of illumination. The source was placed with the exit window a t a distance of 10 cm. from the slit. A cell of 1-cm. length with quartz windows wm used to hold the liquids during their examination. Separate exposures of the solvent and the solutions were taken for a period
dad's
TABLEI. DETERMINATION OF SULFATHIAZOLE AND SULFANIL AMIDE
IN
MIXTURESBY SPECTROPHOTOMETRIC EXAMINATION AT
Mixture
2600 AND 2875 A.
(Values expressed in mg. of comtituent per liter) Sulfathiarole Sulfanilamide DeviaDeviaAdded Found tion Added Found tion 1.17 -0.08 +0.05 1.25 2.50 2.55 -0.18 1.42 1.60 +0.04 8.37 8.33
10.00 2.00 5.00
7.00 3.00 1.25
9.70
1.97 5.20 6.95
3.30
1.29
-0.30 -0.03
2.00 10.00
+0.30
7.00 2.60
+0.20 -0.05
+0.04
5.00
3.00
1.97 10.40 5.09
3.11 7.50 2.70
-0.03
1-0.40 +0.09
+o. 11 +0.50
+0.20
ANALYTICAL EDITION
December 15, 1943
149
From a solution of these equations the number of grams of each constituent in the solution is determined. The results of a group of analyses are given in Table I. 14
SULFA N I L A MIDE
Discussion An examination of Table I shows the order of agreement which may be expected in series of analyses in which the ratios and total amount of the two constituents are varied. The procedure employed involved the assumption of a source of illumination of constant intensity. This assumption was checked by making a series of exposures of the source in which the time was constant for each. The variation was within the range of other experimental errors. It is obvious that if the observations were made with an instrument which did not require the photographic process-for example, the photoelectric spectrophotometer adapted to the ultraviolet range-the errors which are inherent in the photographic method might be eliminated and the process of analysis greatly simplified. It is possible that solutions of higher concentration might be handled with surh equipment and the accuracy of the method improved.
1.4
0 2400
I
2500
I
2600
WAVE
I
I
I
27W
2800,
2 W
FIQURE 1. ABSORPTIONCURVES
i
E: EL E: E; EA E,
= = = = = =
extinction for 1 gram per liter of sulfathiazole at 2600 A. extinction for 1gram per liter of sulfanilamide at 2600 A. extinction for 1 gram per liter of sulfathiazole at 2875 A. extinction for 1 gram per liter of sulfanilamide at 2875 A. extinction for the mixture a t 2600 A. extinction for the mixture at 2875 A.
If z
= grams of sulfathiazoleper liter y = grams of sulfanilamide per liter
Then zE:
zE:
+ yE: = E; + yEl = E ,
AT 2600 A AT 2873 A AT 2000 A AT 2875 A
1.2
1.0
Figure 1 shows the absorption curves for pure sulfathiazole and pure sulfanilamide in 95 per cent ethanol solutions. The sulfanilamide solution shows an absorption peak a t 2610 A. and the sulfathiazole solution has two absorption peaks, one a t 2580 A. and one a t 2875 A. The sulfanilamide has a slight absorption a t 2875 A. also. The absorption values a t different concentrations of each compound were determined and the results are indicated in Figure 2. The solutions of both compounds obey the Beer-Lambert law a t both 2600 and 2875 A. Therefore, a quantitative estimation of each of the constituents is possible in a mixture of the two. The data necessary for making a calculation of the quantity of each are given below:
SULFANILAMIDE SULFATHIAZOLE SULFATHIAZOLE Ip SULFANILAMIDE
m
30
LENGTH IN A.
of 2 minutes each. The spectra were recorded on Eastman Polychromatic plates. Each plate waa calibrated by taking a series of separate successive exposures in which the time interval was varied in a regular manner as follows: 4, 8, 16, 32, 64, and 128 seconds. The plates were developed for 6 minutes in Eastman x-ray developer a t 18" C., then fixed, washed, and dried. After drying, the densities of the spectrograms at selected wavelength intervals were determined with a Leeds & Northrup recording microphotometer. A family of plate calibration curves for the selected wave lengths was then constructed and by reference to the appropriate curve the relative intensity values for the pure solvent and the solution were found and from these the extinction value for the solution was calculated.
I II
=0
-
0.8-
ILJ
z
ae-
X W 0.4
-
CONCENTRATION
I N MG/L.
FIGURE 2. ABSORPTION VALUES
Acknowledgment The authors wish to express their indebtedness to L. A. Hall The Griffith Laboratories, Chicago, Ill., a t whose suggestion the problem was undertaken and from whom the samples employed in this study were obtained.
Literature Cited (1) Anderson, S.,IND.ENG.CHEM., ANAL.ED.,15,29 (1943). (2) Barnard, M., and MacMichael, P., Ibid., 2,363 (1930). (3) Calamari, J. A.,Hubata, R., and Roth, P. B., Ibid., 14, 534 (1942). (4) Knudson, H. W.,Meloche, V. W., and Juday, C., Ibid., 12, 715 (1940). ( 5 ) Lee, S. W., Hannay, N. B., and Hand, W. C., Ibid.. 15, 403 (1943).
