198
A N A L Y T I C A L CHEMISTRY
Trans-olefinic derivatives can be detected by the presence of a band in the 10.20- to 10.35-micron region (980 to 966 cm.-1). The combined use of ultraviolet, visible, and infrared spectra will permit the assignment of the class to which the parent carbonyl compound belongs. The assignment of this class greatly diminishes the number of infrared spectra iyhich must be compared for positive identification. ACKNOWLEDGMEIYT
The authors wish to thank E. K. Chavis, M. D. Edmonds, and F. L. Greene for preparing the solutions and obtaining the spectra and paper chromatograms. Thanks are also due to the members of the Philip Morris Research and Development Department for their many helpful suggestions during the course of this investigation. The authors wish to express their appreciation to Philip Morris, Tnc., for permission to publish this work. LITERATURE CITED
(1) Bellamy, L. J., “Infrared Spectra of Complex Molecules,” New York, Wiley, 1954. (2) Braddock, L. I., Garlow, K. Y., Grim, L. I., Kirkpatrick, d.F.,
Pease, S. W.,Pollard, A. J., Price, E. F., Reissmann, T. L., Rose, H. -4,, and Willard, M. L., ANAL.CHEM.25, 301 (1953). Brady, 0. L., and Elsmie, C. V., Analyst 52, 77 (1926). Braude, F. A., and Jones, E. R. H., J . Chem. SOC.1945, 498. Brederick, H., Ber. 65, 1833 (1932). Brederick, H., and Fritsche, E., Ibid., 70, 802 (1937). Connolly, E. E., J . Chem. SOC.1944, 338. Johnson, G. D., J . Am. Chem. SOC.73, 5888 (1951). Ibid., 75, 2720 (1953). Rlendelowita, A . , and Riley, J. P., Analvst 78, 704 (1953). Roberts, J. D., and Green, C., IND. ENG.CHEM.,AXAL.ED. 18, 335 (1946). Roberts, J. D., and Green, C., J . Am. Chem. SOC.68, 214 (1946). ROSS,J. H., AKAL. CHEM.25, 1288 (1953). Scheidt, U., and Reinwein, H., 2. Naturforsch. 76, 270 (1952). Schepartz, -4.I., and Daubert, B. F., J . Am. Oil Chemists’ SOC. 27, 367 (1950). Seligman, R. B., and Edmonds, A I . D., unpublished data. Stimson, Mi. M., and O’Donnell, M. J., J . Am. Chem. SOC.74, 1807 (1952). Samant, H. H., and Planinsek, H. J., Ibid., 72, 4042 (1950). White, J. W.,ANAL.CHEM.20, 726 (1948). Young, C. W.,DuT’all, R. B., and Wright, N., Ibid., 23, 709 (1951). RECEIVED for review December 17, 1954. hccepted December 8, 1955. Presented in part at the Tobacco Chemists’ Research Conference, Richmond, Ta., Sovember 11 and 12, 1954.
S pectrophotomet ric Determination of Iron with 5411Ifoanthranilic Acid JAMES M. ZEHNER
and
THOMAS
R. SWEET
McPherson Chemical Laboratory, The O h i o State University, Columbus 70, O h i o
Although anthranilic acid has been used for many gears as a precipitating agent in quantitative analysis, the present work represents the first use of the sulfonic acid derivative as an analytical reagent. A new method for the spectrophotometric determination of iron has been developed which involves the addition of ferric iron to a large excess of 5-sulfoanthranilic acid at pH 4.0. The absorbance is measured at 455 mfi.
A
NTHRASILIC acid forms insoluble complexes with many ions and has been used for the quantitative precipitation and determination of cadmium, zinc, lead, mercury, manganese, cobalt, nickel, and copper (1-4). Anthranilic acid was sulfonated in order to make the metal complexes soluble in water. This modified anthranilic acid was studied as a reagent for spectrophotometric analysis. I t was found that ferric iron forms an intense red complex with the reagent and has an absorbance maximum a t 455 m p (Figure 1). This provided the basis for a convenient spectrophotometric determination of iron that was relatively free of interference by other ions. Harris and Sweet (6) have determined the formation constants of the cobalt, nickel, copper, zinc, and cadmium complexes of 5-sulfoanthranilic acid. These are small, varying from a K,, value of 1.19 X lo8 for copper to a K,, value of 3.76 X lo2 for cobalt. REAGERTS
5-Sulfoanthranilic Acid Solution. The s-sulfoanthranilic acid was prepared according to the directions that were given in a previous communication ( 5 ) . A 0.1M aqueous solution was prepared and was adjusted to pH 4 . 0 with 0.5N sodium hydroxide. Standard Iron Solution. Primary standard grade iron wire (0.3040 gram) was dissolved in a minimum volume of 1 to 1 nitric acid. The solution was heated on a steam plate to remove excess acid and oxides of nitrogen. Several 10-ml. por-
tions of water were added to prevent the mixture from going t o dryness. The solution was diluted to 1 liter with water. APPARATUS
All pH measurements n-ere made with a Beckman Model G pH meter equipped with microelectrodes. The absorption measurements were made with a Beckman Model D U quartz spectrophotometer equipped with I-cm. Corex cells. -4 slit width of 0.04 was maintained during all the measurements. PROCEDURE
.4dd 20 ml. of the sample (containing from 5 to 150 p. p.m. of iron) to 25 ml. of the 5-sulfoanthranilic acid solution and dilute to 50 ml. with water. The pH of the resulting solution should be 4.0. (If the sample solution is highly acidic, it may be necessary to add a larger quantity of the reagent solution or to adjust the pH of the 20-ml. sample to approximately 1.5 t o 2 with sodium hydroxide before the addition of the reagent solution.) Measure
hk,
the absorbance, defined as the function loglo at 455 mr. Zeuln. Use a 0.05Jf reagent solution a t p H 4.0 as the blank. Prepare a standard curve in the same manner by using various known aliquots of the standard iron solution. DISCUSSION
As shoun in Figure 2, the absorbance is dependent on the pH and has a maximum value a t pH 4.0. The absorbance is nearly constant over the pH range 3.6 to 4.4. Figure 3 shows the effect of reagent concentration on the absorbance. A final reagent concentration of 0.05M was used in the suggested procedure. This concentration was selected for two reasons. The change in absorbance with reagent concentration is very small and the excess 5-sulfoanthranilic acid [with a pH value of 4.70 ( 5 ) ] is a good buffer a t pH 4.0, thus eliminating the need of finding another suitable buffer system that does not complex with the iron. -4time study was made on the reagent solution. ,4t measured time intervals, aliquots from the same 5-sulfoanthranilic acid solution were used in the determination of a 38.0 p.p.m. iron
V O L U M E 28, NO. 2, F E B R U A R Y 1 9 5 6
199
06tP
W V
0
.a L
0
n
a 00 3
2
I
5
4
PH
i
00 '
+
400
3
-
,.
.
n
4
? .
500
Variation in absorbance with pH
Figure 2.
Solutions were 2.72 X 1O-'M with respect t o iron a n d 0.05M with respect t o S-sulfoanthranilic acid
600
W a v e l e n g t h in rnp
Figure 1. Absorption curves Solution 0.05.W with respect to 5-sulfoanthranilic acid a t pH 4.0 H. Solution 2.72 X IO-4.M with respect t o iron and 0.0511 with reqpect to 3-sulfoanthranilic acid at pH 4.0 I.
solution. LesJ than +I% error byas observed over R period of one week. A time study was made on the complex that formed. A solution was prepared by mixing 20 ml. of a 38.0 p,p.m. iron solution and 25 ml. of the freshly prepared reagent solution and diluting to 50 ml. with mater. The absorbance of this solution was measured a t intervals. One per cent fading was observed during the period from 10 minutes t o 3 days after mixing and an additional 2% fading W R S noted during the next 4 days.
021
0
I
001
I
1
003
00.2
Reagent concn
Table I.
Limiting Concentrations of Interfering Ions Limiting Concentration, P.P.M.
Figure 3.
I
I
004
005
I
006
in r n o l e s / l i t e r
Variation in absorbance with reagent concentration
Iron concentration maintained constant a t 2.72 X l O - d W
20 250
1500
100 75 5000 7500
Standard iron solutions were measured according t o the suggested procedure. Beer's law was obej-ed over the concentration range 5 t o 150 p,p.m. of iron. Interferences were studied by the addition of known concentrations of various ions t o a 38.0 p.p.m. iron solution. The iron solution was then analyzed according t o the suggested procedure. TLtble I shorn the limiting concentrations of several interfering ions. This limiting concentration is the concentration of int,erfering ion that must be present in the iron solution in order t o
