ACKNOWLEDGMENT
The technical assistance of Judith Bushay and Gloria McKinley is gratefully acknowledged.
LITERATURE CITED
(1) Bricker, C. E., Johnson, H. R., IND. ENG.CHEM.,ANAL.ED. 17, 401 (1945).
2. Anal. Chem. 110, 22 (1937). (32,Fruell, W. R MacKenzie, C. .G Methods in B!ochemical Analysis,;’ Vol. VI, 63-77, IMerscience, New York, 1959. (4)Hehner, O.,Analyst 21, 95 (1896). (5) MacFadyen, D. A., J. Biol. Chem. 158, 118 (1945). (6)McLachlan, T., Analyst 60, 752 (1935). (7)Sawicki, E., Hauser, T. R., ANAL. CHEM.32, 1435 (1960). (2) Eegriwe, E. Z.,
(8) West, P. W., Sen, B., 2. Anal. Chem. 153, 177 (1956).
DONALD R. EKBERQ ELAINEC. SILVER Biosciences Operation Missile and Space Division General Electric Co. King of Prussia, Pa. WORKsu ported by NASA under Contract NA82-1538
Quantitative Analysis of Mixtures of Isomeric Aminobenzoic Acids by Gravimetry SIR: Although the qualitative s e p aration of the isomeric aminobenzoic acids has been reported (3, 4), no quantitative results have been published. This paper describes the quantitative analysis of mixtures of o- and m-, mand p-, and o-, m-, and p-aminobenzoic acids using bromination, chelation, and gravimetric methods.
zinc chelate of o-aminobenzoic acid was anal zed according to the procedure of &merman and Selzer ( I ) whereas the mother li uor was analyzed according to Methoa A. RESULTS AND DISCUSSION
benzoic acid as determined by bromination. The second method (Method B) was developed to not only check the accuracy of the first method but also to permit the analysis of mixtures of 0-, .m-, and paminobenzoic acids. 0Aminobenzoic acid was separated from m-aminobenzoic acid by treating the solution with a 50% excess of zinc nitrate solution to form the insoluble zinc chelate of o-aminobenzoic acid at pH 5.5 (2). The chelate was dissolved in 4N hydrochloric acid and analyzed as well as the mother liquor, containing m-aminobenzoic acid, by titration with a standard solution of potassium bromide/bromate. Since paminobenzoic acid is converted quantitatively to 2,4,&tribromoaniline, mixtures of m- and p-aminobenzoic acids were analyzed according to the procedure described in Method A. To analyze a mixture of o-, m-, and p-aminobenzoic acid it is necessary to remove the ortho isomer by chelation with zinc ion since both 0- and p-aminobenzoic acids are converted to the same product, 2,4,6-tribromoaniline. The isolated zinc chelate was analyzed according to the procedure of Cimerman
Two methods for the quantitative analysis of mixtures of o- and m-aminobenzoic acids were developed. The EXPERIMENTAL first method (Method A) involved the conversion of both isomers to a triChemicals. The isomeric aminobenzoic acids were purified by recrystalbromoderivative by means of standard lization from water. Isomeric aminopotassium bromide/bromate solution benzoic acid solutions in 4N hydro( I ) , o-Aminobenzoic acid (anthranilic chloric acid were employed at various acid) is converted quantitatively to the concentrations: 1, 2, 5, and 10 grams base insoluble compound 2,4,6tribromoper liter. Standard solutions of potasaniline whereas m-aminobenzoic acid is sium bromide/bromate, sodium thioconverted quantitatively to the base sulfate and zinc nitrate were prepared soluble compound, 2,4,6-tribromo-3from “Baker Analyzed” reagent grade aminobenzoic acid. The mixture was chemicals. (J. T. Baker Chemical Co.) Analytical Procedure. ANALYSIS treated with base to dissolve the acid OF MIXTURESOF 0- AND m-AMINOand the undissolved 2,4,6tribromoBENZOIC ACIDS. METHOD A. A 25-ml. aniline was determined gravimetrically. solution of 0- and m-aminobenzoic acids The solubility of 2,4,6-tribromo-3was brominated by adding a 50% aminobenzoic acid is too great in water excess of a standard solution of 0.1N to permit gravimetric analysis. The potassium bromide/bromate according weight of m-aminobenzoic acid in the to the procedure of Cimerman and mixture w w determined by subtracting Selzer ( I ) . After standing in the dark the weight of o-aminobenzoic acid from for one hour, an excess of potassium the total weight of the isomeric aminoiodide was added and the solution titrated with a standard solution of 0.1N sodium thiosulfate. The mixture containing 2,4.&tribromoaniline and 2,4,6-tribromo-3-aminobenzoic acid was made basic by the addition of 20% Table I. Analysis of Isomeric Aminobenzoic Acid Mixtures. sodium hydroxide. The base insoluble Weight, mg. compound, 2,4,6-tribromoanilineJ was Taken Founda obtained by filtration, dried and weighed. 0mP 0-0 Sd mS Pb METHODB. A 25-ml. solution of 0and m-aminobenzoic acids was treated (40.0) (40.0) ... (39.7)b (0.1) (40.3)* (0.1) . . . with a 50% excess of 0.LV zinc nitrate 40.0 40.0 ... 39.7 0.1 40.2c 0.1 ... 190.0 io.0 ... 189.3 0.3 10.4c 0.2 ... solution at a controlled pH of 5.5 to 10.0 190.0 . . . 9.9 0 I 189.3c 0.2 ... precipitate the zinc chelate of o-amino50.0 50.0 . . . . . 5O.lb 0.1 49.8 benzoic acid (2). The precipitate was 356.3 18.7 . . . 356.1b 0.3 18.6 dissolved in 4147 hydrochloric acid and 5 n ~ . 5n 5.2b 0.2 94.3 . . . ... ... this solution as well as the mother 0.4 29.7 0.3 30.1b 30.1 30.0 30.0 30.0 liquor, containing m-aminobenzoic acid, 0.4 89.7 90.6; 9.9 0.1 90.0 10.0 90.0 was analyzed according to the procedure 44.8 5.1 0.2 45.0 45.2 0.1 45.0 .5.0 of Cimernian and Selzer (I ) . 10.0 89.gb 0.3 90.0 0.4 10.0 90.0 90.0 ANALYSIS OF MIXTURESOF m- AND Average standard deviation 0.2 0.2 ~-AMIKOBENZOIC ACIDS. The solution was analyzed eccording to Method A. Average of triplicate. ANALYSIS OF MIXTURESOF 0-, mb Determined by Method A. Determined b,y Method B. AND P - ~ I I N O B E N Z O I C ACIDS. The solud Standard aeviaticn. tion was treated uith a 50% excess of zinc nitrate sol~ition. The precipitated I . .
0
5
1422
e
ANALYTICAL CHEMISTRY
...
... 0.4 0.1 0.2 0.1 0.3 0.1 0.1 0.2
and Selzer (I), whereas the mixture containing the m- and p-isomers was analyzed according to Method A. Table I lists the results obtained for the quantitative analysis of the isomeric aminobenzoic acid mixtures. The results obtqined in these experiments indicate that this method is suitable for the quantitative analysis of
mixtures of the isomeric aminobenzoic acids. LITERATURE CITED
EXPERIMENTAL
Reagents. All reagents were analytical grade or of comparahle purity. Gold (I) and platinum (4) solutions were made by weight from the respective metals. Cerium solutions were made from ceric sulfate by weight. Aqueous solutions of isonicotinic acid hydrazide, (0.2% by weight) and 2,3,5triphenyltetrazolium chloride (O.2Y0 by weight) were prepared. Equal volumes of these solutions were mixed and the resulting mixture was used as a color producing reagent. Apparatus. All absorbance measurements were made with Dr. Lange's photoelectric colorimeter Model VI using green filters To increase the sensitivity of the instrument, the colorimeter was connected with a lamp and scale type spot Cambridge galvanometer. Procedure. GOLD.To gold solutions containing 100 to 600 rg. of metal ion, 1 ml. of 0.25A' hydrochloric acid is added and the solution is diluted to 5 ml. with distilled water so that the pH of the solution is between 1.75 and 2.25. To each of these solutions, 2 ml. of the color producing reagent are added and the solution is allowed to stand for 3 minutes at room temperature. The mixture is shaken with 5 ml. of +amyl alcohol and centrifuged. To each mixture an additional 5 ml. of +amyl alcohol are added and the aqueous layer is carefully removed and discarded, while the organic layer is diluted to 100 ml. with ethyl alcohol. The experiment is repeated with various
Chemistry De artment Southern Me&odist University Dallas, Texas WORKsupported by the Robert A. Welch Foundation, Houston, Texas, in the form of a research grant, N-118.
(1) Cimerman, C. H., Selzer, M., Anal. Chim. Acta 9, 26 (1953). (2) Funk, H., 2. A d . Chem. 123, 241
(1942). (3) Lederer, M., Australian J . Sci. 11, 208 (1949).
Gold, Platinum,
Colorimetric Determination of SIR: In previous papers (2, S),it was reported that an equimolar mixture of isonicotinic acid hydrazide and 2,3,5triphenyltetrazolium chloride in dilute acid gives a pink color with iodate, bromate, thallium, chromium, and iron under different experimental conditions. In the present paper, the same color reaction has been extended to the colorimetric determination of gold, platinum, and cerium. The method is simple and accurate and ths visual limit of identification is 2, 15, and 6 pg. per ml. of gold, platinum, and cerium, respectively. The maximum tolerable limit of various metal ions which do not interfere is reported.
(4) 17ietti-Michelina, Sf., Rass. Chim. 10, 13 (1958). R. BIEHL EDWARD LI HSUEH-MINQ
amounts of gold, and a plot of absorbance us. concentration of gold is prepared.
The reaction obeys Beer's law between 1 to 6 rg. per ml. Gold from the unknown sample may then be directly determined from the curve by measuring the absorbance after the reaction. PLATINUM. The method for the determination of platinum is the same as for gold except that the determination is carried out at 80" to 85' C. using 0.25N hydrochloric acid, and the solution is diluted to 8 ml. with distilled water so that the pH of the solution is between 3.60 and 3.85. To each solution 2 ml. of color-producing reagent are added, and after 3 minutes the solution is diluted to 100 ml. with ethyl alcohol. The reaction obeys Beer's law between 1 and 5 pg. per ml. CERIUM. Only cerium(1V) can be determined. The procedure is the same as in the case of gold except that 1 ml. of 0.25.4' sulfuric acid is used instead of hydrochloric acid, and the pH of the solution before addition of the colorpoducing reagent is between 1.80 and 2.50. The reaction obeys Beer's law between 1 and 5 pg. per ml. Table 1.
and Cerium RESULTS AND DISCUSSION
The effect of time before dilution, temperature, and pH on color intensity was studied. The intensity of color varies with pH, temperature, and time, but is reproducible a t constant conditions. The determinations can be carried out at any set of conditions as long as they remain constant throughout the experiment. The color intensity does not vary with time after the solution is diluted with alcohol. Because the color intensity becomes constant after 3 minutes, the determinations of gold, platinum, and cerium were carried out after 3 minutes of color development at room temperature between the pH range where the color intensity remains constant (cf. procedure), The interferences caused by various cations and anions under the experimental conditions were studied, and a quantitative assessment of the tolerable amounts of different ions is given in Table I. The results for the determination of gold, platinum, and cerium,
of Tolerable Amounts of Different Ions' Maximum amount not interfering, yo* Gold Platinum Cerium
Quantitative Assessment
Ion Na+
K+
3.' Ha
+
H i +1
CU+l
Ca+*
Ba+l Sr +*
Cd +l Mg +1 Zn +* Pb +I Ni +1 c o +1 Mn+*
A1 +a
400 400 5 100 2 2 2 400 200 200 200 500 500 2 40
40 100 500 2 100 20 400
400 400
400 400
20
in
Not tolerable Not toleraible
Not tolerable Not tolerable
2
2 4 4 4 12 200 200 2 2 5
16 200 2
2
5
2 5 5 200 40 4 2 2 F
16 20 2 Not tolerable
Bi +a Cr +a 5 Sn+4 4 2 Th +4 100 100 Iodate, bromate (.a), iron, chromium, and thallium (3)ions also form pink-colored formasan; hence, their presence will interfere. Stannous ion also interferes, a Three solutions containing 200 pg. each of gold, latinum, and cerium were taken and different amounts of various compounds were a d g d under experimental conditions of tern erature and pH. The percentage of various ions is with respect t o amount of gold, pyatinurn, or cerium. 0
VOL 38, NO. 10, SEPTEMBER 1966
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