system w a s reduced to less than 1%, which eliminated the difficulty. This procedure was used with all materials as discussed under Sample Preparation. Corn sirup samples were analyzed by the same technique. Here the ratio of sirup to sorbitol was increased so that the D-glucose to sorbitol ratio would approximate that of sugar samples. Values obtained for several sirups are shown in Table 11. Precision here was Z ! Z O . ~ ~ ~ . T o determine the accuracy of the method, known amounts of D-glucose were added to two corn sugar and two
corn sirup samples and the mixtures analyzed. The results in Table 111 showed that the recovery of added D-glucose was 1 to 2% high, although values were generally in better agreement with paper chromatographic values as seen in Tables I and I I. ACKNOWLEDGMENT
We would like to thank George G. Hazen and James A. Hause of Merck and Co., and William W.Wells of the University of Pittsburgh for their helpful suggestions during the initial phases of this work.
LITERATURE CITED
( 1 ) Dal Nogare, S., Juvet, R. S., “Gas-
Liquid Chromatography,” Interscience Publishers, Inc., Sew York, 1962, p.
256. ( 2 ) Dimler, R. J., Schaefer, W. C., Wise, C. S., Rist, C. E., ANAL.CHEM.24, 1411 (1952). ( 3 ) Somogyi, lf., J . Bzol. Chem. 160, 61 (1945). ( 4 ) Sweeley, C. C., Bentley, R., Makita, M., Wells, W. W., J . Am. Chem. SOC. 35, 2497 (1963).
R. J. ALEX.4NDER J. T. GARBUTT
Grain Processing Corp. Muscatine, Iowa
Spectrophotometric Determination of Boron Using Barium Chloranilate and Saccharic Acid SIR: Srivastava, Van Buren, and Gesser (4) have described a photometric method for the determination of boron which involves the precipitation of a complex borotartrate, formed upon the addition of barium chloranilate to a solution containing boric and tartaric acids, with subsequent measurement of the released chloranilate ion. We find that certain modifications can significantly improve the sensitivity while retaining the simplicity of the method. EXPERIMENTAL
Reagents. A solution of saccharic acid, buffered to a p H of 8.8, was prepared by dissolving 5.17 grams of the calcium salt of saccharic acid (Nutritional Biochemicals Co.) in a minimum amount of dilute hydrochloric acid. This solution was passed through a column containing a cation exchange resin (Rexyn AG 50H) in the hydrogen form, the effluent being collected in a 250-ml. volumetric flask. T h e column was washed with about 150 ml. of distilled water. To the effluent was added 25.0 ml. of 1 5 M ammonium hydroxide and 60.0 grams of ammonium chloride, a n d diluted t o the mark. The buffered solution was stored in a polyethylene container. A similar solution, buffered to a p H of 9.5, was prepared in similar fashion, except t h a t only 11.55 grams of ammonium chloride were used. Standard boron solutions were prepared from recrystallized and fused reagent grade boric acid. Solutions were prepared containing 21.6 mg. of boron per liter. T h e methyl cellosolve (ethylene glycol monomethyl ether) and barium chloranilate (Fisher Scientific Co.) were reagent grade materials. A Beckman DU spectrophotometer was uied in conjunction with matched 1.0 cm. silica cells for all photometric measurements. A mechanical shaker
was utilized to shake the flasks in which t h e reactions were carried out. Procedure. A series of standard boron solutions was prepared by adding appropriate amounts of t h e stock solution t o 10-ml. volumetric flasks. T h e volume of the standard boron solution was not allowed to exceed 4.0 ml. in a n y case. T o each solution was added 1.0 ml. of either the p H 8.8 or 9.5 saccharic acid solution (depending on the boron concentration) and 5.0 ml. of methyl cellosolve. A blank was prepared in t h e same way. All flasks were filled to the mark with water, and 40 mg. of dry barium chloranilate were added to each. The flasks were then shaken mechanically for about 30 minutes. At the end of the shaking period, the solutions were filtered through a fine paper (Schleicher and Schuell No. 589 Red Ribbon), portions were transferred t o t h e photometric cells, and absorbance measurements were made at 346 mM for t h e p H 9.5 solutions or 355 mp for the p H 8.8 solutions. RESULTS AND DISCUSSION
Initially a number of metal chloranilates, including those of barium, magnesium, calcium, strontium, lead, lanthanum, thorium, cadmium, and mercury were studied. Similarly a variety of organic acids, including citric, malic, galacturonic, mucic, and saccharic, were investigated. This survey indicated that the combination of barium chloranilate with saccharic acid showed the most promise. Gautier and Pignard ( 2 ) have indicated that the barium borotartrate complex is formed a t a p H of 8.8. Various water miscible solvents, including acetone, cellosolve, and methyl cellosolve, were studied a t this pH to investigate their effect on the sensitivity. Methyl cellosolve was selected because
of the good sensitivity and excellent linearity exhibited. A study of the temperature effect showed some variance of sensitivity with temperature. The effect is relatively minor, good sensitivity is obtained a t about 25’ C., and nominal variations from room temperature do not cause significant error. Absorbance measurements are made a t 355 mp as discussed by Srivastava and coworkers (4). Table I shows that at this wavelength Beer’s law is obeyed up to about 10 p.p.m., an improvement over the earlier method in which the upper concentration range is about 3.0 1i.p.m. Even though this saccharic acid procedure extends the concentration
Table 1.
Absorbance Measurements at 355 mp
1.0-cm. path length, pH 8.8 methyl
cellosolve, saccharic acid Boron, p.p.m. Absorbance 2.16 4.33 6.49 8.66
Table II.
0.401 0.733 1.070 1 ,490
Absorbance Measurements at 346 mp
1.0-cm. path length, pH 9.5 methyl
cellosolve, saccharic acid Boron, p.p.m. Absorbance 0.05 0.11 0.22 0.43 0.65 0.87
0.060 0 142 0 258 0 519 0 719 0 XR2
VOL. 37, NO. 2, FEBRUARY 1965
e
305
Table 111. Sensitivity of Reagent Quinalizarin Carminic acid Chromotropic acid Xethylene blue Curcumin Tetrabromochrvsazin Barium chloraLilate (tartaric acid) Barium chloranilate (saccharic acid)
Boron Methods
Absorptivity 28-650 190-600 480 7500 560-3400 790-1000 227, 355 mp 19, 530 mp 1207, pH 9.5, 346mp 165, pH 8.8, 355 mp
range over that of the tartaric acid method, sensitivity in the very low concentration range is not appreciably altered. However, a n investigation of the effect of pH indicated a maximum sensitivity at a p H of 9.5. At this p H the blank is also less strongly absorbing, and the opaque region caused by a reaction between the barium chloranilate and the buffer (1) extends only to about 346 mp. This permits making useful photometric measurements at this wavelength, closer to the wavelength of
maximum absorption than the 355 mp used previously. Table I1 shows the sensitivity which can be obtained through these modifications. I n effect, two useful modifications of the chloranilic acid method for the determination of boron have been devised. By substituting saccharic acid for tartaric, modifying the solvent system by the addition of methyl cellosolve, and carrying out the precipitation at a p H of 8.8, a method which is quite satisfactory for concentrations up to about 10 p.p.m. of boron is feasible. By simply altering the p H to a value of 9.5 and making photometric measurements a t 346 mfi, much less concentrated solutions can be readily analyzed. The principal precautions necessary are that the solutions must be agitated vigorously immediately after the addition of the barium chloranilate, and the latter must be thoroughly dry. -4 standard should be run together with each series of unknowns. Table I11 shows a comparison with other procedures. The data used were those compiled by Goward and Wiederkehr (3). The absorp-
tivity values for quinalizarin, carminic acid, and tetrabromochrysazin represent the high and low, corresponding to different reagent and sulfuric acid concentrations. The methylene blue methods as well as those based on other thionine derivatives offer extreme sensitivity, but are time consuming. The saccharic acid modification provides good sensitivity, while retaining the speed and simplicity inherent in chloranilate methods. LITERATURE CITED
(1) Bertolacini, R. J., Barney, J. E., 11, ANAL.CHEM.30, 202-5 (1958).
(2) Gautier, J. A., Pignard, P., Mzkrochem. Jfikroc. Acta 36-37, 793 (1951). (3) Goward, G. W., U'iederkehr, U. R., ANAL.CHEM.35, 1542-5 (1963). (4) Srivastava, R. D., Van Buren, P. R., Gesser, H., Ibid., 34, 209-10 (1962).
DONALD R. PETER SON^ JOHN R. HAYES The Pennsylvania State University University Park, Pa. 1 Present address, Fairway Spring Co., Inc., Elmira, N. Y.
Assay of Ammonium Perchlorate by Precipitation with Tetraphenylarsonium Chloride SIR: The most general method for determining perchlorates depends on determining the chloride ion produced by fusion of the perchlorate compound. Standard gravimetric or volumetric procedures are used for estimating the chloride ion. Perchlorates may also be determined by reduction in solution using titanous ion (2), titanium hydride ( I ) , ferrous ion ( 6 ) , stannous ion (4, or sulfuric acid (oleum) with starch (9). I n addition, perchlorate ion has been determined directly by precipitation as tetraphenylphosphonium perchlorate (5, 7). Although tetraphenylarsonium chloride is mentioned ( 8 ) , quantitative data is lacking except for trace analysis (3).
Table 1.
xH4ClO4 solns., aliquot NO.
1
2 3 4 5 6 7
8 9 10
306
As we were interested in assaying ammonium perchlorate, we decided to find the optimum conditions for the formation of tetraphenylarsonium perchlorate. EXPERIMENTAL
Reagents. All chemicals were C . P . or reagent grade. The ammonium perchlorate used was prepared by neutralizing reagent grade perchloric acid with the same quality ammonium hydroxide, after which the salt was recrystallized twice from water and dried in a desiccator over sulfuric acid. Solutions of tetraphenylarsonium chloride (Hach Chemical Co., Ames, Iowa) were filtered if necessary; otherwise the material was used as received.
Precipitation of Perchlorate Ion with Tetraphenylarsonium Chloride
0.05M Ph4AsC1, ml. diluted to 50 ml. 15 15 20 20 20 20 25 25 50 50
ANALYTICAL CHEMISTRY
Calcd. 0.2409 ... ... ... ...
...
... ... ... ...
Ph4AsC104, g. Found 0.2398 0.2396 0.2400 0.2412 0,2406 0.2404 0.2406 0.2400 0.2436 0.2431
Recovery,
%
99.5 99.5 99.6 100.1 99.9 99.8 99.9 99.6 101.1 100.9
Procedure. Weigh accurately a 2to 2.5-gram sample of ammonium perchlorate into a 1-liter volumetric flask, dissolve in water, and dilute to volume with water. To a 25-ml. aliquot of the above solution in a 100-ml. beaker, add 5 ml. of concentrated hydrochloric acid and mix. To this stirred solution, add 50 ml. of 0.02.V tetraphenylarsonium chloride and allow 15 to 20 minutes for coagulation. Filter the solution through a previously weighed medium porosity, sintered glass crucible, using a wash solution of water saturated with tetraphenylarsonium perchlorate to transfer the precipitate into the crucible. Dry the crucible containing the precipitate at 100' C. for 1 hour, cool, and weigh. RESULTS A N D DISCUSSION
I n exploratory experiments, the perchlorate ion could be recovered nearly quantitatively as the insoluble tetraphenylarsonium salt (Ph4AsC10a) from 0.02121 aqueous solutions using about 100% excess of the reagent. I n the absence of hydrochloric acid, coagulation was slow. The precipitate was not completely filtered in 3 hours. With 0.5, 1.0, and 5.0 ml. of concentrated hydrochloric acid as coagulant, the precipitate required more than 1 hour, more than 0.5 hour, and 10 to 15 minutes for settling, respectively. After each of these solutions was filtered and the precipitate dried at 100" for 40
