stituent on the alpha carbon, and it is indicated that such groups at this point enhance the amount of product obtained. A carboxyl group at this same carbon inhibits the reaction. The latter is illustrated by the inability of the amino acid phenylalanine to afford a product with a measurable amount of absorption at 287 mp (Table 11). The requirement for a primary or secondary amine is indicated by the failure of benzphetamine to react. As a rule primary amines react much better than secondary amines. The requirements of the reaction establish a relatively high degree of specificity for the @phenylethylamirie structure.
The sensitivity limit of the method is approximately 0.5 pg/ml of specimen providing a 10-ml sample is used. The procedure of this report is as sensitive as the spectrophotometric methods for determining barbiturates (15). Barbiturates and amphetamines are often taken concomitantly, and now determination of both compounds at therapeutic levels in urine can be performed by spectrophotometric analysis. Received for review May 15,1968. Accepted August 21,1968. (15) L. R. Goldbauni, ANAL.CHEM., 24, 1604 (1452).
pectrophotometric etermination of Microgram mounts of Tantalum with Victoria Blue G . F. Kirkbright, M. D. Mayhew, and T. S. West Chemistry Department, Imperial College, London, S . W.7, England
SEVERAL spectrophotometric methods are available for the determination of small amounts of tantalum. Hydrogen peroxide ( I ) , pyrogallol (2),gallic acid (3),and various fluorone derivatives (4), have been extensively employed as reagents for this determination. Methods for the determination of tantalum based on the formation of binary complexes in aqueous medium with reagents of this type, however, are basically relatively unselective. More selective methods have been reported for tantalum based on the formation and solvent extraction of ternary complexes of the tantalum with fluoride and methyl violet (5) and malachite green (6). This paper describes the application of the similar triphenylmethane type of dyestuff, Victoria Blue B (Basic Blue 26, Colour Index 44045), to the determination of microgram amounts of tantalum. Victoria Blue B forms a ternary complex with tantalum and fluoride in hydrofluoric-sulfuric acid medium. The complex i s extractable into benzene. The complex has a somewhat higher molar absorptivity in benzene than the corresponding malachite green and methyl violet complexes, and a selective determination of tantalum is possible under the optimum conditions established in this study. EXPERIMENTAL
Apparatus. Beckman model DB recording spectrophotometer fitted with Honeywell Electronik integrating recorder and matched I-cm glass cells were used. Victoria Blue B Reagent. The dyestuff (obtained from CIBA, Manchester, England) was purified by chromatography on an alumina column with isopropanol as solvent. An aqueous solution, 1.2 x lO-*M, of the purified material was prepared by dissolving 0,600 gram of dyestuff in one liter of distilled water. Thermogravimetric analysis of a sample of the chromatographically pure dyestuff revealed a progressive loss of weight of 4.7% between 20 and 80 "C. This corresponds to the (I) P. Klinger and W. Koch, Arch. Eisenhuttenw., 13, 127 (1939). (2) E. C. Hunt and R. A. Wells, Analyst (London), 79, 345 (1954). (3) H. Freund, K. H.Hammill, and F. C . Bissormette, U.S . Bureau of Mines, Investigation Report No. 5242, U. S . Government Printing Office, Washington D. C., 1954. (4) C. L. Luke, ANAL.CHEM.,31,904 (1959). (5) N. S. Poluetkov, L. Z. Konenenko, and R. S . Lauer, J. Anal. Chem. USSR, 13,449 (1958). (6) Y. Kakita and H.Goto, ANAL.CHEM.,34,618 (1962).
210 *
ANALYTICAL CHEMISTRY
"32
Figure 1. Victoria Blue B, C3a& N s C1 presence of 1.5 molecules of water in association with each molecule of the dyestuff. Elemental analysis gave the following results: calculated for CaaHazNaC1,C, 74.6 %; H, 6.0%; N, 7.92%; found C, 74.2%; H, 5.9%; N, 7.6x. Tantalum Stock Solution. Dissolve 0.181 gram of tantalum metal (Specpure reagent, Johnson and Matthey, London, England) in 23 ml of 40% hydrofluoric acid and warm to assist dissolution. Dilute to 100 ml with distilled water and store in a polythene bottle. This stock solution is 10-2M (1800 ppm) with respect to tantalum, and was diluted as required to give a final solution which was 2 ppm in tantalum and 0.01M with respect to hydrofluoric acid. Hydrofluoric and sulfuric acids and salts of diverse ions used in interference studies were analytical reagent grade. Preparation of Calibration Graph for Tantalum. When the tantalum complex was formed and extracted in glass separating funnels, poor reproducibility was obtained in the determination. This may possibly be attributed to the capricious adsorption and release of tantalum onto the glass surface in the dilute hydrofluoric acid solution. Polythene bottles were found satisfactory both for storage of reagents and for formation and extraction of the tantalum complex. To each of a series of six 100-ml polythene screw-top bottles, transfer 3.3 ml of 18N sulfuric acid and 1.5 ml of 5N hydrofluoric acid. Add 0, 2, 4, 6, and 8 ml aliquots of standard tantalum solution (2 ppm) to the six bottles, and sufficient distilled water to make the volume 13 ml. Transfer 2 ml of stock 1.2 X 10-aM Victoria Blue B reagent solution to each bottle. Pipet 10 ml of benzene into each bottle, shake the solutions for ea. 30 seconds, and allow to stand to ensure complete phase separation. Remove an aliquot of the benzene phase from each bottle with a pipet and measure its absorbance at 635 mg in a I-cm glass cell against the blank solution (containing no tantalum) prepared simultaneously.
P I
~~
510
4%
550
590
630
0'
WAVELENGTH^^)
*. MOLARITY
Figure 2. Absorption spectra for (a) tantalum complex against benzene, (6) tantalum complex against reagent blank, and (c) reagent blank against benzene (4 pg tantalum, 10 ml benzene)
RESULTS AND DISCUSSION Spectral Characteristics. The structural formula of Victoria Blue B is shown in Figure 1. The absorption spectra for the tantalum-Victoria Blue B complex and reagent blank are shown in Figure 2. The tantalum complex has a well defined absorption maximum at 635 mp. Only a small amount of the excess Victoria Blue B reagent in the aqueous phase is extracted into the benzene phase under the optimum conditions established in this study. The reagent blank absorption maximum also occurs at 635 mp in benzene. Effect of Concentration of Hydrofluoric and Sulfuric Acids. Figure 3 shows the variation in the net absorbance in benzene with hydrofluoric acid concentration for the tantalum complex after subtraction of the reagent blank. Thus when the original aqueous solution is maintained at 2M with respect to sulfuric acid, the optimum hydrofluoric acid concentration is between 0.25 and 0.75M. Where possible, a medium 0.5M with respect to HF was employed. Similarly, when the hydrofluoric acid concentration is maintained at this value, the optimum sulfuric acid concentration is 2M. The relatively wide tolerance toward hydrofluoric acid minimizes problems encountered during the dissolution of samples for analysis. Effect of Concentration of Victoria Blue B. The effect of the amount of reagent employed in the aqueous phase on the net absorbance in benzene at 635 mp after extraction is shown in Figure 4. In the recommended procedure 2 ml of 1.2 X
H F (XB) 0 . M O L A R I T Y %SO4
DYESTUFF MOLARITY (xio-4)
Figure 3. Effect of hydrofluoric acid ( A ) and sulfuric acid (B) concentration on net absorbance in benzene at 635 mp
10-aM reagent solution was selected to provide a concentration of 2 x 10d4Min the aqueous phase before extraction. This concentration represents a 30-fold molar excess of reagent over the maximum concentration of tantalum determined using the calibration graph under the optimum conditions. During these experiments the acidities were maintained at 2M H&04 and 0.5M HF.
Figure 4. Effect of reagent concentration on absorbance at 635 mp of tantalum complex against a reagent blank
Table I. Determination of Tantalum in Synthetic Samples Composition of Test Solution (ppm) Sample
A1
Cr
300 300 300
Fe
Mo
300 300 300 400
Mn
Nb
Ni
9.3
300 300 300
Ti
500
Zr
300
200 400
300 300 300
Tantalum (ppm] Present Found 7.0
300
19 20
300 300
W
300
300
7 9
co
300
1 2 3 4 5 6 8
cu
300 200
5.0 6.9 6.5 5.0 4.0 3.1 2.0
5.4
VOL. 40, NO. 14, DECEMBER 1968
6.8 4.8 6.9 6.5 5.1 4.1 3.2 1.9 5.6
221 1
Calibration Graph and Range. The calibration graph is linear over the range 1 to 16 pg of tantalum in 10 ml of benzene. The optimum range for absorbance measurements on the spectrophotometer is 0.2 to 0.7 absorbance unit. With the recommended procedure these values correspond to 4.4 to 16 pg of tantalum in 10 ml of benzene. The effective molar absorptivity for the tantalum complex in benzene is 83,000 at 635 mp. Precision and Accuracy. In order to obtain a measure of the reproducibility of the determination of tantalum in pure tantalum solutions, the same amount of tantalum (4 pg) was determined 21 times over a period of several days. The average absorbance was 0.184 and the standard deviation 0.005 absorbance unit or 2.8%. Table I shows the results of analysis for tantalum of some simulated tantalum sample solutions which contained other ions. The table also includes the results for the determination of tantalum in several ferromolybdenum alloys. Effect of Foreign Ions on Determination of Tantalum. Solutions were prepared containing 4 pg of tantalum and a 100-fold weight excess of each ion to be tested. The tantalum was then determined by the recommended procedure. An ion was considered to interfere when an error in the net absorbance for 4 pg of tantalum of greater than 5% was produced. The presence of a 100-fold excess of the following ions caused no interference: Al, Ag, As(V), Ba, Bi, Ca, Cd, Co, Cr(III), Cu(II), Fe(III), Mo(VI), Na, Ni, Pb, Sb(III), Sn(IV), Sn(II), Sr, Ti(IV), U(VI), W(VI), Zn,Zr, acetate, chloride, bromide, citrate, nitrate, silicate, and tartrate. The presence of a 100fold excess of Ce(1V) and V(V) caused interference by oxidation of the Victoria Blue B reagent. The presence of the following ions at 100-fold excess gave rise to the error in absorb-
ance given in parentheses: NH4f (+19%), Hg(I1) (+22%), Th(1V) (loo%), and B40r2- (100%). The presence of a 100fold excess of niobium(V) caused a positive interference (f66Z). The available niobium metal, however, contained ca. 0.02% of tantalum. After allowance for the contribution of the tantalum impurity to the absorbance, this error is reduced considerably. A 10-fold excess of niobium (tantalum free) can be tolerated without interference. Nature of Complex. Victoria Blue B is blue (absorption maximum 635 mp) in aqueous solution between cu. pH 1 and pH 12, and exhibits a yellow color (absorption maximum 475 mp) in acid solution at pH lower than 1. In the recommended procedure for the determination of tantalum, therefore, the aqueous blank solution is yellow. The maximum absorbance of both the reagent blank and tantalum complex occurs at 635 mp after extraction into benzene. The slope ratio method (7, 8) indicates a reagent : tantalum combining ratio of 1 :1. The reagent-tantalum-fluoride ion association complex which is formed and extracted into benzene thus appears to result from the interaction of the protonated reagent cation with the tantalum-fluor0 complex, TaF72-, so that the empirical formula is represented by RH2+TaF72-. The mole ratio method (9) failed to give clear indication of the reagent : tantalum molar ratio, presumably owing to the low stability of the association complex.
RECEIVED for review June 7, 1968. Accepted July 26, 1968. (7) A. E. Harvey and D. L. Manning, J. Amer. Chem. SOC.,72, 4488 (1950). (8) A. E.Harvey and D. L. Manning, ibid., 74,4744 (1952). (9) J. H. Yoe and A. L. Jones, IND.ENO. CHEM.,ANAL.ED., 16, 111 (1944).
Determination of Bisphenol A and Impurities by Gas Chromatography of Their Trimethylsilyl Ether Derivatives L. E. Brydia Chemicals and Plastics, Union Carbide Corp., Bound Brook, N.J . 08805
BISPHENOL A (4,4’-isopropylidenediphenol)is an important chemical which is used in the production of polymers such as epoxy and phenoxy resins, polycarbonates, and polysulfones. Commercial bisphenol A generally exceeds 99 % in purity and a product having a purity greater than 99.8 % is normally considered a requirement for the synthesis of high polymers. The major, high boiling impurities in high purity bisphenol A, originally identified by Anderson, Carter, and Landua ( I ) , are 2,4/-bisphenol A (2,4/-isopropylidenediphenol); Dianin’s compound (4,4’-hydroxyphenyl-2,2,4-trimethylchroman),also called monophenol or codimer ; and trisphenol [2,4-bis(a,adimethyl-4-hydroxybenzyl)phenol],also referred to as BPX. Despite the widespread use of bisphenol A as a raw material for the production of polymers, no quantitative method suitable for rapid analysis of this product was found in the literature. Chromatographic procedures have most frequently been used for the analysis of bisphenol A. Paper chromatography was employed by Anderson, Carter, and Landua ( I ) , Challa (1) W. M. Anderson, G. B. Carter, and A. J. Landua, ANAL. CHEM., 31, 1214 (1959).
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e
ANALYTICAL CHEMISTRY
and Hermans (2), and Reinking and Barnabeo (3). Aurenge, Degeorges, and Normand (4), and Zowall and Lewandowska ( 5 ) used thin-layer chromatography for this analysis. However, quantitative results are difficult to obtain with these techniques. Gas chromatography has also been used for the analysis of bisphenol A. Direct methods have been reported by Tominaga (6> and Davis and Golden (7), but Gill was unable to determine bisphenol A directly because of serious peak tailing (8) and Anderson, Carter, and Landua ( I ) and Freudewald (9) observed decomposition when a direct procedure was employed. (2) G. Challa and P. H. Hermans, ibid., 32, 778 (1960). (3) N. H. Reinking and A. E. Barnabeo, ibid., 37, 395 (1965). (4) J. Aurenge, M. Degeorges, and J. Normand, Bull. SOC.Chim. Fr., 1963, 1732. (5) H. Zowall and T. Lewandowska, Chem. Anal. (Warsaw), 10, 947 (1965). (6) S. Tominaga, Bunseki Kuguku, 12, 137 (1963). (7) A. Davis and J. H. Golden, J. Chromutogr., 26,255(1967). 36, 1201 (1964). (8) H. H. Gill, ANAL.CHEM., (9) J. E. Freudewald, unpublished work, Union Carbide Corp., Bound Brook, N. J., 1964.
