crease in sample size is required for minimum retention time as the molecular weight of the sample components increases. This is shown by the movement of the curve minima to the right as molecular weight decreases. This was also exhibited by the two secondary alcohols. The presence of similar minima vas observed with the dibutyl sebacate column. For this series of runs, the curve minima for the six alcohols occurred a t about the same sample size, 16 to 18 pl. The minimum values of retention times for the components of the ester test mixture occurred over a broader range. I n the dibutyl phthalate column (Figure 4), the optimum sample size was 10 to 15 pl. For the dibutJ.1 sebacate column, it was 6 to 7 , ~ l . KO overlapping or occlusion of peaks was observed \yith sample sizes under 20 111. Above that size, peak overlap became appreciable and increased with sample size. This had no effect on the esperimental results, as all minima n-ere observed a t sample sizes of 15 pl. or smaller. Some tailing was observed in all cases. This would indicate that the solutions formed betn-een substrate and sample constituent were nonideal or adsorption by the solid support for the substrate occurred. The change in
retention time with sample size for methanol in the dibutyl phthalate column is shown in Figure 5. The retention time-sample size curve for this series of runs has been shown in Figure 3. These chromatograms are typical of the ones obtained in this investigation. A curve connecting the points of maximum methanol concentration in Figure 5 shows a definite minimum a t approximately 13 to 15 pl. of sample. This curve has not been drawn in, to avoid crowding on the figure. As the theory cannot be expected to hold exactly for badly tailing peaks such as these (which are obviously nonideal), this could account lor the presence of the minima in the retention time-sample size curves. .Is is apparent from Figure 5 ) the principal effect of tailing is to broaden or enlarge the solute bgnd. As the sample size increased, the inflection points of the elution curves moved away from the base line, causing a change in the z intercept of Equation 1. The inflection tangents are intended to measure only the majority of the peak. I n the case of the lower sample sizes, the inflection tangents also measured part of the broadening of the peak caused by tailing. The percentage change in z with sample size was considerably greater than the variation
in retention time caused by the nonideality explained above. This may explain, in part, the presence of the minima in the HETP-sample size curves. LITERATURE CITED
(1) Davis, It. E., McCrea, J. hl., .4\.4~. CHEX 29, 1114 (1957).
(2) Desty, D. H., ed., ‘Yapour Phase Chromatography,” p. xiii, Butternorth, London, 1957. (3) Ibid., pp. 120-3. (4) Eggertsen, F. T., Groennings, S., - 4 ~ 1 . 4 ~CHEW . 30, 21-2 (1958). ( 5 ) Ewertsen. F. T.. Knight. H. 8..‘ . Grzhings,’S., Ibid.; 28, 385 (1956). (6) Evans, J. B., Willard, J. E., J. Am. Chem. SOC.78, 2809 (1956). (7) Haskin, J. F., Warren, G. W., Priestlev, L. J., Yarborouah, V. A4., ANAL.CHEX 30; 217-19 (1958). ( 8 ) Keulemans. A. I. M.. “Gas Chromatography,” pp. 61-7, ’Reinhold, Sew York. 1957. (9) Lichtenfels, D. H., Fleck, S. A, Burow, F. H., Coggeshall, N. D., AXAL. CHEJI.28, 1576-9 (1956). (10) Oil and Gas J . 54,126 (Dec. 17, 1956). (11) Porter. P. E.. Deal. C. H.. Stross. F. H., J . ’Am. Chem. Sic. 78, 2999-3000 (\ -19%). - - - I -
(12) Thomas, B. W., Znd. Eng. Chem. 47, 85-4 (June 1955). RECEIVED for review June 5, 1958. Accepted March 19, 1959. Investigation carried out as part of development work in gas-liquid partition chromatography sponsored by the Engineering Experiment Station, Iowa State College.
Qua nt ita tive Analysis of Commercial Bisphenol A by Paper Chromatography W. M. ANDERSON, G. 9. CARTER, and A. J. LANDUA Research laboratory, Shell Chemical Corp., Houston, rex.
b A method is presented which permits rapid determination of the impurities normally encountered in commercial grades of bisphenol A. The impurities are separated on two onedimensional paper chromatograms, with water and carbon tetrachloride OS solvents. Variations in the technique permit analyses over a fairly wide concentration range.
phenol], and codimer [4,4’ - hydroxyphenyl-2,2,4-trimethylchroman] are the principal impurities occurring in commercial bisphenol A. The pure compounds have been isolated from commercial bisphenol A by extractioii and fractional crystallization techniques and identified by means of their infrared spectra and physical properties. The structures of these materials are : Codimer
p,p’-BPA
CHI
B
A, 4,4-isopropylidenediphenol, [2,2-bis(4-hydroxyphenyl) propane, or p,p’-BPA], is used as a starting material in the manufacture of epoxide resins and other polymers. Work in this laboratory has shown that o,p ’-BPA [2-( 2-hydroxyphenyl) -2- (4hydroxyphenyl)propane], B P X [2,4bis ((Y,(Y- dimethyl - 4 - hydroxybenzyl) ISPHENOL
1 2 14
ANALYTICAL CHEMISTRY
I
CH, n , p ‘-BPA
-OH
OH
P
3
CHI
/
CHI
Because minor components may have some influence in syntheses invoh-ing
0
CDDlY€R
I O .
0 9 .
os -
on
01
0 5
04
03
-
0,P'-
-
P,P'- *PA 0,P'- SPA ( V I O L E T 1
~
oe
-
0.1
-
BPI
AND
P.P'-BPA
(RED) BPX IRED-VIOLET
bND
SECOND IRRIOATION
IPX
0 .
CODIYER
SOLVENT:
CCI
SOLVENT
GENERAL PROCEDURE
The method involves the preparation
of two paper chromatograms, one irri-
gated with distilled n-ater and one irri-
n20
c
Figure 2. Two-dimensional chromatogram of a bisphenol A mixture with carbon tetrachloride and water
n20
Figure 1. One-dimensional chromatograms obtained for bisphenol A mixtures with carbon tetrachloride and water
coniniercial bisphenol A, analytical procedures usually have two objectives: assay of p,p'-BPA and determination of individual impurities. It is possible to obtain a value for bisphenolrl puritymelting i.e., p,p'-BPA content-by point or freezing point measurements ( I ) , but neither method gives information concerriing the ainount of each individual impurity. Nonaqueous titration can be used to determine the weak acid functionality of the mixtures ( 2 , 3, 6) but not to assay or determine individual compounds. The impurities can be separated by countercurrent distribution, but this method is timeconsuming arid requires sizable samples. Infrared spectroscopy is unsuitable for determination of ininor constituents in a misture containing all four componenk because there are only slight differences in their spectra. The components have been partially separated in this laboratory by high temperature gas-liquid chromatography but thermal decomposition of the materials appears to be extensive. Thus, only paper chromatography attains the t n o analytical objectives by providing a reliable deterniination of individual itnpurities, as ire11 as the major component. Freeman (4, 5 ) has used paper chromatography for qualitative and quantitative analysis of methyIol-phenol mixtures. I n the present study, conditions \\ ere sought n liich u-ould conibine reasonable speed, convenience, and accuracy in the analysis of bisphenol A.
-
gated with carbon tetrahloride. Standard mistures covering the appropriate concentration ranges are ehromatographed along Tyith samples of unknoirn composition. Chromatograms are sprayed with a coupling reagent for color development and spot areas are measured with a planimeter. The percentages of impurities in unknowns are obtained by reference to the spot areas of standard mixtures. EXPERIMENTAL
Apparatus. Whatman No. 1 filter paper was used in all t h e work. Cylindrical glass jars 12 inches in diameter and 24 inches high, with glass cover plates, were used a s chromatographic tanks. T h e inside walls of t h e t a n k s were lined with two sheets of Whatman No. 3 MM filter paper to act as wicks for saturation of the vapor space with solvent vapors. The exterior walls were wrapped with multilayered paper tissue t o insulate the tank from temperature fluctuations. Two tanks were used; in one the solvent was water and in the other, carbon tetrachloride -4small Petri dish containing water and a sponge was placed in the carbon tetrachloride tank to equilibrate the paper with water vapor, and thus overcome difficulties due to day-to-day differences in the moisture content of the paper. All-glass aspirators wcre used for spraying the developed chromatograms. A compensating polar planimeter was used for measuring spot areas. Reagents. Solid p-nitrobenzenediazonium fluoroborate was originally prepared as described by Freeman (4). It is now available commercially (Eastman P-iO78). The spray solution was prepared fresh daily by dissolving 0.2 gram of solid reagent in 60 ml. of acetone. Methanolic potassium hydroxide (0.1A7) was prepared by dissolving 5.6
grams of potassiuiii hydroxide iii 1 liter of absolute methanol. Other chemicals needed were chlorobenzene, water, carbon tetrachloride, acetone, p,~'-BPA, o,p'-BPA, BPX, and codimer. The latter four compounds were obtained from technical bisphenol A by fractional crystallization and extraction; their purity was established by melting point measurements and paper chromatographic examination. The purity of the p,p'-BPA used in calibration mixtures was 99.9%. The purity of each of the other phenolic compounds vias about 98%. Detailed Procedure. Individual stock solutions of p,p'-BPA and each of t h e three inipuritics were prepared by dissolving 0.500 gram of t h e solid material in 100 nil. of acetone. A wide variety of standard solutions was then made up, as needed, by combining appropriate voluines of t h e stock solutions. I n analysis of samples containing 88 to 9iyO p,p'-BPA, 20 111. of 0.5% solution in acetone (100 y of sample) was applied to the chromatographic paper. Four standard solutions representing bisphenol 4 with 1, 2 , 3, and 4% of each impurity were spotted similarly on the same chroniatogram n-ith each set of unlrnowns. For the determination of components present in quantities less than l%, the impurities were first concentrated 5- to 6-fold by a single recrystallization of 1 gram of sample from 50 i d . of warm chlorobenzcne. After cooling and standing for 1 hour a t 20" C., the crystals were removed by filtration through R fritted-glass filter and washed once with a 10-ml. portion of chilled chlorolienzene, and the filtrate was cvaporated to dryness in a tared roundbottomed flask. Evaporation was hastened by the use of vacuum and a rotating evaporator iRinco htodel IT-1000). The residue was diluted to a concentration of 0.1 gram per 20 ml. of acetone and 20 pl. (100 y of bisphenol A) of this solution n as applied to the paper. Again the standards reiiresented 1, 2, and 301, of each iniljurity in bisphenol A. The percentage of each impurity found VOL. 31, NO. 7, JULY 1959
1215
sary to equilibrate the paper in the water tank. The irrigation time in the water tank mas 11/* hours and in the carbon tetrachloride tank, 2 hours. After irrigation and drying, the chromatograms were sprayed first with pnitrobenzenediazonium fluoborate solution and then with methanolic potassium hydroxide. The spots were outlined with a soft lead pencil following boundary lines of equal color intensities. An effort was made to outline all of the spots in an identical manner and this proved easy after a little practice. The o,p‘-BPA and codimer spots, appearing a t Rf values of about 0.3 and 0.7, respectively, were outlined on the carbon tetrachloride chromatogram. B P X ( R f
Table I. Duplicate Analyses by an Experienced Operator
Actual, Wt. 70 o,p’-BPA Codimer BPX 2.5
D
E
Table
1.5
1.5
Found, Wt.
2.5
2.1
1.3
2.3 2.2 2.2 2.4 2.6 2.5
2.0 1.8 1.8 2.0 1.9 1.6
1.2 1.1 1.2 1.3 1.4 1.6
II.
Accuracy and Repeatability of Analyses a t
Range of Impurity Concn., Concn., Wt. yJ
