THE FRACTIONATION AND PHOTOMETRIC ESTIMATION OF THE ESTROGENS IN HUMAN PREGNANCY URINE

BY BENJAMIN F. STIMMEL

(From the Rees-Stealy Medical Research Fund, Ltd,, San Diego, California)

(Received for publication, September 26, 1945)

In a previous publication (1) we described a liquid chromatogram for separating the trihydroxy estrogen (estriol) from the mono- and dihydroxy estrogens (estrone and a-estradiol). We have modified and extended this technique to accomplish quantitative separation of ternary mixtures of crystalline estrone, a-estradiol, and estriol. Furthermore, we have suc- cessfully incorporated the liquid chromatogram in a procedure for the calorimetric estimation of estrone, estradiol, and estriol fractions in human pregnancy urine. Such fractions have been estimated by bioassay tech- niques (2, 3) but, as the work of Taylor et al. (4) has shown, small errors inherent in the fractionation procedures may be enormously magnified by the bioassay.

Bachman and Pettit (5) have adequately discussed the nature of the difficulties encountered in the application of calorimetric methods to the determination of estrogens in human pregnancy urine, in their partial solu- tion to the problem. (Estriol and estrone-estradiol fractions were photo- metrically determined by them in pregnancy urine containing a minimum of 1000 y of estriol and 500 y of estrone-estradiol per liter.) In accord with the Bachman and Pettit concept of the problem we have developed a purification and fractionation procedure which removes most of the chromogenic impurities which might adversely affect reliable photometric determinations with the highly specific Kober reagent (6). This was ac- complished by means of the liquid chromatogram.

This report covers (a) a demonstration of the ability of the liquid chro- matogram quantitatively to fractionate ternary mixtures of crystalline estrone, a-estradiol, and estriol, and (b) a test of its suitability as an adju- vant to the preparation of estrogenic fractions from human pregnancy urine of sufficient purity for satisfactory calorimetry.

EXPERIMENTAL

Reagents- Activated alumina, Alorco F-20 “minus 80 mesh” (Aluminum Ore

Company, East St. Louis, Illinois), was further screened to 100 to 200 mesh by rapid brushing in standard screen scales (W. S. Tyler Company, Cleve-

99

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100 ESTROGENS IN HUMAN PREGNANCY URINE

land, Ohio) in 100 to 200 gm. batches and stored in tightly stoppered bottles. No batch was kept over 30 days after screening.’

Kober’s reagent (6) prepared and employed essentially as described by Venning et al. (8). Crystalline estrone, a-estradiol, and estriol in the concentration range of 10 to 80 y were found to obey Beer’s law and the following calibration constants were used to calculate the amounts of each estrogen in each test in micrograms: K (estrone) 0.00837; K (oc-estradiol) 0.00523; K (estriol) 0.00737. The final Kober color products obtained by testing urine residues from the chromatographic filtrates were further purified by washing with an equal volume of ethyl acetate. This procedure removes impurities without affecting the pink pigment produced by the estrogens. Since the ethyl acetate quickly separates above the aqueous phase, the operation may be carried out in the same colorjmeter tube in which the color was developed. Ethyl acetate is somewhat, soluble in the final Kober test solution and a number of partition experiments have revealed that the final volume of the ethyl acetate-washed Kober test solution is increased to 17.0 f 0.2 ml. Hence, all photometric density measurements on ethyl acetate-washed Kober tests are multiplied by the factor 1.13 in order to utilize the same calibration constants as for un- treated tests, for which the final volume is 15.0 ml.

The Bachman phosphoric acid reagent was used essentially as described by Bachman (9).

The Zimmermann reagent (10) was used as described in a previous publication (1).

Normal butyl alcohol (Baker’s c.P.) was redistilled under reduced pres- sure in an all-glass apparatus.

Benzene (Baker’s c.P., thiophene-free) Jvas stored over sodium wire and distilled in a dry all-glass apparatus.

Methyl alcohol, absolute (Merck reagent), was stored over act’ivated alumina (Alorco F-20, 80 to 100 mesh) and distilled in a dry all-glass apparatus.

1 Standardization studies similar t,o those reported by Brockmann and Schod- der (7) are in progress in this laboratory on a number of adsorbents and will form the subject matter of a subsequent paper. We have found that with ordinary precautions to exclude moisture, surprising uniformity in activated alumina may be maintained. Two 5 pound packages of Alorco F-20, used over a period of 15 mor:ths, have shown very slight deterioration. The following visual standardization technique has proved valuable in checking the activity of our preparations: 1.0 mi. of a 0.2 per cent solution of Sudan I (1.benzeneazo-2-naphthol, The Coleman and Bell Company, Norwood, Ohio) in benzene is diluted to 30 ml. with the same solvent and added to a 200 mm. column (13 X 300 mm. tube). The dye should appear in the filtrate only after washing the column with 45 to 55 ml. of 2 per cent, methanol-benzene and should be completely removed from the column after washing with 80 ml.

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B. F. STIMMEL 101

Ethyl ether, U. S. P., was shaken with a 1 per cent solution of ferrous sulfate in water, washed with water, and distilled. The purified solvent was stored in the refrigerator.

Apparatus- Chromatographic apparatus. The apparatus previously described (1)

was modified to utilize a 13 X 300 mm. instead of a 19 X 200 mm. tube. A cylindrical glass cup of 100 ml. capacity was attached by means of a glass joint to the top of the chromatographic tube.

Urine extractor. The extraction chamber of an unassembled Koch type of extractor (Scientific Glass Apparatus Company, catalogue No. 140, J-1589) was set up to accommodate a motor-driven glass stirrer.

The Evelyn photoelectric calorimeter (11) with the accompanying set of light filters was used for measuring the color intensity of the test solu- tions. The concentration of estrogen in micrograms was calculated in each test from the formula, C = L/K where L = 2 minus the galvanometer reading and where K has been determined by standardization with known quantities of each estrogen.

Procedure

Preparation of Urine Residue Suitable for Liquid Chromatogram-The following example will describe the entire procedure. The 24 hour urine specimen was collected in a bottle containing 100 ml. of butyl alcohol as a preservative. Within 24 hours after completion of the collection, the speci- men was acidified (to Congo red paper) with hydrochloric acid. It was then extracted four times with 0.125 volume of butyl alcohol by slow stir- ring in the extraction chamber (150 to 200 R.P.M.). About 5 minutes were allowed for each stirring and a similar interval for separation of the two phases. Each butanol fraction was drawn off and clarified by slow centri- fugation. The combined extracts were distilled under a partial vacuum and final traces of solvent removed from the flask by the addition and distillation of 30 ml. of water under similar conditions. The residue was dissolved in 100 ml. of 0.2 N sodium hydroxide and the solution diluted to a 400 ml. volume with water. The aqueous extract was transferred to a 500 ml. wide mouthed Erlenmeyer flask and acidified with 10.0 ml. of concentrated hydrochloric acid. The flask was then covered with an inverted beaker and autoclaved at 15 pounds steam pressure for 3 hours.

The cooled hydrolyzed urine extract was extracted four times with 0.25 volume of ethyl ether. The combined ether extract was washed two times with 0.1 volume of 9 per cent sodium bicarbonate solution and two times with 0.05 volume of water. The ether extract, which should be free from any ether-insoluble material at this point, was then concent,rated to a volume of 50 ml. and extracted four times with an equal volume of normal

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102 ESTROGENS IN HUMAN PREGNANCY URINE

sodium hydroxide solution. The combined sodium hydroxide extract was backwashed with 0.1 volume of ether, after which it was acidified (to litmus paper) with hydrochloric acid and reextracted three times with 100 ml. volumes of ether. The ether extract was washed two times with 0.1 volume of 9 per cent sodium bicarbonate solution, two times with 20 ml. and once with 10 ml. of 2.5 per cent sodium carbonate solution. The combined sodium carbonate extracts were backwashed with 100 ml. of ether and the backwashing added to the main ether extract. The combined ether extract was then mashed with 30 ml. of 9 per cent sodium bicarbonate solution and finally washed two times with 25 ml. of water. The ether was evaporated to dryness and the residue taken up in a measured volume of ethanol from which suitable aliquots were transferred to test- tubes for evaporation. The tubes were stored in wxwo over anhydrous calcium chloride until used for preparation of the liquid chromatogram.

Preparation of Liquid Chromatogram-A column of activated alumina of definite length (200 f 2 mm.) was prepared by filling the assembled apparatus to approximately 20 mm. above the 200 mm. mark and vigor- ously tapping the side of the tube with a cork grip penholder until the alumina settled to constant height. A negative pressure was then applied. The estrogen residue was treated as described in a previous publication (1) with t’he following slight modifications. The column was first wet with 20 ml. of pure benzene and the hormone residue (dissolved in 0.4 ml. of absolute methanol and diluted with 20 ml. of pure benzene) added just before the pure benzene had completely entered the column. 50 ml. instead of 75 ml. of benzene were used as a developer. In the distribution experi- ments 10.0 ml. volumes of the appropriate eluent were successively added to the column and collected in separate flasks. In routine fractionation procedures each eluent (100 ml.) was collected in toto. The entire liquid chromatogram operation should not require more than 1 to 2 hours time. After removal of the solvents by distillation, suitable aliquots of the residue were prepared for calorimetry as previously described (1).

Results

Table I summarizes the data from a number of distribution studies on single estrogens in a liquid chromatogram, with various proportions of methanol-benzene mixture as eluents. The results obtained indicate that at least 100 ml. of pure benzene may be used safely without the appearance of a measurable amount of estrogen in the filtrate. Since 2, 5, and 30 per cent methanol-benzene mixtures appeared to be satisfactory eluents respec- tively for estrone, cu-estradiol, and estriol, singly, a number of distribution studies were made on ternary mixtures with these three eluents succes- sively. Fig. 1 shows the distribution of a ternary mixture containing

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B. F. STIMMEL 103

TABLE I Distribution of Single Estrogens Eluted from Chromatographic Column of Activated

Alumina* by Successive 10 Ml. Washings of Various Eluents

Experi- ment NO.

Estrogen, 7.00 Y

1

2 3 4 1 2 3 4 1 2 3 4

Estrone ‘I I‘ I‘

wEstradio “ ‘I “

Estriol IL “

-

_

Eluent

Benzene 2% M.-B. 5% i‘ 10% ‘( Benzene 2% M.-B. 3% “ 570 “ Benzene 20% M.B. 30% “ 40% ‘(

Per cent of total estrozen in each washina determined

- 1st -

0 0 0 0 0 0 0 0 0 0 0 5

- - 2nd 3rd -

0 0 0

80 0 0 0 0 0 0 4

41 -

-

0 0

80 11

0 0 0 5 0 0

20 17 -

-

.-

-

by Ifober reagent -

4th 5th --

0 0 2 40 8 3 5 0 0 0 0 0 0 0

36 30 0 0 5 8

20 15 11 6

6th -_

0

30 2 0 0 0 3

13 0 9

10 3

-

3th

- - 7th - -

0

14 0 0 0 0

13 5 0

11 7 2

-

9th -

0

8

0

0

0

0

24 3 0

15 5 0

-

-

0 4 0 0 0 0

24 2 0

3 0

- M.-B. = methanol-benzene. * Alorco F-20,100 to 200 mesh, column length 200 mm. in 13 X 300 mm. tube.

10th -

0

2 0 0 0 0

18 0 0

3 0

-

M-B= METHANOL. BENZCNE

FIG. 1. The distribution of a ternary mixture of estrone, or-estradiol, tend estriol (1.0 mg. each) in a liquid chromatogram. Each filtrate fraction corresponds to 10 ml. of eluent added. The ordinate gives the percentage recovery of each estrogen and the abscissa, the number of filtrate fractions.

1.0 mg. each of e&one, cu-estradiol, and estriol. In these experiments involving mixtures of the estrogens, the Zimmermann test, which is specific among the three estrogens for e&one, and the Bachman phosphoric acid

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104 ESTROGENS IN HUMAN PREGNANCY URINE

test, which is specific for estriol, were employed. It can be seen that 100 ml. volumes of each of the three methanol-benzene eluents successively applied to a ternary mixture give adequate chromatographic dispersion of the three estrogens to form the basis for quantitative fra,ctionation.

TABLE II

Separation and Recovery of Known Amounts of Crystalline Estrogens from Ternary Mixtures by Liquid Chromatogram

Experi- ment_No.

1

2

3

4

5

6

-

1

--

-

imount estrogen added (e)

_____ Y

200 0. 50 D.

100 T. 100 0. 200 D.

50 T. 50 0.

100 D. 200 T. No 0. No D.

1000 T. 200 0. 100 D. 300 T.

500 0. 500 D.

2000 T.

Color reagent

Zimmermann Kober Bachman Zimmermann Kober Bachman Zimmermann Kober Bachman Zimmermann Kober Bachman Zimmermann Kober Bachman

Zimmermann Kober Ba.chman

-i- Total estrogen found (b)

2 PZecp”.”

(estrone)

Y

200

105

50

0 0

20s

540

-

(’

-

5 gg,nt

a-estradiol

Y

0 55

0 IS0

0 100

0 0

0 110

0 520

-

1

-

75 0

3s 0

160 0

750 0

220 25*

0

1600 125*

61*

- nt

)

per cent

100 110

75 105 DO 76

100 100 so

75 104 110 74

8 108 104

80 6 4

0. = estrone; D. = Lu-estradiol; T. = estriol. M.-B. = methanol-benzene. * 50 ml. of additional 30 per cent methanol-benzene eluent were added.

Detdrmination of Estrogen Content of Known Solutions-Table II presents data from a number of experiments performed to test the quantitative features of the fractionation process. In these experiments, each eluent was collected in toto and tested for estrogen content by means of the three color reagents. A 10 ml. mashing of the column with pure benzene was routinely interspersed between the 2 and 5 per cent methanol-benzene eluents and collected with the 2 per cent methanol-benzene filtrate. There is maximal recovery of estrone and cr-estradiol in the appropriate fractions and there is consistent recovery, to the extent of 70 and 80 per cent of the

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B. F. STIMMEL 105

estriol, in the first 100 ml. of the 30 per cent methanol-benzene filtrate. A number of experiments similar to Experiments 4 to 6 in Table II have demonstrated that the low recovery of estriol is in no way attributable to loss of estriol in the preceding chromatographic fractions, but rather to the diffuse nature of the trailing boundary common to many chromato- graphic zones. Higher concentrations of methanol in benzene or further mashing with 30 per cent methanol-benzene causes contamination of the eluate with impurities which impair the use of color reagents, especially when urine residues are involved.

Recovery of Estrogens Added to Essentially Estrogen-Free Urine Extract- Table III summarizes the data from a series of recovery tests in which known amounts of the three estrogens were added, at various points in the purification process, to extract of pooled urine from a castrated female. The amounts added were of an order anticipated to simulate pregnancy urine. Experiments 1 and 2 in Table III indicate that the reaction of the Kober reagent proceeds independently with estrogens and with urinary impurities present in the filtrat,e residues. The recovery of estrone and a-estradiol added to the urine extract just previous to application of the liquid chromatogram is maximal and recovery of estriol is in the range of 75 to 80 per cent, which would be expected from results with simple benzene solutions (Table II). Experiments 3 to 5 in Table III shorn that known amounts of estrone and oc-estmdiol added immediately after hydrolysis to the butyl alcohol extract. of cast,rated female urine may be carried through the entire purification and fractionation procedure and recovered in satis- factory yields. The low recoveries (57 to 69 per cent) in this series of added amounts of estriol were materially improved in subsequent studies with pregnancy urine by inclusion of an ether backwashing of the aqueous sodium carbonate washings.2

Recovery of Estrogens Added to Pooled Pregnancy Urine Extracts Imme- diately after Hydrolysis-Table IV contains a few of a number of experi- ments which were carried out to test the adequacy of our extraction and purification procedures when applied to pooled pregnancy urine extracts subsequent to hydrolysis. These and other similar studies have demon- strated that estrone and ar-estradiol can be recovered in the appropriate filtrate fractions in the range of 80 to 100 per cent and estriol in the range of 75 to 83 per cent.

2 Partition studies of estriol between equal volumes of et,hyl ether and 2.5 per cent sodium carbonate solution in our laboratory have averaged 60 per cent recovery of the estriol in the organic solvent phase. This is significantly lower than the Bachman and Pettit (5) recovery of 80 per cent with the 9.0 per cent sodium carbonate solution and more nearly in agreement with Mather’s (12) value of 65 per cent with 0.3 N sodium carbonate.

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106 ESTROGENS IN HUMAN PREGNANCY URINE

Measurement of Estrogens Excreted by Normal Subjects in Early to Mid- Pregnancy-Preliminary observations on the estimation of estrone, estra- diol, and estriol fractions in 24 hour urine specimens are presented in Table V. The ratio of L-520 mp/L-420 rnp for each Kober color product

TABLE III Recovery of Crystalline Estrogens Added to Extract of Pooled Urine of Human

Female Castrate, Subsequent to Hydrolysis The results are expressed as micrograms per unit aliquot (800 ml. of urine).

Experi- ment NO.

Point at which estrogen is added

3trat.2 raction

NO. :ested*

estrogen :ontent by

Kober reagent

L-520 L-420

Residue just before calorimetry

Residue just beforc adsorpt,ion

Aliquot just after hydrolysis

I‘ “

‘I “

Y

None

50 0. 50 D. 50 T.

500 0. 250 D.

1000 T. 500 0. 250 D.

1000 T. 500 0. 200 D.

1000 T. 500 0. 500 D.

1000 T.

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

Pd. Y

400 151 400 w 400 301 400 70 400 65 400 77

80 540 200 268 40 810 80 470

200 244 40 620 80 490

200 190 100 715

80 500 200 490 40 600

-

0.59 0.65 0.62 2.6 2.1 2.4 9.2 5.9 8.9 8.2 4.5 7.5 8.5 3.0

10.5 8.0 6.5 7.8

110 92 94.

105 100 81 91 90 59 95 86 60 97 94 57

0. = estrone; D. = a-estradiol T. = estriol. * Fraction 1 = 2 per cent methanol-benzene; Erection 2 = 5 per cent, methanol-

benzene; Fraction 3 = 30 per cent methanol-benzene. t Calculated by subtracting the contribution of atypical Kobes color products in

Experiment 1 and dividing by the amount of each estrogen added. 1 By direct determination at 520 mp with the Kober reagent. These atypical

color products do not give true estrogen content but must be included in calculation of estrogen recovery values for Experiments 2 to 6.

has been included in Table V in order to indicate the spectral purity of the test solutions. Venning et al. (8) have found, and Bachman and Pettit (5) have corkirmed their finding, that the L-520 mp/L-420 rnp ratio of the Kober products obtained with urinary impurities is approximately 0.5. Experiments on a large number of urine specimens from castrated and preadolescent females have given similar results by our method. Bachman

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B. F. STIMMEL 107

TABLE IV

Recovery of Known Amounts of Crystalline Estrone, cr-Estradiol, and EstriolA !ded to Aliquots of Pooled Pregnancy Urine Extracts Immediately after Hydrolysis

The results are expressed as micrograms per unit aliquot.

Experiment No.

Y

None

500 D.

500 0. 1800 T.

500 0. 400 D. 940 T.

1

2 3 1 2 3 1 2 3 1

2 3

-

rota1 estrogen found by Kober reagentt

Y

143 110

1380 140 592

1200 560 136

2800 577 480

2080

1

-

I -

Per cent recovery of added estrogen

96

83

76 87 92 75

0. = estrone; D. = or-estradiol; T. = estriol, * Fraction 1 = 2 per cent methanol-benzene; Fraction 2 = 5 per cent methanol-

benzene; Fraction 3 = 30 per cent methanol-benzene. t The final Kober color product was washed with an equal volume of ethyl acetate.

Exp%?t

1

2 3 4 5 6 7 8 9

10 11 12

-

TABLE V Estrogen Content of Human Early P

wks.

4 8 8

10 18 20 22 23 24 25 26 28

- I L-520 III/I L-420w for Kober color products

Estrone Estradiol Estriol E&one _-

1.2 0.9 1.2 2.7 1.2 3.4 4.1 2.2 2.3 5.1 1.7 3.6 9.2 1.9 11.8 6.4 1.5 11.0 5.9 3.4 10.8 7.6 3.6 10.8 5.5 3.3 9.7 6.7 3.7 12.0 7.0 4.4 14.0 6.1 3.9 12.0

c per 24 hrs.

86 124 209 256 740 800 875 965

1024 848

1000 1460

-

rnancy Urine

Estrogen content

-

--

Y

Estradiol

per 24 hrr

108 61

127 134 206 270 484 520 520 500 570 900

-

_-

‘. Y

Estriol

fier 24 ha.

90 142 215 266

1480 3390 3710 4210 4300 4400 4400 7000

and Pettit (5) have indicated that, with ratios of L-520 mp/L-420 rnE.c as low as 3.0 for contaminated Kober color products, the error in determining the estrogen content directly from the extinction at 520 rnp should not

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108 ESTROGENS IN HUMAN PREGNANCY URINE

exceed 10 per cent, If vve accept this ratio as the lower limit for satis- factory calorimetry, our data in Table V, together with those of unreported experiments, appear to indicate that satisfactory purificat’ion of the estronc and estriol fractions may be anticipated from pregnancy urine collected after the 10th week following the last catamenia. The estradiol fraction consistently gives the lowest L-520 mp/L-420 rnp ratios and usually does not rise above 3.0 until after the 24th week following the last catamenia. Satisfactory Kober color products for all three fractions may be expected from pregnancy urine collected from the 24th week to t.erm, in which period the ratio of estrogens to impurities is most favorable for good calorimetry.

DISCUSSION

Venning et al. (8) have shown that normal butyl alcohol satisfactorily extracts both conjugated and unconjugated forms of the female sex hor- mones from human pregnancy urine, and that the aqueous extract of the butyl alcohol provides a convenient extract for carrying out the hydrolysis of the conjugated forms. Because of its greater freedom from pigmented non-estrogenic material, we have adopted the butyl alcohol extraction .and hydrolysis technique essentially as performed by them. It is desirable to fractionate the hydrolysate into neutral and acidic fractions by distribu- tion between ether and aqueous alkali before employment of the liquid chromatogram, since neutral (androgenic) 17-ketosteroids and other neu- tral ether-soluble substances might conceivably pass into the liquid chro- matogram fractions with the estrogens and interfere with development of color with the Kober reagent. Crystalline androsterone, dehydroisoandro- sterone, and pregnanediol by actual test appeared in the 2 per cent methanol-benzene filtrate.

No attempt has been made in this study to check the calorimetrically determined hormone titers against bioassay determinations. These colori- metric values may well represent summations of space isomers as yet undetected in human pregnancy urine. For example, the estradiol frac- tion might conceivably contain both CY and P forms, although according to the work of Pearlman and Pearlman (13) this seems unlikely.

In addition to fractionating the mixture the liquid chromatogram accom- plishes a measure of purification. Our urines gave a very slight observable residue in the initial filtrate (estrogenically inactive when tested with the spayed rat). There usually is a very weak yellow band which acts as a pace-maker for the estrone fraction. For the present, this has been allowed to pass into the estrone fraction and its presence poses no serious obstacle to the use of the Kober reagent. Fortunately, the major portion of non- estrogenic contaminants of pregnancy urine residues at the conclusion of

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13. F. STIMMEL 109

the liquid chromatogram is still fixed at the very top of the ehromato- graphic column.

Within the limitations discussed in connection with Table V, the pro- cedure which we have described is believed to offer a definite contribution to the fractionation and quantitative determination of the estrogens known to be present in human pregnancy urine.

SUMMARY

A liquid chromatogram has been described which successfully fractionates ternary mixtures of crystalline estrone, a-estradiol, and estriol. The quan- titative features of the technique have been investigated for various ternary mixtures. Estrone and a-estradiol are recovered quantitatively in the 2 and 5 per cent methanol-benzene filtrates respectively, and estriol in the 30 per cent methanol-benzene filtrate to the extent of 75 to 85 per cent. The unrecovered estriol is not lost to the other two fractions, but escapes elution under the conditions employed. The liquid chromatogram has been incorporated in a purification procedure for the estrogens in human pregnancy urine. This procedure yields estrone, estradiol, and estriol fractions which respond satisfactorily to the highly specific Kober reagent.

BIBLIOGRAPHY

1. Stimmel, B. F., J. Bid. Chem., 163, 327 (1944). 2. Smith, G. V. S., and Smith, 0. W., Am. J. Obst. and Gynec., 36, 769 (1938). 3. Smith, G. V. S., and Smith, 0. W., Rm. J. Obst. and Gynec., 39,405 (1940). 4. Taylor, G. C., Jr., Mecke, F. E., and Twombly, G. H., Cancer Res., 3, 180 (1943). 5. Bachman, C., and P&tit, D. S., J. Biol. Chem., 138, 689 (1941). 6. Kober, S., Biochem. Z., 239, 209 (1931). 7. Brockmann, H., and Schodder, I-I., Ber. them. Ges., 74 B, 73 (1941). 8. Venning, E. H., Evelyn, K. A., Harkness, E. V., and Browne, J. S. I>., J. Biol.

Chem., 120, 225 (1937). 9. Bachman, C., J. Biol. Chem., 131, 463 (1939).

10. Zimmermann, W., %. physiol. Chem., 246, 47 (1936-37). 11. Evelyn, K. A., J. Biol. Chem., 116, 63 (1936). 12. Mather, A., J. Biol. Chem., 144, 617 (1942). 13. Pearlman, W. H., and Pearlman, M. It. J., Arch. Biochem., 4.97 (1944).

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Benjamin F. StimmelURINE

ESTROGENS IN HUMAN PREGNANCYPHOTOMETRIC ESTIMATION OF THE

THE FRACTIONATION AND

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