V O L U M E 2 6 , NO. 3, M A R C H 1 9 5 4
521
when 100 y or less of each compound is used. When more than 100 y of these three compounds is present, separation may be achieved using 2 liters of petroleum ether instead of 1 liter. In that case more than 200 fractions must be collected or the numher of drops per tube must be raised. As the commercial fraction collector does not allow for the collection of more than 400 drops per tuhe, this is accomplished by a “doubling” attachment. B y use of this attachment the number of drops collected per tube may be increased u p to 800.
by partition chromatography, identification of the eluates by the sulfuric acid test, and ultraviolet assay of the fractions. The separation of steroids is carried out automatically, using a silicic acid column impregnated with water and a mobile phase of petroleum ether-dirhloromethane of continuously increasing polarity. Small amounts of adrenocortical steroids can be determined in the presence of a large excess of other adrenal steroidq ACKNOWLEDGRlENT
DISCUSSIOX
The separation of adrenocortical steroids described is based largely on partition chromatography, as evidenced by the fact that the position of peaks is pract8icallyindependent of concentration. Partitioning takes place between the stationary water phase and a mobile petroleum ether-dichloromethane phase of gradually increasing pnlarity, The adrenocortical steroids are eluted in the order of increasing polarity. B is apparently more polar than its isomer. S. This agrees with the data on partition coefficic.iits present.ed by Pfrffer et al. (6). They observed that when various adrenocort.ira1 steroids are distributed betn.een equnl volumes of petrolclum ct,her and water, i5yoof compound S and only 2 0 5 of compound B are found in tmhepetroleum ether ph:ise. I ~ c of k material has prevented the determination of the load limitations of the columns used in this work, but Haines ( 2 ) has rcport,ed the separation of 40 mg. of hormone mixture on 30 grams of silica gel. SUMMARY
The determination of the six active adrenocortical steroids in a mixture is based on preliminary separation of individual steroids
The authors gratefully acknowledge the advice and encouragement of Erich Mosettig of this institute. They are indebted to G. C. Riggle of the Instrument Section, National Institutes of Health. for the construction of a doubling attachment. LITERATURE CITED (1) Donaldson, K. O., Tulane, Y. J., and 3Iarshal1, L. 3I., A N i L . CHEM., 24, 185 (1952). ( 2 ) Haines, W. J., “Recent Progress in Hormone Research,” Vol. 7 , p. 255, Sew York, -4cademic Press, 1952. (3) Herrington, B. L., and S t a r r , 31. P., IND.ENG. CHEX.,A 4 x . ~ ~ , ED.,14, 62 (1942). (4) Kataenellenbogen, E. R., Kritchevsky, T. H., and Dobriner, K.. Federation Proc., 11, 238 (1952). (5) 3Iorris, C. J. 0. R., and Williams, D. C., Biochem. J., 54, 470 (1953).
(6) Pfeffer, K. H., Ruppel, W., Staudinger, Hj., and Weissbecker. L., Naunyn-Schmiedeberg’s Arch. exptl. Pathol. Pharmakol., 214, 165 (1952). (7) Zaffaroni, A., J. Am. Chem. Soc., 72, 3828 (1950). RECEIVED for review July 18, 1953. Accepted December 11, 1 9 3 .
Colorimetric Determination of Strontium with Chloranilic Acid PETER J. LUCCHESI, S. Z. LEWIN,
and
JOHN E. VANCE N. Y.
Department of Chemistry, N e w York University, N e w York,
Strontium is determined by means of the diminution in absorbancy of a chloranilic acid solution acconipanying precipitation of strontium chloranilate. Large excesses of mineral acids were successfully removed prior to analysis by the use of Amberlite IRA-410. Filtration of chloranilic acid solutions diminishes the absorbancy and shodd be avoided.
I
ions, including strontium ( I , 3, .5, 8),and a nmn1)er of investigations have shoivn its applicability as a colorimetric reagent for calcium ( 1 , 3, /i, 6-8). These methods are all base1 on the decrease in light absorption of the chloranilic acid solutions accompanying the precipitation of the calcium snlt. In the present work, this approach has been adapted to thri determination of strontium. PROCEDURE
S C O S S E C T I O S \\-it11 311 iiivrstigation of the rate of dissolu-.
tion of stront’ium sulfate iii several aqueous media, the need
arose for an anal?;tical niethorl for strontium(I1) t h a t u ould be: rqiid and convenient, suitable for small samples of the order of 2 to 15 nil. containing strontium in milligram amounts, and
athptahle t o samples coiit.aiiiing high concentrations of hj-drochloric acid, nitric arid, or perchloric acid. Preliminary esperimerits showed that sodium rhotiiaonate, which has been employed for the detection of strontium ( J ) , is not suitalde for quantitative colorimetry olving to thc instnliility of the reagent.; turbidimetry involving strontium carbonate \vas investigated and proved to lie insufficiently rpproducible for satisfactory results. Chloranilic :ic.itl was found to fill the requirements satisfact,orily, and 1)erarise of the convenience of the colorimet,ric technique, ot,her possible approaches were not, investigated. Chloranilic acid (2,5-dichloro-3,6-dihydroxy-p-quinone) is prcripitated as the salt from aqueous solution by a variety of cat-
Neutral Solutions. For solutions having a pH hettveen 5 and i and containing no appreciable concentrations of cations other than st’rontium(11))the following procedure was used.
I n a centrifuge tube, 5.00 ml. of a stock 0.05% solution of chloranilic acid are mised with 5.00 nil. of the solut,ion to be analyzed, and the tube is cooled in ice for a minimum of 3 hours, to ensure complete precipitation, but not for more than 12 hours, as longer periods may cause precipitation of some of the unreacted chloranilic acid. The misture is centrifuged at about 1100 r.p.m. for 5 to 10 minutes, after which some of the supernatant liquid is removed for spectrophotometric measurement. .k control is employed in each determination, consisting of 5.00 ml. of the stock reagent and 5.00 ml. of distilled water; this misture is cooled and centrifuged in exactly the same manner as the other samples. -4bsorbances are measured a t 530 mp b y means of a Beckman Model DU spectrophotometer. The control is used as the spectrophotometric reference-i.e., the instrument is adjusted to read 100% transmittance v i t h the unknown in the path of the light beam and the per cent transmittance of the control is measured relative to this setting. Hence, the
522
ANALYTICAL CHEMISTRY
greater the amount of strontium(I1) in the unknown, the lower the absorbancy of the unknown relative to water and the greater the absorbancy of the control relative to the unknown. Acid Solutions. A 5.00-ml. sample of the solution to be analyzed is added dropwise to the to of a column containing 50 grams of fresh IR.4-410 anion exc%ange resin in a tube 19 mm. in diameter. The sample is allowed to percolate down through the column for about 5 minutes, then 15 to 30 ml. of distilled water is added to the top of the column, and the eluent is collected in 5-ml, portions. The pH of each fraction of eluent is checked, and for those fractions that are basic, standard conditions of pH are conveniently achieved by the addition of a small chip of dry ice to the solution. The eluent is treated with chloranilic acid and analyzed spectrophotometrically as described above. The resin is regenerated after use by means of 60 to 70 ml. of l N potassium hydroxide, followed by washing with distilled water until the effluent is neutral and gives no potassium flame test.
0.3 2
0.28
$
0.24
5
Table I.
Absorbancy at 530 m p of Chloranilic Acid Solutions
Paper Whatman h-0. 40 Whatman S o . 4 1 Whatman S o . 4 1 H Whatman No. 42
Stock Soln.
One
Two
Three
Four
0.630 0,630 0.630 0.630
0.570 0.580 0.610 0.550
0,530 0.560 0.580 0.520
0.500 0,540 0,560 0.490
0.490 0,530 0 550 0.470
The chloranilic acid reagent employed in the present work was the product of Jasonols Chemical Corp., and had an absorption maximum a t 530 =k 5 mp a t 0.02570 concentration; Tyner (8) gives 550 mp for the maximum and Koroleff ( 6 ) , 523 mp. The stock solution was relatively stable; over a period of 6 weeks there was only a 15% decrease in the absorbancy at the absorption maximum. As the procedure employed involves the comparison of test and control samples, both prepared from the same stock reagent, no difficulty was created by the slow fading of the reagent. Although previous workers have filtered their chloranilate precipitates prior to colorimetric measurement, this appears to be far less satisfactory than centrifugation, for some chloranilic acid is lost owing to adsorption on the paper. [Frost-Jones and Yardley ( 3 )describe centrifugation as an alternative to filtration. They obtained very similar results for calcium on aliquots of the same solution treated by filtration and by centrifugation. In both procedures their stock solutions had been filtered before use (Q).] This is illustrated by the data in Table I which shows the effect on the absorbancy of passing a clear solution of 0.025% chloranilic acid through successive dry filter papers Tyner (8) showed that control of hydrogen-ion concentration is important for successful results with chloranilic acid, and the authors have found that in the concentration range of interest (0.1 to 35), mineral acids cause precipitation of the reagent. Thus, in the analysis of solutions containing mineral acids some means must be employed to eliminate the interference due to the hydrogen ion. Neutralization of the acid with base does not offer a satisfactory solution to the problem if moderate amounts of acid are involved, for the cations introduced in the neutralization process also cause precipitation or decolorization of the chloranilic acid reagent. A possible approach might be based upon the procedures of Le Peintre ( 7 ) and Frost-Jones and Yardley (5), who obtained reproducible results by swamping both test and control mixtures with excess of a salt, but it seemed more deairable to remove the source of interference completely, and an anion exchange resin was successfully employed for this purpose. Several Amberlite resins were investigated, of which the most satisfactory for the present purpose proved to be IRA-410. The chloranilic acid reagent is very sensitive to certain substances present in many of these anion exchange resins-probably decomposition products of the resins-and only fresh batches of IRA-410 were found to be sufficiently free of these substance5
t
0.44
3 0.20 9 0.I 6
t
0.08
40
80
120
160
200
S T R O N T I U M C O N C N . , MG. PER LITER
Figure 1. Absorption Law Plot for Analyses by Chloranilic Acid Procedure
Table 11. Analyses of Neutral Strontium Chloride Solutions by Chloranilic Acid Procedure Actual Found Error, %
62 58 -6.4
Concentrations of Sr, hlg. per Liter 73 103 114 I55 69 105 118 157 -5 4 +1.9 +3.5 f1.3
168 167 -0.8
under the conditions of use to be suitable. The presence of these interfering substances in the eluent from the column is readily detected, since upon addition of the chloranilic acid an immediate fading is observed; the diminution in color of the reagent due to precipitation of strontium chloranilate occurs much more slowly. The resin could be used and regenerated many times before beginning to show evidence of deterioration. RESULTS
’ Figure 1 shows the absorbance law plot for this system; the abscissas give the concentration of strontium(I1) in milligrams per liter, and the ordinates give the absorbancy, loglo(Z/Ic), a t 530 m p of the control relative to the unknown. The standard solutions used were made up from strontium chloride hexahydrate and standardized by analysis of the solid, and by evaporation of aliquots after addition of sulfuric acid and heating to constant weight as strontium sulfate. Table I1 shows some analyses of neutral solutions of strontium chloride on the basis of the calibration curve given. Analyses carried out on solutions of strontium chloride in 3A7 hydrochloric acid, 3 N perchloric acid, and 3 N nitric acid are shown in Table 111. It is evident from Table I11 that equally satisfactory results are obtained with samples containing each of the three acids. Higher acid concentrations than 3.V appeared to affect the resin adverseIy, giving Iess accurate and reproducible results.
V O L U M E 26, NO. 3, M A R C H 1 9 5 4
523
Table 111. Analyses by Chloranilic Acid Procedure after Removal of Excess Mineral Acid by IRA-410 R u n Solution 1 3X-HC1, l a ml. 2 3NHCI, 15 ml. 3 3NHC1, 15 ml. 4 3NHC1, 15 ml. 5 3 N HNOa, 5 ml. 6 3NHKO1, 5 nil. 7 3 N HClOa, 5 ml. 8 3”fHC101, 5 ml. 9 3NHC1, 2 ml. 10 3 N H C 1 , 2 ml. 0
I
Mg. of Sr in Successive 5-MI. Fractions of Eluent I1 111 IV J’
VI
0.59
0.59
0.65 0.44
0.05
0.11
0.23
0.57
0.62
0.61
0.23
. . , O
0.12
0.60
0.55
0.46
0.16
0.35
0.40
0.19
0.31
0 35 0 . 0 9
0.07
0.25
0.07
0.09
0.45
0.73
0.14
0.23
0.41
0.11
0.37
0.Oi
...a
...a
0.29
0.07
0.03
...a
...a
...a
0.07
...= ...= 0.11
. . . O
...= ... . . . 5
...
...... ... ...... ...... . . . 5
T o t a l Sr Found Bctual 2.43 2.50 2.26
2.50
1.73
1.67
1.21
1.17
0.82
0.83
0.86
0.83
0.87
0.83
0.82
0.83
0.44
0.33
0.39
0.33
Too small t o be detected.
I t was found possible to concentrate most of the strontium in the first 5-mI. fraction of the eluent by using dry resin. Runs 1 through 6 and 8 were carried out with a moist column-Le., the column had been regenerated, washed, and the excess water removed by gentle aspirator suction. In these runs, the strontium is distributed among the first three or four fractions. In runs 7, 9, and 10, the resin was thoroughly dried between filter papers after washing, then was replaced in the column. With this technique, the bulk of the strontium is found in the first fraction of eluent.
The calibration curve given in Figure 1 can, in certain cases, be used for the analysis of ions other than strontium(I1). For example, three 5.00-ml. samples of calcium chloride solution containing 0.20 mg. of calcium ion in each sample gave the following analytical results: 0.19,0.20, and 0.20mg. of calcium, respectively. Whereas the calcium chloranilate precipitates more rapidly than the strontium salt, the precipitation of barium from barium chloride by chloranilic acid is much slower than that of strontium, and low results were consistently obtained in analyses for barium. The analyses reported in this paper have been carried out on solutions which contain no cation (except hydrogen) other than the one of interest. I n view of the widespread interference that would result from the presence of other ions, (3) this method is recommended only for solutions of the type described above. LITERATURE CITED (1) Barreto, A., BoZ. soc. b r a d agron. (Rio de J a n e i r o ) , 8 , 351 (1945). (2) Feigl, F., Mikrochemie, 2, 187 (1924). (3) Frost-Jones, R. E. U., and Yardley, J. T., Analyst, 77, 468 (1952). (4) Gammon, N., and Forbes, R. B., ANAL.CHEM.,21, 1391 (1949). (5) Jackson, C. L., and MacLaurin, R. D., Am. C h e m J., 37, 87 (1907). (6) Koroleff, F., Finska Kemistsamfundets Medd., 60, 56 (1951). (7) Le Peintre, M., Compt. rend., 231, 968 (1950). (8) Tyner, E. H., ANAL. CHEM.,20, 76 (1948). (9) Yardley, J. T., personal communication. RECEIVEDfor review August 24, 1953. Accepted December 1, 1953 Presented before t h e Division of Analytical Chemistry a t t h e 124th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill. Research supported in part b y the Atomic Energy Commission under contract No. AT (30-1)1256.
Detection, Estimation, and Removal of Impurities in Fluorocarbon liquids DANIEL GRAFSTEIN Westinghouse Research Laboratories, East Pittsburgh, Pa.
This work was initiated in order to minimize the corrosion problems associated with the use of perfluorinated liquids in electrical apparatus. Methods were sought by which impurities in commercial preparations of fluorocarbons could be quantitatively determined and removed. Ultraviolet absorption spectrophotometry proved to be a surprisingly sensitive tool for the estimation of trace olefinic impurities and a procedure was developed in which both olefinic and hydrogen-containing impurities are eliminated by degradation with potassium hydroxide pellets at elevated temperatures. The results should prove useful in applications requiring inert fluorocarbon media of known purity and in the preparationof perfluorocarbonswhere completeness of fluorination can now be appraised.
I
N COSXECTIOX with certain studies in this laboratory, a
need developed for fluorocarbon liquids free of reactive impurities. Polyamides, polyesters, and copper underwent visible deterioration upon continuous contact with commercially available perfluorinated compounds at elevated temperatures. Fractional distillation and repeated mashing of the liquids with aqueous alkali and water failed to alter these effects.
-4n apparent reaction was observed by ?*IcCulloch (3) of this laboratory between perfluorodimethylcyclohexane and alkali metal hydroxide pellets at room temperatures. The solid became coated with a brown substance which was shown by analysis to be composed primarily of alkali fluorides. ilfter repeated treatments, using fresh quantities of alkali, the liquid no longer exhibited this reaction. The treatment was accompanied at first by a rapid increase and then by a slow decrease in the amount of unsaturation in the liquid, as shown by titration with potassium permanganate in acetone, until finally the liquid was no longer reactive to permanganate. I n a further study, it was found that the reaction was accelerated a t elevated temperature and was given by other impure fluorocarbon liquids. Throughout the alkali treatments, less than 5% of the perfluorinated compounds treated were lost, mainly through handling. -4marked decrease in corrosion was observed with the treated fluorocarbons. Ultraviolet absorption spectra display a remarkable sensitivity towards purity. Figures 1 through 4 show the spectra of several commercial preparations of perfluorinated liquids, both before and after the alkali treatment. Throughout this paper, liquids exhaustively treated with potassium hydroxide are referred t o as purified. The recent availability of perfluorinated olefins permits a calibration of the ultraviolet spectra and allows a quantitative esti-
