regions belongs to the inherent qualities of photographic material, as well as to the conditions of exposure and development. The characteristic curves for estrone and estradiol seem to differ only by their slope, designated photographically as gamma (y), and not by their ext,rapolated intercept on the abscissa. Estradiol s h o w a greater fluorescence than estrone, and it is likely that the difference in their photographic effects is due to quantitative differences in intensities of emitted light and not to any appreciable difference in their wavelengths of maximum emission. Estradiol ‘is also slightly closer to the source of exciting light. Estriol, on the other hand, exhibits both a difference in y and intercept on the abscissa compared t o the other two estrogens. The underlying cause is probably a shift in the emission spectra and a concomitant loss in intensity of light emitted. Indeed, the visual appearance of est,riol illuminated with ultraviolet light of 254 mp is purple, whereas estrone and estradiol appear bright yellow. Similar shifts in characteristic curves with wavelength have been observed ( 2 ) .
The usable portions of the standard curves for assay of unknown amounts of estrone and estradiol lie between 0.9 and 2.7 pg. of each and three times as much for estriol, all under the experimental conditions described. The concentration ranges examined appear to fall on a curve with a continuously decreasing slope. Slopes for the lesser concentrations are larger than for the higher ones. When the amounts of each substance vary in the ratio of 1:2 : 3, the density curve is probably most useful for practical purposes. For this reason, equations have been calculated only for the first three points on the curve and lines were drawn accordingly. Each point was taken as the average of three determinations. It would be possible to increase the sensitivity by increasing time of exposure or of development or both. .ilthough the background would be increased simultaneously, it is not known what the lowest ratio of absorbance of a spot to background density can be and still permit quantitation within a permissible margin of error. The procedure outlined above shows that it is possible to quantitate material on thin layer plates with a minimum of
effort. It is well known that elution of material from chromatographic adsorption media is always accompanied by a loss which must be taken into consideration in a subsequent quantitative assay. Quantitation by the photogrammetric procedure is as reliable as many colorimetric assays performed in test tubes, and only small amounts of substances are required. ACKNOWLEDGMENT
The author gratefully acknowledges the technical assistance of Ihor Shpernal. LITERATURE CITED
(1) Jacobsohn, G. hl., AKAL.CHEM.36, 275 (1964). ( 2 ) Mees, C. E. K., “TPe Theory of the Photographic Process, ’ p. 192, Macmillan, ?Jew York, 1954.
GERTM. JACOBSOHN Department of Biological Chemistry Hahnemann Medical College Philadelphia 2, Pa. Work supported by the Sational Institutes of Health through Grant No. AM-06746.
Separation a n d Spectrophotometric Determination of Submilligram Quantities of Aluminum in Aluminum-Plutonium Alloys SIR: Several methods have been reported for the determination of aluminum in plutonium-aluminum alloys where the major problem is one of separation. Cleveland and Nance ( 1 ) measured the absorbance of the aluminum 8-quinolinol complex in chloroform after separating plutonium by precipitation and extraction as the plutonium cupferrate. Jones and Phillips ( 7 ) also used the extraction-photometric method for the aluminum after removing plutonium by an anion exchange method, and other impurities by extraction with 2-methyl-8-quinolinol. Miner et al. (9) separated plutonium by anion exchange and evaluated statistically the gravimetric and yolumetric 8-quinolinol methods, the spectrophotometric 8-quinolinol and aluminon methods, and the E D T A method for aluminum. The 8-quinolinol indirect spectrophotometric method (2, 3, 10) for the analysis of aluminum which measures the absorbance of the combined 8-quinolinol has not been used extensively. This is probably because of the many interferences in the ultraviolet region where the sensitivity is a t a maximum. The new plutonium wet chemistry laboratory complex consists of a series of plastic glove boxes and hoods 2032
e
ANALYTICAL CHEMISTRY
specifically designed to facilitate the handling of various levels of the hazardous plutonium. Wherever possible, small samples of plutonium alloys are selected for analysis using methods that are precise and rapid and which require minimum manipulation and equipment. The authors present here such an indirect spectrophotometric method for the determination of submilligram amounts of aluminum that is easily adapted to routine glove boxhood procedures. EXPERIMENTAL
Reagents. T o prepare 8-quinolinol standard stock solution, dissolve 3.2292 grams of 8-quinolinol in 5 ml. of concentrated hydrochloric acid and dilute to 1 liter with water. Other chemicals were C.P. or reagent grade quality. Equipment. Spectrophotometer, Model D C , equipped with dual light source and 1-em. quartz cells was used. The column apparatus used for the anion exchange separation has been described previously ( 4 ) . The apparatus used for the filtration, washing, and dissolving of the precipitate is shown in Figure 1. Resin Column Preparation. The 6-mm. column was prepared and con-
ditioned essentially by the same method described by Evans, Bloomquist, and Hughes (4). Here the Dowex ;Ig 1 X 8 resin height was adjusted to 5 inches and washed with 1 2 V hydrochloric-0.12JI nitric acid eluting solution before use. Calibration Procedure. The calibration d a t a were obtainpd by carrying aliquots of standard aluminum solution through the procedure and measuring the absorbance caused by varying amounts of 8-quinolinol in the range of 360 to 390 mp. Linearity was observed over the range 100 to 600 pg. with the sensitivity varying from 1.81 X 10-3 absorbance unit per pg. per nil. at 360 mp to 0.987 X 10-3 at 390 mp, with a standard deviation of slightly less than & 2 pg. over the entire range. PROCEDURE
Dissolution of Samples. Transfer 0.5 gram or less of the alloy to a 40-ml. glass graduated centrifuge tube. Cover the sample with a minimum amount of water and carefully add 5 ml. of concentrated hydrochloric acid. Complete the dissolution by heating the solution on a sand bath. Cool and transfer the contents to a 50-ml. volumetric flask with 6Jf hydrochloric acid. Dilute to volume. Anion Exchange Separation of Plutonium. Select an aliquot containing 100 to 500 pg. of aluminum and transfer
TWO-WAY COCK-
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Side view of filter apparatus
to a 40-ml. glass graduated centrifuge tube. Evaporate to a volume not greater than 0.5 ml. Add 3 ml. of concentrated nitric acid to the cool solution and continut> evaporation t o a volume of about 0.2 ml. .4dd 5 ml. of concentrated hydrochloric acid to the solution, and heat again until gas evolution occurs. Cool the solution to room temperature and transfer to the resin column, prepared as previously described. Use three 5-ml. portions of the 1 2 X hydrochloric + O . l M nitric acid eluting solution to wash out the sample container, adding each to the column when the level of the proceding portion of the eluent nears the top of the resin bed. The bolutions are passed through the column, with the aid of gentle suction, into a 25-ml. volumetric flask, a t a drop rate of 40 =k 5 drops per minute. Transfer the eluate along with dilute hydrochloric acid washings t o a 50-ml. beaker and evaporate almost to dryness. The plutonium can be eluted from the column with 0.5M hydrochloric acid and transferred to waste. Precipitation of Aluminum 8Quinolinolate. Dilute t h e solution to about 10 ml. with water and heat to 60' t o 70" C. T h e aluminum is then precipitated by adding 1 ml. of 2% 8-quinolinol solution, 1 ml. of 1-11 potassium cyanitde solution, and 3 ml. of 2Jf ammonium acetate solution with swirling of the beaker. Digest t h e precipitate at the above temperature for 15 minutes. Cool to room temperature and separate the precipitate using the filter apparatus (Figure 1). Wash the precipitate nith small portions of water while evacuating. Turn the cock and dissolve the precipitate with hydrochloric acid which is transferred to the beaker from the reservoir, with the aid of pressurized air. Dissolve the adhering precipitate
on the walls of the beaker and on the filter stick with hydrochloric acid from a dropping bottle. Do not use more than 15 ml. of concentrated hydrochloric acid to dissolve the precipitate. Transfer the solution to a 100-ml. volumetric flask and dilute to mark with water. Measure the absorbance of the resulting solution at 360 mp, using water as reference. RESULTS A N D DISCUSSION
Some of the plutonium metal which was used in this investigation contained several hundred parts per million of aluminum as impurity. This was ascertained by using a n extractionphotometric method with 8-quinolinol (6). . Americium-241 which always accompanies plutonium was also removed by this operation. One hundred milliliters of the hydrochloric-nitric acid eluting solution contained about 10 fig. of aluminum. The quantity of aluminum was determined by the extraction-photometric method previously described. Precipitation of Aluminum 8-Quinolinolate. Three series of solutions containing 106, 212, and 318 pg. of aluminum, respectively, were treated in different volumes of solutions by the suggested procedure. The importance of the volume parameter for quantitative recovery is shown in Figure 2. The state of coagulation after the digestion period should be observed by the analyst. A volume of less than 5 ml. is not recommended because of the limited solubility of 8-quinolinol. The p H range for the precipitation of aluminum was reported by Hollingshead (6). The precipitation, filtration, washing, and dissolving of less than 100 fig. of
aluminum are not easy tasks even with the filter apparatus (Figure 1). Effect of Plutonium on Aluminum Determination. Plutonium forms a n 8-quinolinolate and interferes in the indirect method by Patton (11), who precipitated plutonium(1V) 8-quinolinolate, and by Harvey et al. ( 5 ) , who precipitated plutonyl 8-quinolinolate. When 212 pg. of aluminum were determined in the presence of 25 pg. of plutonium, a +3y0 mean error was observed. One hundred micrograms gave a +9% mean error. Several agents such as acetate, tartrate, carbonate, hydroxylamine, and E D T A were used unsuccessfully in trying to prevent the precipitation of plutonium. Separation of Plutonium. Kraus a n d Nelson (8) have summarized the anion exchange behavior of a number of elements in hydrochloric acid. Plutonium is retained on the resin as the anionic chloride complex, while aluminum does not form an anionic chloride complex a t any hydrochloric acid concentration. I n a series of experiments, about 200 mg. of plutonium in 12M hydrochloric acid were passed through the column by the suggested procedure using resin heights varying from 2 to 8 inches. Approximately 3 pg. of plutonium were found in 20 ml. of each eluate. Spectrophotometric Measurement of 8-Quinolinol. Phillips and Merritt (12) reported absorlition peaks of 250, 318-19, and 358 mp for the 8-quinolinolinium ion which was formed in hydrochloric acid solution. The spectrum shows only slight variation a t 360 mfi over the range 0.006 to 10.0.11 hydrochloric acid. At other wavelengths, the acid concentration must be controlled. When other acid solutions such as nitric, sulfuric, perchloric, and phosphoric acids were used, peak shifts and acid dependence were observed in the VOL. 36, NO. 10, SEPTEMBER 1964
2033
absorption of the 8-quinolinolinium ion in the ultraviolet region. Interferences. For the type of sample discussed here, the interference caused by plutonium only needs be considered. However, sometimes the components of stainless steel may be present as contaminants. Potassium cyanide does not prevent the precipitation of the aluminum, and it eliminates the interference of 200 pg. of nickel, copper, and cobalt, respectively. The filtrate and washings containing potassium cyanide should be treated with hydrochloric acid in a well ventilated hood before disposal. RESULTS
Recovery data for this method were obtained by carrying aluminum through the suggested ion exchange-precipitaLion procedure in the absence of plutonium. The amount of aluminum was
varied from 100 to 400 p g . The absorbances were measured a t 360 to 390 mp, The relative standard deviation was less than 2% over the various measured wavelengths. In the analysis of six Pu-A1 samples, repeat analyses on the same samples had a range of slightly less than 2 pg, with a sample which contained approximately 200 Mg. of aluminum. LITERATURE CITED
(1) Cleveland, J. M., Nance, P. D., U. S. Atomic Energy Comrn. Rept, RFP-53 (1955). ( 2 ) Darbey, A,, Am. Dyestug Reptr. 42, 453 (1953). (3) Deterding, H. C., Taylor, R. G., IND.ENG. CHEM.ANAL.ED. 18, 127 (1946). (4)Evans, H. B., Bloornquist, C. A . , Hughes. J. P.. ANAL. CHEM.34, 1962 (1982).' (5) Harvey, B. G., Heal, H. G., Maddock, A. G., Rowley, E . L., J . Chem. SOC. 1947, p' 1010.
(6) Hollingshead, ,R. G. IT.,"Osine and
Its Derivatives, T'ol. 1, Butterworths, London, 1954. ( 7 ) Jones, I. G., Phillips, G , , UKAEA, AERE-R-2879 (1960). 18) ~, Kraus. K . A , . Xelson. F.. Proc. Intern. Conf. Peaceful 'Uses At: Energy, Geneva, 1955 Vol. VII, P/837, United Sations Pub., New York, 1956. (9) Miner, F. J., Degrazio, R. P., Forrey, C. R., Jones, T. C., -4nal. Chim. d c t a 22. 214 11960). (10) 'Motojima, ' K , Hashitani, H., Bunseki Kagaku 8, 526 (1959j , (11) Patton, It. L., "The Transuranium Elements," part 1, p. 853, McGrawHill, Sew York, 1949. (12) Phillias. J. P.. Merritt. L. L.. J . Am. C&m: SOC. 71, 3984 (i040). H. B. Evass HIROSHIH . 4 S H I T A S I ' Chemistry Division Argonne National Laboratory Argonne, Ill. WORK performed under the auspices of the U. S.Atomic Energy Commission. 1 Present address, Japan Atomic Energy Research Institute, Tokai, Ibaraki, Japan
Comparison of Electron Capture and Hydrogen Flame Detectors for Gas Chromatographic Determination of Trace Amounts of Metal Chelates SIR: Various detectors-e.g., hydrogen flame ionization (3, 4),thermionic emission ionization (g), argon ionization ( I ) , thermal conductivity (9),electron capture ( 7 , 8))and flame photometric (5)-have been used for the gas chromatographic determination of metal chelates, primarily acetylacetonates and fluorinated acetylacetonates. Although quantitative aspects of these detectors have been studied, especially of the electron capture ( 7 , 8) and flame ionization detectors (3, 4), investigations of their relative performances have been limited. The present investigation comprised a comparison of the electron capture and flame ionization detectors, and lower limits of detection were determined for both detectors for trifluoroacetylacetonates of chromium(II1) , aluminum(II1) , copl)er(II), and chromium(II1)-acetylacetonate. Satisfactory accuracy and
precision for both detectors were demonstrated by analyzing known mix. tures. EXPERIMENTAL
Preparation of Samples. Trifluoroacetylacetonates (tfa) were synthesized by published procedures (1, 9). hcetylacetonates (aa) were obtained from the MacKenzie Chemical Works, Inc. Stock solutions were prepared b dissolving 0.1 gram, accurately weighel of chelate in benzene ( 7 ) and diluting to 50 ml. in volumetric flasks. Dilutions to give concentrations of to 10-8 gram per ml. were made with benzene. Apparatus. An herograph .I-90 chromatograph equipped with a n herograph electron capture detector (concentric design) was used with a variable cathode voltage. T h e detector was operated with a n electrometer input impedance of 107 ohms
Table I. Lower Limits of Detection for Metal Chelates" Hydrogen flame, amt. detectable Electron capture, amt. detectable Com__________ pound Moles Moles/sec. Moles hloles/sec. 1 2 x 10-10 5 9 x 10-13 1 1 x 10-14 4 1 x 10-13 Cr( aa )3 3 7 x 10-10 9 3 x 10-13 1 3 x lo-'@ 3 1 x 10-1' Cr( tfa j 3 1 7 x 10-10 7 2 x 10-13 1 2 x 10-14 1 2 x 10-13 Al(tfa)n 16 X 3 2 x 10-12 2 0 x 10-1" 2 0 x 10-12 Cu(tfa)s Column temperature mas 160' C for Cr(aa)3and 110' C for trifluoroacetylacetonates; nitrogen carrier gas flow rates were 60 and 50 nil /min for the electron capture and hydrogen flame detectors, respectively
2034
ANALYTICAL CHEMISTRY
and a I-mv. recorder. At conditions for optimum sensitivity the noise level of the system was about 2 X ampere. Detector voltages for Cr(aa)b, Cr(tfa)3, and Cu(tfa)* were 35, 30, 35, and 40 volts, respectively. The hydrogen flame detector wac of conventional design and was operated with an electrometer input impedance of 108 ohms and a 10-mv. recorder. At conditions for optimum sensitivity the noice level of the system was about 2x ampere. Columns of borosilicate glass tubing (3 feet long by l/s-inch i d . ) were packed with glass microbeads (60- to 80- mesh) coated with 0 2% silicone oil (Dow Corning 550). Traces of iron particles were removed from the glass beads with a magnet before coating. General operating conditions mere similar to those described by Sievers et al. (9). Procedures. Calibration curves relating peak areas (planimetered) to weight c ; were obtained by an internal standard technique (n-hexadecane as the reference compound) for the flame ionization detector and by a constant volume technique for the electron capture detector. Some electron capture analyses were made with chloroform (8) or carbon tetrachloride ac an internal standard; however, the high electron affinities of these compourids necessitated large dilutions (with increased possibilities for errors) to obtain desired sample to ctandard ratios. For this reason the conytant volume method was generally preferred.
