V O L U M E 2 5 , NO. 4, A P R I L 1 9 5 3
651
Table IV. Composition of Alloys KO. 7%Lia % AIgb R Alb 9% Na5 % Ka
Alloy 3960 3964 3969 3957 3950 3958 3956
1.39 84.13 14.57 0,005 0.009 2.77 81.30 lL45 0.014 0,014 6.58 84.12 9.28 0,032 0.029 7.37 81.54 11.11 0,020 0.020 90.00 7.83 1.97 0.024 0.030 88.42 9.47 2.08 0,013 0.025 10.34 84.30 5.37 0.023 0.013 Li Ka,and K were determined by flame photometer method. b Mg and AI were determined gravimetrically.
% Total 100.10 99.55 100.04 100.06 99.85 100.01 100.05
plotted for each series of samples to compensate for variables such as gas, air, and oxygen pressures. DISCUSSION AND RESULTS
The data in Table I shorn- that sodium and/or potassium, in the concentration studied, have no effect on the intensity of the lithium flame. The data also show that high concentrations of magnesium and/or aluminum have a depressing effect. A ratio of magnesium and/or aluminum to lithium of 10 to 1 depresses the intensity only slightly, while a ratio of 100 to 1 has consider’able effect. This damping can be compensated by adding a p proximately the same concentration of alloying elements to the standard solution used in obtaining the reference curve. The nominal composition of the alloy is usually known and is sufficient t o prepare a working standard. In operating the flame photometer, the slit opening used must be adjusted for the concentrations encountered. In this investigation, a slit opening of 0.1 mm. was satisfactory. A larger slit, using the same concentrations, would have increased the readings but would also increase the instability or certainty of the meter readings for the blank and sample. The flame photometer method for determining lithium is much
faster than the gravimetric, volumetric, or colorimetric methods, since all tedious separations are eliminated. The readings on the flame photometer can be made easily a t the rate of 5 per minute. Using a series of 12 standard lithium solutions, about 12 lithium samples can be completed 2 hours after initial solution of the sample. This would mean that a set of 12 lithium samples would be completed in 1 day compared to an estimated 3 or 4 days for the various other methods. The method described has been used for a number of magnesium-lithium-aluminum alloys (Table IV) and has given good results. It is particularly recommended for its speed without loss of accuracy. LITERATURE CITED (1) Barnes, R. B., Berry, J. W,, and Hill, W , B., Eng M f n . J . , 149, No. 9, 92 (1948). (2) Barnes, R. B., Richardson, D., Berry, J. W., and Hood, R. L., IND. ENQ.CHEM..A k v a ~ED., . 17, GO5 (1945). (3) Beckman Instruments, Inc., South Pasadena, Calii , Beckman Bull. 193-A. (4) Berry, J. R . , Chappel, D. G., and Barnes, R. B., I s n . EVQ. CHEM.,ANAL.ED.,18, 19 (1946). (5) Fox, C. L., ANAL.CHEY.,23, 137 (1951). (6) Gooch, F. A , , Am. Chem. J . , 9, 33 (1887). (7) Mosher, R. E., Bird, E. J., and Boyle A . J., ANAL.CHEM.,22, 715 (1950). (8) hfyers, A. T., Dyal, R. S., and Borland, J. W., Soil Sci. SOC. A m , Proc., 12, 127 (1947). (9) Rogers, L. B., and Caley, E. R., ISD.ENG.CHEX.,IXAL. ED., 15, 209 (1943). (10) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” p. 301, 1st ed., Xew York. Interscience Publishers, 1944. (11) Standford, G., and English, L., A P Q O I L . J., 41,446 (1949). (12) West, P. W., Folse, P., and Uontgomery, D., ANAL.CHEM.,22, GG7 (1950). RECEIVED f o r review February 27,1952. Accepted December 13. 1952
Colorimetric Determination of Rhenium A Modi$ed Tribalat Method JOSEPH M. BEESTON AND JOHN R. LEWIS Department of Metallurgy, University of Ctah, Salt Lake City, L‘tah
like other less well-known metals, has received considerable attention of late. One of the important problems in rhenium studies where routine analyses are to be made is to find an accurate and rapid analytical method for its determination. A slight modification of the Tribalat ( 4 ) method developed in this laboratory has resulted in an appreciable saving of time with increased precision. The Tribalat method is based on the separation of rhenium from molybdenum by the formation of tetraphenyl arsonium perrhenate in an aqueous solution of pH 8 to 9. The extraction of the tetraphenyl arsonium perrhenate is made with chloroform. while molybdenum remains in the aqueous phase. The chloroform containing the rhenium is evapwated to a small volume, and the perrhenate ion is freed from the chloroform with concentrated hydrochloric acid. The colored thiocyanate complex of rhenium is made by addition of thiocyanate and stannous chloride. The colored thiocyanate complex is then extracted by adding isoamyl alcohol to form a mixture with the chloroform, and the per cent transmission is determined. In the Tribalat method, as originally outlined, considerable care must be taken in the evaporation of the chloroform containing the tetraphenyl arsonium perrhenate and development of the colored thiocyanate complex in order that the precision of 5 to 10% claimed by Tribalat can be realized. A fading of the colored HENIUM,
thiocyanate complex with time as the hydrochloric acid strength is increased has been noted by Geilman, Krigge, and Weibke (I), by Snyder (S), and by others. Since a volume of 25 nil. is convenient for the transmittancy determination of the colored solution on a Coleman or Beckman spectrophotometer, it wy&5 necessary to dilute the extracted solution; hence, an elimination of the evaporation step would decrease the chance of error and result in a considerable saving of time. After a number of experiments with 4.5, 5, 6, 7, and 8 .V hydrochloric acid, it was found that the quantitative separation of the tetraphenyl arsonium perrhenate in the chloroform can he best made in 6 N hydrochloric acid aithout evaporation of the chloroform. The quantitative separation in 6 *L’hydrochloric acid is apparently due to the removal from the acid solution of the perrhenate ions by the passing of the perrhenate ions into a reduced state as the colored thiocyanate complex. The quantitative removal of the perrhenate from the chloroform is fairly rapid. Solutions containing 0.8 microgram of rhenium per ml. showed the same optical density whether the color was developed for 10, 20, or 30 minutes. The colored thiocyanate complex is apparently very stable in the extract solution, since the extract solutions checked after 14 hours shon ed no significant change in the optical density. Three checks of the modified proceduie were made. .1 com-
652
ANALYTICAL CHEMISTRY
parison of the optical density of the extracted colored solutions of 16 samples having the same rhenium content (eight samples prepared by the procedure as described by Tribalat and eight prepared by the modified method) showed that those extracted in 6 N hydrochloric acid had a slightly greater optical density than those extracted in concentrated hydrochloric acid following evaporation. A comparison of the optical density of eight extracted thiocyanate colored solutions, prepared as standards (same neutral ionic strength, color developed in 6 N hydrochloric acid, not extracted by using tetraphenyl arsonium chloride) ~ i t height solutions having the same rhenium content and extracted by the modified method, showed that those extracted by the modified method had a slightly greater optical density. A comparison of the results of analyses by the modified method with that of Nalouf and White ( d ) by taking aliquots of solutions of various minerals showed that the two methods gave, within experimental error, the same rhenium content. PROCEDURE
The procedure foi the preparation of the standard curve for the modified Tribalat method consisted of taking four samples each of 1, 2, 5, and 10 ml. of a standard solution containing 0.01 mg. of rhenium per ml. and proceeding exactly as outlined in the modified method using the same molarity of initial chloride and sulfate ions. Concentrates R ere prepared for analysis by sodium hydroxide and sodium peroxide fusion, or by treatment with fuming nitric acid and concentrated hydrochloric acid as described by Malouf and White and by Tribalat. A 20-ml. aliquot of the sample which had been put into solution by fusion was pipetted from the 250-ml. volumetric flask into a 250-ml. separatory funnel. Concentrated hydrochloric acid was added to make the chloride ion content about 0.3 M, and the solution \\as nearly neutralized with concentrated sulfuric acid, making the sulfate ion content near 1 M . Sodium bicarbonate \\as then added to bring the pH to betpveen 8 and 9. One milliliter of 0.05 M tetraphenyl arsonium chloride aqueous solution was added to the separatory funnel and the solution agitated. Then 8 ml. of chloroform were added, and the mixture was shaken for 2 minutes. The phases were allowed to separate, and the chloroform \vas drained into a 100-ml. beaker containing approximately 0.5 gram of powdered anhydrous calcium chloride to remove entrained aqueous molybdenum solution from the .chloroform. The chloroform was swirled in the beaker and filtered into a second separatory funnel through about 0.5 gram of anhydrous calcium chloride. The filtering tube was made from a glass cylinder by drawing dom n the bottom to hold glass wool for a filtering medium. T Mo successive portions of chloroform (4 ml. each) ere added to the first separatory funnel; the mixture was shaken for 40 seconds and drained into the beaker, Additional calcium chloride was added each time so that all the entrained Kater containing molybdenum was absorbed by the calcium chloride, and the chloroform was filtered in the glass tube into the second separatory funnel. Most of the chloroform held by the glass wool Tvas removed from the glass tube each time by a stream of air before washing with the 4mI. portions. To the separatory funnel containing the chloroform and absorbed tetraphenyl arsonium perrhenate were added 20 ml. of 6 N hydrochloric acid. The mixture was shaken for 20 seconds; then 1 ml. of 20% solution of sodium thiocyanate m-as added. The mixture was shaken for 5 seconds, 1 ml. of a 35% solution of stannous chloride was added, the mixture was shaken again for 5 seconds, and then allowed to stand 30 minutes. After standing, 8 ml. of isoamyl alcohol were added, and the mixture was shaken for 20 seconds; then the phases were allowed t o separate. The chloroform plus isoamyl alcohol mixture containing the colored complex was drained into a 25-ml. volumetric flask, and the separatory funnel and solution were washed with enough chloroform and isoamyl alcohol mixture to finish filling the 25-ml. volumetric flask. The solution had a clear yellow or yellow-red color. If there was any cloudiness due to entrained water, the solution was cleared by centrifuging for about 1 minute. The per cent transmittance was then read on a Beckman spectrophotometer, using a blank sample to set the zero point on the photometer. The blank containing all ions except the rhenium had approximately the same transmittance as a mixture of the same volume of chloroform plus isoamyl alcohol. From the standard curve the amount of rhenium present was calculated.
The Malouf and White method was used as a comparison as to accuracy, precision, and time required for analysis of a sample. In analysis by the Malouf and White method it was observed that synthetic samples of the same rhenium content gave greater optical density when prepared using sodium molybdate. The sodium molybdate was analytical reagent grade. The possibility of a small amount of rhenium being in the sodium molybdate was discounted, since no color was found in blanks by the modified Tribalat method when using the same sodium molybdate. Malouf and White noted that partially reduced molybdenum is not extracted. I t may be that a small amount of molybdenum is reduced upon decomposition of the xanthate complex. A blank containing no molybdenum, but using purified xanthate and proceeding as with the analysis of a sample gave the same per cent transmittance as ether used for dilution. The presence of reduced molybdenum must be canceled out in the 3Ialouf and White method of analysis. This can be done by using molybdenum in the blanks used to set the spectrophotometer when the samples contain molybdenum, or by preparing a standard curve from synthetic samples containing molybdenum tvith the spectrophotometer Pet against blanks not rontaining molybdenum. RESULTS
Table I s h o w the results of analyses of synthetic samples by the modified Tribalat met.hod using the corresponding standard curve. The synt,hetic samples contained approximately 0.Oi gram of molybdenum and known amounts of rhenium. All color density measurements were made on a Beckmnn spectrophot'ometer at a light xave lengt,h of 430 mk. Table I1 contains the results of analyses by the two methods on aliquot portions of molybdenite solutions of different rhenium content. The values given are for 2 and 3 aliquots for each method. Geilman et al. ( 1 ) state that the thiocyanate reaction is suited t,o the detection of 0.05 microgram of rhenium per ml.of solution when the color is extracted with ether. This agrees with the results: of the authors when using either method as is shown in
Table I.
Valves Obtained by Modified Tribalat Analyses, of Synthetic Samples yo Error
Rhenium Taken, mg. Found, m g .
Error 0 2 4 2 0 4 5 5 10 10
0.100 0 098 0 048 0 049 0 050 0 048 0 019 0 019 0 009 0 009
0,100 0.100 0.050 0.050 0.050 0.050 0.020 0.020 0.010 0.010
Using JIaloufWhite Method 3 3 4 0 2 2 5 15 10 20
Table 11. Analyses of Ore Samples by Malouf-White and Modified Tribalat Method Malouf-White Method Precision error of Rhenium Standard (rO found, deviation standard y per ml. (+) deviation) 0.10 1.20 0.65 0.60 1.40 1.40 4.15 0.40 3.03 1.80 1 35
0.02 0.08 0 04 0.04 0.05 0.14 0.30 0.03 0.29 0.16 0.06
20 7 6
i
10 7
8 10 9 4
Uodified Tribalat Method Precision Rhenium Standard (70 error of found, deviation standard y per ml. (&) deviation) 0.15 1.40 0.70 0.60 1.40 1 45 4 25 0.30 2.35 1.50 0.80
0 03 0.08 0.04 0.02 0.09 0.11 0.25 0.02 0.15 0.06 0.03
20 6 6 3 6 8 6
7
6
4 4
V O L U M E 25, NO. 4, A P R I L 1 9 5 3
653
Table 11, and with the results of Malouf and White; hence, values in Table I1 are given to the nearest 0.05 microgram. DISCUSSION
An examination of Tables I and I1 s h o w that the two methods give approximately the same rhenium content. The precision of the modified method is slightly better. When no chloride ion was present in the solution to be analyzed by the modified Tribalat method, there was a greater loss of rhenium by adsorption on the calcium chloride used for drying the chloroform extract; accordingly, a 0.3 M initial chloride ion solution was used. The modified Tribalat method requires approximately 2 hours for analysis of a sample; hence, is shorter than the Malouf and White method. I n addition, it is much more economical from the standpoint of chemicals.
ACKNOW LEDG llENT
The authors wish to acknowledge financial assistance from the University of Utah Research Committee and from the University of Utah Kennecott research grant. They also wish to thank E. E. Malouf of the Kennecott Copper Co. for his valuable suggestions. LITERATURE CITED (1) Geilrnan, IT.,JT‘rigge, F. IT.,and Weibke, F., Z. anory. allgem. Chem., 208, 220 (1932). (23 hlalouf, E. E . , and White, hf. G., A b i ~ 4CHEM., ~ . 23, 497-9 (1961). (3) Snyder, Harold H., Ph.D. thesis, University of Wisconsin, 1946. (4) Tribalat, Suzanne, A n a l . Chi?%.Acta., 3, 113-26 (1949). RECEIT-ED for rex-iew September 8, 1952.
.iccept?d December 6, 1952
A Modification of Winnick’s Method for the Raoid Determination of Ethyl Alcohol in Biological Flu/ds IRVING SCNSHINE AND ROBERT NEYAD Cuyahoga County Coroner’s Ofice Laboratory, Znstitute of Pathology of Western Reserce University, and C‘nirersity Hospital, Cleveland, Ohio 4 ? * potentially ~
preventable deaths from trauma or disease have resulted from the erroneous assumption that the odor of alcohol combined with staggering gait and slurred speech. or with coma, is valid evidence that the individual is under the influence of alcohol. A simple qu:tutitative determination for ethyl alcohol in biological fluids is obviously desirable to aid in rapidly establishing a dingnosic of alcoholic intosication in the hospital emergency room. 80
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70
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OTHER ACCIDENTS
0
~ 6 0 -
HOME ACCIDENTS
P 10-
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10 20-
ACCIDEWTS
HOMICIDES
nI SUICIDES
I I
Figure 1. Incidence of Alcohol in Violent Deaths in Cugahoga County, Ohio, 1943-51
Ethyl alcohol determinations are the most common laboratory analyses in forensic medicine (Figure 1). 1Iore than 45% of all individuals involved in vehicular fatalities are found to have recently ingested an alcoholic beverage. I t is reasonable to assum& that in many instances the resulting impairment of judgment and reflex response has contributed to the occurrence of these accidents. In Cuyahoga County (Cleveland) it has been found that 6170 of the victims of homicide and 30% of all suicides are under the influence of alcohol at the time of their death. Prompt and accurate determination of ethvl alcohol is essential to the administration of justice. The large metropolitan police laboratorv concerned with a surge of alcohol determinations after a week end of activity would benefit from a rapid test that could be done “en masse.” Sunierous methods have been described in the literature for the quantitative determination of ethyl alcohol. Most of these are based on its volatility and reducing power. I n the main these procedures separate the ethyl alcohol from other biological ma-
terial by distillation ( 4 , 6, 8). Some aeration procedures have been described ( 2 , 6 ) , but these are seldom used because they are not adapted to multiple analyses. Diffusion desiccation methods (1, 9 ) , particularly Widmark’s, have been favored on the European continent but are not used extensively in this country. The distillate (diffusate) is then oxidized, usually by potassium dichromate. Two procedures have been described using Conway ( 3 ) cells for the determination of alcohol. Winnick (10)placed the test material in the outer compartment of the Conway cell, and the alcohol which diffused reduced potassium dichromate which was placed in the inner compartment. The excess dichromate ion then was determined iodometrically. MacLeod ( 7 ) used a similar apparatus but absorbed the alcohol in alkaline potassium permanganate. T o determine the excess permanganate, the contents of the center well were reduced by thiourea in the presence of barium ions. Potassium carbonate was added to the outer section to hasten the diffusion of the ethyl alcohol. The present method also uses potassium dichromate in the central well of the Conway cell. The complete diffusion (evaporation) takes 20 minutes. Results are thus obtained quickly so that they have clinical value. The amount of alcohol present is determined colorimetrically. The contents of the center well are compared with prepared standards, or the optical density is measured with a photoelectric photometer. RE4GEYTS
Potassium Dichromate. Dissolve 4.262 grams of analytical reagent grade potassium dichromate in 100 ml. of distilled water. Carefully add, while cooling, 500 ml. of reagent grade sulfuric acid, and then dilute this mixture, while cooling, to 1000 nil. with distilled water. One nil. of this reagent is equivalent to one mg. of ethyl alcohol. Sodium Carbonate, 20% Solution. Dissolve 20 grams of sodium carbonate in water and dilute to 100 ml. Standard Alcohol Solutions. Dilute absolute ethyl alcohol with distilled water to known concentrations varying from 50 mg. to 600 mg. per 100 ml. solution. Dow Corning Silicon‘Stopcock Grease. PROCEDURE
Pipet 3.00 ml. of potassium dichromate into the center well of reservoir buret will facilitate the performthe Conway cell. (-4 ance of a large number of analyses.) .idd 1 ml. of 20y0 sodium carbonate to the outer compartment. Apply silicone stopcock
