Table 1. Alkylate Content of Reaction Mixiures
Detd. by Cald. from spectroscopic alkylate content of differencemethod nonacidic material 0.7
1.6
0.7 1.6
1 9
1 9. _
012
0.2 0.6
0.6 1 .o
1.o
isolated by the procedure outlined above and examined by infrared spectrophotometry. By comparison rrith synthetic mivtures of alkylate and sulfone, the unsulforiated alkylate content of the isolated nonacidic material was less than 2Yc. The calibration data for the alkylate content of ynthetic mixtures, which contained 0 to 5% of added alkylate, showed that Beer's law n as obeyed over this concentration range. I n Table I is recorded the alkylate content determined for a series of reaction mixtures. These results have been compared with the alkylate content of the mixtures calculated from the alkylate content of the nonacidic material extracted by the above method,
the alkylate content of these isolated nonacidic materials having been determined from the alkylate absorption a t 699 cm.-l using a calibration curve. The standard deviation 'of the infrared spectrophotometric determination was 1 0 . 1 and the limit of detection of unsulfonated alkylate in reaction mixtures by this method was estimated from the calibration curve as = t O . l % . For any given alkylate and set of plant operating conditions the total amount of sulfone and unsulfonatable material present in the reaction mixtures mas constant. Hence it is possible to determine the total nonacidic material present in the reaction mixtures by determining the unsulfonated alkylate content by the differential spectrometric method and adding a standard constant for the sulfone and unsulfonatable material. Such determinations are important since the amount of nonacidjc material present in an alkylbenaene sulfonic acid has a marked effect on its detergent properties. The spectrophotometric method, which required only a few minutes per determination, provided a rapid means for the control of the sulfonation compared to the extraction method which required about 1 hour. With time, a deposit was formed on
the potassium bromide windows of the cells but this deposit showed no absorptions over the range 690 to 800 cm.-l Examination of a sample of this deposit in a potassium bromide disk showed that it was a sulfate ryith a broad absorption band centered at 1113 cni.-I ( 3 ) . This sulfate would arise from traces of sulfuric acid present in the reaction mixtures. ACKNOWLEDGMENT
Thanks are due to the Directors, Colgate-Palmolive, Ltd., for permission to publish these results. LITERATURE CITED
(1) Blakeway, J. M., Thomas, D. B., J . Chromatog. 6 , 74 (1961). ( 2 ) Cleverleg, B., i i x a ~ CHEM. . 33, 1621 (1961). (3) Harkins. T. R., Harris. J. T., Shreve, 0. D., Ibid., 31, 541 (1959). ( 4 ) Rlchlurrav, H. L., Thornton, V., Ibid., 24. 318 11952). ( 5 ) CIcTaggart, K. G., Thornton, E., Harford, A. D., Pyrethmm Post 4, ( 4 ) , 12 11958).
(6) Powell, H., J . Appl. Chem. (London)6, 488 (1956). ( 7 ) Kashburn, W. H., Mahoney, 11. J., AXAL.CHEW30, 1053 (1958). RECEIVEDfor review June 25, 1962. Accepted December 20, 1962.
Rapid Radiochemical Procedure for Antimony and Arsenic ALLEN E. GREENDALE and DANIEL L. LOVE
U. S. Naval Radiological
Defense Laboratory, San Francisco 24, Calif.
b A very rapid radiochemical procedure has been developed for antimony and arsenic. Stibine (SbH3) and arsine (AsH3) are formed b y reduction with the nascent hydrogen generated b y dropping acid onto dry granular zinc warmed to 100' C., rapidly swept from the solution, and decomposed to the metal in a heated quartz tube. The metallic mirror formed is dissolved in acid and assayed. The chemical yield is consistently between 70 and 80%. About 10 seconds is required for separation of the metal from the other elements of a fission product solution. The decontamination factors for the antimony procedure are: mixed fission products ( 2 weeks old) = lo5, I = 3 X lo4, Te = 4 X lo4, Sn = >106, As = 20 to 50. The decontamination factors for the arsenic procedure are: mixed fission products = lo7, Sb = 2 X 103,Sn = >lo6. 632
ANALYTICAL CHEMISTRY
A
one-step radiochemical method of separating antimony from fission products was needed for the determination of independent fission yields of antimony nuclides. The separation must be completed before the antimony decays, and the exact time of separation after f i 4 o n must be known. The brief half live- (minute. or less) preclude oxidation-reduction reactions to effect isotopic exchange and repeated precipitation to achie\ e the required radiochemical purity. A\l~o,the decontamination factors from tin, tellurium, and iodine must be large, qince the independent fi-cion yield of the antimony nuclide is finally determined from the number of atoms of the longer-li\ ed iodine daughters. Preaent radiochemical procedures for separation of antimony and arsenic (1, 4 ) include solvent extraction, ion exchange, reduction to the metal, sulfide precipitation, hydride formation, and RAPID,
combinations of these methods. The time for separation varies from 5 minutes to 5 hours. Chemical yields vary from 25 to 90%. Decontamination factorq for individual elements vary 11-idely and usually are from IO* to 104. Hi.;torically, small quantities of arsenic and antimony have been determined by the Marsh test ( S ) , or a simple variation of it, in which arsine (or stibine) iq formed by the reduction with zinc in hydrochloric acid. This method promised to meet the requirements, if the relatively low yield ah-ays obtained could be increaqed and the antimony and arsenic could be collected without contamination by iodine and other T olatile fission products. The method n as modified in the separation of the volatile hydrides of antimony and arsenic, and was developed into the de-ired radiochemical procedure. Use of heated reactants caused the
FURNACE
Figure 1. arsenic
Apparatus
0UBBLER
for separation of antimony and
volatile hvdride to be formed quickly and snept from the solution by evolved hydrogen before it decomposed. This was the main method of increasing the yield from about 15 to 80%. A filter system nas addcd to remove the gaseous fission products and the contaminated aerosol carried by the evolved hydrogen ga;. Khile thi, procedure a as developed for the ieparation of ii specific nuclide from a fission product miyture, its use is by no means so imited. Carrierfree separations are achieved by simply omitting the carrier;. The procedure has been u-ed for quicakly separating antimony activitie; ai, a uell defined time from iriistures clf antimony and it* radioactive daughters. Also, antimony can be rapidly determined through isotopic dilution, with radioactive antimony used for the rsdioidopic yield determination. EXPERlMEhTAl
Materials. The concentrations of carrier used are: :tntirnony(III), 10 mg of Sb per ml. a. SbC13 in concentrated HC1; arsenic(II1). 10 mg. of As per ml. as. -4sC13 in 1 s NaOH. The Drierite desiccani, used is 8-mesh anhydrous CaS04, the zinc metal is 20 mesh and low in arsenic, and the H 8 0 4 has a specific gravity of 1.84 and is also 101% in arsenic. Apparatus. The apparatus for the determination of an1 imony and arsenic iq shown in Figure 1 . Unit A holds the solution of acid, carriers, and niiyed fiqsion products (NFP), I t is fitted with a tno-way stopcock t o provide L-acuuni fo1 introducing the RIFP iiito the \-ei+el. a i d nitrogen for
flushing air out of the unit and forcing the solution rapidly into flask B. A hot plate is used for heating the zinc to 100" C. (via the water bath, and flask B ) . Drying tube C contains Drierite. A 1320-watt tube furnace, connected to a variable transformer, is used to heat quartz tube D , 4 X 20 mm. long, to 600" C. to decompose SbH3. A fine sintered-glass filter is located between D and E to catch the fine particulate black antimony which forms from the rapid cooling of antimony vapor. A Meker-type burner is used to heat quartz tube E for the decomposition and collection of elemental arsenic. A bubbler placed after E indicates the flow rate of the flushing gas. Finally, tubing attached to the bubbler leads the escaping gases to a well ventilated hood. Extreme care should be taken to prevent escape of the very poisonous arsine and stibine from the system. Procedure for Antimony and Arsenic. The furnace temperature is held a t 600" C. by adjustment of a variable transformer. The second quartz tube, E, is heated until it has a reddish glow. Five grams of zinc metal is spread evenly over the flat bottom of flask B, and held a t 100" C. in the mater bath. Flask B and the system are flushed for a fe\v minutes with an inert gas-e.g., Nz-before starting the analysis. The gas inlet for flushing is shown just under the bottom stopcock of A (Figure 1). Four milliliters of 30% HzS04, 1 mg. each of antimony and arsenic carriers, and the MFP's are added to unit A. The unit is flushed for a few seconds with an inert gas by way of the threeway stopcock and then put under a few pounds' pressure. The solution in A is then added to the zinc in B. Within about 10 seconds, the antimony metal
deposits on D and the sintered-glass filter, and the arsenic on the hotter quartz tube, E. The collected sample is dissolved from the tubes and the filter with warm concentrated HzS04. Other reagents may be used for this solution step. The chemical yields may be determined by any convenient method. Procedure for Antimony. To determine antimony, the apparatus is set up as described, except for the furnace and quartz tube, E . Quartz tube D is heated with the Meker-type burner until it has a reddish glow. The sample is introduced as before or with a transfer pipet. After mixing, the air is flushed out by the inert gas. A is put under a few pounds' pressure to force the reagents into B. The antimony metal deposits on D and the sintered-glass filter. The metal dissolves easily in warm concentrated sulfuric acid. If it is desirable to study the decay products of antimony, the metal can be dissolved in tartaric acid with tellurium or iodine carrier present. The chemical yield can be determined by either a spectrophotometric method, using the Rhodamine B colored complex formed viith antimony ( 5 ) or with an isotope tracer-e.g.. Sblz4. In this separation the arsenic deposits with the antimony. Since the fission yield of arsenic is low compared to antimony and the half lives of arsenic fission product nuclides are short compared to those of antimony fission product nuclides, this contamination by arsenic is insignificant in the usual antimony analysis performed on fission product samples several days old. When the procedure is used for both antimony and arsenic, the arsenic contamination is less than 5%. RESULTS A N D DISCUSSION
Application. I n separating antimony radionuclides rapidly from mixed fission products, a pneumatic system carried the fission products rapidly from the reactor t o the apparatus where the separation of antimony was to be made. A rabbit holding the fission product solution and antimony carrier in 307, H2S04impales itself onto a hypodermic needle and the solution is drawn into A , along with a 1-ml. 1N HCl wash (Figure 1) by means of a vacuum ( 2 ) . After a brief mixing, the fission products, 307, HzS04, and antimony carriers (inactive antimony plus SbIz4) are dropped onto zinc in B , where SbH3 is formed. The stibine is swept out by the generated Hz and passes through the Drierite in C, which picks up any spray from the reaction in B. This trap also is very efficient in preventing the volatile fission products, such as I?which come? over as Sb13,from passing through the system. The stibine (SbH3) is decomposed by passing through the hot quartz tube, D , and deposits as an antimony mirror on the cold portion of the quartz tube and as black antimony on the sintered-glass VOL. 35, NO. 6, M A Y 1963
a
633
filter. In the determination of the Sb133 independent fission yield, the antimony was given time (-1 day) to decay completely to 21-hour P3. The antimony metal was dissolved in tartaric acid containing iodine carrier instead of hot H,SOI, so that none of the iodine would be lost by volatilization. A radiochemical determination was then carried out for iodine. All the 1133 present had decayed from the Sb133. The chemical yield of antimony was determined by counting the Sblz4, which was added for this purpose. Figure 2 shows the results of a series of separations of antimony a t various times after a 10-second irradiation of using the method described. The half life of Sb133was found to be 2.62 f 0.46 minutes. In a similar manner the half life of Sb131was found to be 19.4 f 2.3 minutes. The independent fission yields of Sb133, Sb132,and SbIal from thermal-neutron irradiation of U2'5 were found to be 2.4, 3.3, and 2.0%, respectively, from measurement of the number of iodine-daughter atoms and total fissions occurring in the sample. Other Uses, During development of this procedure it was apparent t h a t the use of carriers was not essential, and it could thus be used for highyield, carrier-free preparations of these elements. Since the deposition characteristics of the antimony and arsenic can be determined with carriers, the carrier-free material is leached from the position on the tube where the carriers would normally deposit. The general procedure is also useful when it is desirable to separate an antimony or arsenic activity from a mixture of its radioactive daughters. The collection takes only a few seconds and the time of separation can be determined very accurately. This is of value when making a correction for or a study of the growth and decay of daughter activities. This procedure may be used for the determination of antimony in mineral or other samples, with isotopic dilution techniques. One may dissolve the sample in sulfuric acid, collect the metallic antimony on the quartz tube, dissolve it, and determine the quantity of antimony spectrophotometrically. The yield is determined by the added radioactive antimony, whose contribution to total antimony is insignificant. This method is faster than present analytical methods for antimony. These techniques may also be applied to the determination of arsenic. Study of Variables. Since the major weakness of procedures using separations of stibine and arsine is low yield, the major effort in developing this procedure was concentrated on this problem. It was found that the yield could be improved by reducing the normal carrier concentration. One milligram of carrier gives a
634
ANALYTICAL CHEMISTRY
SblJ3
0 0
I
I
I
I
1
2
3
4
I
I
I
I
I
I
5
6
7
8
9
10
1
TIME I M l N l
Figure 2. Amount after fission
of Sbla3 separated a t various times
satisfactory yield and is enough to give good results with the spectrophotometric method used in the measurement of chemical yield. The chemical yield is also dependent on the total volume of reagents (in the apparatus used). Since it was desirable to keep the volume as small as possible for rapid SbH3 evolution, a total volume of 5 ml. seemed optimum, 4 ml. of this being 30% HOSOd. Since a 10 mg. per ml. standardized carrier solution was used, there remained 0.8 to 0.9 ml. for sample solution. If 1.2 ml. of concentrated Has04 is used instead of 4 ml. of the 30% acid, 3.6 to 3.7 ml. of sample solution can be taken. Variations in total volume of 10% in either direction have little effect on the chemical yield. The chemical yield is also somewhat dependent on the mass of zinc and its particle size. There is an increase in yield up to a mass of 5 grams of zinc, but from 5 to 15 grams there is no noticeable improvement. Thus, 5 grams was chosen as the best weight of zinc in relation to the other conditions chosen. There is a small increase in yield when 20-mesh instead of 10-mesh particle size zinc is used. Since still finer particle sizes tend to cause excessive foaming, the 20-mesh size was chosen. The factor of greatest importance in attaining the maximum yield was found to be the temperature of reagents. Initially the temperature of the solution was raised, in order to have the reaction start quickly so that the time for separation could be reduced to a minimum. Increasing the temperature of the solu-
tion gave an increased yield as well &s a faster separation. -4 yield of about 25% was the best that could be obtained with this arrangement. Heating the solution led to difficulties in drawing in the fission products rapidly from the rabbit by the use of a vacuum, since the vacuum could not be maintained over a boiling solution. To avoid this difficulty, the zinc and its container were heated. With this simple change in conditions the yield went up to a consistent 70 to 80%. ii temperature of about 100" C. was found to be optimum. This temperature is easily maintained through the use of a water bath. The yield was reduced by a third by lowering the temperature to 80' C. Exchange of carrier with tracer is usually a problem in radiochemical procedures where the element in question can exist in two or more oxidation states. This problem was studied in the following manner. SblZ4(III)was mixed with Sb1*5(V). The gamma spectrum of the mixture was observed on a 256channel pulse-height analyzer. The mixture was then run through the antimony separation procedure, the antimony was collected, and the r-ray spectrum of this mixture was compared with the initial mixture. There was no detectable difference in the two spectra, indicating that the oxidation state has no measurable effect upon the yield of the antimony. Thus, it is not necessary to perform a series of oxidation-reduction steps to ensure exchange. However, there is a possibility of Sb(0) being formed in irradiations under reducing conditions. Since reducing conditions did not exist in
these studies, the existence of tracer amounts of Sb(0) was not experimentally verified. It is very unlikely that Sb(0) would bc, formed or exist in the H2S04 solution used here. Since a clean separstion of antimony from iodine was essential for our needs, various traps, such as heated copper and other metals, w r e tried. The desiccant Drierite, a ?hydrous calcium sulfate, did by far the best job in removing the iodine aztivity, which was actually volatilized a< antimony iodide. It holds back other volatile fission product activities a!: well. A glass wool plug just befcre the desiccant stops most of the spray and enables one to make several runs before changing the desiccant. Decontamination :Factors. I n the determination of decontamination factors, a measured quantity of the nuclide to be studied was added to the acid and carriers, and arsenic or antimony mas separ,ited. The ratio of activity added to that collected on the arsenic or antimony recovered is the decontamination factor. Table I lists a number of these which were of interest
Table 1.
Decontamination Factors
Contaminant Te I Sn LIixed fission products ( 2 weeks old)
Arsenic
Sb
2
>lo’ 107
As
x
Antimony 4 x 104 3 x 104 > 106 106
20-50 io8
...
in this work. Generally, decontamination factors for arsenic are better than those for antimony, as expected, since arsenic is collected after antimony in the train. Reasons for High Yield. The speed and high yield attained with this method compared to older separations using arsine and stibine are felt to be primarily due to the heating of the zinc and the consequent rapid removal of the hydrides from the solution before they decompose, and to the reduction in volume of acid reacting with the zinc. With a large volume
of acid the stibine map be oxidized to the metal before it escapes from the solution. With a volume of solution just large enough to wet the zinc, the stibine escapes easily, along with the voluminous amount of H? produced by the reaction of the hot zinc with the sulfuric acid. LITERATURE CITED
(1) Beard, H. C.,“The Radiochemistry of Arsenic,” Natl. Acad. Sciences, Nuclear Science Series, Monograph 3002 (1960). ( 2 ) Greendale, A. E., Love, D. L., “A System for Rapidly Handling an Irradiated Solution,” U. S.Naval Radiological Research Lab., USNRDL-TR601 (Nov. 13, 1962). (3) Hildebrand, I. H., Latimer, mi. M., “Refyrence Book of Inorganic Chemistry, p. 85, Macmillan, New York, 1936. (4) Maeck, W. J., “The Radiochemistry of Antimony,” Natl. Acad. Sciences, Nuclear Science Series, Monograph 3033 (1961). (5) Van Aman, R. E., Hollibaugh, F. D., Kanzelmeyer, J. H., ANAL.CHEM.31, 1783 (1959). RECEIVEDfor review March 12, 1962. Resubmitted January 21, 1963. Accepted February 25,1963.
Estimatioci of Mercury in Biological Material by Neutron Activation Analysis HAMILTON SMITH Deparfmenf o f Forensic Medicine, The University, Glasgow, Scotland, and Wesfern Regional Hospital Board, Regional Physics Deparfmenf, Glasgow, Scotland
b Neutron activation analysis combined with chemical separation is a quick, accurate method for the estimation of mercury in small samples of biological materials. After nitric-sulfuric acid digestion of the activated sample a precipitatilm separation is combined with a gravimetric yield determination. The activity is detected by scintillation counting.
T
HE PRoRLEhIs in the quantitative determination of mercury in biological tissue were: the cestruction of the tissue while retaining mercury in the reaction medium; the development of a simple and specific sepm~tionprocedure; a yield recovery eqtiination and final mercury determination. The following outline covered these points and acted as B basis for the invet.tigation. After neutron activation samples were placed in flasks with some inactive carrier and digested with a mixture of nitric and sulfuric acids, a preliminary precipitation was macle using ascorbic acid ‘and the rema ning interfering
materials were removed by a silver precipitation. Finally the mercury was precipitated as mercury iodidecopper ethylene diamine complex. A yield determination was made and the activity was measured and compared with a standard. EXPERIMENTAL
Preparation and Irradiation of Samples. The samples, preferably about 20 mg., were weighed into aluminium or silica tubes which were then sealed. A sample of high purity metallic mercury (about 1 mg.) was weighed into a silica tube which was then sealed. The samples and standard were packed into a standard aluminium can and irradiated in a reactor a t a thermal neutron flux of 1012 neutrons per square centimeter per second for a week. The unit was returned and processed as described below. The standard was dissolved in nitric acid and diluted as necessary. Mercury Isotopes. Two isotopes were available for study by activation analysis. Both mercury-196 and mercury-202 after irradiation for 1
week became reasonably active by neutron capture as shown below. Irn
Hg1g6 (tl/s - 65 hours) and Hg197m (tl/g - 24 hours) gave out rather low energy x-rays which were not so easy to detect as the 0.279-m.e.v. y-rays from Hg203 ( t 1 / 2 - 47 days), so the latter was used. Westermark and Sjostrand ( d ) , however, have used Hg197 with y-ray spectrometry. It was possible to have interference from T1203(n,p) Hg203 with a TI matrix and from Pb206 (n,cr) Hg203 with a Pb matrix. Reagents. Where possible, high purity reagents were used. The complexing agent for mercury was prepared by mixing one part of lOyo copper sulfate solution (w./v.) with 10 parts of 10% 1,2-ethylenediamine (v./y.) * Digestion of Samples. For the success of the separation procedure it was necessary to make sure that any organic mercury compounds were destroyed and yet keep the mercury in solution as a simple compound. This VOL 35, NO. 6, MAY 1963
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