standard length reaction coil (1 1.25-ml. volume). The results are expressed in terms of two standard deviations (95% probability). Thus, the average accuracy and precision in the 0.1- to 0.5-pmole sample range is 100 + 3% and 100 3%, respectively. To determine the resolution at higher flow rates, the 57.0-cm. column was operated (using the same buffer and ninhydrin system previously mentioned) at 120 ml./hour for the buffer and 60 ml./hour for the ninhydrin reagent. The operating back pressure was 210 p.s.i. A sample load of a synthetic amino acid mixture containing 0.25 pmole (G.50-ml. volume) of each amino acid was tested. The analysis was conducted a t 55’ C. and a buffer change from the p H 3.28, 0.20N to the p H 4.25, 0.20N sodium citrate buffer occurred a t 41 minutes. A slight loss of resolution was experienced. However, it is possible to quantitate accurately (height-width method) those peaks affected; namely, the threonine-serine and tyrosine-phenylalanine doublets. If the standard length rwction coil ( 7 ) is used, reproducibility of recoveries will be 100 f 6%. With a doublelength reaction coil, normal r+ producibility of recoveries will be 100 f 3%. An analysis time of 1 hour, 35 minutes for the analysis of the acidic and neutral amino acids is possible.
DISCUSSION
The goal of this work has been the optimization of resin, column length, column diameter, and flow rate to achieve the complete analysis of a protein hydrolysate in the minimum time. Limiting conditions imposed were; maintenance of precision and accuracy, operation at reasonable pressures, with maximal resolution and a minimum of change of existing equipment. We found no commercially available ion exchange resin that would allow us to meet these specifications using the conditions described above. In the accomplishment of these aims, the geometry and chemical composition of the resin column packing is crucial. The resin was designed specifically to meet the above goals. That these aims have been met adequately is demonstrated by the results obtained. The results with this resin are also in agreement with expectation indicated for the hydraulic characteristics of narrowly graded spherical column packing material (3, 6). The good resolution with fine particles that has been previously obtained with other systems (4, 6) is also confirmed for this system. Because of rigid control in the manufacture of the resin to ensure constancy of cross-linking, spherical shape, and predetermined particle diameter range, the results shown here are typical;
*
identical results have been consistently obtained from batch to batch. Another resin system has been developed which will allow two complete analyses of physiological fluids in 24 hours; the details of this analysis are to be reported, later. ACKNOWLEDGMENT
The authors gratefully acknowledge the editorial assistance of P. B. Hamilton and the technical assistance of Jean Cormick. LITERATURE CITED
Benson, J. V., Jr., Patterson, J. A., Federation Proc. 23:2. 371 11964). (2) “Beckman Technical Bulletin;” T B (1)
6028A, March 1962. (3) Dallavalle, J. M., “Micromeritics,” 2nd ed., pp. 134-43, Pitman Publishing CorD.. New York. 1948. (4) kamiiton P. B., Ann. N . Y . Acad.
Sci. 102, 5: (1962). (5) Hamilton, P.‘ B., ANAL. CHEM. 35, 2055 (1963) :hemica1 Engineers’ (6) ~, Perrv. J.’ H.. HandKook,” 3rd ed., pp. 327-340, McGraw-Hi 11, New York, 1950. (7) Spackman , D. H., Stein, W. H., Moore, S., ANAL.CHEM.30,1190 (19,58). 18) SDackman. D. H.. Fedei.ation Proc. 22:&2, 244 (1963). ~I
RECEIVEDfor review November 2, 1964. Accepted May 24, 1965.
ion Exchange Separation of Americium and Cerium HAZEL
D. PERDUE
and HARRY G. HICKS
Lawrence Radiation Laboratory, University o f California, Livermore, Calif.
b Tracer quantities of americium-24 1 ( 1 06 disintegrations per minute) and 30 mg. of cerium have been separated quantitatively using Dowex 50W X12, 100- to 200-mesh, ion exchange resin and ammonium lactate as the eluant. In the present procedure small cdumns are used, and the use of a fraction collector is eliminated.
C
can be separated from the rare earths by extraction (3) of Ce(1V) by diethylhexyl phosphoric acid; radiochemical analyses for fission product cerium have been developed using this property. Usually the cerium is back-extracted, precipitated as the oxalate, ignited, and weighed. In this case, there is a small amount of phosphate (either organic or inorganic) carried along with the cerium, which renders the composition of the ignited oxalate indefinite. To eliminate the contamination, the cerium is absorbed ERIUM
1 1 10
e
ANALYTICAL CHEMISTRY
on cation exchange resin, washed well with dilute nitric acid, and eluted rapidly with ammonium lactate before the oxalate precipitation. When the analysis is made from gram amounts of plutonium, there is, in addition, a large amount of Am*41(IO9 disintegrations per minute) present from the decay of Puzrl. The oxidation of Ce(II1) to Ce(1V) with in strong H N 0 3 solutions will oxidize a small fraction (-0.1%) of the Am(II1) to Am(V) which extracts into diethylhexyl phosphoric acid ( I ) and is not subsequently separated from the cerium. The radioactivity of the remaining Amzr1 is enough to interfere seriously with the measurement of CeI4l and Ce144 radioactivities. The object of this study is to find a rapid, simple separation of americium from 30 mg. of cerium that is compatible with the existing radiochemical procedures. The relatively large difference in cation exchange behavior between Ce(II1) and Am(II1)
(4) suggested that the separation could be carried out using a variation of the ion exchange procedure already in use. EXPERIMENTAL
Apparatus. The ion exchange column was 9 cm. long, 6 mm. in diameter, and had a reservoir 16 mm. in diameter. Solutions were added to the reservoir a t the top of the resin column and allowed to flow by gravity into collection tubes. Gamma radiations from Am241and Ce144-Pr*44 in the collection tubes were counted directly by a well-type NaI(T1) scintillation crvstal. a photomultiplier tube, an aiplifier, and a scaling unit. Reaeents. The Dowex 50W X12 100- co 200-mesh resin used was purchased from the BioRad Co., Richmond, Calif., and was used without further treatment. Lactic acid was purchased from J. T. Baker and was used without further purification. Ammonium lactate solutions were prepared by diluting the
Figure 2. Elution of Am(lll) and Ce (111) using 1M initial lactic acid adjusted to pH 2.97 with NHdOH RESULTS AND DISCUSSION
2.84 2.92 3.00 308 3.16 3. pH O F l M INITIAL L A C T I C A C I D SOLUTION Figure 1 , Position of Am(lll) and Ce(lll) elution peaks as a function of pH of a 1M initial lactic acid eluting solution
lactic acid with water to 1-44 and neutralizing with concentrated ",OH to the proper pH as measured with a Beckman p H meter. T o retard bacterial degradation of the ammonium lactate solution, saturated aqueous phenol solution was added during dilution (5 ml. per liter of ammonium lactate solution). Procedure. About lo5 counts per minute of either Am2" or Ce144-Pr144 were added to 30 mg. of inactive cerium in dilute acid. I n general, only a single radioactive species was used in a given column elution to avoid ambiguity in the results; duplicate or triplicate experiments were performed to check reproducibility. The Ce(0H)a was precipitated with ",OH, centrifuged, and washed with water. The hydroxides were dissolved in 15 ml. of 0.5M HNOs with 2 drops of 30% H202 added. The solution wm heated to reduce Ce(1V) formed by air oxidation of the hydroxides because Ce(1V) elutes with Am(II1) under the conditions of these experiments. The solution was then transferred to the resin column which had previously been equilibrated by passing about 10 ml. of 0.5.W HNO, through the column. After the solution containing the cerium and tracer had passed through the column, 5 ml. of H 2 0 was added as a wash. Then the collection tube was changed and 5 ml. of the ammonium lactate eluant was added to the top of the column. When the solution had passed through the column the collection tube was changed, and the procedure was repeated. Each portion of eluate was counted separately to measure the elution curve. The initial flow rate of
20 drops per minute (obtained by adding 5 ml. of ammonium lactate solution to the reservoir) was the maximum flow rate which maintained chemical equilibrium in the system. Initial conditions were chosen rather arbitrarily, based on previous experience with rare earth separations ( 9 ) ; Le., a resin column 9 cm. in length and an initial lactic acid concentration before neutralization of 1M. Other concentrations of initial lactic acid were used (0.5M and 2.OM), but no significant difference in separation or eluate volumes wm found.
Elution curves were made a t pH values of 2.85, 2.93, 2.95, 2.97, 3.03, 3.06, 3.10, and 3.20. The results are summarized in Figure 1. The leading edge of the elution band was taken to be the point a t which the radioactivity in the collection tube rose over 100 counts per minute above a counter background of 150 counts per minute, or roughly O.lyoof the total radioactivity. The trailing edge was taken to be when the activity fell to the same value. Separation was considered adequate when there were a t least two collection tubes (10 ml.) between the trailing edge of the americium band and the leading edge of the cerium band. The condition for optimum separation was taken to be the pH at which there was a minimum of ammonium lactate to effect adequate separation. Under the conditions of the experiment, the optimum pH was 2.97 for 1iZl initial lactic acid concentrations; there was less than 0.01% of the Am241 in the cerium subsequently eluted from the column by 15 ml. of pH 5 ammonium lactate solution. In one experiment, both Am241and Ce144-Pr144 were
DOWEX 5 o W X 1 2
I ELUATE VOLUME(ml.)
ELUATE VOLUME lml.)
Figure 3. Comparison of separotion of Am(lll) and Ce(lll) using Dowex 5 0 W X 1 2 and Dowex 5 0 W X8 with a 1M initial lactic acid eluting solution adjusted to pH 3.10 with N H 4 0 H VOL. 37, NO. 9, AUGUST 1965
0
1111
added to 30 mg. of cerium, and the elution was made with ammonium lactate made by adjusting 1M lactic acid to pH 2.97. The elution curve is shown in Figure 2. In the course of the work, experiments were made with resins of lower cross linkage to check the possibility of faster separations. In general, under the conditions of our experiments, the results were unsatisfactory. Figure 3 shows a comparison between experiments made with Dowex 50W X12 and
Dowex 50W X8, both 100- to 200-mesh, with pH 3.10 ammonium lactate. Interference of any diverse ions, except phosphate, was not checked because the prior extraction of the cerium into diethylhexyl phosphoric acid had eliminated them all. Phosphate does not interfere. ACKNOWLEDGMENT
LITERATURE CITED
(l).Campbell, M. H., ANAL.CHEM.36, 2065 (1964).
(2bi"(i$;,w.
E.,
J.
Phys.
59*
(3) peppard, D. F., hfason, G , w,, Moline, S. W., J . Inorg. Nucl. Chem. 59 141 (1957). (4) Stevenson, P. C., Nervik, W. E., Nut. Acad. Sci.-Nat. Res. Council, Nucl. Sci. Ser. NAS-NS-3020, 1961.
for review February 19, 1965. The thank p, C, stevenson RECEIVED Accepted June 9, 1965. This work was and W. E. Nervik for their continued performed under the auspices of the interest and advice. U. S. Atomic Energy Commission.
Determination of Strontium in Environmental Media Using Neutron Activation PAUL J. MAGNO and FORREST E. KNOWLES, JR. U. S. Department of Health, Education, and Welfare, Northeastern Radiological Health laboratory, Winchester, Mass.
b A neutron activation procedure for the determination of strontium in environmental media is described. The method presented simplifies the handling and flux monitoring problems associated with activation analyses. Prior to irradiation, the strontium is separated from the sample by oxalate and nitrate precipitations using the calcium present in the sample as a carrier. Copper is then added to the purified strontium as in internal monitor and the sample is irradiated in a thermal neutron flux of 1012neutrons per square centimeter per second. After irradiation, strontium carrier is added and the strontium further purified by nitrate and chromate precipitations. Copper is separated by dithizone extraction and the strontium is then calculated from the induced activities of strontium-87m and copper-64. Strontium-85 is used to measure the strontium recovery. This method has been applied to the determination of strontium in food, milk, bone, hair, and blood.
S
occurs in low concentrations in foods and in the human body. Considerable interest has been shown in the concentrations of this element in these media because of the presence of its radioisotopes in the environment due to nuclear weapons testing and development of atomic energy programs. Several studies are being carried on a t this laboratory to develop a better understanding of the behavior of strontium in man. Associated with these programs was a need for a method of analysis of trace TRONTIUM
1 1 12
ANALYTICAL CHEMISTRY
quantities of stable strontium in environmental and biological media. Trace quantities of stable strontium in environmental media have been measured by emission spectrometry ( I , I 2 ) , x-ray spectrometry (3, 6, 8 ) , flame photometry (4, 7, f S), absorption spectrometry (IO), and by neutron activation (2, 5 , 9, f I ) . Although neutron activation is a reliable and extremely sensitive method for the analysis of strontium, it has not been routinely applied to the analysis of environmental or biological samples. This has probably been due to the lack of availability of a source of neutrons; but also contributing have been problems associated with handling the large amounts of induced activities produced in these samples and the care required to assure proper flux monitoring. With neutron generators now commercially available and nuclear reactors more readily accessible, neutron activation for the determination of strontium should find wider application. A method is presented which simplifies the handling procedures and flux monitoring problems associated with this technique and allows it to be applied on a routine basis. In previous applications of neutron activation for the determination of strontium in environmental media, direct irradiation of the sample was made so that large quantities of induced activities were produced. Because of the resulting high dose rates, the handling of these samples required considerable care. To avoid this problem, an extension of Harrison's (6) technique of concentrating the strontium in blood and urine prior to irradiation was used. The strontium
was separated by oxalate and nitrate precipitations using the calcium naturally present in the sample as a carrier. Strontium-85 tracer, added to the original sample and measured simultaneously with the induced activity of strontium-87m, was used to measure strontium recoveries during these separations. This pretreatment reduces the induced activity of the irradiated sample such that the radiation level is
