Pittsburgh, Pennsylvania 15219 I A radiochemical separation experiment

Most courses in radiochemistry contain several experiments illustrating some of the techniques employed in the separation of radioactive substances. Those experiments usually include precipitation and coprecipitation, distillation, solvent extraction, ion exchange, electrodeposition, and various chromato- graphic procedures. The latter are particularly suit- able for radiochemical separations (1-4), and have been recommended when it is desirable to obtain the element free from other radioactive elements in order to study its nuclear properties.

Some of the most interesting radiochemical sepa- ration experiments involve radioactive equilibrium mixtures. Radium DEF (210Pb, %l0Bi, and 210Po) is probably one of the most frequently used substances for various experiments in a radiochemistry course. The components of this equilibrium mixture can be separated by ascending solvent partition chroma- tography on paper hut the development of the chro- matogram takes several hours (6).

We were interested in developing a procedure for the separation of 2'oPb and 21°Bi which could be easily carried out within a single laboratory period by means of readily available apparatus. If possible, we wished this procedure to be suitable for a lecture demonstra- tion: i.e., requiring less than 45-50 min. Preliminary literature search indicated that Ra DEF mixture was separated in 1 hr by high voltage electrophoresis and in 45 min by paper electrophoresis. However, the latter method was accompanied by considerable "tailing." In order to reduce this undesirable side effect and further decrease electrophoresis time, we decided to use cellulose polyacetate as the supporting medium.

Experimental

Cellulose polyacetate strips (e.g., Gelman Sepraphore 111, 1 X 6 in.) were soaked in cold 2% citric acid solution until thoroughly wet (approximately 5-7 min), and then blotted be-

tween two sheets of absorbent paper. Five or 10 pl of Ra DEF solution (specific activity 2 mCi/ml) was applied to the center of one strip by means of a micropipet. Similarly 5-10 pl samples of 0.1 M Pb(NOl)n and 0.1 M B ~ Z ( N O ~ ) ~ were applied to two separate cellulose polyacetste strips. The samples were dried a t room temperature for 3 4 min, then placed in an electrophoresis chamber (e.g., Gelman No. 51101) and subjected to a potential of 350 V (approximately 1.5 mA per strip) from a regulated power supply (e.g., Heathkit IP-17) for 10 min. Then the strips were removed from the electrophoresis chamber and dried between two sheets of absorbent paper. The strip containing the Ra DEF sample was scanned with an end-window G-M detector (window thickness 1.4r1.9 mg/em2) connected to a ratemeter, and the areas of radioactivity marked off. S u b sequently, all three strips were subjected to ammonia fumes and then dipped into the spot locating reagent prepared by saturating water with Hi3 and adjusting the pH to 8 with a few drops of dilute NH,OH. The positions of lloPb and ELDBi on the strip were verified by comparing their locations with those of the spots obtained by electrophoresis of individual samples of 0.1 M pb(N0,)~ and 0.1 M BL(NOJ)~.

Results a n d Discussion

Under the described experimental conditions 210Pb migrates approximately 4 cm towards the anode from the point of sample application while 210Bi remains a t the point' of application. When electrophoresis time is extended to 1 hr, 21OBi moves towards the anode. "Tailing" of separated spots occurs when sample size is increased above 10 pl or when electrophoresis time is extended beyond 1 hr. We found that the use of cellulose polyacetate strips as the supporting medium in the electrophoresis of Ra DEF provided the desired separation of 2'OPb and Z'OBi within reasonable time and without "tailing."

Literature Cited

(1) Fn~nnsos, W. J., AND Joms, I. W., Anal. Chsm., 23, 1447 (1951) (2) D~cxer, E. E., J. C m r . Enuo.. 30, 525 (1953). (3) LIMA. F. W.. J. CREM. EDUC.. 31. 153 (1954). i4 j COX&, w. E:. A ~ . z . them.. 26,498 (1948). (5) c ~ ~ e e . G. D. AND R ~ n m o w l ~ z , J . L.. "Principles of Radioisotope

Methodology" (3rd. ed.). Burgeaa Publishing Co.. Minneapolis. 1967, p. 346.

Volume 48, Number 10, October 1971 / 699