Paul K. Glasoe Wittenberg University Springfield, Ohio 45501
I
A Simple Separation and ldentifica 01.- adium D, E, and F
A chromatographic method for separating the equilibrium mixture of Radium D, E, and F has been described previously in THIS JOURNAL.'.^ However, both of these procedures are too time-consuming for the usual general chemistry laboratory period. The following modification of the procedures described in these references makes possible the separation and identification by radiation counting in a 3-hr laboratory period. The apparatus consists of a 500-ml erlenmeyer flask fitted with a cork holding a wire hook on which a piece of Whatman No. 1chromatographic paper can be hung. The strip of paper is cut just wide enough to pass freely through the neck of the erlenmeyer flask and long enough to just clear the bottom of the flask when the stopper is inserted in the neck. The solvent is prepared by shaking up in a separatory funnel normal butyl alcohol and 1 M HC1 and saving the less dense organic layer. About 30 ml of solvent is required for each flask. The strip of paper is marked off in 1-cm sections, using a pencil, and each section is numbered sequentially. A solution of 210Pband 2'0Bi in Pb(N03)~containing 1 &i per ml is used as the ample.^ The sample is placed on a spot in the center of section number 1. The sample should be of such size as to give a count of 1000-3000 cpm after the spot has dried. This will be obtained with about 15 pl of the lead solution. The high-numbered end of the strip is fastened to the wire hook in the cork and the cork placed tightly in the flask. The strip should just touch the butyl alcohol solvent. After about an hour the solvent will have progressed about 2/5 of the length of the strip. The strip is removed and the position of the solvent front is marked with pencil. The strip is dried and then cut into the marked off sections. Each section is counted. The number of counts of each section will
depend somewhat on the time available. We have found that one two-minute count is adequate for these purposes. A background count is also made. We have made counts using a Nuclear Chicago Model 151A Counter and Scaler. A table of typical data is given. A plot of cpm versus the position on the strip can be made. The lead (Radium D) will be found principally in section 1 and bismuth (Radium E) in the region of sections 4-5. Since polonium (Radium F) is an alpha emitter, it is not indicated on this counter. If alpha counts can be made, the Po will be found a t the solvent front. The half life of Radium E and the reestablishment of the secular equilibrium with Radium D can be shown by re-counting the sections of paper at the next laboratory period. The half life of Radium D is about 5l/2 days so its count will be reduced by about '/2. The activity in the Radium D section will have increased markedly. If it is desired to show the presence of RaF in the strip although alpha counts cannot be made, a radiograph can be made on X-ray film. An exposure of 3-5 days will be necessary to get a good image. This experiment can serve the double purpose of introducing the student to paper chromatography and simple counting of radioactive samples. Counts on Chromatographed Mixture of Ra D and Ro E; Original Count of Mixture 1380 cpm
No. of section on paper strip 1
CPM on day of Separation RQ 8 mound
CPlM six days later RIR ... 160 Baekarol
' D I C K E Y ~ E DE.,J. ~ A R CHEM. , EDUC.,30,525 (1953). 2
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LIMA,FAUSWW., J. CHEM. EDUC.,31,153 (1954). Nuclear Chicago Company.
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Journal o f Chemicd Education
Tabulated counts corrected for background
