AIDS F O R THE ANALYST Preparation of Pressed Sam Counthg Carbon-14-Labele
which had been platted directly after active samples and were used t o measure any contamination present in consecutive mounts. Similar information as to precision was obtained on four
.
. .... . . .
.
and alanine indicates the uniformity of samples prepared by this method. The procedure is furtherrecomlhended by its simplicity. Its use becomes practical and a whose activity is to be determined must, for other reasons, he dried &nd weighed Prior to counting. The procedure requires a fairly
of for the preparation of solid samples are in general use for determining piltration techniques (1,9,6), centrifugation (a),or the removal of a solvent or fluid (8) are often for plating a substance. but there are instances when it is advantageous to . mounts of infinite thickness from a dry solid. The authors have found it desirable to employ infinitely thick samples in in vivo experiments where respiratory carbon dioxide is traDped, precipitated as barium carbonate, collected, dried, weighkd, and counted. Such mounts have been prepared by manually packing the solid material in the planchet with the aid of a small spatula. The method is time-consuming and extremely difficult with most materials, and the problem oi obtaining a smooth flat surface with granular solids is also encountered.
A
. "
. .
NUMBER
. .
1
.
. . ...
.. . .
-
Table I. Radioactivity of.Barium Carbonate 'and Alanine
"..""" "~...~.....I.,I~ .-.... " ......~ 8 2 4
BaCOs BaCOsb liantne
80-130 4846
32-47
""..l".""".r
_"....".".1
It6
"0
253
5:B
422
0.8
804
8.8
LITERATURE CITED
(1) Armstrong, W. D., and Sohubei-t, J.. ANAL. C n ~ w . .20, 270 (1948). (2) Calvin. M., Heidelberger, C.. Reid. J. C., Tolbert. B. M.. and Yankwich. P. F.. "Tsotopio Carbon," PP. 121, 117, 122, Wiley. N P W York. 1949. (3) Henriques. F. C., Jr., Kistiakowsky, G. B., Mwgnetti, C , aniJ Sohneida', W. G.,IND. EN& C ~ E M .ANAL. , ED., 18, 34 Q
Figure 1. Press for preparing solid mounts
To avoid these difficulties, a small inexpensive press has been designed and built to prepare uniform solid mounts. This method has been tested for the uniformity of the sample prepared, contamination of successive samples, and adaptability to materials other than barium carbonate.
(1946).
.- ,.. ._~.
..^ ,.,..". .,^
(4) Reid, A. F., ana noooms, IYI., o c z m e , i n , 140 u u o z , . (5) Tamer. H., m d Schmidt. C. L. A,, J . Bid. Chern.. 130, 67 (1939).
METHODS AND MATERIALS
Rapid Preparation of Mineral Oil Mulls K. Presernell, The Andrew Jergenr Co, Cincinndi, Ohio
This press is shown in Figure 1, both disassembled and in its operating position.
A.
The base of the press measures 0.5 X Z 5 / 8 X 4 inches. The cvlinder has a height of 2 inches and the cvlinder bore has a
A oil mulls for infrared spectroscopy may easily be prepared.
SIMPLE apparatus
for rapid and efficient grinding of mineral
A pestle is formed from a borosilicate glass rod abont C!/L/CX inch in diameter aud 4 inches 7 long. One end of this is heated until a roughly spherical portion approximately ' h inch in diameter is formed on it. The enlarged portion should be accurately aligned with the rod. A mortar is made from a No. 27 standard-taper borosilicate glass stopper or some similar piece of glass. The stopper is strongly heated and a carbon rod is pressed into the flat end to form a depression about '/a inch deep, r o u g h l y fitting the pestle. The pestle is mounted in the chuck of 8. stirring motor and ground to give a spherical fit with the mortar, using No. 180 C a r h o r u n d u m a n d water.
&t& even manner in a 1-i'nch aluminum planchet and'&ced in the press, considerable p~essureis applied, and thd sample is
in plating are v+e$ from t&epacking piston between p;e:epmrations of successive samples. Mounts prepared in this manner display
windowless gas flow counter. A minimu% of 10,000 counts was made on each radioactive sample. When the gas flow counter was used, the mount8 were covered with aluminum foil in an attempt t o improve counting (4). The usual precautions must be observed for handling radioactive compounds. Periodically the press must be thoroughly cleaned.
a.
RESULTS
The radioactivity of samples of carbon-14-labelPd barium carbonate measured with both counters is shown in Table I. Two planchets contained samples of nonactive barium carbonate 571
