’Ol
D I S T A N C E (cm)
DISTANCE (cm)
140
LO
S.f.
DISTANCE (cm)
DISTANCE (cm)
Figute 1. Effect of developing agent on the chromatographic behavior of 140Ba and 140La
Figure 2. Effect of sample spot drying time on the chromatographic behavior of 140Ba and lroLa.
0.1N H2S04. (b) 9 parts 0.1N %SO4 s.f. = solventfront (a)
+ 1 part 1,Cdioxane.
The dried filter paper strips were sprayed with 0.1N sulfuric acid solution using an aerosol spray kit, and again dried in air. A 5-pl sample of approximately 1 M HC1 containing the 140Ba and 40La radioactive equilibrium mixture (C.F.) was applied an inch from one end of the paper strip, and a line was drawn with a pencil at a distance of 25 cm from the point of sample application. The spot was dried in air for 1 hour and then developed by the ascending technique with a solvent system consisting of 9 parts of 0.1N sulfuric acid and 1 part of 1,4-dioxane. When the solvent reached the pencil line, the paper was removed from the chamber and allowed to dry in air. I40Ba and 140La were detected by scanning of the chromatogram and detecting the corresponding radioactivity. The radiochromatogram scanner was equipped with a windowless Geiger-Muller detector with an adjustable slit set of 0.5 mm. Location of the 1 4 0 L a spot was confirmed by exposing the dried strips to ammonia fumes, then spraying with a 0.5x alizarin in ethanol and finally with 5x acetic acid solution. The sprayed chromatogram showed a purple spot (due to Laa+) near the solvent front on a yellow background (due to Ba2+).
(a) 30 minutes.
(b)1 hour. s.f. = solvent front
bility with 0.1 N H&04. By using a solvent system consisting of 9 parts 0.1NH2S04and 1 part 1,4-dioxane, both “leading” and “tailing” were significantly decreased (Figure 1). The drying time of the applied sample affected the extent of isotopic exchange and, consequently, the quality of separation improved and the ‘‘leading’’ effect of the barium spot decreased with the increase in the sample spot drying time (Figure 2). There was no significant improvement in these phenomena when the drying time was extended beyond 1 hour. Undoubtedly, isotopic exchange between the stable and radioactive barium ions in the solid phase reached equilibrium by 1 hour. In spite of the solubility of BaS04 in H N 0 3 and in HC1, either acid (0.1N)could be satisfactorily substituted for €&SO4 in the developing system, yielding R, values of 0.84-0.89 for lanthanum. RECEIVED for rekiew March 24, 1972. Accepted May 25, 1972.
RESULTS AND DISCUSSION
Under the described experimental conditions, 40Ba was retained by isotopic exchange at the point of sample application, while 140Lamoved upward with the solvent front, showing an R, value of approximately 0.86. Preliminary experiments indicated that 0.1NH & 0 4 was more satisfactory as the developer than either 0.01N or 1 N H2S04. Since the chromatogram showed some “leading” of the barium spot and “tailing” of the lanthanum, it was decided to incorporate a small amount of a nonpolar liquid in order to decrease both these effects. 1,4-Dioxane was chosen because of its misci-
COR RECTlON Improved Tissue Solubilization for Atomic Absorption In this paper by Andre J. Jackson, Leslie W. Michael, 44, 1064 (197211, and Herbert J. Schumacher [ANAL.CHEM., the middle initial of the second author appeared incorrectly as M .
ANALYTICAL CHEMISTRY, VOL. 44, NO. 12, OCTOBER 1972
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