Dissolution of Elementa I Boron SIR: Eberle, Pinto, and Lerner ( I ) , recommend the use of large quantities of potassium persulfate for the dissolution by fusion of boron samples. It may be of interest to quote the experience a t the -4tomic Weapons Research Establishment in dealing with a variety of elemental boron samples, including amorphous powder, lightly sintered powder, fused lump and crystalline boron. One of the difficulties we experienced with fusion involving sodium carbonate, was the buffering effect of large amounts of dissolved salts, although this does not appear to apply to the persulfate fusion technique. We found that all types of elemental boron could be dissolved using the following technique. PROCEDURE
Accurately weigh 0.10-0.15 gram of the sample into a flat-bottomed glass capsule approximately 7 mm. in diameter X 1 cm. tall and drop the capsule and contents into a large Carius tube containing 4 ml. of concentrated nitric acid and 0.1 gram of potassium bromide. Allow any initial reaction to subside, cooling the bottom of the tube if necessary. When the initial reaction has ceased, seal off the Carius tube and heat for 2 to 3 hours in the Carius furnace, a t 250" C. Allow the furnace to cool and open the end of the tube, observing the usual precautions. Transfer the contents of the tube to a beaker.
rinsing the tube thoroughly and add the washings to the beaker. Remove any insoluble siliceous matter by filtering the solution into a 250-ml. volumetric flask and make the v o k m e up to the mark. Remove a 50-ml. aliquot for titration, add 0.5 gram of urea and heat on a water-bath for 5 minutes. Neutralize the solution by adding one or two pellets of sodium hydroxide and make just acid with dilute hydrochloric acid. Titrate by the mannitol procedure. RESULTS
Examples of the results are compared with those obtained by sodium carbonate fusion. Many elemental boron samples, particularly sintered, fused, and crystalline boron, do not dissolve completely on refluxing with nitric acid. The potassium bromide appears to speed up the dissolution of crybtalline boron, but it is not essential to add it. Both boron carbide and boron nitride dissolve using the Carius tube technique, and the method has been used by us for the analysis of a sample of boron nitride powder. Where the iron content of the sample is sufficiently high to cause serious errors, we have used a preliminary precipitation step in which excess barium carbonate was added prior to the filtration step. After acidifying. the solution was boiled to remove carbon dioxide.
Table I. comparison of Results Obtained by Carius Oxidation and Sodium Carbonate Fusion
Boron, qc Carius Sodium oxidation carbonate method fusion
-
Boron sample type and no. Amorphous A 87 7 B 87 1 C 88 0 Sintered A 89.0, 89.7 B 87.3,87.3 Crystalline A 68.5, 68.8 69.5
88 2 87.3 88 2
88.6, 90.0 86.5, 8 5 . 5 69.3, 6 9 . 5
LITERATURE CITED
(1) Eberle, A. R., Pinto, L. J., Lerner, M. W., ANAL.CHEM.36, 1282 (1964).
J. M. DOXALDSOX F. TROWELL Cnited Kingdom Atomic Energy -. huthority Atomic Weapons Research Establishment Aldermaston, Berkshire, England THEauthors thank the Director, Atomic Weapons Research Establishment, Aldermaston, Berkshire, England, for permission to publish this note.
Paper Partition Chromatographic Determination of Per Cent Solute Extracted into Organic Phase SIR: In the pharmaceutical industry it is often necessary to perform liquidliquid (aqueous-organic) extractions before the active compound in complex dosage form can be quantitatively determined. The optimization of the extraction conditions usually invoIx-es the determination of the pH profiles of the compound in several solvents. To do this by actual liquid-liquid extraction followed by quantitative chemical analysis of the two phases is not only tedious but requires large quantities of material, solvents, and glassware. There has been available in most laboratories for some time a technique well suited to this problem. I t is paper partition chromatography. The utility of the paper partition chromatographic method is based on the little appreciated fact ( 5 , 7 ) that the R/ value of a compound in paper partition chromatography is equal to 2202
ANALYTICAL CHEMISTRY
f , the fraction extracted into the mobile phase, or 100 X R, equals the per cent solute extracted into the organic phase, a term more familiar to analytical chemists doing liquid-liquid partition studies. Carless and Woodhead (3) introduced the concept of filter paper buffered a t different pH's in the development of chromatographs of alkaloids. Munier (8, 9) showed that paper partition chromatography carried out a t different pH levels produced marked changes in R, values of acidic and basic compounds. Goldbaum and Kazyak (6) reported a method for the identification of alkaloids and other basic drugs based on the pattern produced by the R, values a t four different pH's. Betina ( I , 2) used paper chromatography for the determination of suitable pH values for the extraction of acidic and basic antibiotics. Waksmundzki
and Soczewinski ( I 7-1 9) developed the formula describing the relationship between R, values of organic acids and bases and amphoteric compounds and their partition coefficients and ionization constants, the pH of the buffered paper, and the ratio of volumes of mobile and stationary phase. Debska (4) used llunier and Soczewinski's method to determine the dissociation constants of two alkaloids from R f measurements. Kaksmundzki (26, 19) and Soczeivinski (16, 16) used paper chromatography for the determination of suitable buffer systems for countercurrent distributions. Soczewinski (10-14) extended these studies to multicomponent t'wo-phase paper chromatographic syst'ems. The partition coefficient of the solute between the stationary (aqueous) and the mobile (organic) phase, CY, is related to f , the fraction of solute extracted
