is . nhhined. chromatoeranhic _ . . . - ~ The ~ ~ ~
~~
tube is approximately 2.5 X ~ ~ O ' c m . equipped at the bottom with a coarse, fritted disk and ending in a stopcock (preferably Teflon) to control flow rate, and a t the top with a female 24/40 T joint toreceiviasolv ent reservoir. Some of the solvent to be p urifiedis poured into the column. Anhydrous eranular sodium sulfate, reagent gra& is added to a depth of app roximately 10 em., and then 160 grarns of the sulfuric acid-Celite adsorberit is added in portiqns, tp.mpi?g .ea(:h portion tightly before the auaition of the next. This section of the column is approximately 30 em. long. The column is topped off with 7 to S cm. of crystalline sodium sulfate. Flow rates of 3 to 5 ml. per minute nre satisfactory. Carbonyl compounds present in a 50ml. aliquot of solvent both before and after purification were converted to their DNPH's. The monocarhonyl DPNH's were isolated according t o the method of Schwartz and Parks (93,then dissolved in chloroform and diluted to the necessary volume for reading in the spectrophotometer. Absorbance was measured 362 mp and corrected for ,.,.. t, oatcorrespona aimaon ' t' o the carbonyl DNPH absorbance attribi itable t o the carbonyl concentration in the original solvent sample. RESULTS AND DISCUSSION
Three hydrocarbon and three chlorinated hydrocarbon solvents were analvi~rlfnr their rnrhnnvl m n t m t hofnro
Table I. Absorbance Corrected for Blank Attributable to Aliphatic Monocarbonyl Content of Several Nonoxvaenated. Water Immiscible ts
in chloroform at
At
I".
Solvent CEaCI, CHC1,
cc4
Hexane Skelly F Benzene
Absorbance Before After cleanup cleanup 0.06 1.69 1.06 1.92 5.64 0.00
0.002 0.004 0,009
0.009 0.000
n.unn
and after cleanup. The monocarbonyl DNPH absorbance corrected for blanks is given in Table I. The blanks are attributed to impurities present in D N P H (3). Blanks have been minimized by recrystallization and by washing the DNPH crystals with the solvent under study prior t o use; nevertheless, blanks ranged in value from 0.007 absorbance unit for hexane to 0.090 absorbance unit for methylene chloride. Absorbance values of 0.02 roughly correspond, in terms of n-alkanals, to 1 micromole of carbonyl per liter of solvent. All solvents were essentially carbonyl-free after one pass through the column. Methylene chloride and ben-
Bene contained very little carbonyl impurity prior t o purification. The carbonyl impurities for the other solvents ranged from approximately 50 micromoles per liter for carbon tetrachloride t o 280 micromoles per liter for Skelly F. Hexane was analyzed at frequent intervals during a 2-week period in which the purification column was in constant use and was carbonyl-free at all times. The hexane was ready for use without further treatment after passing throngh the column. Chloroform prior to cleanup required a preliminary water wash, followed by drying over anhydrous sodium sulfate to remove alcohol. Methylene cliloride emerged from the column with a slight pink tinge. This was readily removed by shaking with a small amount of activated alumina. The column itself darkened with continued use, but the efficiency was apparently unimpaired. We have also used columns with only 50 grams of the sulfuric acid-Celite adsorbent and have obtained just as efficient results. No effort was made, hoaever, to evaluate their period of usefulness
.-
,.
LITERATURE CITED
.
. - - .
--
( 1 1 uaviaow, B., J . ASSOC. wfic a g r . Chemzsts 33,130 (1956). (2). Schwarts, D. P., Parks, 0. W., ANAL.
CHEM.33,1396(1961).
Trade names are mentioned for identification, implying no endorsement.
l o w Temperature Infrared Gas Cell of Simple Construction Hulon W. Myers and William W. Martin, Stauffer-Aerojet Chemical Co., Richmond, Calif.
HE THERMAL instability of
the chloro-
Tboranes under study in this lahora-
tory has dictated the use of low temperature techniques in all analytical procedures. One of the important tools developed for infrared absorption measurements of these compounds has been a gas cell capable of operation at -60" C. Other than custom built models, no infrared gas cells for low temperature use are available commercially. Those discussed in the scientific literature not only require elaborate and costly construction but often cannot be used with standard lahoratory spectrophotometers. The gas cell described here consists of relatively inexpensive materials and can be designed for use with any laboratory analyzer. One entire assembly, shown in Figure 1, was constructed to fit within a PerkinElmer 10-em. cellholder. The glass cell consists of a jacketed sample cham1038
ANALYTICAL CHEMISTRY
Ser
ber with two sodium chloride windows at each end forming evacuated compartments, which are kept a t
