Table I. Specific Retention Volume for nButane as a Function of Carrier Gas at 100’ C Po, 740 torr; T,, 22.5”C; weight of F-1 alumina, 16.4 grams; flow rate, 65.0 ml/min Carrier gas Hydrogen Nitrogen Helium Argon
t’R,
min
4.29 4.96 5.14 5.24
Pi,torr
f
1025 1290 1320 1420
0.830
d/gm 16.8 f 0.1 16.6 f 0.1 16.9 f 0 . 1 16.3 i.0 . 1
V,T,
0.710 0.695 0.660
where Pi and Po are the column inlet and outlet pressures, respectively. The total system dead volume, V d , was determined to be 15.5 + 0.4 ml by methane injection upon an initial methane base line to eliminate possible adsorptive contributions. RESULTS AND CONCLUSIONS
Table I lists the specific retention volumes for n-butane in four different carrier gases as calculated by Equation 1. As was observed in the work of Hoffmann and Evans ( I ) , the retention time of n-butane varies considerably with carrier gas. However, the inlet pressure, Pi, for a given outlet flow also varies greatly from gas to gas and, because the pressure averaged flow rate is the important quantity,
the change in ffrom gas to gas must be considered as well. This correction is included in V,* as calculated using Equation l . For gas-solid chromatography
VgT= KAs where K is the distribution constant, and A , is the specific surface area of the adsorbent. Thus, the results shown in Table I indicate that K remains the same from gas to gas to within 1-3 %. This establishes that, for the series studied, the nature of the carrier gas has little or no influence on the partition process. The changes in Piand flisted in Table I result from the different carrier gas viscosities and bring about the variation in the values of f ’ R . Thus, the values of the f f R follow the order of the viscosities for the carrier gases; Ar > He > N2 > H2
(10 DAVIDJ. BROOKMAN GARRARD L. HARGROVE DONALD T. SAWYER Department of Chemistry University of California Riverside, Calif. 92502 RECEIVED for review May 8, 1967. Accepted May 29, 1967. Work supported by the U. S. Atomic Energy Commission under Contract No. AT(11-1)-34, Project No. 45. (1 1) E. A. Moelwyn-Hughes, “Physical Chemistry,” 2nd ed., Pergamon Press, New York, 1961, p. 610.
Simple Method for Preparation of Both Calcium- and Carbonate-Free Sodiurn Hydroxide SIR: Dr. Harvey Diehl’s interesting paper on the “Development of Metallochromatic Indicators” ( I ) emphasized the need for a method for preparing calcium-free sodium hydroxide. It may be of interest to chemists that for a number of years I have been successfully using the following method to prepare both calcium- and carbonate-free sodium hydroxide for use in my (unpublished) modification of the Glyoxal bis (2-hydroxyanil) method for the determination of calcium of Williams and Wilson (2). Approximately 100 grams of NaOH pellets are dissolved in 500 ml of 95 ethanol and allowed to settle at 5 ’C overnight. The supernatant is then poured off, centrifuged, and subjected to flash evaporation at 37’ C using ice water to cool the condenser. The NaOH is then quickly dissolved to the (1) Harvey Diehl, ANAL. CHEM.,39, (3) 30A (1967). (2) Kenneth T. Williams and John R. Wilson, Ibid., 33, 244-5 (1961).
approximate strength required, standardized, and stored in very tightly sealed thick walled polyethylene bottles. When this modification of the calcium method is used, as little as 0.005 pg of calcium can be detected. Color development is achieved by the addition of 0.25 pmole of NaOH. Carbonate-free sodium hydroxide prepared from a saturated aqueous solution contains in the order of 0.25 pg of calcium per 100 pmoles. Even when 100 pmoles of NaOH, prepared in this way, is added to the blanks, they do not read above that of chloroform alone. ANNV. KUCZERPA Department of Physiology University of British Columbia Vancouver 8, B. C., Canada
RECEIVED for review May 22, 1967. Accepted June 5 , 1967.
VOL. 39, NO. 10, AUGUST 1967
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