I AIDS FOR ANALYTICAL CHEMISTS Calculation of Equivalent Stationary Phase Loadings in Gas Chromatography D. E. Durbin Honeywell, Inc., 6625 McGrew, Houston, Texas 77017
When evaluating solid supports for columns in gas chromatography, it is often necessary to compare one or more supports at equivalent stationary phase loadings (ESPL). The calculations for determining ESPL, although straightforward, are tedious and time consuming. Consequently, it would be desirable to have a t hand a single equation from which ESPL could be calculated for any support at any phase loading. The weight of stationary phase per unit column volume (X)is given by:
X = pA
A = P/(100 - P)
(2)
where P i s the phase loading in weight per cent. Substituting Equation 2 in 1 and equating two supports for the same phase loading gives:
- P2 pz
= P1/100
Chromosorb P, W t %
Chromosorb W , wt %
Chromosorb G wt Yo
5.0 10.0 15.0 20.0 25.0 30.0
9.3 12.9 25.7 32.8 39.5 45.6
4.1 8.3 12.5 16.8 21.3 25.8
(1)
where p is the packed density of the support, and A is the mass ratio of the phase to the support. For a column of a given phase loading,
P2/100
Table I . Equivalent Stationary Phase Loadings for Three Solid Supports
- PI p1
(3)
Rearranging Equation 3 and solving for P2 gives:
P2
= 100PlP,/P2(100 - P1) + P l P l
(4)
Equation 4 was used to compile the following Table I of ESPL for three common GC supports, Chromsorbs P, W, and G. The packed densities were 0.47, 0.24, and 0.58 gram/cm3, respectively (1). Received for review October 18, 1972. Accepted December 20, 1972. ( I ) C. Horvath, "The Practice of Gas Chromatography,'! L. Ettre and A . Zlatkis, Ed., interscience, New York, N . Y . , p 189.
Improved Ferrule for Glass Gas Chromatographic Columns Sanford P. Markey,' and Sanford L. Simons2 University of Colorado Medical Center. Denver, Colo. 80220
In the design of an all-glass gas chromatograph-mass spectrometer system, a removable union between the GC column and other fixed glass lines is desirable. Previous experience with Teflon (Du Pont) ferrules or silicone rubber O-rings combined with metal ferrules showed that the lifetime of these polymers was severely limited by the temperature cycling ordinarily employed (ambient to 320 "C). Consequently, one piece polyimide ferrules (Vespel SP-1, E. I. du Pont Plastics Department, Wilmington, Del., 19898) were machined to fit standard %-in. Swage-
'
Departments of Pediatrics and Pharmacology *Division of Bioengineering
818
ANALYTICAL CHEMISTRY, VOL. 45, NO. 4, APRIL 1973
lok (Crawford Fitting Co., Solon, Ohio 44139) unions. These ferrules have been in continuous use for the past twelve months and have displayed remarkable stability. Because Vespel does not cold-flow, the ferrules maintain their original shape and can be re-used on other columns with other unions. With relatively low fastening torque polyimide ferrules have been found to form helium leak tight seals (as measured with a thermal conductivity typt leak detector) operating a t 50-70 psi head pressure anc 300 "C. Received for review November 22, 1972. Accepted Decem ber '21, 1972. The funds received under NIH HD-0487f have supported this work.
