It appears, therefore, that the oxidized products adhere to the coal surface during ozonolysis a n d are removed only by Hg02. I t has also been shown that a t any stage of the oxidative degradation, the residual coal retained virtually the same properties as the original coal prior to oxidation. A 6.6-g sample of coal was ozonized for 5 hours, and 407 mg of acidic products was isolated. The unreacted coal was thoroughly dried and subsequently subjected to a second ozonization producing 480 mg of acids. The procedure was repeated a third time with similar results. Again, comparison of gas chromatograms, infrared, and ultraviolet spectra revealed products of essentially the same nature. The oxidation could perhaps be visualized as a “peeling” process whereby the “polymer-like” material is removed layer by layer. This same phenomenon was noted by Mazumdar and Lahiri (19) with permanganate oxidation of coal.
ACKNOWLEDGMENT
The authors thank Harold C. Urey for his interest and support of the project as well as Ernil J. Moriconi and Richard Franck of Fordham University for their helpful suggestions. They are indebted to Fred W. McLafferty and Maurice M. Bursey of Purdue University for recording the mass spectra in their laboratory and to William D. MacLeod for his critical reading of the manuscript.
RECEIVED for review May 5, 1967. Accepted June 23, 1967. Research supported by the National Aeronautics and Space Administration under Grants NsG-341 and NsG-541. (19) B. K. Mazumdar and A. Lahiri, American Chemical Society,
Division of Fuel Chemistry, Preprints, 1962.
Simple Approximation for Pressure Correction Factor in Gas Chromatography Istvan Halasz and Erwin Heine Institut f iir Ph),sikalische Chemie der Unifiersitat, Frankfurt am Main, Germany
JAMESAND MARTIN( I ) have shown that the use of the factor j allows for the fact that in gas chromatography the mobile
phase is compressible. The pressure gradient correcting factor is defined as:
-
,j =
3 P___ ’-1 - U - F - 2 P3 - 1 u, F,
._
e!
j/j* lan\--.
-.-m
(1)
i?
Tabulated j values such as, for example, those given by Purnell ( 2 ) , are often wanted in gas chromatography calculations. From Equation 1 :
1
+ 23 (P - 1) - -31 + 23- P 1f l -
~
(2)
Neglecting the last two terms on the right side of Equation 2: 3
,j* = -
2P
4- I
(3)
As is seen j * is a simple calculable approximation for j . The comparison of Equations 2 and 3 shows, that j = j*, if P = 1 or P a . In all other cases: j * < j . The fraction j / j * as a function of P is shown in Figure 1 . The maximum deviation equals 7.74% a t P = 2.74 (where 2.74 = 1 In practical gas chromatography relative pressure P between 1.6 and 6.5 is the most important. An even better approximation for this region is: --f
+ d3>.
j+ =
3.2 -
2P
+1
(4)
Using j + in the pressure-region, P = 1.6-6.5, the deviation of the correct value j from the approximation j + shall be smaller than i 1.1 %. ( I ) A. T. James and A . J . P. Martin, Bioclleni. J . , 50, 679 (1952). ( 2 ) Howard Purnell, “Gas Chromatography,’’ Wiley, New York, 1962, p. 69. i
-
P = Pi/%
Figure 1. Fraction of j / j * as a function of relative pressure P = PtJPo The approximations given in Equations 3 and 4 are good enough for routine work in gas chromatography. I n theoretical calculations, it may be of some importance to introduce the simple Equation 3 instead of Equation 1 , LIST OF SYMBOLS
F, = volumetric flow rate of carrier gas at outlet pressure F = time average of volumetric flow rate p o = outlet pressure pi = inlet pressure p = length average of pressure P = p i / p o = relative pressure uo = carrier gas velocity a t outlet pressure = time average of carrier gas velocity RECEIVED for review June 5, 1967. Accepted June 14, 1967. VOL. 39, NO. 11, SEPTEMBER 1967
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