REPORT FOR ANALYTICAL CHEMISTS Additional Correlations Table I Some Variables Affecting Gas Chromatographic Results Particle size Particle size distribution Packing Coating variations Surface contamination Surface area Physical availability of surface area Pore size and distribution
vitreosil
PURE FUSED QUARTZ LABORATORY WARE OF HIGHEST PURITY
• For excellent thermal shock resistance, and Inertness • For guarding the real purity of your compounds in crucibles, retorts, muffles, dishes, tanks, pots, trays • For outstanding electrical properties, strength, impermeability in ball & socket joints, standard taper joints, graded seals • Quartz to metal seals A wide variety of laboratory ware is available in ail types and sizes. Also, we fabricate to your specifications. See our ad in Chemical Engineering, Electronic Engineers Master and Electronic Designers' Catalogues. Write for complete, illuttrated
catalog.
THERMAL AMERICAN FUSED Q U A R T Z CO.
INC.
krkkfvvlvlfvlfljlfclvcmbvklfblkklfmbklfmbk
Circle No.93onReaders'Service Card 28 A
•
ANALYTICAL CHEMISTRY
Carrier gas flow Pressure drop Temperature Temperature gradients Partition isotherms Sample introduction Adsorption effects on flow Dead space
hanced appreciation of the effects of operational parameters. Despite its simplicity, gas chromatography is beset with a tremendous number of variables. A partial list is included in Table I. There are undoubtedly a good many more. The failure to realize what these variables are and what effect they will have continues to impede progress on the theory due to the lack of definitive experimentation. Fortunately the major items seem to be in hand, but the minor ones still become very significant in many specialized situations. The other problems raised by Golay's discovery of the advantage of tubular columns are not appropriate to this discussion. We all recognize that the need for high sensitivity detectors created by the use of Golay's columns brought about some fascinating situations. Everyone wanted equipment all at once. The instrument people were hard pressed. There was no time to go into the laboratory and study the situation and get the necessary know-how. The demand was fierce. Sample introduction and splitting problems contributed generously to the misunderstanding of both column and detector behavior. Detector inadequacies gave the columns a bad name. Claims and counter claims sometimes almost got out of band. Fortunately this era has passed. I t is now possible to get reliable data on highly satisfactory splitters, columns, and detectors.
There has also been progress in other areas of gas chromatography, such as speed of separations. Chromatograms can be run in minutes instead of hours. R. J. Loyd, B. O. Ayers, and F. W. Karasek at Phillips and J. H. Purncll at Cambridge have been busy optimizing gas chromatography for minimum time rather than minimum H.E.T.P. One of the most striking developments provided an excellent verification of Golay's theory about the gaseous diffusion. They found that at high flow rates the light gases give a better performance than the heavy ones. This seemed to contradict the evidence supporting the van Deemter equation previously cited. However, earlier studies had stopped a t too low flow rates. There is a crossover and hydrogen is much better than nitrogen at higher flow rates. In simple terms it says t h a t equal or better efficiency is possible in hydrogen at much higher flow rates. By combining this big advantage with the reduced retention of thinner liquid layers, a factor of ten in speed is achieved easily. Preparative scale chromatography is just beginning a big surge. Much is yet to come. However, Golay has already benefitted this area with a prediction. At a recent meeting he suggested that restrictions placed along a column to provide remixing would improve the velocity profile situation. Work by Huyten has shown t h a t the flow down the outside of the column is much higher than down the center. The wider the column, the greater the discrepancy. Again, gaseous diffusion perpendicular to flow is important. At Pittsburgh this year J. W. Amy, L. Brand, and W. Baitinger showed that the insertion of Teflon rings l 1 /* inches apart along a 1-inch column permitted the use of three to four times larger samples with the same resolution. Evaluation
Any evaluation of the various types of columns is bound to be influenced by personal prejudices. I will try to keep them to a minimum while assessing where we seem
