Free Books and Brochures

Courtesy of Mr. Andrew Lynn of the Dexsil Corporation Figure 36 The Separation of a High Molecular Weight Hydrocarbon Wax on a High Temperature Stationary Phase As would be expected the more polar the stationary phase the lower the temperature stability. An example of the use of Dexsil 400 to separate some very high boiling waxes is shown in figure 36. The column was programmed from 50˚C to 380˚C at 4˚C /min. and held at 380˚C for 6.5 min. The carrier gas flow rate was 30 ml/min. The wax components are well resolved and the baseline appears very stable even a 380˚C. The stable base line, with no drift, indicates there is little or no decomposition of the solutes or the stationary phase, even at 380˚C. Stationary phases based on the carborane structure, can extend the

Electrode Construction The choice of electrode construction material is restricted due to the need for mechanically ruggeness and long term stability. The most common material is carbon paste made from a mixture of graphite and some suitable dielectric substance. This material has the disadvantage that it is soluble in some solvents, although, using special waxes or polymers as dielectric binders to contain the graphite, helps reduce the solubility problem. Vitreous or 'glassy' carbon is an excellent electrode material particularly if organic solvents are to be used and is probably the most popular contemporary electrode material. Glassy carbon is produced by slowly baking a suitable resin at elevated temperatures until it is carbonized and then heating it to a very high temperature to cause vitriation. Vitreous carbon is relatively pure,

nbsp; It is clear, that the peaks depicted on the single ion monitoring chromatograms represent metabolites in which the D-ring has been preserved. This example illustrates how the GC/MS technique can be a valuable tool for following the metabolic processes associated with the 17a-alkyl anabolic steroids.   Analysis of Waxes and Lipid Type Materials   The metabolism of fatty acids in cell cultures can be very important, particularly with regard to cancer cells. The possible conversion of the fatty acids to peroxides and the role of these compounds in carcinogenesis is still not completely understood. To aid in this type of work Wallace and Coleman (20) developed a procedure for the fatty acid assay of cell tissue employing a GC/MS instrument. According to their publication, they studied two human colon