of an oligomeric phase, the presence of water may cause linear polymerization. Consequently, stringent precautions must be taken to eliminate all traces of water. A slight excess of the chlorosilane is then added to the silica dispersion together with 5 ml of pyridine. The pyridine acts as scavenger for the hydrochloric acid released during the reaction. The mixture is refluxed for about 5 hours and the product is then filtered on a sintered glass filter, washed sequentially with toluene, tetrahydrofuran (THF), methanol, methanol water (50:50 v/v) and finally with methanol and dried under suction. The bonded phase now needs end-capping; that is, any unreacted silanol groups are treated with a small molecular weight silanizing reagent to react with those hydroxyl groups that were stearically unavailable to the larger reagent due to exclusion. To end-cap the product, the bonded phase is refluxed for two hours in a mixture of 100 ml of toluene and 25 ml of hexamethyldisilazane. The

and, in particular render microbore columns virtually useless. Because of the nature of the experiments, the major source of dispersion can not be identified and the effect of Newtonian flow through the cell can not be differentiated from the dispersion due to sensor volume. The combined effect of the two types of dispersion are shown as elution curves in figure 17. The column used to produce the elution curves in the upper chromatogram was 24 cm long, 4.6 mm I.D. The mobile phase was tetrahydrofuran and the column was operated at a flow rate of 1 ml/min. The solute injected was benzene. The column used to produced the elution curves in the lower chromatogram was 1 m long, 1 mm I.D. and the same solvent was used at a flow rate of 40 ml/min Benzene was also used a the solute. It is seen that the reduction in cell volume has a dramatic effect on both peak width and peak shape. The large 25 ml cell causes significant peak asymmetry as well as excessive peak dispersion A result

wide (4.6 mm I.D.) columns but, the solvent consumption for such columns would be enormous. The retention volume of a solute eluted at a capacity ratio of 20  on a 10 m column 4.6 mm I.D. would be about 2.8 liters, an unacceptably large solvent consumption An equivalent column 1 mm I.D. would require only 132 ml to elute the same solute. Results from small bore columns up to 14 m in length have been reported.     J. Chromatogr.,169(1979)51 Column, length 14 m, I.D. 1 mm, mobile phase tetrahydrofuran, flow-rate 25ml/min, adsorbent Spherisorb 5. Solutes benzene, ethyl benzene, butyl benzene, hexyl benzene, Figure 33. Chromatogram of a Series of Alkyl Benzenes Separated on a Column having 650,000 Theoretical Plates

writing this book, still is. Originally the distribution coefficient of a solute, which has been shown to be directly proportional to its retention volume (see book 6), was thought to be an exponential function of the concentration of solvent in the mixed phase. The reason for this is uncertain, but appears to have arisen from the apparent approximate relationship between the logarithm of the retention volume and solvent composition for aqueous solvents such as methanol/water mixtures and tetrahydrofuran/water mixtures. There appears to be no rational physical chemical explanation given for this relationship but was assumed from the result of an arbitrary curve fitting procedure. This approximate fit appears, in retrospect, to be a fortuitous result of the strong association between the water and the solvent. The true interactive character of mixed phases was disclosed by the pioneering work of Purnell et al.(4-6), who carried out some very simple GC experiments to identify

accounts for the fact that proteins can tolerate a significant amount of methanol in the mobile phase without them becoming denatured. This surprising tolerance to methanol is because there is very little unassociated methanol present in the mixture to cause protein denaturation, since all the methanol is associated with water and, thus, in a deactivated state. Katz, Lochmüller and Scott (11) also showed that there was significant association between the water and acetonitrile and water and tetrahydrofuran, but not nearly to the same extent as methanol and water. At the point of maximum association in methanol-water mixtures, the solvent contained nearly 60% of the methanol/water associate. In contrast the maximum amount of THF associate that was formed was only 17%, and that for acetonitrile as little as 8%. It follows that acetonitrile/water mixtures would be expected to behave more nearly as binary mixtures than methanol/water or THF/water mixtures. The components of the mobile

The adsorbed acids can provide ionic interactions with a solute, in fact, the so-called ion pair reagents function largely as adsorbed ion exchangers. A typical ion pair reagent is tertiary butyl ammonium bromide whic is strongly adsorbed on a reversed phase as a result of the strong dispersive interacions with the butyl chains and acts as an adsorbed cation exchanger.. Bi-layer Adsorption The adsorption isotherms of the more polar solvents, ethyl acetate, isopropanol and  tetrahydrofuran from n-heptane solutions on silica gel were also determined experimentally by Scott and Kucera (12). They found that experimental results for the more polar solvents, did not fit the simple mono-layer adsorption equation. As a consequence, the possibility of bi-layer adsorption on the silica gel surface was examined. Bi-layer adsorption is not uncommon and the development of the bi-layer adsorption isotherm equation is a simple extension of the procedure used for the mono-layer