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arises from the tailing that again results from the formation of a non-linear adsorption isotherm. In samples where the two components are present in the mixture at similar levels and are less well resolved, as in the separation of a pair of enantiomers, this compromise must be taken with caution. As both peaks will be overloaded, and asymmetrical, the tail of one peak will merge with a high concentration at the sharp front of the following peak, and thus significant contamination of the second peak will occur. The results of the overload experiment are better examined quantitatively. Curves relating the retention distance of the front and back of each peak to the sample load are shown in figure 8.The retention distances of the front and back of each peak (measured at the points of injection, 0.6065 x peak height) are shown plotted against sample mass. The change in retention with mass of benzene injected is clearly demonstrated, the maximum effect being for the solute anthracene (the

later, the separation shown in figure 2 is still probably the fastest separation of this particular mixture that has so far been obtained .   Despite the apparent practical success of the soft glass capillary it still had certain disadvantages. The tube was rigid and. thus, difficult to fit to the chromatographic system (e.g., the sample injector and the detector) and it also possessed significant surface activity that caused solute oxidation, molecular rearrangement together with peak tailing. The rigidity of the column evoked the use of a rather clumsy procedure fro straightening the ends of the column. In addition, glass column were still difficult to coat with and even film of stationary phase. There followed the development of a series of different methods for coating glass capillaries which extended over nearly 20 years. A number of those introduces were quite effective (including etching the surface with acid) but some, to say the least, were exotic and appeared to need

TBDMS. The mixture is then heated to 60˚C for about 15 minutes, an equal volume of 5% NaCl is added and the esters extracted with 1 ml of ether.   Acylation Reactions Acylation is also a popular reaction for the production of volatile derivatives of highly polar and involatile organic materials. The technique, however, has a number of other advantages. In addition to improving volatility, acylation reduces the polarity of the substance and thus can improve the peak shape and, reduce peak tailing. As a consequence amide esters are usually well separated with symmetrical peaks. By inserting protecting groups into the molecule, acylation also improves the stability of those compounds that are thermally labile. Acylation can render extremely polar materials such as sugars amenable to separation by GC and, consequently, are a useful alternative to the silyl reagents. Acylation is frequently used to derivatize amines, amides, alcohols, thiols,

nbsp; .   In this way the strongly polar silanol groups are methylated and assume dispersive characteristics that do not produce peak tailing. Although the major contributors to adsorption by the support are the silanol groups, a residual adsorption results from the presence of trace quantities of heavy metals such as iron. which can be largely removed by acid washing prior to silanization. All three types of support are commercially available. None of these supports, however, are completely devoid of adsorptive properties and in may cases the effect of the residual adsorption must be further reduced by suitable