DIRECT ON-COLUMN DERIVATIZATION IN GAS-CHROMATOGRAPHY .2. COMPARISON OF VARIOUS ON-COLUMN METHYLATION REAGENTS AND THE DEVELOPMENT OF A NEWSELECTIVE METHYLATION REAGENT

It has been demonstrated that judicious choice of the derivatisation r eagent used for direct on-column methylations can have a profound effe ct of the products produced, often with little effect on the overall m ethylation efficiency of the process. Trimethylsulfonium acetate, trim ethylsulfonium cyanide and phenyltrimethylammonium acetate are three n ew selective methylation reagents for direct on-column derivatisation in gas chromatography. Phenyltrimethylammonium acetate is a particular ly stable, selective and efficient new direct on-column methylation re agent. This work demonstrates that, for routine on-column methylation where no selectivity is required, phenyltrimethylammonium fluoride (PT MA-F) is as efficient as phenyltrimethylammonium hydroxide. PTMA-F is the preferred reagent because it is neutral and produces less column d eterioration than the hydroxide. Where methylation selectivity is requ ired, both phenyltrimethylammonium acetate has very similar efficiency and selectivity as the previously reported cyanide salt. However, the acetate is the more stable and readily utilised than the cyanide and is the best of a number of selective on-column methylation reagents su rveyed in this work.