METHYLATION REAGENTS FOR THE DIRECT ON-COLUMN DERIVATIZATION OF VETERINARY RESIDUES

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. MethElute (PTMA-OH) and MethPrep (TTMA-OH) are perfectly satisfactory in the derivatisation of mono-fu nctional compounds but produce mixtures, often very complex, when used for methylation of multi-functional substances. Phenyltrimethylammoni um cyanide (PTMA-CN) is readily prepared and is a far more selective a lternative to MethElute for direct on-column methylation whilst still providing good yields of methylation products. Overall methylation eff iciency is also dependent on the GC injector temperature whilst the co ndition of the injection liner can exert a significant effect on both methylation efficiency and selectivity.