Comparison of methods for extraction, storage, and silylation of pentafluorobenzyl derivatives of carbonyl compounds and multi-functional carbonyl compounds

摘要

The employment of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatization along with bis(trimethylsilyl)trifluoroacetamide (BSTFA) or N,N-(tertbutyldimethylsilyl)trifluoroacetamide (MTBSTFA) derivatization is a popular method for measurement of oxygenated organics in environmental and biological samples. Most notably, the derivatization method enables the measurement of atmospheric photooxidation products not detected by using other methods. PFBHA derivatization is often conducted in an aqueous solution. Accordingly, experiments were performed to compare the efficiency of hexane, methyl-tert-butyl ether (MTBE), and dichloromethane (CH_2Cl_2) for extraction of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatives of carbonly compounds from water. Further, the stability of these compounds when stored at 4 ℃ in CH_2Cl_2 was determined, and commonly used methods for silylation of -OH and -COOH groups on the PFBHA derivatives were compared. Overall, CH_2Cl_2 was the most efficient solvent for extraction of PFBHA derivatives of hydroxycarbonyl compounds, dicarbonyl compunds, and keto-acids from water. Derivatives of carbonyl compounds that do not have secondary functional groups were extracted with approximately equal efficiency by each of the three solvents examined. The PFBHA derivatives of aromatic and saturated aliphatic carbonyl compounds and hydroxycarbonyl compounds were stable in CH_2Cl_2 at 4 ℃ for ≥66 days whereas the derivatives of keto-acids and unsaturated aliphatic aldehydes begin to degrade after approximately 38 days. Comparison of four procedures for bis-(trimethylsilyl)trifluoroacetamide (BSTFA) derivatization of -OH and -COOH groups on PFBHA derivatives revealed that primary -OH groups react efficiently in 20-100% BSTFA in CH_2Cl_2, and do not require a catalyst. Secondary -OH groups also react efficiently in 20-100% BSTFA, but the reaction yield improves slightly when trimethylchlorosilane (TMCS) is added as a catalyst. Reaction of tertiary -OH groups with BSTFA was very inefficient, but improved with addition of 10% TMCS to the BSTFA solution. Finally, -COOH groups seemed to react most efficiently and consistently in 100% BSTFA, without catalyst.