ANALYSIS OF ALDEHYDES AND KETONES FROM BEER AS O-(2,3,4,5,6-PENTAFLUOROBENZYL)HYDROXYLAMINE DERIVATIVES

O-(2,3,4,5,6-pentafluorobenzyl)Hydroxylamine (PFBOA) was used as a der ivatization reagent for carbonyl compounds in beer. Derivatization was carried out in aqueous solution without extraction or concentration o f the sample. The effects of antifoam agent, reaction time and pH on t he reaction efficiency were studied. Antifoam RD, a silicone polymer-b ased antifoam reagent, was the best antifoaming agent since it did not cause interferences. Reaction time studies showed that the yield of a ldehydes increased up to 12 hr and then decreased slightly. The yield of 3-hydroxybutanone, a test compound for ketones, increased throughou t the 48 hr test period. The natural pH of beer (ca 4.5) was favourabl e for the determination of carbonyl compounds as PFBOA derivatives. Hi gher pH values caused yield losses and some compounds, such as butaned ione, 2,3-pentanedione and 5-hydroxymethyl-2-furfural, could not be me asured at all in neutral or basic conditions. Carbonyl compounds were identified by GC-MS, using three different ionization techniques, elec tron impact ionization, chemical ionization, and negative chemical ion ization. The formation of the protonated molecules by ammonia chemical ionization and formation of the negative molecular ions and [M - HF]- . ions by negative chemical ionization permitted reliable identificati on of the various carbonyl compounds studied. Sixteen carbonyl compoun ds from the 32 standard compounds were identified in beer and 11 of th e most significant were quantiated using GC-ECD. Reproducibility of qu antitation for beer samples was good, the relative standard deviations varied between 2.7 and 6.7%. The estimated detection limits of the PF BOA derivatives of the carbonyl compounds in beer varied in the range of 0.01-1 mug/dm3.