GC-MS quantitation of benzoic and aralkyl carboxylic acids as their trimethylsilyl derivatives:: in model solutions I.

This paper describes the fragmentation patterns and the GC-MS quantitation possibilities of the trimethylsilyl derivatives of thirty-one aromatic carboxylic acids, using ion trap detection (ITD). Sixteen aralkyl carboxylic acids, including those containing a saturated aliphatic side chain {phenylacetic, 2-phenylbutyric, phenylglycolic (mandelic acid), beta-phenyllactic, 3-hydroxyphenylacetic, beta-phenylpyruvic and 3-(4-hydroxyphenyl)-propionic acids} and those with an unsaturated aliphatic side chain {cinnamic, 2-hydroxycinnamic (o-coumaric), 4-methoxycinnamic, 3-hydroxycinnamic (m-coumaric), 4-hydroxycinnamic (p-coumaric), 4-hydroxy-3-methoxycinnamic (ferulic acid), 3,4-dihydroxycinnamic (caffeic), and 4-dihydroxy-3,5-dimethoxycinnamic (sinapic) acids}, as well as, the fifteen hydroxy(methoxy)benzoic acids {benzoic, 2-hydroxybenzoic (salicylic), 3-hydroxybenzoic, 4-hydroxybenzoic, 3,5-dimethoxybenzoic, 3,4-dimethoxybenzoic (veratric), 2,6-dihydroxybenzoic (gamma-asorcylic), 3-methoxy-4-hydroxybenzoic (vanillic), 2,5-dihydroxybenzoic (gentisic), 2,4-dihydroxybenzoic (beta-resorcylic), 3,4-dihydroxybenzoic (protocatechuic), 3,5-dihydroxybenzoic (alpha-resorcylic), 2,4,5-trimethoxybenzoic (asaronic), 3,5-dimethoxy-4-hydroxybenzoic (syringic) and 3,4,5,-trihydroxybenzoic (gallic) acids}, provided distinct fragmentation characteristics that were very useful for their identification and simultaneously quantitation. Based on 1-20 ng amounts of acids, very informative ions of high mass with considerable intensities ([M+TMS](+), [M+1](+)), ([M]radical cation), [M-CH(3)](+)) were obtained. In the case of the cinnamic acid derivatives, several odd electron fragments are formed by the loss of CO, HCHO and/or Si(CH(3))(4) molecules. In the case of benzoic acids the molecular ion ([M]radical cation) proved to be abundant in three, the [M-CH(3)](+) ion in nine cases out of fifteen. The special MacLafferty rearrangement product ([C(6)H(5)Si(CH(3))(2)](+)) was obtained in different yields. In addition to the TIC values, at least three, and in most cases four, selective fragment ions could be utilized for quantitation. The reproducibility of the data in the concentration range of 1-20 ng acids proved to be between 1.2 and 13.0 % (R.S.D.).