Quantitation of isomeric ethyl pyridine mixtures by multivariate calibration applied to ion-molecule reaction/collision-induced dissociation triple-stage mass spectra.

In reactions of the distonic ion (+)CH(2)OCH(2) with the three isomeric ethyl pyridines, ionized methylene transfer occurs readily yielding distonic N-methylene-ethylpyridinium ions. On-line mass selection and 10 eV collision-induced dissociation (CID) of the CH(2)(+) transfer products yields characteristic fragment ions, which are formed via processes greatly influenced by the ortho, meta or para location of the ethyl substituent in the pyridine ring. Quantitation of mixtures of isomeric 2-, 3-, and 4-ethyl pyridines of varying compositions was then performed by multivariate calibration in the form of the partial least square (PLS) model applied to both single-stage (MS) 70 eV electron ionization (EI) and pentaquadrupole triple-stage sequential ion-molecule reaction/CID product ion mass spectra.

Direct sampling tandem mass spectrometry (MS/MS) and multiway calibration for isomer quantitation.

Direct sampling tandem mass spectrometry (MS/MS) was used for the quantitation of mixtures of the isomers 2-, 3- and 4-ethyl pyridine. The similarity between the analytes and the second-order nature of MS/MS data require the use of multivariate calibration techniques capable of handling multiway data. Multilinear PLS (N-PLS) was applied here, as well as the alternative technique of unfolding the data and using standard two-way PLS.