Chemistry of bonded electron-acceptor phases in liquid chromatography: Application in on-line coupled HPLC-GC-MS

New electron acceptor (EA) stationary bonded phases (BP) for liquid chromatography were synthesized and compared with existing EA BP. The following EA BP were compared: Dinitrophenylmercaptopropylsilica (DNPMP); dinitrodibenzoylmercaptopropylsilica (DNBMP); dinitroanilinopropylsilica (DNAP); dinitrobenzamidopropylsilica (DNBAP); tetranitrofluoreniminopropylsilica (TNFP); tetranitrodibenzosuberiminopropylsilica (TNDBSP); trinitrophenylmercaptopropylsilica (TNPMP); pentafluorophenylsilica (PFPh); aminopropylsilica (NH2) and Nucleosil$\sp{\rm TM}$ 5-NO$\sb2$ (5-NO2). Entropy-enthalpy compensation data indicated that the mechanism of retention (first 6 BP) was the same for planar and nonplanar aromatic solutes, but it was less informative than the vector-analysis techniques of linear correlation coefficient and Euclidian distance calculations. The latter provided a quantitative comparison of the BP. All EA BP had close similarity except for TNFP. NH2 and 5-NO2 were somewhat similar to the EA BP. PFPh was not similar to the other EA BP. The EA BP were also examined for their ability to group aromatic solutes of similar ring size regardless of alkyl substitution. A new performance parameter R$\sb\Gamma$ (group resolution) was proposed and applied to these data. Using the calculated values for R$\sb\Gamma$, the group-resolution effectiveness of the various BP followed the sequence: DNAP $\gg$ DNPMP, TNPMP, 5-NO2 $\u3e$ TNDBSP, DNBMP, DNBAP $\u3e$ NH2 $\u3e$ TNFP $\gg$ PFPh. Retention of aromatic solutes as a function of planarity was also investigated. DNPMP was found to be slightly better than DNAP at separating bridged biphenyls. DNPMP was packed into a 0.32-mm x 300-mm microcapillary liquid chromatographic ($\mu$LC) column. The $\mu$LC system was interfaced with a gas chromatograph mass spectrometer (GC-MS) by a ten-port switching valve with 50 and 7.6-$\mu$L loops. Concurrent cosolvent evaporation occurred in a 0.32-mm x 3-m precolumn ahead of a 0.25-mm x 30-m DB-5 analytical column. Solvent vapors exited through an open-split interface. The $\mu$LC-GC-MS system was demonstrated through the analyses of solvent refined coal, kerosene, crude oil and a mixture of polychlorinated biphenyls, 2,7-dichlorodibenzodioxin and 3,6-dichlorodibenzofuran. The precision for the quantitative transfer of an analyte from the $\mu$LC to the GC-MS was $\pm$6.9% RSD