SummaryThe composition and concentration of polycyclic aromatic compounds (PAC) in fuels, their combustion products and in the atmosphere remains a topic of considerable interest. Despite the wealth of literature on the identification of PAC, speciation at low concentrations remains difficult due to instrument limitation and the complexity of fuel and environmental samples. Consequently online sample preparation procedures (SPE, SFE, LC, etc.) are becoming an increasingly important step in the analysis procedure particularly where sample clean-up and fractionation are essential for improving analytical resolution. In this study a normal phase high pressure liquid chromatography-gas chromatography (LC-GC) system has been developed to provide quantitative analysis of samples, as diverse as coal liquids, petroleum fuels, diesel exhaust particulates and urban air particulates. Separation and identification of parent and alkylated PAH, heterocyclic, nitro-and oxy-PAC can be achieved by direct coupling to an atomic emission detector and a bench top mass spectrometer. For both systems the primary LC separation combined with the large sample volume transferred to GC vastly improves detection limits. Furthermore the complimentary nature of the two detectors used enables the positive identification of many unknowns.

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Solutions of Mg(NCS), in methanol contain an equimolar mixture of free thiocyanate and the complex [Mg(NCS)]+. The complex exists in two forms, with or without a hydrogen bond from the sulfur atom to a solvent molecule.We have previously reported the IR spectra, in the v(C-N) stretching region, of alkali-metal thiocyanates in methanol solutions. ' The spectra showed that the salts are highly dissociated in this solvent, and that the thiocyanate ion is extensively hydrogen bonded. This gives rise to an unexpectedly complex profile to the spectrum of the thiocyanate ion. To account for the apparent complexity of the spectra we proposed that there are at least six hydrogen-bonded varieties of thiocyanate present in the solutions. The work presented in this paper was undertaken in order to extend the observations to a salt of a divalent cation. It was designed to obtain quantitative information on the stability of the complex(es) that may be formed.

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Conventional operation of the GC Atomic Emission Detector (AED) system involves backflushing of the microwave induced plasma (MIP) during the elution of small volumes of solvent from the GC column. When performing multi‐dimensional, on‐line LC‐GC‐AED, significantly larger solvent volumes are introduced into the system and must subsequently be removed. Thus solvent venting procedures are required and the backflushing of the plasma must be extended to facilitate solvent but not solute removal. This study demonstrates the significance of memory effects imparted upon the MIP of the AED if solvent venting is incomplete. Comparison of conventional GC‐AED and multi‐dimensional LC‐GC‐AED is made with respect to a fossil fuel sample.