On‐line liquid chromatography – gas chromatography for automated clean‐up and analysis of polycyclic aromatic hydrocarbons

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Abstract
A fully automated system, comprising a liquid chromatograph (LC) coupled on‐line to a gas chromatograph (GC) by means of a loop interface, has been constructed for clean‐up and analysis of polycyclic aromatic hydrocarbons (PAH). An autosampler was utilized for sample injection into the LC. By the use of a back‐flush technique in conjunction with an ordinary analytical aminopropylsilica column, PAH could be isolated by LC: a concurrent solvent evaporation injection technique was then used for on‐line transfer of the PAH fraction to the GC, where the PAH analysis was completed.Compared with ordinary off‐line LC clean‐up followed by GC analysis, the sensitivity has been increased by a factor of 50–100, yielding a detection limit for individual PAH of a few nanograms per sample when using flame ionization detection. Further, irreproducible losses of low molecular weight PAH as a result of solvent evaporation steps in off‐line clean‐up procedures have been eliminated. Reproducibility of retention times and relative peak areas is high, facilitating automatic peak identification and calculation of concentrations, and the system can thus be used for automatic sample evaluation. The total time required for clean‐up and analysis is only 1.5 hours, and the demand on personnel time for the analysis of PAH has been drastically reduced.The technique has been demonstrated with samples of urban air and of used automobile engine lubricating oil.

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