A Retention Index Library for Commonly Encountered Drugs and Metabolites Using Tri-n-alkylamines as Reference Compounds, Nitrogen-Phosphorus Detectors, and Dual Capillary Chromatography

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Abstract
The retention index system is a reproducible means for the identification of drugs in toxicology samples analyzed by gas chromatography with flame ionization detectors. Nitrogen-phosphorus (NP) detectors do not respond well to the standard n-alkanes, which lack nitrogen and phosphorus groups and which are used to obtain the Kovats index. A method is presented that creates a retention index library based upon a homologous series of tri-n-alkylamines for a series of 125 drugs and metabolltes. Standards were analyzed under temperature programmed conditions by simultaneous dual column chromatography using a 5% phenyl and a 50% phenyl methyl silicone fused-silica capillary column. By increasing the hydrogen and air flows to the NP detectors, the Kovats Indices were calculated on the system using the n-alkanes C8 through C32 Tri-n-alkylamine indices calculated under the same conditions were compared to the Kovats indices for 14 drugs on the 5% phenyl column and for 12 drugs on the 50% phenyl column. The correlation was found to be linear. The Kovats Indices on the 5% phenyl column were compared to previously reported values and found to be consistent.