A Novel Method for the Calibration of Kovats Retention Indices Using n-Alkanes with a Thermionic Nitrogen-Phosphorus Specific Detector

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Abstract
This paper describes a novel method for the detection of compounds that do not contain nitrogen or phosphorus by a thermionic nitrogen-phosphorus specific detector (NPD), which normally detects only nitrogen- or phosphoruscontaining compounds. This method allows for the calibration of gas chromatographic columns with NPD detectors using n-alkanes instead of nitrogen-containing drug mixtures. This results in a more rapid and accurate calibration for the calculation of relative retention indices (RRI), such as Kováts indices, than was previously possible when employing an NPD detector. The proposed method describes the temporary conversion of the NPD detector into a detector with properties much like a flame ionization detector. After a deliberate increase in the hydrogen gas flow rate to the thermionic bead from 4 ml/min to 8 ml/min, the n-alkanes (containing no nitrogen) can be detected and used as RRI calibrators. Once the column has been calibrated, the hydrogen gas flow rate is lowered to the normal rate of 4 ml/min. The detector then behaves as a normal NPD, no longer detecting the n-alkanes.