The gas-liquid chromatograph and the electron capture detection in equine drug testing.

This research article discusses the use of gas-liquid chromatographic procedures in equine drug testing. The proposed methods are designed to detect very low drug levels in horse blood, making them suitable for both pre-race and post-race testing.

Overview

Gas-liquid chromatography (GLC) is a technique used to separate and analyze compounds that can be vaporized without decomposition. In equine drug testing, this process was designed considering the four ‘esses’ — speed, sensitivity, simplicity, and specificity. The research aimed at accurate detection of drug levels in blood samples during pre-race and post-race conditions. Drugs were detected using an electron capture detector (ECD), which often required a derivatization step.

Derivatization in Gas-Liquid Chromatography

• Derivatization is a chemical process used to convert substances to a more recognizable form. In this case, the drugs needed to be altered to develop high electron affinity – a characteristic trait that enables their detection by the ECD.
• The research discusses the use of two derivatizing agents – heptafluorobutyric (HFBA) and pentafluorpropionic (PFPA) anhydrides, which were chosen for their broad applicability in this context.

Three Techniques

The research put forth three different GLC techniques for the various classes of drugs. These methods included:

• Direct derivatization of drugs to form strongly electron capturing amides and esters: In this process, the drugs are directly converted into amides and esters, which can be easily detected due to their strong electron attraction.
• Reductive fragmentation of drugs with lithium aluminum hydride to form alcohols, with conversion to ester derivatives: The drugs are broken down with lithium aluminum hydride to convert them into alcohols. These alcohols are then converted into ester derivatives, making them recognizable by the ECD.
• Oxidative fragmentation of drugs with potassium dichromate to form derivatizable groups, followed by direct derivatization: The drugs are broken down using potassium dichromate, forming derivatizable groups, which are then directly derivatized for easier detection.