Drugs and the impaired driver in Northern Ireland: an analytical survey

The techniques used to analyse 212 "under-the-limit" drink-driving blood and urine specimens for drugs during a 3-year period (1982-85) in Northern Ireland are described. In all of these specimens (representing 15% of all below-limit cases) either the police surgeon who carried out the clinical examination, or the police, strongly suspected that drugs may have been a contributory factor in driving impairment, considering the lower than expected alcohol concentration. Thirty-eight (18%) samples were found to contain significant drug(s). Benzodiazepines were the most frequently encountered group of drugs (87% of all positive cases) with diazepam being that most frequently encountered (18 cases). The analytical procedures were radioimmunoassay, gas chromatography using nitrogen selective and electron capture detection along with high performance liquid chromatography (HPLC) using ultra-violet detection. Drugs and their metabolites were identified using a mixture of these techniques along with GC/MS where possible. The usefulness of HPLC coupled with a rapid-scanning diode-array spectrophotometer is also demonstrated, the technique being particularly useful in the analysis of some of the more "difficult" benzodiazepines (e.g. lorazepam, temazepam, nitrazepam) not directly amenable to gas chromatography without derivatisation.