Summary An ultra-high pressure liquid chromatograph was interfaced to a moderately high-resolution nanoelectrospray ionization ion mobility spectrometer operating at ambient temperature and pressure to achieve fast multidimensional separations. The potential of using ion mobility spectrometry as the second dimension in a comprehensive arrangement with liquid chromatography to offer improved qualitative information for compounds under specific operating conditions, is discussed. Separation and detection of selected benzodiazepines and triazine herbicides are demonstrated. Composite peak capacities of 39 and 33 for benzodiazepine and triazine herbicide mixtures, respectively, were achieved in less than 75 s using a 16.5 cm×50 μm internal diameter fused silica capillary liquid chromatographic column packed with 1.5 μm diameter ODS-bonded silica particles. Key Words Column liquid chromatography - Ion mobility spectrometry - Nanoelectrospray ionization - Comprehensive multidimensional separations

Benzodiazepines are a commonly abused class of drugs; requiring analytical techniques that can separate and detect the drugs in a rapid time period. In this paper, the two-dimensional separation of five benzodiazepines was shown by electrospray ionization (ESI) ion mobility spectrometry (IMS)–mass spectrometry (MS). In this study, both the two dimensions of separation (m/z and mobility) and the high resolution of our IMS instrument enabled confident identification of each of the five benzodiazepines studied. This was a significant improvement over previous IMS studies that could not separate many of the analytes due to low instrumental resolution. The benzodiazepines that contain a hydroxyl group in their molecular structure (lorazepam and oxazepam) were found to form both the protonated molecular ion and dehydration product as predominant ions. Experiments to isolate the parametric reasons for the dehydration ion formation showed that it was not the result of corona discharge processes or the potential applied to the needle. However, the potential difference between the needle and first drift ring did influence both the relative intensity ratios of the two ions and the ion sensitivity. Author Keywords: Electrospray; Ion mobility spectrometry; Benzodiazepines

There has been increasing recognition of the problem of fatal opioid overdose. This review examines the pharmacological basis of respiratory depression following opioid administration. Respiration is controlled principally through medullary respiratory centres with peripheral input from chemoreceptors and other sources. Opioids produce inhibition at the chemoreceptors via mu opioid receptors and in the medulla via mu and delta receptors. While there are a number of neurotransmitters mediating the control of respiration, glutamate and GABA are the major excitatory and inhibitory neurotransmitters, respectively. This explains the potential for interaction of opioids with benzodiazepines and alcohol: both benzodiazepines and alcohol facilitate the inhibitory effect of GABA at the GABAA receptor, while alcohol also decreases the excitatory effect of glutamate at NMDA receptors. Heroin and methadone are the major opioids implicated in fatal overdose. Heroin has three metabolites with opioid activity. Variation in the formation of these metabolites due to genetic factors and the use of other drugs could explain differential sensitivity to overdose. Metabolites of methadone contribute little to its action. However, variation in rate of metabolism due to genetic factors and other drugs used can modify methadone concentration and hence overdose risk. The degree of tolerance also determines risk. Tolerance to respiratory depression is less than complete, and may be slower than tolerance to euphoric and other effects. One consequence of this may be a relatively high risk of overdose among experienced opioid users. While agonist administration modifies receptor function, changes (usually in the opposite direction) also result from use of antagonists. The potential for supersensitivity to opioids following a period of administration of antagonists such as naltrexone warrants further investigation. While our understanding of the pharmacological basis of opioid-related respiratory depression has advanced, better understanding of the role of heroin metabolites, the metabolism of methadone, drug interactions and tolerance would all be of considerable value in knowing how best to respond to this problem.