R.J. Flanagan

High-performance liquid chromatographic analysis of basic drugs on silica columns using non-aqueous ionic eluents. II: Application of UV, fluorescence and electrochemical oxidation detection

Unmodified silica columns together with non-aqueous ionic eluents give stable yet flexible systems for the analysis of basic drugs by high-performance liquid chromatography. Low-wavelength UV and fluorescence detection may be used, and fluorescence may be optimised by, for example, post-column pH change or derivatisation of some primary aliphatic amines with o-phthaldialdehyde. A novel feature is that electrochemical oxidation can be used for the detection of most analytes and this detection mode is thus discussed in detail. Retention and relative response data (UV, 254 nm and electrochemical, +1.2 V) have been generated for 462 compounds using a 125-mm Spherisorb S5W silica column and methanolic ammonium perchlorate (10 mM, pH 6.7) as eluent. This system can be used isocratically in qualitative analyses and also for quantitative work, when either the wavelength or the applied potential can be adjusted to optimise the response.

Use of N-acetylcysteine in clinical toxicology

The major use of N-acetylcysteine in clinical toxicology is in the treatment of acetaminophen (paracetamol) overdosage. The hepatorenal toxicity of acetaminophen is mediated by a reactive metabolite normally detoxified by reduced glutathione. If glutathione is depleted, covalent binding to macromolecules and/or oxidation of thiol enzymes can lead to cell death. Oral or intravenous N-acetylcysteine or oral D,L-methionine mitigates acetaminophen-induced hepatorenal damage if given within 10 hours, but becomes less effective thereafter. In vivo, N-acetylcysteine forms L-cysteine, cystine, L-methionine, glutathione, and mixed disulfides; L-methionine also forms cysteine, thus giving rise to glutathione and other products. Oral therapy with N-acetylcysteine or methionine for acetaminophen poisoning is contraindicated in the presence of coma or vomiting, or if activated charcoal has been given by mouth. Nausea, vomiting, and diarrhea may also occur as a result of oral N-acetylcysteine administration. Anaphylactoid reactions including angioedema, bronchospasm, flushing, hypotension, nausea/vomiting, rash, tachycardia, and respiratory distress may occur 15-60 minutes into N-acetylcysteine infusion (20 hours intravenous regimen) in up to 10% of patients. Following accidental intravenous overdosage, the adverse reactions of N-acetylcysteine are similar but more severe; fatalities have occurred. A reduction in the loading dose of N-acetylcysteine may reduce the risk of adverse reactions while maintaining efficacy. Administration of N-acetylcysteine for a longer period might provide enhanced protection for patients in whom acetaminophen absorption or elimination is delayed. N-acetylcysteine may also have a role in the treatment of toxicity from carbon tetrachloride, chloroform, 1,2-dichloropropane, and other compounds. The possible use of N-acetylcysteine and other agents in the prevention of the neuropsychiatric sequelae of acute carbon monoxide poisoning is an important area for future research.

An Introduction to the Clinical Toxicology of Volatile Substances

SummaryAcute poisoning with organic solvents and other volatile compounds now usually follows deliberate inhalation (volatile substance abuse) or ingestion of these compounds. Solvents from adhesives, typewriter correction and dry cleaning fluids, cigarette lighter refills (butane) and aerosol propellants are commonly abused. The major risk is that of sudden death. Arrhythmias leading to cardiac arrest are thought to cause most deaths, but anoxia, respiratory depression and vagal stimulation leading to cardiac arrest may also contribute, as may indirect causes such as aspiration of vomit or trauma.In the United Kingdom (UK), 3.5 to 10% of young people have at least experimented with volatile substance abuse and mortality is more than 100 per annum. The products abused are cheap and readily available despite legislation designed to limit supply. Volatile substance abuse is not illegal and only a minority of abusers are known to progress to heavy alcohol or illicit drug use. Prevention of abuse by education, not only of children but also of parents, teachers, retailers and health care workers, is important in limiting the problem. However, volatile substance abuse-related deaths are still increasing in the UK despite many measures aimed at prevention.Clinically, volatile substance abuse is characterised by a rapid onset of intoxication and rapid recovery. Euphoria and disinhibition may be followed by hallucinations, tinnitus, ataxia, confusion, nausea and vomiting. It is important not to further alarm the patient if signs of serious toxicity are present, since a cardiac arrest may be precipitated. Further exposure should be prevented and the patient resuscitated and given supplemental oxygen if necessary. Cardiac arrhythmias should be treated conventionally and respiratory failure managed supportively. Long term exposure to n-hexane is associated with the development of peripheral neuropathy, while prolonged abuse (notably of toluene or chlorinated solvents) can cause permanent damage to the central nervous system, heart, liver, kidney and lungs.Knowledge of the routes of absorption, distribution and excretion of volatile compounds, and of the rates governing these processes, is important in understanding the rate of onset, intensity and duration of intoxication, and rate of recovery after volatile substance abuse. In addition, such knowledge is helpful when the clinician is attempting to interpret the results of toxicological analyses performed on samples (blood, other tissues, urine) from such patients. Many volatile substances are partly metabolised, the metabolites being eliminated in exhaled air or in urine. Although metabolism normally results in detoxification, enhanced toxicity may also result as with carbon tetrachloride, chloroform, dichloromethane, n-hexane, trichloroethylene and possibly halothane.Identification of volatile substance abusers can be difficult, but the hair, breath and clothing may smell of solvent, and empty containers may be found. Perioral eczema (‘glue-sniffer’s rash’) from direct contact with glue poured into a plastic bag occurs rarely. Headspace gas chromatography of blood can detect exposure to many compounds but not to complex mixtures such as petrol; detection of metabolites is only useful with a few compounds, notably toluene, trichloroethylene and xylene.Prevalence studies suggest that volatile substance abuse is increasing worldwide yet the UK is the only country to collate and regularly publish data on abuse-related deaths. Such data, although difficult to collect, are important in identifying and monitoring the problem. A coordinated approach to the collation of analogous data on an international basis would be valuable in monitoring the efficacy of preventative programmes.

Rapid high-performance liquid chromatographic method for the measurement of amiodarone in blood plasma or serum at the concentrations attained during therapy

A simple high-performance liquid chromatographic method has been developed for the measurement of the antiarrhythmic drug amiodarone in small (200 microliter) volumes of plasma or serum. After addition of 2 mole/l phosphate solution, pH 4.5 (20 microliter), containing the internal standard, the sample is vortex-mixed with diisopropyl ether (200 microliter) for 30 sec. A portion (100 microliter) of the resulting extract is analysed on a microparticulate (5 micron) silica column using methanol-diethyl ether (85:15) containing perchloric acid (0.02% v/v) as the mobile phase, and the absorption of the column effluent is monitored at 240 nm. No endogenous sources of interference have been observed, and interference from other drugs is minimal. The procedure is rapid, an analysis in duplicate taking less than 15 min to complete. The limit of sensitivity of the assay is 0.05 mg/l, and the concentrations of amiodarone measured in plasma samples from patients under treatment with this compound ranged from 0.15 to 4.5 mg/l.

Detection and identification of volatile organic compounds in blood by headspace gas chromatography as an aid to the diagnosis of solvent abuse

A gas chromatographic method has been developed for the detection and identification of some volatile organic compounds in whole blood, plasma or serum. After incubation of the sample (200 microliters) together with the internal standard solution in a sealed vial, a portion of the headspace is analysed using a 2-m glass column packed with 0.3% (w/w) Carbowax 20M on Carbopack C, 80-100 mesh. The column oven, after a 2-min isothermal period, is programmed from 35 to 175 degrees C at 5 degrees/min and held for 8 min. The effluent is monitored by both flame-ionisation and electron-capture detection, and peak assignment is by means of retention time and relative detector response. The method has proved applicable to the detection of bromochlorodifluoromethane, n-butane, carbon tetrachloride, chlorobutanol, cryofluorane (Halon 114), dichlorodifluoromethane (Halon 12), ethyl acetate, halothane, isobutane, isopropanol, isopropyl nitrate, methyl ethyl ketone, propane, tetrachloroethylene, toluene, 1,1,1-trichloroethane, 2,2,2-trichloroethanol, trichloroethylene and trichlorofluoromethane (Halon 11) in blood specimens obtained from patients suspected of abusing these agents.

High performance liquid chromatographic analysis of basic drugs on silica columns using non-aqueous ionic eluents

Abstract The addition of ionic modifiers at low concentration to non-aqueous, primarily methanolic, eluents can facilitate the high-performance liquid chromatographic analysis of a wide range of basic compounds using microparticulate silica columns. The major factors influencing both the selectivity of the system and the retention volumes of individual analytes are the pH and teh ionic strength of the eluent, although changes in the organic component of the eluent can give useful changes in selectivity, as can the use of chemically bonded stationary phases, e.g., octadecylsilyl. In general, retention can be predicted to a large extent by pKa, and even very weak bases such as benzodiazepines can be retained under strongly acidic conditions. These non-aqueous system show high efficiency, stability and reproducibility, and give long column life. In addition, they are suitable for use with low-weavelength UV, fluorescence and electrochemical oxidation detectin. The preparation of the eluent is simple, and the direct analysis of extracts performed using a non-eluting solvent is easily possible. It is clear that these systems have many advantages over bonded-phase systems using aqueous eluents in the liquid chromatographic analysis of basic drugs.

High-performance liquid chromatographic analysis of basic drugs on silica columns using non-aqueous ionic eluents. I. Factors influencing retention, peak shape and detector response.

The use of silica columns together with non-aqueous ionic eluents provides a stable yet flexible system for the high-performance liquid chromatographic analysis of basic drugs. At constant ionic strength, eluent pH influences retention via ionisation of surface silanols and protonation of basic analytes, pKa values indicating the pH of maximum retention. At constant pH, retention is proportional to the reciprocal of the eluent ionic strength for fully protonated analytes and quaternary ammonium compounds. The addition of water up to 10% (v/v) has little effect on retention if the protonation of the analytes is unaffected. Thus, it is likely that retention is mediated primarily via cation exchange with surface silanols. However, additional factors must play a part with compounds such as morphine which give tailing peaks at acidic or neutral eluent pHs.

Identification and measurement of desethylamiodarone in blood plasma specimens from amiodarone‐treated patients

Desethylamiodarone has been identified as the principal lipophilic metabolite of amiodarone present in plasma specimens from amiodarone‐treated patients. This structure has been confirmed by probe‐injection mass spectrometry of column effluent fractions and comparison with the authentic compound using both chromatographic and mass spectrometric techniques. Although there is no information available as to the pharmacological activity of desethylamiodarone in man, the plasma concentrations of this metabolite attained during chronic amiodarone therapy are similar to those of the parent compound (0.1–4 mg litre−1).

Rapid high-performance liquid chromatographic method for the measurement of verapamil and norverapamil in blood plasma or serum.

A simple high-performance liquid chromatographic method for the simultaneous measurement of plasma verapamil and norverapamil concentrations has been developed. The sample (100 microliters) is vortex-mixed for 30 sec with 4 M sodium hydroxide solution, pH 13 (50 microliters), internal standard solution (aqueous 5,6-benzoquinoline, 0.20 mg/l) (50 microliters) and methyl tert.-butyl ether (200 microliters). After centrifugation at 9950 x g for 2 min, a portion (100 microliters) of the resulting extract is analysed on a microparticulate (5 microns) silica column using a methanolic solution of potassium bromide (3.0 mM) and perchloric acid (0.37 mM) as the mobile phase, and the column effluent is monitored by fluorescence detection using an excitation wavelength of 203 nm. A specimen, together with a quality control sample, can be analysed, in duplicate, within 30 min. The limit of accurate measurement of the assay is 2 micrograms/l, and no potential sources of interference have been identified. The method has advantages of speed, small sample requirement and complete resolution of the three major metabolites of verapamil.

Simple gas—liquid chromatographic method for measurement of mexiletine and lignocaine in blood-plasma or serum

A simple method has been developed for the measurement of mexiletine and lignocaine in blood-plasma or serum at the concentrations attained during therapy. A relatively small (200 microliter) sample volume is made basic and extracted with 50 microliter of chloroform containing internal standards, and the extract is analysed directly by gas-liquid chromatography with flame-ionisation detection on two separate columns. The instrument calibrations are linear and pass through the origin of the graphs. Neither solvent transfer nor evaporation steps are used in the extraction procedure, which takes less than 3 min to complete, and no interference from either endogenous sample constituents or other drugs has been observed.