A solvent microextraction technique has been developed to perform simultaneous forward- and back-extraction across a microliter-size organic liquid membrane. The organic liquid membrane phase (o), consisting of 40 or 80 μL of n-octane, is layered over 0.5 or 1.0 mL of aqueous sample phase (a1) contained in a 1- or 2-mL microreaction vial and is stabilized against mechanical disruption by a small Teflon ring, even when the a1 phase is stirred at a speed of 2000 rpm. A 0.1- or 0.2-mL aqueous receiving phase (a2) is layered over the o phase. After extraction for a prescribed time, an aliquot of the a2 phase is injected directly into an HPLC for quantification. The technique is efficient and selective for ionizable compounds. In 30 min, the model compounds, mephentermine and 2-phenylethylamine, in the a1 phase buffered at pH 13 are 100% and 90% extracted, respectively, into the a2 phase buffered at pH 2.1. A kinetic model has been developed, based on the Whitman two-film theory, to describe the extraction pro...

Solvent Microextraction with Simultaneous Back-Extraction for Sample Cleanup and Preconcentration: Quantitative Extraction

Only three drugs are commonly used as oral decongestants--phenylpropanolamine (PPA), pseudoephedrine (PDE), and phenylephrine (PE). They are all chiral drugs that exist as stereoisomers. It is possible that each enantiomer can reflect significant enantioselective differences with regard to both pharmacokinetic and pharmacodynamic effects. Both PPA and PDE are readily and completely absorbed, whereas PE, with a bioavailability of only approximately 38%, is subject to gut wall metabolism and is thought to be absorbed erratically. Peak concentrations are reached between 0.5 and 2 hours after administration. All three drugs are extensively distributed into extravascular sites (apparent volume of distribution between 2.6 and 5.0 L/kg). No protein-binding data in humans are available. Whereas PPA and PDE are not substantially metabolized, PE undergoes extensive biotransformation in the gut wall and the liver. Elimination of PPA and PDE is predominantly renal, with urinary excretion being pH dependent. Half-lives are relatively short, approximately 2.5 hours for PE, 4 hours for PPA, and 6 hours for PDE. Elimination of PPA and PDE may be rapid in children, and the agents should be used with caution in patients with renal impairment. In addition, PPA increases caffeine plasma levels and decreases theophylline clearance. Reduced metabolism of PE occurs with concurrent administration of monoamine oxidase inhibitors. No direct relationship between nasal decongestant effect and plasma concentration has been established.

Pharmacokinetics of oral decongestants.

(1) In order to provide an efficient and reliable service for drugs of abuse screening in urine, the laboratory should analyse 20-30 samples per week, and the staff should include a scientist with special expertise in the subject. (2) Turnaround times should be between 2-3 days of sample collection. To achieve this aim it may be necessary to make special arrangements for the delivery of samples to the laboratory. Results should preferably be transmitted by electronic mail or facsimile with the necessary precautions for security and confidentiality: hardcopy reports may also be required. (3) Good communications between the requesting clinician and the laboratory are essential. An advisory service should be provided by the laboratory and clinicians should be encouraged to discuss requests and results with laboratory staff. It is important that the laboratory inform doctors of the range of substances detected and the sensitivity and specificity of laboratory assays. (4) Assays should be performed according to the manufacturer's protocols, or by modified methods that have been rigorously validated. Quality control samples should be included in each analytical run and participation in an external quality assessment scheme, e.g. UKNEQAS, is essential to provide independent confirmation and confidence that results compare with those from other laboratories. Other requirements include adequate training and supervision of staff, and careful recording of samples and results. (5) Drugs to be tested will depend on the drug 'scene' in the area but should include those drugs regularly prescribed for maintenance therapy (e.g. methadone, dihydrocodeine, benzodiazepines), and drugs frequently misused (e.g. heroin, buprenorphine, amphetamines, cocaine). (6) Positive results obtained by preliminary screening methods e.g. EMIT, should be confirmed by another analytical technique, e.g. TLC, GC or GC-MS. If there are potentially serious or legal implications, and in employment and preemployment testing, confirmation of positive results is mandatory. In some cases, e.g. checking for methadone or benzodiazepine compliance, it may be considered unnecessary to confirm positive results although possible spiking of samples cannot be excluded without checking for the presence of metabolites by a chromatographic procedure.

https://journals.sagepub.com/doi/pdf/10.1177/000456329503200203

Screening for Drugs of Abuse. I: Opiates, Amphetamines and Cocaine

We have demonstrated the use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of the phenylalkylamines amphetamine and methamphetamine. This work can be viewed as the first phase of development toward a one-step drug detection method with a selective reactive coating on a SERS substrate. This work involves a fairly complicated coupling reaction prior to surface derivatization. Future efforts will be directed at creating a reactive coating directly on the surface. The amines were derivatized by a coupling reaction with 2-mercaptonicotinic acid (2-MNA) with the use of dicyclohexylcarbodiimide (DCC) as the coupling reagent to form the amide compounds AMNA [N-(1-methyl-2-phenylethyl)2-mercaptopyridine-3-carboxamide] and MMNA [N-methyl-N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide]. The amides were qualitatively identified from SERS spectra. Quantification of the amides was accomplished by adding the internal standard pentachlorothiophenol (PCTP) and measuring the intensity of Raman bands of the analyte relative to a Raman band of the internal standard. Calibration curves were plotted of the relative peak intensity ratios as a function of analyte concentration. Detection limits of 19 ppm and 17 ppm were found for amphetamine/2-MNA (AMNA) amide and methamphetamine/2-MNA (MMNA) amide, respectively.

Surface-Enhanced Raman Scattering Detection of Amphetamine and Methamphetamine by Modification with 2-Mercaptonicotinic Acid

An investigation of high-performance liquid chromatographic methods for the analysis of amphetamines.

7-Chloro-4-nitrobenzo-2-oxa -1,3-diazole reacts with primary and secondary amines to produce highly fluorescent compounds. The resulting emission spectra for primary and secondary amines are similar; however, when the excitation spectra of these compounds are determined when the emission wavelength is kept at 520 nm, distinctly different results are obtained. Thin-layer chromatography of suitably concentrated aliquots of these solutions yield characteristic spots, the Rf values of which can be used to help identify the substances involved. This reaction was applied to the quantitative determination of amphetamine in biological extracts. If amphetamine is the only drug present it can be quantitated by fluorometry and confirmed by the thin-layer chromatographic procedure. If more than one drug is present, the fluorometric procedure is unsatisfactory for quantitative analysis. Thin-layer chromatography can be useful to identify qualitatively the drugs involved. Gas chromatography is the procedure of choice in these situations.

Fluorometric Determination of Primary and Secondary Amines in Blood and Urine after Thin-Layer Chromatography

With use of a sample/solvent ratio of 8.5 ml to 100 µl, certain drugs may be extracted efficiently from urine that has been saturated with a solid buffer. An aliquot of this extract may be injected directly into a gas chromatograph. We show how this procedure is applied to confirmation of some drugs of abuse.

Raymond J. Bath

Papers

Fluorometric Determination of Primary and Secondary Amines in Blood and Urine after Thin-Layer Chromatography

Technique for Rapidly Separating Drugs from Biological Samples