Novel methylcellulose-immobilized cation-exchange precolumn for on-line enrichment of cationic drugs in plasma

Atypical antipsychotics: trends in analysis and sample preparation of various biological samples

Atypical antipsychotics are increasingly popular and increasingly prescribed. In some countries, they can even be obtained over-the-counter, without a prescription, making their abuse quite easy. Although atypical antipsychotics are thought to be safer than typical antipsychotics, they still have severe side effects. Intoxications are not rare and some of them have a fatal outcome. Drug interactions involving atypical antipsychotics complicate patient management in clinical settings and the determination of the cause of death in fatalities. In view of the above, analytical strategies that can efficiently isolate atypical antipsychotics from a variety of biological samples and quantify them accurately, sensitively and reliably, are of utmost importance both for the clinical, as well as for the forensic toxicologist. In this review, we will present and discuss novel analytical strategies that have been developed from 2004 to the present day for the determination of atypical antipsychotics in various biological samples.

Two charge-transfer complex spectrophotometric methods for the determination of sulpiride in pharmaceutical formulations

Two simple, rapid, accurate and sensitive spectrophotometric methods are described for the determination of sulpiride. They are based on charge transfer complexation between the drug as n-electron donor and p-chloranilic acid as π acceptor or iodine as σ-acceptor. These give highly coloured complexes with absorption maxima at 518 and 363, 294 nm, respectively. Beer’s law linear ranges were 13.7–341.4 and 1.7–20.5 µg mL−1 for the p-chloranilic acid and iodine methods. The methods were successfully applied to the determination of the drug in Dogmatil® Fort tablets and the results compared with the official method. The complex association constants and standard free energy changes were calculated using Benesi-Hildebrand plots.

Restricted-access media supports for direct high-throughput analysis of biological fluid samples: review of recent applications

This review presents an update on the use of restricted-access materials (RAMs) for direct injection of biological samples. The fundamental improvements in the preparation of tailored RAMs and the diversity of applications with these phases are presented. Insights into diminishing the matrix effect by the use of RAM supports in methods by LC–MS and into the low number of methods for enantiomeric separations by direct injections of biological samples are addressed. The diversity of systems that incorporate RAMs for selective sample clean-up or fractionation in proteome and peptidome analysis is also covered.

Reduction of carry-over in column-switching HPLC/MS system with automated system washing procedure for highly sensitive direct analysis of donepezil in dog plasma

To solve the problem of carry-over--a persistent chromatographic challenge for bioanalytical assays with highly sensitive detector such as a mass spectrometry (MS)--a new on-line sample pretreatment HPLC/MS system using a column-switching technique was established. This system was designed to reduce carry-over based on a hydrophobic interaction mechanism using a washing function (multi-mobile phase flow system), as well as to remove impurities on-line in a mobile phase for the pretreatment. As a result, a washing function in this system was enabled to reduce carry-over and to remove impurities in a mobile phase by automatic operation. Therefore, concentration levels of donepezil (DH) in dog plasma as low as 10 pg/mL could be determined using this on-line sample pretreatment HPLC/MS system. In addition, method validation results of specificity, linearity, accuracy, precision, lower limit of quantitation (LLOQ), and carry-over demonstrated that this on-line sample pretreatment HPLC/MS system was robust and valid as a practical assay of drugs and metabolites in the biological samples.

Reliable on-line sample preparation of basic compounds from plasma using a reversed phase restricted access media in column-switching LC

We investigated on-line sample preparation of basic compounds from plasma using a methylcellulose-immobilized reversed-phase restricted-access media in column-switching liquid chromatography (LC). Dilution of the plasma sample with phosphate buffered saline prevented or delayed the formation of fibrin clots at 4 degrees C and resulted in reproducible on-line sample preparation over a 30-h period. The use of an ion-pair reagent in the extraction LC enhanced recoveries of hydrophilic basic compounds. The ability of the methods to quantify compounds in plasma were validated and the method was successfully applied to the pharmacokinetic study of a hydrophilic basic compound injected into the bloodstream of rats.

Sensitive determination of aspirin and its metabolites in plasma by LC-UV using on-line solid-phase extraction with methylcellulose-immobilized anion-exchange restricted access media

We describe a sensitive determination of aspirin (ASA) and its three metabolites (salicylic acid [SA], 2,3-dihydroxybenzoic acid [2,3-DHBA], and 2,5-dihydroxybenzoic acid [gentisic acid (GA)]) in rat plasma. Analysis was carried out by on-line solid-phase extraction (SPE) using a methylcellulose-immobilized-strong anion-exchanger (MC-SAX), followed by liquid chromatography (LC) coupled with UV detection. The lower limits of quantitation for ASA and SA were 60 ng/mL in 100 microL of plasma, respectively. This method was validated with respect to intra- and inter-day precision, accuracy, and linearity up to concentrations of 20,000 ng/mL for ASA, SA, 2,3-DHBA and gentisic acid, respectively. The method was successfully applied to an analysis of the pharmacokinetics of ASA and SA in rats.

Effective on-line purification for cationic compounds in rat bile using a column-switching LC technique

An on-line purification method for cationic compounds and their metabolites in rat bile was investigated using a column-switching technique. 8-Hydroxyquinoline and its glucuronide were used as test compounds. Bile samples were injected directly into the system and successful on-line extraction with high purification efficiency for analytes was achieved using two-dimensional extraction LC; that is, reversed-phase chromatography followed by cation-exchange chromatography. After removal of the endogenous component by extraction LC, chromatographic separation of the target analyte was performed on an analytical ODS column, followed by identification using UV detection. The quantitative ability of the method was evaluated on the basis of injection repeatability, linearity and accuracy. This novel method was also applied to LC/MS analysis in order to characterise the pharmacokinetics of propranolol in rats, and the metabolites were successfully identified.

On-line pretreatment using methylcellulose-immobilized cation-exchange restricted access media for direct liquid chromatography/mass spectrometric determination of basic drugs in plasma

A novel methylcellulose-immobilized restricted access media column with strong cation-exchange groups on an internal surface (MC-SCX) was evaluated for the direct injection analysis of basic polar drugs in plasma by column-switching liquid chromatography/mass spectrometry (LC/MS). Analytical conditions, including an automated pretreatment step and MS detection, were optimized for a series of basic drugs (doxepin, desipramine, imipramine, nortriptyline, amitriptyline, clomipramine). On-line pretreatment with the MC-SCX column followed by fast gradient analysis using a C18 column resulted in a total analysis cycle time of 7 min for each spiked plasma sample. More than 150 plasma samples spiked with target compounds were measured without compromising MS detection (relative standard deviations less than 11% for all compounds, and regression coefficients greater than 0.99).