High-performance liquid chromatographic analysis of lacosamide in canine serum using ultraviolet detection: application to pre-clinical pharmacokinetics in dogs

A method for analysis of lacosamide [(R)‐2‐acetamido‐N‐benzyl‐3‐methoxypropionamide] is needed for both human and veterinary pharmacokinetic investigations. While lacosamide is currently used to manage partial‐onset seizures in humans suffering from epilepsy, it is also presently being investigated for use in the treatment of canine epilepsy in veterinary medicine. Currently, no dosing regimen for the drug exists in dogs. A novel and simple high‐performance liquid chromatography method was developed for determination of lacosamide in dog serum. Serum proteins (0.1 mL) were precipitated with ?20.0°C acetonitrile after addition of the internal standard, daidzein. Separation was achieved with a Phenomenex® Luna® C₁₈ (2) (5 µm, 250 × 4.60 mm) column with ultraviolet detection at 210 nm. The calibration curves were linear ranging from 0.5 to 25 µg/mL. Precision of the assay was <13% (RSD) and was within 12% for all points in the calibration curve. The limit of quantitation for this method was 0.5 µg/mL. The assay was applied successfully to a pre‐clinical study of lacosamide pharmacokinetics in dogs. Copyright © 2011 John Wiley & Sons, Ltd.     

Perfluorinated Bis(dihydrooxazole) Complexes Immobilized on Fluorous Reversed‐Phase Silica Gel as Recyclable Catalysts for Enantioselective Diels?Alder Reactions

The three different perfluoroalkyl‐tagged bis(dihydrooxazole)copper complexes 19 – 21 were synthesized and immobilized noncovalently on fluorous reversed‐phase silica gel (FRPSG) by fluorous? fluorous interactions (Schemes 2 and 3). These supported catalysts were successfully applied to asymmetric Diels? Alder reactions in H₂O and in CH₂Cl₂ (Scheme 4). Besides high conversion of the dienophile, we observed enantiomer excesses of up to 88% in H₂O and 97% in CH₂Cl₂, and we were able to recover and re‐use these catalytic systems several times. Despite the relatively high catalyst loading, the leaching of copper was remarkably low ranging from 2.4 to 5.9 ppm.     

Comparison of Ion-Pairing and Reversed Phase Liquid Chromatography in Determination of Sulfamethoxazole and Trimethoprim

Abstract

Two simple, rapid, and sensitive HPLC methods have been developed for the simultaneous determination of sulfamethoxazole and trimethoprim in their pure and dosage forms, one utilizing reversed phase HPLC and the other ion-pair HPLC. In the reversed phase HPLC method (A) the mobile phase consists of 0.05% aqueous solution of formic acid with pH adjusted to 4.5±0.2 with triethylamine : acetonitrile:tetrahydrofuran 50 : 49 : 1 (v/v), and the mobile phase pumped at flow rate of 1.0 ml min^?1. An Appolo LC18 column (5.0 µm), 250 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. In the ion-pair HPLC method (B) the mobile phase consisted of methanol : buffer 35 : 65 (v/v) with the buffer composed of potassium dihydrogen phosphate 0.3 M and sodium heptan sulfonic acid 5.0 mM. To 500 ml of buffer was added 2.0 ml triethylamine, and then the pH was adjusted to 5.0 with phosphoric acid, and the mobile phase was pumped at a flow rate of 1.2 ml min^?1. A Hypersil C₁₈ column (5.0 µm), 150 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. Linearity ranges for sulfamethoxazole and trimethoprim were 1.0–110 and 1.5–98 µg ml^?1, respectively, with method A and 0.5–100 and 1.0–125 µg ml^?1, respectively, with method (B). Minimum detection limits obtained were 0.1969 and 0.3451 µg ml^?1 for sulfamethoxazole and trimethoprim, respectively, with method A, and 0.1377 and 0.2454 µg ml^?1 with method (B). The proposed methods were further applied to the analysis of tablets containing the two drugs, and the results were satisfied.     

Silica-based monolithic columns with mixed-mode reversed-phase/weak anion-exchange selectivity principle for high-performance liquid chromatography

This article describes the synthesis, chromatographic characterization, and performance evaluation of analytical (100 x 4.6 mm id) and semipreparative (100 x 10 mm id) monolithic silica columns with mixed-mode RP/weak anion-exchange (RP/WAX) surface modification. The monolithic RP/WAX columns were obtained by immobilization of N-(10-undecenoyl)-3-aminoquinuclidine onto thiol-modified monolithic silica columns (Chromolith) by a radical addition reaction. Their chromatographic characterization by Engelhardt and Tanaka tests revealed slightly lower hydrophobic selectivities than C-8 phases, as well as higher polarity and also improved shape selectivity than RP-18e silica rods. The surface modification enabled separation by both RP and anion-exchange chromatography principles, and thus showed complementary selectivities to the RP-18e monoliths. The mixed-mode monoliths have been tested for the separation of peptides and turned out to be particularly useful for hydrophilic acidic peptides, which are usually insufficiently retained on RP-18e monolithic columns. Compared to a corresponding particulate RP/WAX column (5 microm, 10 nm pore diameter), the analytical RP/WAX monolith caused lower system pressure drops and showed, as expected, higher efficiency (e.g. by a factor of about 2.5 lower C-term for a tetrapeptide). The upscaling from the analytical to semipreparative column dimension was also successful.     

Some new results involving general standby systems

This article presents a stochastic comparison on the total lifetime of the general standby system and a discussion of the optimal allocation of a general standby component in a series system with two independent components. Several examples are also presented to justify the main results, which provide nice generalizations of some existing conclusions in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization of reversed-phase solid-phase extraction for shotgun proteomics analysis By Fanni Bugyi,Lilla Turiák,László Drahos and Gábor Tóth

Reversed-phase solid-phase extraction (SPE) is the method of choice for the purification of proteomics samples. Even though the efficacy of SPE methods is sample type-dependent, the manufacturers' protocols are used in most studies. Using an optimized SPE method can lead to a substantial gain in identification and recovery. In this tutorial, we give a brief introduction to the most important parameters influencing SPE performance, and we present a short workflow (16 measurements) for optimizing the SPE procedure. This is complemented by method performance assessment instructions and a short troubleshooting guide to help users further understand and investigate their SPE methods.