Electrochemical Oxidation of Different Therapeutic Classes of Pharmaceuticals Using Graphite-PVC Composite Electrode.

This study reports electrochemical treatment of different therapeutic classes of pharmaceuticals (caffeine, prazosin, enalapril, carbamazepine, nifedipine, levonorgestrel, and simvastatin) in a mixture. The electrochemical process was investigated using graphite-PVC anode at different applied voltages (3, 5, and 12 V), initial concentrations of studied pharmaceuticals in aqueous solution (5 and 10 mg/L), and concentrations of sodium chloride (1 and 2 g/L). The % removal of pharmaceuticals increased with the applied voltage, and was found higher than 98% after 50 min of electrolysis at 5 V. Energy consumption ranged between 0.760 and 3.300 Wh/mg using 12 V being the highest value compared to 3 and 5 V. The formation of chlorinated by-products from four selected pharmaceuticals, simvastatin (C11H13Cl3O5, and C10H12Cl4O3), prazosin (C13H12Cl3N5O3 and C10H11Cl4N2O2), carbamazepine and caffeine (C15H11N2O2Cl and C8H9N4O2Cl) was identified and elucidated using liquid chromatography-time of flight mass spectrometry (LC-TOF/MS).

A novel liquid-liquid-solid microextraction strategy for bio-sample preparation by in situ self-assembly of zeolitic imidazolate framework 8 on hollow fiber membrane.

A novel liquid-liquid-solid membrane microextraction (LLSMME) method which integrates hollow fiber liquid phase microextraction (HF-LPME) and solid phase microextraction (SPME) was developed for bio-sample preparation. The homogeneous zeolitic imidazolate framework 8 mixed matrix membrane (ZIF-8-MMM) was prepared by in situ self-assembly of ZIF-8 on the inner surface of hollow fiber membrane and employed as a flexible LLSMME device. Incorporating the advantages of both HF-LPME and SPME, the as-fabricated ZIF-8-MMM exhibited excellent performance on the extraction and preconcentration of small molecule drugs of different polarity from complex biological matrices. As a case study, ZIF-8-MMM-based LLSMME coupled with UPLC-MS/MS were developed and validated for determination of ibuprofen, simvastatin and ranitidine at trace levels in rat plasma. The method showed good linearity (r2 > 0.99) and repeatability (RSD < 15%), low limits of detection (2-3 ng mL-1) and high relative recoveries (97.42-103.8%). The enrichment factors were between 87.3 and 112.6. Our study provided a promising strategy for developing more efficient, cost-effective and environmentally friendly technique for bio-sample pretreatment.

Cetyl-alcohol-reinforced hollow fiber solid/liquid-phase microextraction and HPLC-DAD analysis of ezetimibe and simvastatin in human plasma and urine.

A new cetyl-alcohol-reinforced hollow fiber solid/liquid-phase microextraction (CA-HF-SLPME) followed by high-performance liquid chromatography-diode array detection (HPLC-DAD) method was developed for simultaneous determination of ezetimibe and simvastatin in human plasma and urine samples. To prepare the CA-HF-SLPME device, the cetyl-alcohol was immobilized into the pores of a 2.5 cm hollow fiber micro-tube and the lumen of the micro-tube was filled with 1-octanol with the two ends sealed. Afterwards, the prepared device was introduced into 10 mL of the sample solution containing the analytes with agitation. Under optimized conditions, calibration curves plotted in spiked plasma and urine samples were linear in the ranges of 0.363-25/0.49-25 µg L-1 for ezetimibe/simvastatin and 0.193-25/0.312-25 µg L-1 for ezetimibe/simvastatin in plasma and urine samples, respectively. The limit of detection was 0.109/0.174 µg L-1 for ezetimibe/simvastatin in plasma and 0.058/0.093 µg L-1 for ezetimibe/simvastatin in urine. As a potential application, the proposed method was applied to determine the concentration of selected analytes in patient plasma and urine samples after medication and satisfactory results were achieved. In comparison with reference methods, the CA-HF-SLPME-HPLC-DAD method demonstrates considerable potential in the biopharmaceutical analysis of selected drugs.

A dispersive liquid-liquid microextraction method based on the solidification of a floating organic drop combined with HPLC for the determination of lovastatin and simvastatin in rat urine.

A dispersive liquid-liquid microextraction method based on solidification of floating organic drop combined with HPLC was developed for the determination of lovastatin and simvastatin in rat urine for the first time. 1-Dodecanol and methanol were used as the extraction and disperser solvents, respectively. Several important parameters influencing the micro-extraction efficiency were studied and systematically optimized, including the type and volume of extraction solvent and disperser solvent, extraction time, pH and salt concentration. The analytes were separated on a Kromasil C18 column at 30°C with a mobile phase of methanol and 0.2% acetic acid in water (83:17, v/v) and detected at 238 nm. Under the optimal conditions, the maximum number of enrichment factors for both analytes was 27. The linear ranges were 20.08-1004 and 20.00-1000 µg/L with the correlation coefficients ranging from 0.9990 to 0.9994 for lovastatin and simvastatin, respectively. The volume of organic solvent consumed in extraction was <0.3 mL, and the extraction time was 10 min. The newly developed environment-friendly sample pretreatment method will be a good alternative to conventional techniques, such as solid-phase extraction, liquid-liquid extraction and protein precipitation, for the HPLC determination of lovastatin and simvastatin in biological samples.

Evaluation of a method using high performance liquid chromatography with ultraviolet detection for the determination of statins in macromycetes of the genus Pleurotus cultivated by fermentation processes.

The applicability of high-performance liquid chromatography with ultraviolet light (HPLC-UV) for the determination of the presence of statins in macromycetes of the genus Pleurotus was analyzed. The fungi were obtained by liquid-state fermentation (LSF) using unconventional sources of carbon as substrates and solid-state fermentation (SSF) employing agro industrial wastes. Five statins were used as standards: lovastatin and simvastatin in the lactone form (LOVL and SIML), their corresponding hydro-acidic forms (LOVH and SIMH) and pravastatin (PRA). The following measures were evaluated: the linearity, accuracy and precision, detection limit (DL) and quantification limit (QL). The results demonstrated HPLC-UV to be an effective tool for detecting the presence of statins in extracts of LSF and SSF products. Likewise, it was hypothesized that the strains that were used for the study do not produce statins. This finding highlights the importance of continuing to evaluate other strains of the same genus by using techniques such as HPLC to first separate sufficient quantities of the compounds that were detected using the standard technique but that did not match the retention time (tR) of any of the standards used.

High-throughput salting-out assisted liquid/liquid extraction with acetonitrile for the simultaneous determination of simvastatin and simvastatin acid in human plasma with liquid chromatography.

Simvastatin (SS) is an effective cholesterol-lowering medicine, and is hydrolyzed to simvastatin acid (SSA) after oral administration. Due to SS and SSA inter-conversion and its pH and temperature dependence, SS and SSA quantitation is analytically challenging. Here we report a high-throughput salting-out assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry compatible salts for simultaneous LC-MS/MS analysis of SS and SSA. The sample preparation of a 96-well plate using SALLE was completed within 20 min, and the SALLE extract was diluted and injected into an LC-MS/MS system with a cycle time of 2.0 min/sample. The seamless interface of SALLE and LC-MS eliminated drying down step and thus potential sample exposure to room or higher temperature. The stability of SS and SSA in various concentration ratios in plasma was evaluated at room and low (4 degrees C) temperature and the low temperature (4 degrees C) was found necessary to maintain sample integrity. The short sample preparation time along with controlled temperature (2-4 degrees C) and acidity (pH 4.5) throughout sample preparation minimized the conversion of SS-->SSA to < or = 0.10% and the conversion of SSA-->SS to 0.00% The method was validated with a lower limit of quantitation (LLOQ) of 0.094 ng mL(-1) for both SS and SSA and a sample volume of 100 microL. The method was used for a bioequivalence study with 4048 samples. Incurred sample reproducibility (ISR) analysis of 362 samples from the study exceeded ISR requirement with 99% re-analysis results within 100+/-20% of the original analysis results.

Determination of 17alpha-ethynylestradiol, carbamazepine, diazepam, simvastatin, and oxybenzone in fish livers.

A method using liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed for the determination of 17alpha-ethynylestradiol in fish liver; a second method using LC/MS was developed for the determination of carbamazepine, diazepam, simvastatin, and oxybenzone in fish liver. The fish liver samples were extracted and cleaned up by using liquid-liquid extraction and solid-phase extraction before the extracts were analyzed by LC/MS or LC/MS/MS with electrospray negative and positive ionization. Recoveries of the 5 target compounds from spiked catfish liver ranged from 72 +/- 2 to 100 +/- 3%. Limits of quantification for the 5 compounds were between 4.2 and 12.3 ng/g (wet weight). Ten turbot (Pleuronichthys verticalis) liver samples were analyzed; levels of 17alpha-ethynylestradiol, carbamazepine, simvastatin, and oxybenzone were below the detection limits. Diazepam was detected in all 10 fish liver samples at concentrations ranging from 23 to 110 ng/g (wet weight).

Influence of structural and interfacial properties of microemulsion eluent on chromatographic separation of simvastatin and its impurities.

In order to calculate the structural and compositional characteristics of microemulsions, used as eluents in the investigation of HPLC separation of simvastatin and its six impurities, predictive molecular thermodynamic approach is developed. For calculating fundamental interfacial properties of microemulsions, from pure component properties, the lattice fluid self-consistent field theory (SCF), in conjunction with new classical thermodynamic expressions, was applied. Calculation of predicted radii (PR), area per surfactant (ApS) and film thickness (FT), as well as is interfacial tension and bending moment enabled better understanding of separation of such a complex mixture. The microemulsion, which contained 1% (w/w) of diisopropyl ether, 2% (w/w) of sodium dodecyl sulphate (SDS), 6.6% (w/w) of co-surfactant such as n-butanol and 90.4% (w/w) of aqueous 25 mM disodium phosphate pH 7.0 enabled appropriate chromatographic separation between investigated compounds. It has been proved that this microemulsion had the smallest droplet radii and film thickness, which enabled optimal separation. Also the interfacial tension is the smallest, so the free energy change associated with dispersing the drops favoured a large number of small droplets. Hydrophobic interactions between solutes and stationary phase, as well as the microstructural characteristics of microemulsion eluents had a significant influence on chromatographic behavior of simvastatin and its six impurities.

Application of a novel ultra-low elution volume 96-well solid-phase extraction method to the LC/MS/MS determination of simvastatin and simvastatin acid in human plasma.

A novel extraction method has been utilized in the LC/MS/MS determination of simvastatin and simvastatin acid in human plasma. In this method, 300 microl of plasma sample was loaded onto a Waters Oasis 96-well HLB microElution plate, the stationary phase was washed using 2 x 400 microl of 5% methanol in water, and the analytes were eluted using 35 microl of 95/5 acetonitrile/H(2)O twice. The sample extracts were diluted with 40 microl of methyl ammonium acetate (1mM, pH 4.5). Chromatography was performed on a Phenomenex Synergi Max-RP column (2.0 mm x 50 mm, 4 microm). A PE Sciex API 3000 tandem mass spectrometer interfaced with a turbo ionspray source was used for mass detection. Compared to solid-phase extraction, liquid-liquid extraction and solid-supported liquid-liquid extraction methods that were developed and previously used in our laboratory, this method reduced the labor cost and was less time consuming in sample preparation, due to the fact that post-extraction solvent evaporation and reconstitution steps were avoided using this microElution solid-phase extraction plate. The method has been proved to be fast, reliable and reproducible.

Retention modelling in liquid chromatographic separation of simvastatin and six impurities using a microemulsion as eluent.

A novel and unique approach was used for retention modelling in the separation of simvastatin and six impurities by liquid chromatographic using a microemulsion as mobile phase. A microemulsion is a modification of a micellar system where a lipophilic organic solvent is dissolved in the micelles; for that reason, microemulsions are usually treated as solvent-modified micellar solutions. When microemulsions are used as eluents in HPLC separations, solutes partition between the charged oil droplets and the aqueous buffer phase. The complexity of the composition of the microemulsion permits extensive manipulations to be made during method development in order to achieve acceptable resolution of such a complex mixture of substances. In order to avoid a laborious "trial and error" procedure, a 2(3) full factorial design was applied for choosing an optimal microemulsion composition to obtain good separation in a reasonable run time. Organic solvent, sodium dodecyl sulphate, and n-butanol content were varied within defined experimental domain. Optimal conditions for the separation of simvastatin and its six impurities were obtained using an X Terra 50 x 4.6 mm, 3.5 microm particle size column at 30 degrees C. The mobile phase consisted of 0.9% w/w of diisopropyl ether, 2.2% w/w of sodium dodecylsulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol, and 89.9% w/w of aqueous 25 mM disodium phosphate pH 7.0.

Chromatographic purification of some 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors.

The purification of pravastatin, simvastatin and lovastatin in the sodium salt or lactone form and of mevastatin in the lactone form by reversed-phase displacement chromatography is presented. The mobile phases consisted of water or mixtures of water-methanol and water-acetonitrile. Six different displacers were successfully used. Up to 0.14 g of raw sample per gram of stationary phase was loaded on a column packed with silica-based octadecyl phase. Crude substances from 85 to 88% chromatographic purity were purified and at least 99.5% purity was achieved.