A Note on First-Fit Coloring of Interval Graphs

We apply the Column Construction Method (Varadarajan et al., Proceedings of the Fifteenth Annual ACM-SIAM Symposium On Discrete Algorithms, pp. 562–571, 2004) to a minimal clique cover of an interval graph to obtain a new proof that First-Fit is 8-competitive for online coloring interval graphs. This proof also yields a new discovery that in each minimal clique cover of an interval graph G, there is a clique of size .     

Column temperature programming in enantioseparation of dihydropyrimidinone compounds using derivatized cellulose and amylose chiral stationary phases

We report the application of column temperature programs as a tool to examine unusual temperature-induced behaviors of polysaccharide chiral stationary phases (CSPs). Using dihydropyrimidinone (DHP) compounds as probes we observed the heating (10-50 degrees C) and cooling (50-10 degrees C) van't Hoff plots of retention factors and/or selectivities of DHP compounds were not superimposable on AD, IA, and AS-H columns solvated with ethanol (EtOH)/n-hexane (n-Hex) mobile phases. The plots were not superimposable on AD, IB, and AS-H columns solvated with 2-propanol (2-PrOH)/n-Hex mobile phases. The thermally induced path-dependant behaviors were caused by slow equilibration as evidenced by the disappearance of the hysteresis in the second heating to cooling cycle and in a cooling to heating cycle. From the step-temperature program (10-50-10 degrees C), only EtOH solvated AD and AS-H phases showed the change of retention factors and/or selectivities with time while only 2-PrOH solvated AS-H phase showed similar behaviors.     

Comparison of performance of Chirobiotic T, T2 and TAG columns in the separation of beta2- and beta3-homoamino acids

The enantiomers of eight unusual beta(2)- and beta(3)-homoamino acids were separated on chiral stationary phases containing the macrocyclic glycopeptide antibiotic teicoplanin (Chirobiotic T or T2) or teicoplanin aglycone (Chirobiotic TAG) as chiral selectors. The effects of the organic modifier, the mobile phase composition, and temperature on the separations were investigated. Linear van't Hoff plots were observed in the studied temperature range, 280-318 K, and the changes in enthalpy, Delta(DeltaH(o)), entropy, Delta(DeltaS(o)), and free energy, Delta(DeltaG(o)) were calculated. The values of the thermodynamic parameters depended on the nature of the selectors, the structures of the analytes, and especially the positions of the substituents on the analytes. A comparison of the separation performances of the macrocyclic glycopeptide stationary phases revealed that the Chirobiotic TAG column exhibited much better selectivity for beta(2)-homoamino acids, while the separation of beta(3)-homoamino acid enantiomers was better on Chirobiotic T or T2. The elution sequence was determined in some cases and was observed to be R < S.     

Reversed phase-HPLC for rapid determination of polyphenols in flowers of rose species

A rapid, simple, sensitive, robust, and improved HPLC method was developed and validated for determination of 10 polyphenols, namely gallic acid, catechin, epicatechin, rutin, m-coumaric acid, quercitrin, myricetin, quercetin, apigenin, and kaempferol in fresh flowers of Rosa bourboniana and R. brunonii and in both fresh flowers and marc (left after industrial distillation of rose oil) of R. damascena. Six polyphenols, gallic acid, rutin, quercitrin, myricetin, quercetin, and kaempferol, were detected and quantified in all extracts. The chromatographic separation of 10 polyphenols was achieved in less than 16 min by RP-HPLC (Phenomenex, Luna C18 (2) column, 5 microm, 250 mm x 4.6 mm) using linear gradient elution of water and acetonitrile (0.02% trifluroacetic acid) with a flow rate of 1 mL/min at lambda 280 nm. Standard calibration curves were linear in the range of 0.39-500 microg/mL. Good results were achieved with respect to repeatability (RSD <3%) and recovery (98.6-100.8%). The method was validated for linearity, accuracy, repeatability, LOD, and LOQ.     

Stress Degradation Studies on Tadalafil and Development of a Validated Stability-Indicating LC Assay for Bulk Drug and Pharmaceutical Dosage Form

A stability-indicating HPLC assay method was developed for the quantitative determination of tadalafil in bulk samples and in pharmaceutical dosage forms in the presence of the degradation products. It involved a 250 mm × 4.6 mm, 5 μm C-18 column. The gradient LC method employs solution A and B as mobile phase. Solution A contains a mixture of buffer (phosphate buffer and tetra-n-butyl ammonium hydrogen sulfate) pH 2.5: acetonitrile (80:20, v/v) and solution B contains a mixture of water: acetonitrile (20:80, v/v). The flow rate was 1.0 mL min⁻¹ and the detection wavelength was 220 nm. The retention time of tadalafil is about 17 min. Tadalafil was subjected to different ICH prescribed stress conditions. Degradation was found to occur in hydrolytic and to some extent in oxidative stress conditions, while the drug was stable to photolytic and thermal stress. The drug was particularly labile under alkaline hydrolytic conditions. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. The assay of stress samples was calculated against a qualified reference standard and the mass balance was close to 99.5%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and ruggedness.     

Determination and Pharmacokinetic Study of 10-O-Dimethylaminoethylginkgolide B in Rat Plasma by LC–MS

To evaluate the pharmacokinetics of a novel analogue of ginkgolide B, 10-O-dimethylaminoethylginkgolide B (XQ-1) in rat plasma in pre-clinical studies, a sensitive and specific liquid chromatographic method with electrospray ionization mass spectrometry detection (LC–ESI–MS) was developed and validated. After a simple extraction with ethyl acetate, XQ-1 was analyzed on a Shim-pack C18 column with a mobile phase of a mixture of 1 μmol L⁻¹ ammonium acetate containing 0.02% formic acid and methanol (55:45, v/v) at a flowrate of 0.3 mL min⁻¹. Detection was performed in selected ion monitoring (SIM) mode using target ions at [M + H]⁺ m/z 496.05 for XQ-1 and m/z 432.10 for the internal standard (lafutidine). Linearity was established for the concentration range from 2 to 1,000 ng mL⁻¹ . The extraction recoveries ranged from 86.0 to 89.9% in plasma at concentrations of 5, 50, and 500 ng mL⁻¹. The lower limit of quantification was 2 ng mL⁻¹ with 100 μL plasma. The validated method was successfully applied to a pharmacokinetic study after intragastic administration of XQ-1 mesylate in rats at a dose of 20 mg kg⁻¹.     

Simultaneous LC Determination of Spinosin, Danshensu, and Protocatechuic Aldehyde in Traditional Chinese Zaoren-An-Shen Capsules

A simple, sensitive, and accurate liquid-chromatographic method with UV detection has been developed for simultaneous determination of spinosin, danshensu, and protocatechuic aldehyde in traditional Chinese Zaoren-an-shen capsules. Chromatographic separation was achieved on a C₁₈ column. Vanillin was used as internal standard and the UV detection wavelength was 280 nm. Excellent linear behavior was observed over the concentration ranges investigated, with R values higher than 0.9997 for all the analytes. The limits of quantification for spinosin, danshensu, and protocatechuic aldehyde were 1.31, 0.74, and 0.27 μg mL⁻¹, respectively. This validated method can be used for routine quality control of Zaoren-an-shen capsules.     

A Rapid Analytical Method for Free Choline by LC and Its Application for Bacterial Culture Medium Samples

A rapid, and inexpensive analytical method for free choline is described here. Choline was derivatized with benzoyl chloride and analyzed by HPLC with UV detection. Choline samples in the micro-molar range were determined with good repeatability. The precision (RSD) was not greater than 10%. The quantification limit was 10 μM (3σ), and the linear calibration range was between 10 and 1,500 μM. This method was applied to the measurement of free choline in a culture medium of bacteria and was shown to be suitable for aqueous samples with a wide concentration range and for routine analyses.     

Determination of Abamectin Residues in Avocados by Microwave-Assisted Extraction and HPLC with Fluorescence Detection

In this article a new analytical method for the confirmation and quantification of abamectin residues in avocados is described. The method allows a fast analysis of abamectin homologues using microwave assisted extraction (MAE), solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with fluorescence (FL) detection using trifluoroacetic anhydride (TFAA) and N-methylimidazole (NMIM) as derivatizing agents. The mobile phase consisted of water, methanol and acetonitrile (5:47.5:47.5 v/v/v) and was pumped at a rate of 1.1 mL min⁻¹ (isocratic elution). Homogenized avocado samples were extracted once with 20 mL acetonitrile:water 4:1 (v/v) in a microwave oven for 26 min at 700 W with a maximum temperature of 80 °C. MAE operational parameters were optimized by means of an experimental design. Extracts were cleaned using C₁₈ SPE cartridges. Average recoveries of the method at four spiked levels (0.005, 0.01, 0.10 and 1.0 mg kg⁻¹) were found to be in the range 90–100% with good precision (RSD < 12%). The limits of detection (LODs) and quantification (LOQs) of the whole method were 0.001 and 0.003 mg kg⁻¹, respectively, which are lower than the maximum residue limit (MRL) established by the Spanish and the European legislation in avocados (0.01 mg kg⁻¹). Several avocado samples previously treated with the pesticide were also analyzed.     

High-Performance Liquid Chromatographic Determination of Cefepime and Cefazolin in Human Plasma and Dialysate

A simple high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of cefepime and cefazolin in human plasma and dialysate. For component separation, the method utilized a C₁₈ column with an aqueous mobile phase of dibasic potassium hydrogen phosphate (pH 7.0) and methanol gradient at a flow rate of 1 mL min⁻¹. The method demonstrated linearity from 2.0 to 100.0 μg mL⁻¹ (r > 0.999) with detection limit of 1 μg mL⁻¹ for both cefepime and cefazolin. The method was utilized for evaluation of plasma and dialysate samples in a clinical study evaluating the dialyzer clearance of cefepime and cefazolin using high-flux hemodialysis with varying blood flow rates in chronic kidney failure patients undergoing hemodialysis and peritoneal dialysis treatment.