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Reverse-phase Column (reverse-phase + column)
Selected AbstractsCyclic fatty acids in sunflower oils during frying of frozen foods with oil replenishment,EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2007Antonio Romero Abstract Frying of frozen foods has become popular because it considerably reduces cooking time. Polymers and cyclic fatty acid monomers (CFAM) formed during frying are potentially toxic and therefore their production should be minimized. Twenty discontinuous fryings of different frozen foods were carried out over ten consecutive days, in sunflower oil (SO) and in high-oleic acid sunflower oil (HOSO), by adding fresh oil after each frying to bring the volume of the fryer oil back to 3,L. CFAM methyl ester derivates were hydrogenated, isolated, concentrated and quantified by HPLC using a reverse-phase column, followed by gas chromatography. After 20,fryings, significantly higher contents of polar material, polymers and CFAM (all p,<0.001) were found in SO than in HOSO. Bicyclic compound formation was four times higher in SO (p,<0.001). The fat from the fried potatoes presented a polymer content very similar to that of their corresponding oils. The 100-g rations of the SO-fried potatoes from the 20th frying supply 49 or 15%, respectively, more polymers and CFAM and 1,mg more bicyclic fatty acids than the 100-g rations of HOSO-fried potatoes. Because digestion and absorption of polar material, polymers and CFAM occur, the data clearly show the advantageousness and advisability of frying with HOSO rather than SO. [source] Simultaneous quantification of a non-nucleoside reverse transcriptase inhibitor efavirenz, a nucleoside reverse transcriptase inhibitor emtricitabine and a nucleotide reverse transcriptase inhibitor tenofovir in plasma by liquid chromatography positive ion electrospray tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 4 2009Ramakrishna Nirogi Abstract A high-performance liquid chromatography/positive ion electrospray tandem mass spectrometry method for the simultaneous quantification of efavirenz, emtricitabine and tenofovir was developed and validated with 100 µL human plasma. Following solid-phase extraction, the analytes were separated using a gradient mobile phase on a reverse-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M + H]+ ions, m/z 316 to 168 for efavirenz, m/z 248,130 for emtricitabine and m/z 288,176 for tenofovir, m/z 482,258 for rosuvastatin (IS), m/z 260,116 for propranolol (IS). The method exhibited a 100-fold linear dynamic range for all the three analytes in human plasma (20,2000, 2,200 and 20,2000 ng/mL for efavirenz, emtricitabine and tenofovir respectively). The lower limit of quantification was 2 ng/mL for emtricitabine and 20 ng/mL for both efavirenz and tenofovir with a relative standard deviation of less than 11%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The total chromatographic run time of 4 min for each sample made it possible to analyze more than 250 human plasma samples per day. The method is precise and sensitive enough for its intended purpose. The method is also successfully applied to quantify efavirenz, emtricitabine and tenofovir concentrations in a rodent pharmacokinetic study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Rapid screening of polysaccharide-based plasma volume expanders dextran and hydroxyethyl starch in human urine by liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 7 2008Sven Guddat Abstract The increasing number of samples and target substances in doping control requires continuously improved screening methods, combining high-throughput analysis, simplified sample preparation, robustness and reliability. Hence, a rapid screening procedure based on liquid chromatography,electrospray ionization,tandem mass spectrometry with in-source collision-induced dissociation was developed. The detection of the polysaccharide-based plasma volume expanders dextran and hydroxyethyl starch (HES) in human urine was established without further sample preparation. The in-source fragmentation strategy of the approach represented a valuable tool in the analysis of the polysaccharide-based compounds, allowing the use of tandem mass spectrometry. After direct injection of urine specimens, analytes were chromatographically separated on a monolithic reverse-phase column and detected via multiple reaction monitoring of diagnostic ions at detection limits of 10 µg/mL for HES and 30 µg/mL for dextran. Validation was performed regarding the parameters specificity, linearity, precision (8,18%) and accuracy (77,105%) and the method was applied to the investigation of approximately 400 doping control samples and seven dextran and two hydroxyethyl starch post-administration samples. The approach demonstrated its capability as a rapid screening tool for the detection of dextran and hydroxyethyl starch and represents an alternative to existing screening procedures since time consuming hydrolysis or derivatization steps were omitted. Copyright © 2008 John Wiley & Sons, Ltd. [source] Sensitive liquid chromatography tandem mass spectrometry method for the quantification of sitagliptin, a DPP-4 inhibitor, in human plasma using liquid,liquid extractionBIOMEDICAL CHROMATOGRAPHY, Issue 2 2008Ramakrishna Nirogi Abstract A sensitive high-performance liquid chromatography,positive ion electrospray tandem mass spectrometry method was developed and validated for the quantification of sitagliptin, a DPP-4 inhibitor, in human plasma. Following liquid,liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M + H]+ ions, m/z 408,235 for sitagliptin and m/z 310,148 for the internal standard. The assay exhibited a linear dynamic range of 0.1,250 ng/mL for sitagliptin in human plasma. The lower limit of quantification was 0.1 ng/mL with a relative standard deviation of less than 6%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 300 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic studies. Copyright © 2007 John Wiley & Sons, Ltd. [source] A validated new method for nevirapine quantitation in human plasma via high-performance liquid chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 1 2006Courtney F. Silverthorn Abstract A fully validated and clinically relevant assay was developed for the assessment of nevirapine concentrations in neonate blood plasma samples. Solid-phase extraction with an acid,base wash series was used to prepare subject samples for analysis. Samples were separated by high performance liquid chromatography and detected at 280 nm on a C8 reverse-phase column in an isocratic mobile phase. The retention times of nevirapine and its internal standard were 5.0 and 6.9 min, respectively. The method was validated by assessment of accuracy and precision (statistical values <15%), specificity, and stability. The assay was linear in the range 25,10,000 ng[sol ]mL (r2 > 0.996) and the average recovery was 93% (n = 18). The lower limit of quantification (relative standard deviation <20%) was determined to be 25 ng[sol ]mL for 50 µL of plasma, allowing detection of as little as 1.25 ng of nevirapine in a sample. This value represents an increase in sensitivity of up to 30-fold over previously published methods. Copyright © 2005 John Wiley & Sons, Ltd. [source] Quantitative determination of saquinavir from Caco-2 cell monolayers by HPLC-UVBIOMEDICAL CHROMATOGRAPHY, Issue 1 2003Sibel Demirbas Ucpinar Abstract The validation and quantitative determination of the protease inhibitor, saquinavir, from confluent Caco-2 monolayers and from aqueous solution is reported. The high performance liquid chromatographic method consisted of an UltramexÔ 5 C8 reverse-phase column (250,×,4.6,mm i.d.) and a mobile phase of acetonitrile:water:triethylamine (55:44:1, v/v/v, pH 6.5). Samples were analyzed using an ultraviolet detector at 238,nm, and diltiazem hydrochloride (66,µg/mL) was used as an internal standard. A linear response over a broad concentration range (0.4,8.0,µg/mL, r2,=,0.997) was obtained. The limit of detection and quantitation was set at 0.14 and 0.4,µg/mL, respectively. Over a 4 day period, the intra-day and inter-day precision ranged from 1 to 7% with a mean of 4%, and from 1 to 2% with a mean of 1.5%, respectively. Bench,top and storage stability of saquinavir was found to be satisfactory. The permeability of saquinavir through Caco-2 monolayers was estimated using this assay. Copyright © 2002 John Wiley & Sons, Ltd. [source] Isolation, purification, crystallization and preliminary crystallographic studies of sagitoxin, an oligomeric cardiotoxin from the venom of Naja naja saggitiferaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2008Rafia Mir Sagitoxin, a novel cardiotoxin from the venom of Naja naja saggitifera, has been successfully isolated, purified to homogeneity and crystallized. The toxin was purified using successive separation steps on a CM-Sephadex C-50 column and a reverse-phase column. The 6.75,kDa toxin was sequenced by the Edman method using a PPSQ-21 protein sequencer. It was crystallized using the hanging-drop vapour-diffusion method. The hexagonal-shaped crystals diffracted to 3.0,Å resolution and belonged to space group P64, with unit-cell parameters a = b = 111.1, c = 137.3,Å, , = 120°. There are 36 molecules in the unit cell, which has an approximate solvent content of 80%. Structure determination revealed that the molecules of sagitoxin associate in a hexameric form and create a pore in the centre which has functional significance. [source] | ||||||||||