Home About us Contact
|
Home About us Contact | ||
|
|
||
Switching Valve (switching + valve)
Selected AbstractsSeparation of benzene and deuterated benzenes by reversed-phase and recycle liquid chromatography using monolithic capillary columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2004Lee Wah Lim Abstract An alternate pumping-recycle system utilizing a commercially available low dead-volume switching valve was developed for microcolumn LC. The recycle system had two separation columns, and the dead volume of the recycling lines was kept to a minimum by avoiding passage of the sample through the pump chamber, sample injector, and the normal path length of a conventional UV detector. The drawback of the high total back pressure caused by the second column that is placed after the detector was overcome by on-column detection, and this eliminated the need for a high pressure flow cell. The system was used for the separation of an authentic mixture of benzene, benzene-1,3,5-d3, and benzene-d6. Baseline separation was accomplished after six cycles and the calculated theoretical plate number for benzene was 230,000. It was observed that the theoretical plate number (N) increased linearly with increasing number of cycles, and the N per unit time increased with increasing inlet pressure. The separation conditions were optimized and the separation of benzene and benzene-d6 was accomplished within 75 min at 2.5 MPa inlet pressure. [source] High-throughput quantification of selenium in individual serum proteins from a healthy human population using HPLC on-line with isotope dilution inductively coupled plasma-MSPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 19 2010Sophia Letsiou Abstract In this study, a method, based on dual column affinity chromatography hyphenated to isotope dilution inductively coupled plasma,quadrupole MS, was developed for selenium determination in selenoprotein P, glutathione peroxidase, and selenoalbumin in human serum samples from a group of healthy volunteers (n=399). Method improvement was achieved using methanol-enhanced isotope dilution which resulted in improved sensitivity and removal of isobaric interferences. Although no human serum reference materials are currently certified for their selenium species levels, method development was conducted using human serum reference material BCR 637 and 639 as their Se species content has been reported in the previous studies, and thus comparisons were possible. The mean selenium concentrations determined for the 399 healthy volunteer serum samples were 23±10,ng Se mL,1 for glutathione peroxidase, 49±15,ng Se mL,1 for selenoprotein P and 11±4,ng Se mL,1 for selenoalbumin. These values are found to be in close agreement with published values for a limited number of healthy volunteer samples, and to establish baseline Se levels in serum proteins for an apparently healthy group of individuals, thus allowing for subsequent comparisons with respective values determined for groups of individuals with selenium related health issues, as well as assist in the discovery of potential selenium biomarkers. Also, the relationship between Se serum protein levels and some anthropometric characteristics of the volunteer population were investigated. Additionally, further development of the analytical method used in this study was achieved by adding a size exclusion chromatography column after the two affinity columns via a switching valve. This allowed for the separation of small selenium-containing molecules from glutathione peroxidase and thus enhanced the overall confidence in its identification. [source] Direct determination of nucleosides in the urine of patients with breast cancer using column-switching liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 11 2006Sung-Hee Cho Abstract We developed an analytical method for a simple, sensitive and simultaneous determination of oxidized nucleosides in urine using column-switching liquid chromatography,electrospray/tandem mass spectrometry (LC-ESI/MS/MS). We connected two columns through a six-way switching valve and effectively separated nucleosides in the urine from the interference by column-switching liquid chromatography. We monitored separated nucleosides using positive ionization tandem mass spectrometry in selective reaction monitoring (SRM) mode. The calibration ranges of nucleosides were 0.2,100 nmol/mL. The linearity of the method was 0.994,0.999, and the limits-of-detection (LOD) at a signal-to-noise (S/N) ratio of 3 were 0.1,0.2 nmol/mL. The coefficients of variation were in the range 2.28,11.74% for within-day variation and 4.36,11.15% for day-to-day variation, respectively. To explore the relationship between breast cancer and the nucleosides level in human urine, we measured the concentrations of nucleosides in female patients with breast cancer (n = 30) and in normal female subjects (n = 30). The concentration of nucleosides was significantly increased in patients with breast cancer when compared with the normal controls (1-methyladenosine; p < 0.005, N2,N2 -dimethylguanosine; p < 0.01, 5-hydroxymethyl-2,-deoxyuridine; p < 0.001, 8-hydroxy-2-deoxyguanosine; p < 0.001). Therefore, the elevated levels of nucleosides could be used as an important biomarker for breast-cancer research. Copyright © 2006 John Wiley & Sons, Ltd. [source] Determination of bevantolol enantiomers in human plasma by coupled achiral,chiral high performance-liquid chromatographyCHIRALITY, Issue 7 2007Joung Weon Oh Abstract A coupled achiral,chiral high performance liquid chromatographic method was developed and fully validated for the determination of bevantolol enantiomers, (,)-(S)-bevantolol and (+)-(R)-bevantolol, in human plasma. Plasma samples were prepared by solid phase extraction with Sep-Pak Plus C18 cartridges followed by HPLC. Bevantolol enantiomers and (+)-(R)-Propranolol as internal standard (IS) were preseparated from interfering components in plasma on a Phenomenex silica column and bevantolol enantiomers and IS were resolved and determined on a Chiralcel OJ-H chiral stationary phase. The two columns were connected by a switching valve equipped with silica precolumn. The Precolumn was used to concentrate bevantolol in the eluent from the achiral column before back flushing onto chiral phase. A detailed validation of the method was performed accordingly to FDA guidelines. For each enantiomer the assay was linear between 20 and 1600 ng/ml. The quantification limits of both bevantolol enantiomers were 20 ng/ml. The intraday variation was between 1.07 and 12.64% in relation to the measured concentration and the interday variation was 0.91 and 11.79%. The method has been applied to the determination of (,)-(S)- and (+)-(R)-bevantolol in plasma from healthy volunteers dosed with racemic bevantolol hydrochloride. hydrochloride. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source] Assessment of the repeatability and reproducibility of hydrogen/deuterium exchange mass spectrometry measurements,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2008William Burkitt A system to perform automated hydrogen/deuterium exchange mass spectrometry measurements was constructed using an XYZ robotic autosampler that was capable of performing solvent manipulations and a 4.7 T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The system included features such as the first demonstration of a ,dual column' high-performance liquid chromatography (HPLC) setup, and a novel digestion strategy. The performance of the system, in terms of the repeatability and reproducibility of the measurement of protein hydrogen/deuterium exchange, was assessed over a 2-month period. The sensitivity of the measurement of hydrogen exchange towards several parameters was assessed, which allowed their impact on the reproducibility to be discussed. The parameters assessed were the temperature of the HPLC columns and switching valves, the temperature of the quench solutions, the pH of the mobile phase, the pH of the quenched solution, the acid used in the mobile phase and the analytical column used. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||