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Column Pressure (column + pressure)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Speciation of volatile antimony compounds in culture headspace gases of Cryptococcus humicolus using solid phase microextraction and gas chromatography,mass spectrometry

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2002
L. M. Smith
Abstract Direct analysis of the volatile antimony compounds stibine (SbH3), monomethylantimony, dimethylantimony (Me2Sb) and trimethylantimony (Me3Sb) using solid phase microextraction (SPME) with polydimethylsiloxane fibres and gas chromatography,mass spectrometry (GC,MS) is described. The best analyte to background signal ratio was achieved using a 20,min extraction time. Antimony species were separated using a 3% phenylmethylsilicone capillary column operated at a column pressure of 70,kPa, a flow rate of 1.4,ml min,1 and temperature ramping from 30 to 36,°C at 0.1,°C min,1. Cryogenic focusing of desorbed species was required to achieve resolution of antimony species. The optimized SPME,GC,MS method was applied to the analysis of headspace gases from cultures of Cryptococcus humicolus incubated with inorganic antimony(III) and (V) substrates. The headspace gases from biphasic (aerobic,anaerobic) biomass-concentrated culture incubations revealed the presence of SbH3, Me2Sb and Me3Sb. Stibine was the major antimony species detected in cultures amended with inorganic antimony(V). Me3Sb was the sole volatile antimony species detected when cultures were amended with antimony(III). Copyright © 2002 John Wiley & Sons, Ltd. [source]

True and Apparent Temperature Dependence of Protein Adsorption Equilibrium in Reversed-Phase HPLC

BIOTECHNOLOGY PROGRESS, Issue 6 2002
Szabelski
The adsorption behavior of bovine insulin on a C8 -bonded silica stationary phase was investigated at different column pressures and temperatures in isocratic reversed-phase HPLC. Changes in the molar volume of insulin (, Vm) upon adsorption were derived from the pressure dependence of the isothermal retention factor ( k,). The values of , Vm were found to be practically independent of the temperature between 25 and 50 °C at ,96 mL/mol and to increase with increasing temperature, up to ,108 mL/mol reached at 50 °C. This trend was confirmed by two separate series of measurements of the thermal dependence of ln( k,). In the first series the average column pressure was kept constant. The second series involved measurements of ln( k,) under constant mobile-phase flow rate, the average column pressure varying with the temperature. In both cases, a parabolic shape relationship was observed between ln( k,) and the temperature, but the values obtained for ln k, were higher in the first than in the second case. The relative difference in ln( k,), caused by the change in pressure drop induced by the temperature, is equivalent to a systematic error in the estimate of the Gibbs free energy of 12%. Thus, a substantial error is made in the estimates of the enthalpy and entropy of adsorption when neglecting the pressure effects associated with the change in the molar volume of insulin. This work proves that the average column pressure must be kept constant during thermodynamic measurements of protein adsorption constants, especially in RPLC and HIC. Our results show also that there is a critical temperature, Tc , 53 °C, at which ln( k,) is maximum and the insulin adsorption process changes from an exothermic to an endothermic one. This temperature determines also the transition point in the molecular mechanism of insulin adsorption that involves successive unfolding of the protein chain. [source]

Dynamic control of split flow in packed column supercritical fluid chromatography using dual resistively heated restrictors

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2009
Jian Jun Li
Abstract Remote control of the vent/detector split flow ratio in packed column supercritical fluid chromatography (pSFC) with flame ionization detector (FID) is demonstrated using a dual heated restrictor method. Restrictors stemming from a Tee at the separation column outlet were, respectively, fixed into an FID and a vent port, and their individual temperatures were controlled using resistively heated wires. Subsequently, both system pressure and split flow could be manipulated. For example, for applied restrictor temperatures examined up to 600°C, corresponding vent/FID split flow ratios between 2 and 7 were observed depending on the port heated. As well, column pressures around 16,23 MPa were also achievable over the same range. Conversely, isobaric altering of the split flow ratio was possible when opposing positive and negative temperature gradients were applied at the two restrictors. Under these conditions, the system pressure varied less than 1% RSD over a 10 min period. As an application, the method was used to establish stable detector operation in the analysis of n -alkanes under pSFC-FID conditions that initiated flame instability. Results indicate that this technique could be a relatively simple and inexpensive means of controlling system pressure and detector split flow ratios in pSFC-FID. [source]