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T M Allen

Publications and source records attributed to T M Allen.

132 records · Page 8Linked to original sources
PubMedDate not supplied

Membrane introduction mass spectrometry: trends and applications.

Recent advances in membrane introduction mass spectrometry (MIMS) are reviewed. On-line monitoring is treated by focusing on critical variables, including the nature and dimensions of the membrane, and the analyte vapor pressure, diffusivity, and solubility in the membrane barrier. Sample introduction by MIMS is applied in (i) on-line monitoring of chemical and biological reactors, (ii) analysis of volatile organic compounds in environmental matrices, including air, water and soil, and (iii) in more fundamental studies, such as measurements of thermochemical properties, reaction mechanisms, and kinetics. New semipermeable membranes are discussed, including those consisting of thin polymers, low vapor pressure liquids, and zeolites. These membranes have been used to monitor polar compounds, selectively differentiate compounds through affinity-binding, and provide isomer differentiation based on molecular size. Measurements at high spatial resolution, for example, using silicone-capped hypodermic needle inlets, are also covered, as is electrically driven sampling through microporous membranes. Other variations on the basic MIMS experiment include analyte preconcentration through cryotrapping (CT-MIMS) or trapping in the membrane (trap-and-release), as well as differential thermal release methods and reverse phase (i.e., organic solvent) MIMS. Method limitations center on semivolatile compounds and complex mixture analysis, and novel solutions are discussed. Semivolatile compounds have been monitored with thermally assisted desorption, ultrathin membranes and derivatization techniques. Taking advantage of the differences in time of membrane permeation, mixtures of structurally similar compounds have been differentiated by using sample modulation techniques and by temperature-programmed desorption from a membrane interface. Selective ionization techniques that increase instrument sensitivity towards polar compounds are also described, and comparisons are made with other direct sampling (nonchromatographic) methods that are useful in mixture analysis.

Bioreactors↗
PubMedDate not supplied

Use of targeted cationic liposomes in enhanced DNA delivery to cancer cells.

Cationic liposomes are considered to be safe vectors for gene transfer, but they are less efficient at delivering DNA to cells when compared with retroviral vectors. Cationic liposomes complexed with DNA were targeted to specific cells in vitro by means of monoclonal antibodies (mAbs) or ligands associated with the liposomes. Significant increases in expression of a beta-galactosidase reporter gene were observed in vitro in mAb-targeted liposomes, compared with non-targeted liposomes, in both an adherent tumor cell line (human adenocarcinoma) and a suspension cell line (human T-lymphoma). Also, use of asialofetuin as a targeting ligand significantly increased expression of the reporter gene in human hepatoma cells. Our results suggest that site-specific targeting of cationic liposomes is a good strategy for increasing both the selectivity and the efficiency of DNA delivery to cells and with further development may lead to targeted DNA delivery in vivo.

Adenocarcinoma↗