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Laser-activated voltammetry Aqueous iodine undergoes a series of reactions on platinum electtodes, which lead to the deposition of atomic iodine and eventually the formation of molecular iodine. Understanding the kinetics of this electrochemistry is complicated by the continual formation of fodine, which coats the electrode eo dissolves into solution and creates constantly changing electrode conditions. Richard G. Compton and colleagues at Oxford University (U.K.) got around this problem by using a 532-nm, 10-Hz Nd:YAG laser to keep the electrode surface clean of iodine without damaging it. What the authors call laseractivated voltammetry was then used to study the electrochemical oxidation of aqueous iodide at a platinum electrode under stationary and hydrodynamic channel flow conditions Atomic force microscopy confirmed that
the surfaces were being cleaned. Ultrasound was also investigated and shown to dissolve water-insoluble redox products off the electrode surface and into an organic phase. In this case, the ultrasound induced an emulsion between water and dichloromethane. With the surfaces kept clean, numerical modeling of the channel flow voltammetry under zxperimental setup for laser-activated voltammetry in stationary hydrodynamic condisolution. tions provided qualitative information on the mechanism and the reaction. The authors conclude that quantitative data on the kinetics. Modeling laser-activated voltammetry offers a way to of the concentration and flow rate depenstudy electrode processes that produce dence of the voltammetric wave shapes surface-active intermediates. (J. Phys. then helped determine the mechanism of Chem.. B 1999,103, 8319-27)
gens were used to prepare columns of different porosity and permeability. Covalent anchoring of the monolith to the tube prevented cleft formation between Frits are frequently blamed for bubble formation in capillary electrochromatog- the wall and the polymeric packing. raphy (CEC). A solution to the problem The conductivity ratios and parameis to use monolithic columns. Csaba ters of the simplified van Deemter equaHorvath and colleagues at Yale Univertion for the most promising columns sity investigated the in situ formed were evaluated for both micro-LC and monolithic stationary phases that have CEC. The efficiency was higher for CEC relatively high Darcy's law permeability. than for micro-LC. Thus, the requirement Although these monolithic columns for high packing uniformity for high effiwere especially designed for CEC, they ciency may be relaxed in CEC. can also be used in micro-LC. To demonstrate the approach, angiotensin-type peptides were separated The columns were prepared in siby CEC on columns withfixed«-octyl lanized fused-silica capillaries of 75 urn i.d. by in situ copolymerization of divichains and quaternary ammonium nylbenzene with either styrene or vinyl- groups at the surface. Plate heights of benzyl chloride in the presence of a 8 um were routinely obtained. Separasuitable porogen. Five different porotion is based on the interplay between electroosmotic flow, chromatographic retention, and electrophoretic migration of the positively charged peptides. Because the migration process is so complex, neither classical chromatographic electrophoretic theory can be used to interpret the results (J Chromatogr A 1999 855 Schematic illustration of a monolithic packing. (Adapted 273-90)' with permission. Copyright 1999 Elsevier Science.)
Monolithic capillary columns for CEC
788 A
Analytical Chemistry News & Features, December 1, 1999
Toward well-characterized adenovirus products Recombinant adenovirus preparations increasingly are being pursued as a gene therapy strategy, and it is anticipated that commercial production of these preparations wiil be needed soon. However, ,he adenovirus particle is complex, consisting of double-stranded DNA and at least 11 distinct structural proteins in multiple copies, and, to obtain the "well-characterized biological product" regulatory status, better analytical tools are needed. Elisabeth Lehmberg and co-workers at Berlex Laboratories and HP Laboratories describe a reversed-phase (RP) HPLC assay that supports a systematic analysis of the viral structural proteins for recombinant adenovirus type 5 preparations. During the chromatographic separation, the adenovirus dissociates into its DNA and protein structural components. Further separation and analysis of the individual structural proteins by N-terminal protein sequencing and MALDI time-of-flight MS provide afingerprintof the viral proteome. In addition to characterizing individual structural proteins, the RP-HPLC assay was used to measure the concentration of the virus particles through quantification of the structural proteins. The researchers compared the results of this new protein-based assay with those obtained from the current standard method—absorbance of the lysed
