PubMed · 9267183
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
E W Johnson. The positive wave.. https://doi.org/10.1097/00002060-199707000-00001
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
A contact conductivity detection cell for capillary zone electrophoresis (CZE) with an electrolyte solution mediated contact of the separated constituents with the detection electrodes (ESMC cell) was developed in this work. This new approach to the conductivity sensing in CZE is intended to eliminate detection disturbances due to electrode reactions and adsorption of the separated constituents when these are coming into direct contact with the detection electrodes. An optimum detection performance of the cell was achieved when the carrier electrolyte solution mediated the electric contact of the detection electrodes with the separated constituents. Different compositions of the mediator and carrier electrolyte solutions led to large drifts of the detection signals. Isotachophoresis experiments performed in this context with the ESMC cell revealed that origins of these drifts are in transport processes (diffusion and electromigration) between the detection compartment and the detection electrodes in the cell. These processes affected, to some extent, other analytically relevant performance parameters of the ESMC cell of the present construction as well [e.g., concentration limits of detection (LODs), a contribution of the cell to the band broadening]. For example, the ESMC cell gave, under optimum operating conditions, 3-4 times higher concentration LODs for the test analytes than a current on-column conductivity cell employed under identical working conditions. On the other hand, these LOD values (25-150 nmol/l) were still 20-25 times lower than those estimated from reference experiments for a contactless conductivity detector. CZE experiments with iodide, carried out under working conditions leading to electrochemical reactions of this anion on the detection electrodes of current conductivity cells, did not occur in the ESMC cell. In addition, this cell, contrary to a reference contact conductivity cell, required no special care (e.g., cleaning of the surfaces of the detection electrodes by chemical or electrochemical means) to maintain its reliable long-term performance. Anionic CZE analyses of tap and mineral water samples monitored by the conductivity detector provided with the ESMC cell demonstrated a practical applicability and certain limitations of this detection approach in the analysis of ionic constituents present in high ionic strength sample matrices.
A flow injection analysis (FIA) system comprising a tartrate-(TAT) selective electrode has been developed for determination of tartaric acid in wines. Several electrodes constructed for this purpose had a PVC membrane with a complex of quaternary ammonium and TAT as anion exchanger, a phenol derivative as additive, and a more or less polar mediator solvent. Characterization of the electrodes showed behavior was best for membranes with o-nitrophenyl octyl ether as solvent. On injection of 500 microL into a phosphate buffer carrier (pH = 3.1; ionic strength 10(-2) mol/L) flowing at 3 mL/min, the slope was 58.06 +/- 0.6 with a lower limit of linear range of 5.0 x 10(-4) mol/L TAT and R2 = 0.9989. The interference of several species, e.g. chloride, bromide, iodide, nitrate, gallic acid, tannin, sucrose, glucose, fructose, acetate, and citrate, was evaluated in terms of potentiometric selectivity coefficients. The Hofmeister series was followed for inorganic species and the most interfering organic ion was citrate. When red and white wines were analyzed and the results compared with those from an independent method they were found to be accurate, with relative standard deviations below 5.0%.
A rotating electrode configuration is evaluated as a means to lower the detection limits of newly devised polyion-sensitive membrane electrodes (PSEs). Planar potentiometric polycation and polyanion PSEs are prepared by incorporating tridodecylmethylammonium chloride and calcium dinonylnaphthalenesulfonate, respectively, into plasticized PVC or polyurethane membranes and mounting disks of such films on an electrode body housed in a conventional rotating disk electrode apparatus. Rotation of the PSEs at 5000 rpm results in an enhancement in the detection limits toward heparin (polyanion) and protamine (polycation) of at least 1 order of magnitude (to 0.01 unit/mL for heparin; 0.02 microg/mL for protamine) over that observed when the EMF responses of the same electrodes are assessed using a stir-bar to achieve convective mass transport. A linear relationship between omega(-1/2), where omega is the rotating angular frequency, and C1/2, the polyion concentration corresponding to half the total maximum deltaEMF response toward the polyion species, is observed. It is further shown that the rotating polycation sensor can be used as an end-point detector to greatly enhance (relative to nonrotated indicator electrode) the analytical resolution and precision for measurement of low concentrations of heparin when such samples are titrated with protamine. The theoretical basis for lowering the detection limits by rotating PSEs is discussed based on the unique nonequilibrium response mechanism of such sensors.