Selectivity of the ISE was checked by comparison with chloride concentrations measured by coulometric
titration on a Model 925 chloride analyzer (Corning).
The latter method was modified by the use of (a) different solid-phase extraction columns, (b) a different chromatographic system (column material, mobile phase), and (c) a coulometric
detector with a different analytical cell, which allowed improved selective setting of oxidizing and reducing potentials.
James, entitled "Measurement of Plasma and Intracellular S-Adenosylmethionine and S-Adenosylhomocysteine Utilizing Coulometric
Electrochemical Detection: Alterations with Plasma Homocysteine and Pyridoxal 5'-Phosphate Concentrations" (Clin Chem 2000;46: 265-72), the values reported for plasma S-adenosylmethionine (SAM) were overestimated by a factor of 2.1 because of a calibration error.
This process uses coulometric
or volumetric titration to determine the trace amounts of water in a sample.
We therefore developed a simple and rapid HPLC procedure with coulometric
detection for simultaneous determination of Co[Q.sub.10] and Co[Q.sub.10][H.sub.2] in human plasma.
Featuring the latest in headspace KF technology, the 885 Compact Oven Sample Changer works with both coulometric
and volumetric titrators.
The electrochemical detector was an array detector consisting of four flow-through porous-carbon graphite coulometric
electrodes each set at incrementally higher potentials (against a palladium reference electrode).