Porous layer flow injection analysis with potentiometric chloride detection.

A porous paper stream with propulsion by a wider porous paper downstream 'pump' provided constant flow rate. Microliter size droplets touched to the surface served as sample injections. Dispersion was controlled by injection position. Potentiometric detection of chloride showed a range of 0.1 mM to 1M. Fifty or more samples per hour are possible.

Electroosmotic flow and injection: application to conductimetry.

Electroosmotic solution propulsion and sample injection using fused silica tube was investigated. Capillary tube dimensions were 50-100 microm i.d. by 4-7 cm length with a break in the capillary wall near one end through which electrolytic contact with the capillary solution was established. The applied field was typically 150 V/cm. The voltage at the break in the column was monitored by potentiometry with a bridge configuration. Concentrations ranging from 10 microM to 100 mM were accommodated. The basis for high sensitivity, e.g. 70 mV/microM, together with low cell volume, e.g. 20 nl, was established. Tap water conductivity measurements were made using CaCl(2) reference solution.

Chemical and electrochemical reduction rates of cyclic nitroxides (nitroxyls).

The reduction rates of five-membered pyrrolidine and pyrroline, and six-membered piperidine nitroxides (alternatively termed nitroxyls) containing various substituents were determined under homogeneous conditions using ascorbate, and electrochemically under heterogeneous conditions. The results were compared with data from the literature. It was shown that the increased rates of reduction of six-membered nitroxides, compared with those of the five-membered nitroxides, cannot be explained on the basis of differences in electrochemical potentials but, rather, can be ascribed to differences in the accessibility of the nitroxide group. A double bond in the five-membered nitroxyls increases the reduction rate. Within any ring system, the reduction rates of nitroxides using ascorbate can be correlated with the inductive substituent constants. The half-way potentials for electrochemical reduction within a series of nitroxides based on the same ring correlate with logarithms of the rates using ascorbate and with the inductive constants. The potentials for one-electron oxidation of the nitroxides were related to the inductive constants.

Amperometric nonenzymatic determination of serum glucose by means of a nickel-catalyst electrode.

We describe a new, nonenzymatic method for determining serum glucose. This method is based upon the direct electrochemical oxidation of glucose by means of stable nickel-catalyst that is electrodeposited onto a lead dioxide electrode surface. Linear calibration plots are obtained for glucose in the 0.1 to 4500 mg/liter range. Values for 23 sera with glucose concentrations ranging from 300 to 4300 mg/liter showed a linear correlation coefficient of 0.996 when compared with values reported by a hospital laboratory using the hexokinase method. Typically a 25-microliter sample is used, but samples as small as 5 microliter have been successfully analyzed. The sample is added to 25.00 ml of pH 13 electrolyte containing 1 mmol of NiSO4 per liter; the amount of increase in anodic current comproses the analytical signal. For 20 repetitive analyses of a serum specimen, the CV was less than 4%. Ascorbic acid is rapidly decomposed in the electrolyte used and thus does not interfere. Uric acid is inactive at the concentrations present in serum samples. The sensitivity and simplicity of the new method suggest it as an alternative to currently available procedures.

Direct titration of glycerol by constant current potentiometry.

A direct, constant-current potentiometric titration method allows quantitative determination of 0.50-5.00 mg samples of glycerol in aqueous solution with errors ranging from 0.2% for the large samples to 2.0% for the smaller samples. Perchloratocerate is used as the standard oxidant and pyrolytic graphite as the electrode material. A direct determination is made possible by elevated temperatures, high acidity, and a relatively large constant current. Sources of error and possible interferences are discussed.