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P C Hauser

Publications and source records attributed to P C Hauser.

8 recordsLinked to original sources
PubMed2001

Rapid chiral on-chip separation with simplified amperometric detection.

The enantiomers of adrenaline, noradrenaline, ephedrine and pseudoephedrine were separated by capillary electrophoresis on a micromachined device. Detection was carried out with a new two-electrode amperometric detector, eliminating the need for individual counter and reference electrodes. Separation of the isomers was achieved by employing carboxymethyl-beta-cyclodextrin as chiral selector in the buffer, partly with the additional inclusion of the crown ether 18-crown-6. Plate numbers of up to 20,000, chiral resolutions of 2.5 and detection limits of the order of 10(-7) M were achieved. All separations were completed in less then 3 min.

Electrochemistry↗
PubMed2001

Recent developments in detection methods for microfabricated analytical devices.

Sensitive detection in microfluidic analytical devices is a challenge because of the extremely small detection volumes available. Considerable efforts have been made lately to further address this aspect and to investigate techniques other than fluorescence. Among the newly introduced techniques are the optical methods of chemiluminescence, refraction and thermooptics, as well as the electrochemical methods of amperometry, conductimetry and potentiometry. Developments are also in progress to create miniaturized plasma-emission spectrometers and sensitive detectors for gas-chromatographic separations.

Journal Article↗
PubMed2001

A two-electrode configuration for simplified amperometric detection in a microfabricated electrophoretic separation device.

The simplified amperometric detection scheme demonstrated is based on the amperometric working and electrophoretic ground electrodes only. The latter serves as counter and pseudo-reference as well. It is shown via the successful determination of neurotransmitters, ascorbic acid and phenols on gold or platinum working electrodes that this approach is feasible for detection on a channel based electrophoretic separation device. Also presented is the detection of carbohydrates and amino acids with copper electrodes. The results were found to be similar to those obtained with conventional capillary systems with amperometric detection, albeit at much reduced analysis times.

Journal Article↗
PubMed2000

Amperometric sensing of ethylene oxide in the gas phase.

The sensing device used is based on a porous Pt electrode, which is supported on an ion-exchange membrane and directly exposed to the gas phase. Under acid conditions, ethylene oxide was found to be oxidized on the platinum oxide surface at +550 mV vs MSE, thus enabling its monitoring via the measurement of the associated current. A detection limit of 15 ppb was obtained, based on a signal-to-noise ratio of three, and a linear dynamic range was found up to 100 ppm. The effects of mass transport, humidity, and oxygen on the cell response, as well as the cross sensitivity to other organic vapors and inorganic gases are discussed.

Carcinogens↗
PubMed2000

Evaluation of the potentiometric detection of acetylcholine and other neurotransmitters in capillary electrophoresis.

It is demonstrated that acetylcholine may be determined potentiometrically in capillary electrophoresis down to 6 x 10(-7) M with a miniature coated-wire ion selective electrode. The more established amperometric method is not possible for this compound. Similarly, 4-aminobutyric acid (GABA) is not accessible amperometrically; although potentiometric detection was possible, the sensitivity is not good. Other neurotransmitters may be determined by either method, but in these cases amperometric determination is generally favorable. For serotonin the potentiometric detection limit was 4 x 10(-5) M, while for the amperometric method a detection limit of 10(-7) M was found.

Acetylcholine↗
PubMed1996

Flow-injection determination of lead by hydride generation and conductometric detection.

Plumbane produced from the lead analyte in a flow-injection manifold by reaction with sodium borohydride is passed through a porous poly(tetrafluoroethylene) membrane in a gas-diffusion cell. The hydride reacts with bromine in the acceptor stream resulting in ionization which is detected by conductivity measurement. Direct mixing of the carrier with a reagent stream yields a limit of detection of approximately 1 mg/L. An improved detection limit of about 200 microg/L can be achieved by the incorporation of an auxiliary stream containing persulphate as oxidizing agent. The application of the method to the determination of lead in road dust and soil samples is demonstrated.

Journal Article↗
PubMedDate not supplied

Surface charge reversal for inorganic anion determination in capillary electrophoresis with an ion-selective microelectrode as detector.

The effect of surface charge reversal of a fused-silica capillary was investigated for the conditions used in the determination of inorganic anions with potentiometric detection. A 25-micron-i.d. capillary was coated with permanently bonded polyacrylamide incorporating a quaternary amine, and a sodium sulfate solution was employed as electrolyte. As expected, it was found that the analysis time is reduced in comparison with an uncoated column of the same length. However, the effect is much less pronounced than that for the common chromate buffer. Since the reduction in analysis time also causes a loss of resolution, the effect is very close to that obtained simply by using a shorter capillary; therefore, coating was not found to be of benefit here. This is in contrast to results reported for the conditions usually employed for the indirect photometric detection of anions.

Anions↗