Biomedical subjects

Peter C Hauser

Publications and source records attributed to Peter C Hauser.

33 records · Page 2Linked to original sources

PubMed2004

Capacitively coupled microplasma for on-column detection of chromatographically separated inorganic gases by optical emission spectrometry.

Two tubular electrodes placed on a capillary tubing are used to couple an electrical ac field of high voltage (20 kV) but low frequency (20 kHz) and about 8 W power inside for generation of the plasma. The emitted radiation is passed to a spectrometer via an optical fibre butted to the side of the capillary. The excitation temperature of the plasma determined from helium emission lines is about 4000 K. It was found possible to detect oxygen from its emission at 777 and 845 nm, hydrogen at 656 nm and sulfur containing species from emission at 923 nm. The carbon-containing species CH4, CO, and CO2 could be determined from an emission band at 385 nm due to CN. Detection limits in the range between about 1 and 10 ng were obtained using a miniature diode array spectrometer.

Chromatography, Gas↗

PubMed2004

Detection of human immunoglobulin in microchip and conventional capillary electrophoresis with contactless conductivity measurements.

The detection of human immunoglobulin M (IgM) was performed using capacitively coupled contactless conductivity detection (CCD) in electrophoresis carried out in conventional capillaries as well as on glass and poly(meth-yl methacrylate) (PMMA) microdevices. Also achieved was the analyses of IgG (an anti-human IgM) and the complex formed in the reaction between the two immunoreagents. It is demonstrated that CCD is a powerful tool suitable not only for the detection of antibodies but also for monitoring an immunological interaction. Conductivity measurements allow the direct determination of immunoreagents, and it is advantageous, since no labels are required. The immunoglobulin IgM has been taken as model analyte. The reproducibility of the analytical signal (RSD = 1%), sensitivity and limits of detection obtained for IgM (0.15 ng/mL in conventional capillaries and 34 ng/mL in microchips) are comparable to those previously obtained with amperometric detection. The immunological reaction was performed either in conventional microtiter plates as used in ELISA or in situ on the glass chip.

Electric Conductivity↗

PubMed2004

On-site simultaneous determination of anions and cations in drainage water using a flow injection-capillary electrophoresis system with contactless conductivity detection.

Drainage water diverted from a farm pasture, which was heavily loaded with manure, was monitored during a rain event. Concurrent anion and cation determinations at intervals of 10 min could be achieved with a new capillary electrophoresis system employing dual injection at opposite ends of the separation capillary. The flow injection approach enabled automation of the sampling process. Interruption of the separation voltage was not necessary. Contactless conductivity detection with an electrolyte solution optimized for the purpose allowed the facile simultaneous detection of the inorganic ions Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), NO(2)(-), NH(4)(+), K(+), Ca(2+), Na(+) and Mg(2+) and the acquisition of temporal concentration profiles of these species. The detection limits achieved were between 20 and 200 [micro sign]g l(-1) for all ions and the repeatability of peak areas and peak heights was better than 1%. The quantitative results were verified by analysing individual samples later in the laboratory with photometry and ion chromatography and the average deviations were found to be between 4 and 12%. This contribution presents a further step in the development of capillary electrophoresis towards a fully automated, low maintenance field method.

Anions↗

PubMed2004

A flow injection-capillary electrophoresis system with high-voltage contactless conductivity detection for automated dual opposite end injection.

The system comprises two flow injection-capillary electrophoresis interfaces into which the opposite ends of the separation capillary are inserted. The electrolyte solution flows through both interfaces by use of hydrostatic pressure. The injection of the samples into the electrolyte flow is accomplished by a rotary-type chromatographic valve at the grounded side and by a pinch-valve injector at the high-voltage side that provides sufficient isolation from the high electric field. The system allows a fully automated dual-injection sequence of samples from both capillary ends and simultaneous electrophoretic separation of anions and cations in the samples. The analytes are detected by a high-voltage contactless conductometric detector positioned approximately in the middle of the separation capillary. The parameters of the system were evaluated. The repeatability of the flow injection-capillary electrophoresis system for the simultaneous determination of anions and cations was evaluated for ten consecutive injections and relative standard deviation (RSD) values for peak areas were better than 1.0%. The sample throughput for total ionic analysis was estimated to be 25 samples per hour. The system was used for automated simultaneous analysis of anions and cations in various real samples. Using a short separation capillary, rapid total ionic analysis in less then 1 min is demonstrated.

Anions↗

PubMed2004

Contactless conductivity detection of selected organic ions in on-chip electrophoresis.

The detection of underivatized anionic sulfonates, carboxylates, amino acids, sugars, and artificial sweeteners, and of cationic dopamine, ephedrine, and metanephrine in microfabricated electrophoresis devices is demonstrated. This was achieved by high-voltage contactless conductivity measurements with external electrodes. Poly(methyl methacrylate) chips with thin covers to enable sensitive contactless detection were used for most determinations but glass microchips had to be employed for amino acids and sugars. The plastic chips were found not be stable in the alkaline media required to render those two classes of species in the ionic form amenable for separation and detection. The reproducibility of peak area measurements was about 1% or better and the detection limits ranged between 1 and 30 microM for the different compounds examined.

Alkanesulfonates↗

PubMed2004

Capillary and microchip electrophoresis of basic drugs with contactless conductivity detection.

The extension of contactless conductivity detection in electrophoresis to the determination of basic drugs is demonstrated using beta-adrenergic blocking agents (beta-blockers) and other physiologically active amines as examples. The high-voltage approach to conductivity detection was employed for conventional capillaries as well as microchip devices. Acidic buffers were used in all cases. A buffer consisting of 100 mM acetic acid and 1 mM histidine was deemed most optimal for the separation of six beta-blockers and best results for the analysis of the other amines were achieved with a 20 mM lactic acid buffer at low pH-value. The detection limits ranged from 0.06 to 5 microM. To demonstrate potential practical applications, a main component assay was conducted for three pharmaceutical formulations. On-chip, five pharmaceutical amines could be baseline-resolved in a 8 cm long microchannel in 90 s, albeit a reduced sensitivity and peak capacity compared to conventional capillary electrophoresis.

Adrenergic beta-Antagonists↗

PubMed2004

Fundamental aspects of contactless conductivity detection for capillary electrophoresis. Part I: Frequency behavior and cell geometry.

A better understanding of the characteristics of the axial contactless conductivity cell could be obtained by carefully studying the effect of the cell geometry on its frequency behavior. A good fit between theoretical and experimental results shows that the axial contactless conductometric detector can effectively be described by the simplest possible equivalent circuitry consisting of a capacitor, resistor, and a second capacitor. The cell constant is largely defined by the length of the gap between the electrodes. The effective electrode size is thus not related to the dimensions of the real electrodes but more closely to the cross-sectional area of the internal diameter of the capillary. Typical experimental values of 20 MOmega and 0.1 pF were obtained for the resistance and capacitances, respectively, of a cell formed by a 2 mm gap between two 4 mm long electrodes fitted with a capillary of 50 microm ID. It could be shown that the diameter of the electrode is not critical and tight coupling of the electrodes to the outer wall of the capillary is not needed. The peak overshoot phenomenon, which has frequently been reported, is an artefact that can be minimized by optimizing the frequency for cell excitation. The frequency setting has to be optimized for each cell design, operational amplifier, electrolyte solution and capillary.

Cations↗

PubMed2004

Fundamental aspects of contactless conductivity detection for capillary electrophoresis. Part II: Signal-to-noise ratio and stray capacitance.

The signal-to-noise ratio of a contactless conductivity detector for capillary electrophoresis was examined for different cell arrangements and operating parameters. The best signal-to-noise ratios, and hence the best detection limits, are obtained for frequencies which give highest sensitivity. Comparative experiments for three different excitation voltages (20, 100, and 200 V(pp)) showed that the best signal-to-noise ratios were achieved for the highest excitation voltage of 200 V(pp). Low conductivity of the background electrolyte solution is mandatory to obtain lowest noise levels, and also the improvement on applying high excitation voltages was best for the electrolyte solution with lowest conductivity. The diameter of the electrodes was found to have only a negligible effect, so that a tight fitting of the electrodes to the external diameter of the capillary is not necessary. A cell without shielding between the two electrodes showed significant direct coupling (stray capacitance) and lower signal-to-noise ratios for all experimental conditions used. A serious distortion of the peak shapes was also observed for this cell arrangement.

Electric Capacitance↗

PubMed2003

Chiral on-chip separations of neurotransmitters.

The fast on-chip determination of a range of compounds of relevance in the study and treatment of neurological disorders is demonstrated. These include dopamine and its metabolites methoxytyramine, homovanillic acid, noradrenaline, adrenaline, normetanephrine, and metanephrine, its artificial precursors DOPA and tyrosine; and the related compounds DOPS and CDOPA. Two runs are needed for the determination of these compounds. The enantiomers of adrenaline, noradrenaline, and dopamine can be separated in a buffer containing the novel combination of a cyclodextrin and a dendrimer. The isomers of homovanillic acid, DOPA, CDOPA, methoxytyramine, metanephrine, and normetanephrine, which were found to interact more weakly with cyclodextrins, could be separated in approximately 3 min with a buffer containing a cyclodextrin and a crown ether. To our knowledge, this is the first report of a fast chiral separation of such a complex mixture on an electrophoresis chip. Detection was carried out amperometrically; derivatization of the analytes is not necessary.

Buffers↗

PubMed2003

High-voltage contactless conductivity detection of underivatized amino acids in capillary electrophoresis.

High-voltage contactless conductivity detection of underivatized amino acids in both acidic and basic media is demonstrated. The suitability of different acidic buffer solutions at pH values of about 2.5 was investigated with 12 amino acids. Lactic acid as background electrolyte gave the best results in terms of detection limits for arginine, lysine and histidine, which were approximately 2 x 10(-7), 3 x 10(-7) and 4 x 10(-7) M, respectively. However, the sensitivity for other species was not quite as good and the detection limits in the order of 0.5-1 x 10 (-5) M. The use of basic conditions at pH 10-11 generally led to more stable baselines and more consistent sensitivities. A range of 20 amino acids was investigated with alkaline buffers and detection limits were typically about 10(-6) M. Urine and beer samples were analyzed. Nine and eleven amino acids could be identified, respectively.

Electrophoresis, Capillary↗

PubMed2002

High-voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis.

Contactless conductivity detection was carried out on a planar electrophoresis device by capacitive coupling using an ac excitation voltage of 500 V(p-p) and a frequency of 100 kHz. It was possible to carry out detection in this way through a cover plate of 1 mm thickness. Better sensitivity is obtained, however, by placing the electrodes into troughs that allow tighter coupling to the separation channel. The 3 x S/N detection limits are 0.49, 0.41, and 0.35 microM for the small inorganic ions K+, Na+, and Mg2+. The detection of heavy metals is demonstrated with the example of Mn2+, Zn2+, and Cr3+ with detection limits of 2.1, 2.8, and 6.8 microM, respectively. The universal nature of the method is further illustrated by the detection of citric and lactic acids, which are of interest in food and beverage analysis, and detection of three antiinflammatory nonsteroid drugs, 4-acetamidophenol, ibuprofen, and salicylic acid, as examples of species of pharmaceutical interest.

Acetaminophen↗

PubMed2002

Electrophoretic separations with polyether ether ketone capillaries and capacitively coupled contactless conductivity detection.

Polyether ether ketone (PEEK) capillaries were found to be compatible with capacitively-coupled contactless-conductivity detection (C4D). Detection limits in the order of 10(-7) M were obtained with C4D employing a high excitation voltage (HV-C4D) for inorganic cations and anions. The organic polymer capillary shows a relatively low electroosmotic flow of 2.6 x 10(-4) cm2 V(-1) s(-1). Thus inorganic anions and slower organic anions can be separated with a PEEK capillary in a single run without flow modifier. This feature also enables the analysis of both, cations and (fast and slow) anions, in a sample in two subsequent runs just by reversing the polarity or in a single run if dual opposite end injection is employed.

Electrochemistry↗

PubMed2002

Conductimetric and potentiometric detection in conventional and microchip capillary electrophoresis.

Potentiometric detection is rarely used in separation methods but is promising for certain classes of analytes which can only with difficulty be quantified by more standard methods. Conductimetric detection of ions is very versatile and has recently received renewed interest spurned by the introduction of the capacitively coupled contactless configuration. Both are useful and complementary alternatives to the established optical detection methods, and to the more widely known electrochemical method of amperometry. The simplicity of the electrochemical methods makes them particularly attractive for microfabricated devices, but relatively little work has to date been carried out with regard to potentiometric and conductimetric detection.

Conductometry↗

PubMed2002

High-voltage contactless conductivity detection of metal ions in capillary electrophoresis.

The detection of alkali, alkaline earth and heavy metal ions with a high-voltage capacitively coupled contactless conductivity detector (HV-C(4)D) was investigated. Eight alkali, alkaline earth metal ions and ammonium could be separated in less than 4 min with detection limits in the order of 5 x 10(-8) M. The heavy metals Mn2+, Pb2+, Cd2+ Fe2+, Zn2+, Co2+, Cu2+ and Ni2+ could also be successfully resolved with a 10 mM 2-(N-morpholino)ethanesulfonic acid/DL-histidine (MES/His)-buffer. Zn2+, Co2+, Cu2+ and Ni2+ showed an indirect response. The detection limits for the heavy metals were determined to range from about 1 to 5 microM.

Cations↗

PubMed2002

A direct comparison of amperometric gas sensors with gas-diffusion and ion-exchange membrane based electrodes.

The effect of the nature of the working electrode used in amperometric gas sensors on the performance criteria of sensitivity, detection limit, gas flow rate and humidity dependence was evaluated. The arrangement based on metallized ion-exchange membranes (Nafion) was compared with gas-diffusion electrodes based on porous poly(tetrafluoroethylene) (PTFE) with metallic electrodes deposited on the rear side. Two representative analyte gases were chosen: SO2, which has fast reaction kinetics, and NO, which has slow reaction kinetics. It was found that both types of electrodes showed a similar performance. A dependence on the flow rate of the sample gas was found in both cases. The sensitivities were higher for the ion-exchange membrane-backed electrodes; however, the 3sigma detection limits were all in the lower ppb range and for NO were significantly lower on the Nafion membrane than on the PTFE membrane. The Nafion electrode was found to show a dependence on the relative humidity of the gas stream, but not the PTFE-based electrode.

Journal Article↗