Biomedical subjects

Peter C Hauser

Publications and source records attributed to Peter C Hauser.

At least 19 recordsLinked to original sources

PubMed2007

Mercury speciation by CE: a review.

CE methods for the speciation of inorganic and organomercury compounds are reviewed. Sample preparation, separation conditions and detection modes are discussed. Efficient separation and sensitive determination of mercury species by CE typically involves complexation with various thiols, chromogenic and other chelating agents; however, some methods do not require complexation. Spectrophotometric detection based on UV-visible absorption is by far the most commonly used. Hyphenated techniques, such as CE/inductively coupled plasma (ICP)-MS, hydride generation coupled to ICP-MS or atomic fluorescence spectrometry and CE/atomic absorption spectrometry are gaining popularity due to their high sensitivity and selectivity. Last, but not least, the potential and applications of electrochemical methods for detection of separated mercury species are outlined.

Electrochemistry↗

PubMed2006

Visual constructive and visual-motor skills in deaf native signers.

Visual constructive and visual-motor skills in the deaf population were investigated by comparing performance of deaf native signers (n=20) to that of hearing nonsigners (n=20) on the Beery-Buktenica Developmental Test of Visual-Motor Integration, Rey-Osterrieth Complex Figure Test, Wechsler Memory Scale Visual Reproduction subtest, and Stanford-Binet Intelligence Scale Paper Folding and Cutting subtest. Deaf signers were found to perform similarly to hearing controls, suggesting that these tests are valid assessment instruments to use with deaf individuals.

Adult↗

PubMed2006

Direct determination of valproic acid in biological fluids by capillary electrophoresis with contactless conductivity detection.

Capacitively coupled contactless conductivity detection (C(4)D) is a new technique providing high sensitivity in capillary electrophoresis (CE) especially for small ions that can otherwise only be determined with indirect methods. In this work, direct determination and validation of valproic acid (VPA) in biological fluids was achieved using CE with C(4)D. VPA is of pharmacological interest because of its use in epilepsy and bipolar disorder. The running electrolyte solution used consisted of 10mM 2-(N-morpholino)ethane sulfonic acid (MES)/dl-histidine (His) and 50microM hexadecyltrimethylammonium bromide (HTAB) at pH 6.0. Caproic acid (CA) was selected as internal standard (IS). Analyses of VPA in serum, plasma and urine samples were performed in less than 3min. The interference of the sample matrix was reduced by deproteinization of the sample with acetonitrile (ACN). The effect of the solvent type and ratio on interference was investigated. The limits of detection (LOD) and quantitation (LOQ) of VPA in plasma samples were determined as 24 and 80ng/ml, respectively. The method is linear between the 2 and 150microg/ml, covering well the therapeutic range of VPA (50-100microg/ml).

Electric Conductivity↗

PubMed2006

Do deaf individuals see better?

The possibility that, following early auditory deprivation, the remaining senses such as vision are enhanced has been met with much excitement. However, deaf individuals exhibit both better and worse visual skills than hearing controls. We show that, when deafness is considered to the exclusion of other confounds, enhancements in visual cognition are noted. The changes are not, however, widespread but are selective, limited, as we propose, to those aspects of vision that are attentionally demanding and would normally benefit from auditory-visual convergence. The behavioral changes are accompanied by a reorganization of multisensory areas, ranging from higher-order cortex to early cortical areas, highlighting cross-modal interactions as a fundamental feature of brain organization and cognitive processing.

Attention↗

PubMed2006

Application of gradient programs for the determination of underivatized amino acids and small peptides in reversed-phase high-performance liquid chromatography with contactless conductivity detection.

The application of gradient methods in HPLC determinations with capacitively coupled contactless conductivity detection was successfully demonstrated for non-UV-absorbing amino acids as well as for small peptides as analytes. The drift in baseline which is caused by the change in the conductivity of the mobile phase during the elution could be minimized by careful optimization of the composition of the mobile phase. For such conditions the remaining baseline drift could be corrected for either by subtraction of a blank chromatogram or by baseline normalization using a software package for chromatographic data processing. Reverse phase separations were carried out using aqueous eluents containing either methanol or acetonitrile and acetic acid or trifluoroacetic acid. Detection limits between 1 and 40 microM were achieved for the amino acids and the di- and tri-peptides investigated. The reproducibilities for the peak areas were typically found to be about 2% and good linearity was obtained for the concentration range tested (up to 1000 microM).

Acetic Acid↗

PubMed2006

Rapid electrophoretic separations in short capillaries using contactless conductivity detection and a sequential injection analysis manifold for hydrodynamic sample loading.

A sequential injection-capillary electrophoresis (SI-CE) system for the fast and automated quantitative analysis of anions and cations is described. Because of the low sample load in capillary electrophoresis a split injection approach had to be used to achieve reliable hydrodynamic injection. The use of a capillary of 8 cm effective length allowed for the separation of five inorganic cations within 11 s. One common electrolyte solution containing 12 mM l-histidine and 2 mM 18-crown-6 whose pH value was adjusted to 4.0 with 10% v/v acetic acid was used for anions and cations, thus the analysis of both groups of analytes could be carried out in rapid sequence simply by switching the polarity of the high voltage supply. The system also allows automated flushing of the capillary. Detection limits between about 2 and 5 micromol l(-1) could be achieved with the contactless conductivity detector employed.

Journal Article↗

PubMed2006

Evaluation of contactless conductivity detection for the determination of UV absorbing and non-UV absorbing species in reversed-phase high-performance liquid chromatography.

A capacitively coupled contactless conductivity detector (C(4)D) was used for the determination of three groups of ionizable species in reversed-phase HPLC with isocratic elution. These were non-steroidal anti-inflammatory drugs which are arylpropionic acid derivatives and represent anionic analytes, beta-blockers which are amines and therefore cationic, and zwitterionic amino acids. Optimization of the eluents led to detection limits in the order of 1 microM for all species. The precision in peak areas was typically between 0.2 and 2.1% and calibration curves were linear up to 500 microM. The determination of ibuprofen, acetylsalicylic acid and atenolol in real samples was also demonstrated by direct injection of dissolved pharmaceutical formulations into the HPLC-C(4)D system.

Adrenergic beta-Antagonists↗

PubMed2006

Determination of different classes of amines with capillary zone electrophoresis and contactless conductivity detection.

The use of contactless conductivity detection for the determination of different organic amines in CE was successfully demonstrated. Aliphatic non UV-absorbing species could be determined along absorbing compounds by measuring the conductivity of their protonated forms. The species tested included short-chained aliphatic primary, secondary and tertiary amines, branched aliphatic amines, diamines, hydroxyl-substituted amines as well as species incorporating aromatic and non-aromatic cyclic moieties. Highest sensitivity was obtained with BGE solutions containing solely acetic acid. A concentration of 0.5 M at a pH value of 2.5 was used. Detection limits were in the order of 1 microM. Complete separation of cis- and trans-1,2-diaminocyclohexane could be achieved by adding 18-crown-6 as modifier to the electrolyte solution.

Acetates↗

PubMed2006

Determination of tobramycin in human serum by capillary electrophoresis with contactless conductivity detection.

A study on the determination of the antibiotic tobramycin by CE with capacitively coupled contactless conductivity detection is presented. This method enabled the direct quantification of the non-UV-absorbing species without incurring the disadvantages of the indirect approaches which would be needed for optical detection. The separation of tobramycin from inorganic cations present in serum samples was achieved by optimizing the composition of the acetic acid buffer. Field-amplified sample stacking was employed to enhance the sensitivity of the method and a detection limit of 50 microg/L (S/N = 3) was reached. The RSDs obtained for migration time and peak area using kanamycin B as internal standard were typically 0.12 and 4%, respectively. The newly developed method was validated by measuring the concentration of tobramycin in serum standards containing typical therapeutic concentrations of 2 and 10 mg/L. The recoveries were 96 and 97% for the two concentrations, respectively.

Acetic Acid↗

PubMed2006

Enantiomeric separation of underivatized small amines in conventional and on-chip capillary electrophoresis with contactless conductivity detection.

The determination of the enantiomers of small non-UV-absorbing amines which otherwise can only be achieved with difficulty was possible by using a combination of the chiral crown ether (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H4) and dimethyl-beta-CD as selectors in CE and contactless conductivity measurement for detection. Alkylamines without any other functional group, amino alcohols, species with ether or ester groups and with a cyclic moiety were investigated. The detection limits were found to be about 1.0 microM and the determination is possible up to at least 1.0 mM. The determination of enantiomeric ratios of up to 99.5:0.5 was also found feasible.

Amines↗

PubMed2006

Evaluation of the detection of biomolecules in capillary electrophoresis by contactless conductivity measurement.

The sensitivity of contactless conductivity detection to amino acids, peptides and proteins in CE was studied for BGE solutions of different pH values. The LOD and analytical characteristics were compared for acidic and basic conditions and better results were in most cases found for buffers of low pH values. Linear dynamic ranges varied between two orders of magnitude for amino acids and peptides and three orders of magnitude for larger proteins. The concentration detection limits were found to be between 1.2 and 7.5 microM for the amino acids tested and for the larger molecules they varied between 2.6 microM for leucine enkephalin and 0.2 microM for HSA when using a buffer at pH 2.1.

Amino Acids↗

PubMed2005

Enantiomeric separation of 1-phenylethylamine and 1-cyclohexylethylamine in capillary electrophoresis with contactless conductivity detection.

Contactless conductivity detection was employed for the detection of the enantiomers of 1-phenylethylamine and 1-cyclohexylethylamine which were separated in capillary electrophoresis with unprecedented high resolutions R(s) of 2.3 and 3.3, respectively, by using a combination of dimethyl-beta-cyclodextrin and the chiral crown ether 18C6H4 as chiral selectors in a citric acid buffer of pH 2.4. The conductivity measurement enabled the direct detection, i.e. without having to derivatize or resort to indirect methods, of all species including the non-UV-absorbing enantiomers of cyclohexylamine. Detection limits of 0.5 microM were achieved and the determination of enantiomeric ratios of up to 99:1 was found possible.

Electric Conductivity↗

PubMed2005

Separation of enantiomers in capillary electrophoresis with contactless conductivity detection.

Contactless conductivity detection is successfully demonstrated for the enantiomeric separation of basic drugs and amino acids in capillary electrophoresis (CE). Derivatization of the compounds or the addition of a visualization agent as for indirect optical detection schemes were not needed. Non-charged chiral selectors were employed, hydroxypropylated cyclodextrin (CD) for the more lipophilic basic drugs and 18-crown-6-tetracarboxylic acid (18C6H4) for the amino acids. Acidic buffer solutions based on lactic or citric acid were used. The detection limits were determined as 0.3 microM for pseudoephedrine as an example of a basic drug and were in the range from 2.5 to 20 microM for the amino acids.

Amino Acids↗

PubMed2005

Effects of the cell geometry and operating parameters on the performance of an external contactless conductivity detector for microchip electrophoresis.

Quantitative data on the effect of the electrode geometry on the signal strength and the signal-to-noise ratio is given. The measurements are affected by the unavoidable presence of stray capacitance. Best results are achieved for short and narrow electrodes arranged in an antiparallel configuration and separated by a minimal gap, which determines the dimensions of the actual detection volume. Limits of detection between 150 and 250 microg l(-1) and separation efficiencies from 13,000 to 17,000 theoretical plates were achieved for six inorganic cations (NH(4)(+), K(+), Ca(2+), Na(+), Mg(2+)and Li(+)) with electrodes of 1 mm width and a detection gap of 0.5 mm (separation channel length: 7.5 cm) when operating the detector at 20 V(pp) and 500 kHz. The analyses of all major inorganic cations in tap and rain water samples were demonstrated for the first time in microchip electrophoresis with contactless conductivity detection.

Cations↗

PubMed2005

Fast electrophoresis in conventional capillaries by employing a rapid injection device and contactless conductivity detection.

A purpose-made set-up featuring an automated fast injector allowed the easy optimization of the injected amount and the adjustment of the separation length of conventional capillaries from a minimum of 5 cm upward. It was found that a compromise in capillary length for separation efficiency and analysis time also has to take into account the injected amount, which in turn affects the sensitivity and hence the detection limit. The versatility of the system was demonstrated by the analysis of the major cations and anions in natural water samples in less than 1 min, the concurrent determination of a mixture of amino acids and carbohydrates in 160 s, and of three active ingredients in a pharmaceutical preparation in 40 s. Plate numbers were typically around 50,000 and detection limits down to 1 muM could be achieved.

Journal Article↗

PubMed2005

Determination of biochemical species on electrophoresis chips with an external contactless conductivity detector.

Contactless conductivity measurements were found to be suitable for the direct detection, i.e., without needing any labels, of a range of biochemically relevant species, namely amino acids, peptides, proteins, immunoglobulin, and DNA. It was also possible to monitor the products of the enzymatic digestion of HSA with pepsin. Detection was carried out on bare electrophoresis chips made from poly(methyl methacrylate) by probing the conductivity in the channel with a pair of external electrodes, which are fixed on the chip holder. Separation efficiencies up to 15,000 plates could be obtained and LODs are in the low muM-range, except for immunoglobulin G (IgG) which could be determined down to 0.4 nM. Linear dynamic ranges of two to three orders of magnitude were obtained for the peptides as examples.

Amino Acids↗

PubMed2005

Application of an external contactless conductivity detector for the analysis of beverages by microchip capillary electrophoresis.

Quantitative total ionic analysis of alcoholic and nonalcoholic beverages was performed by microchip capillary electrophoresis with external contactless conductivity detection. An electrolyte solution consisting of 10.5 mM histidine, 50 mM acetic acid, and 2 mM 18-crown-6 at pH 4.1 was used for the determination of NH(4) (+), K(+), Ca(2+), Na(+), and Mg(2+). Fast analysis of Cl(-), NO(3) (-), and SO(4) (2-) was achieved in 20 mM 2-(N-morpholino)ethanesulfonic acid /histidine electrolyte solution at pH 6.0 and the simultaneous separation of up to 12 inorganic and organic anions was performed in a solution containing 10 mM His and 7 mM glutamic acid at pH 5.75. Limits of detection ranged from 90 to 250 mug/L for inorganic cations and anions, and from 200 to 2000 mug/L for organic anions and phosphate. Calibration curves showed linear dependencies over one to two orders of magnitude when the stacking effect was minimized by injecting standard solutions prepared in background electrolyte solutions. Total analysis times of 35 and 90 s were achieved for the determination of 5 inorganic cations and for the simultaneous determination of 12 inorganic and organic anions, respectively, which represents a considerable reduction of analysis time compared to conventional separation methods used in food analysis.

Animals↗

PubMed2005

Determination of vitamin C and preservatives in beverages by conventional capillary electrophoresis and microchip electrophoresis with capacitively coupled contactless conductivity detection.

The separation and detection of commonly used preservatives (benzoate, sorbate) and vitamin C by both conventional CE and microchip electrophoresis with capacitively coupled contactless conductivity detection is presented. The separation was optimized by adjusting the pH-value of the buffer and the use of hydroxypropyl-beta-CD (HP-beta-CD) and CTAB as additives. For conventional CE, optimal separation conditions were achieved in a histidine/tartrate buffer at pH 6.5, containing 0.025% HP-beta-CD and 0.1 mM CTAB. LOD ranged from 0.5 to 3 mg/L (S/N = 3) and the RSDs for migration time and peak area were less than 0.1 and 2%, respectively. A considerable reduction of analysis time can be accomplished by using microchip electrophoresis without significant loss in sensitivity under optimal separation conditions. A histidine/tartrate buffer at pH 6.5, incorporating 0.06% HP-beta-CD and 0.25 mM CTAB, gave detection limits ranging between 3 and 10 mg/L and satisfactory reproducibilities of < or =0.4% for the migration time and < or =3.5% for the peak area. The methods developed are useful for the quantitative determination of food additives in real samples such as soft drinks and vitamin C tablets.

2-Hydroxypropyl-beta-cyclodextrin↗