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Biomedical subjects

B Welz

Publications and source records attributed to B Welz.

9 recordsLinked to original sources
PubMed2001

[Transanal ultrasonography for diagnosis of obstetric anal sphincter trauma].

Fecal incontinence affects up to 2% of the general population. The major cause of it is related to the birth trauma of the anal sphincters. In this paper the possibilities of transanal endosonography in the assessment of the anal canal muscles defects after deliveries were presented. Anal canal sonographic anatomy together with the technique of the examination with the use of rotating endoprobe were presented. Transanal rotating endoprobe was compared with exoanal probes for visualization of the anal canal. Ultrasonic images of internal and external anal sphincters defects were shown with specific patterns of defects allowing differentiation between morphological and neurological damages of the sphincters. Anal endosonography was compared with clinical examination, electromyography and manometry in the assessment of the integrity of the anal sphincters.

Adult↗
PubMed1999

On-line coupling flow injection microcolumn separation and preconcentration to electrothermal atomic absorption spectrometry for determination of (ultra)trace selenite and selenate in water.

A flow injection manifold with an air-segmented and air-transported operational sequence for on-line coupling of microcolumn separation and preconcentration to electro-thermal atomic absorption spectrometry (ETAAS) was developed for the determination of (ultra)trace selenite and selenate in water. The determination of selenite was achieved by selective reaction with pyrrolidine dithiocarbamate (PDC), sorption of the resultant Se-PDC compound onto a conical microcolumn (10.2 microL) packed with RP C18 sorbent, elution with ethanol, and detection by ETAAS. The concentration of selenate was obtained as the difference between the concentrations of selenite after and before prereduction of selenate to selenite. With the developed manifold and operation sequence,the dispersion during elution and eluate transport and the eluent volume required for complete elution of the sorbed analyte were minimized. As a result, the sorbed analyte was quantitatively eluted from the column with only 26 microL of ethanol, and all the eluate was automatically introduced into the graphite tube by an air flow without the need of preheating the graphite tube or precise timing. Pretreatment of the graphite tube with iridium as a long-term "permanent" modifier effectively prevented analyte loss arising from the high volatility of the Se-PDC compound and greatly improved the precision, sensitivity, and detection limit. One thermal pretreatment of the graphite tube with injection of 150 microgram of iridium made possible at least 200 repetitive atomization cycles. With a preconcentration time of 180 s and a sample flow rate of 1.4 mL min(-1), an enhancement factor of 112 was achieved in comparison with direct injection of 30 microL of aqueous solution. The detection limit (3s) was 4.5 ng L(-1)Se. The RSD (n = 7) was 3.8% at 20 ng L(-1)Se. The concentrations of selenite and selenate determined in synthetic aqueous mixtures were in good agreement with the expected values. The recoveries for selenite from spiked seawater samples ranged from 98 to 102%. The concentrations of selenite in several seawater reference materials obtained with simple aqueous standard solutions for calibration agreed well with the certified and information values, respectively. In addition, the developed method was successfully applied to the certification of selenite and selenate in water.

Fresh Water↗
PubMed1999

Application of a macrocycle immobilized silica gel sorbent to flow injection on-line microcolumn preconcentration and separation coupled with flame atomic absorption spectrometry for interference-free determination of trace lead in biological and environmental samples.

A simple and highly selective flow injection on-line pre-concentration and separation-flame atomic absorption spectrometric method was developed for routine analysis of trace amounts of lead in biological and environmental samples. The selective preconcentration of lead was achieved in a wide range of sample acidity (0.075 to > or = 3 mol L(-1)HNO3) on a microcolumn (145 microL) packed with a macrocycle immobilized on silica gel. The lead retained on the column was effectively eluted with an EDTA solution (0.03 mol L(-1), pH 10.5). Three kinds of potential interferences, i.e., preconcentration inferences from metal ions with an ionic radius similar to that of Pb(II) due to their competition for the cavity of the macrocyle, elution kinetic interferences from ions which form stable complexes with EDTA due to their competition for EDTA, and interferences in the atomizer from residual matrix, were evaluated and compared in view of the read-out mode of the analyte response (peak area vs peak height), column wash step (with vs without), column capacity (50 vs 145 microL), and column shape (conical vs cylindrical). The results showed that a combination of increase in column capacity, quantitation based on peak area, and use of dilute nitric acid for column wash before elution efficiently avoid the above-mentioned potential interferences. With the use of a 145 microL column the present system tolerated up to 0.1 g L(-1) Ba(II), 1 g L(-1) Sr(II), and at least 10 g L(-1) Fe(III), Cu(II), Ni(II), Zn(II), Cd(II), Al(III), K(I), Na(I), CaII), and Mg(II) in the sample digest. Further improvement of the interference tolerance can be achieved by increasing column capacity if more complicated samples need to be analyzed. At a sample loading rate of 3.9 mL min(-1) with 30-s preconcentration, an enrichment factor of 52, a detection limit (3s) of 5 micrograms L(-1) Pb in the digest and a sampling frequency of 63 h(-1) were obtained. The precision (RSD, n = 11) at the 200 micrograms L(-1) level was 1.9%. The enrichment factor and the detection limit can be further improved by increasing sample loading rate without degradation in the efficiency due to the favorable kinetics and low hydrodynamic impedance of the present system. The analytical results obtained by the proposed method for a number of biological and environmental standard reference materials were in good agreement with the certified and recommended values.

Animals↗
PubMed1998

Speciation determination of arsenic in urine by high-performance liquid chromatography-hydride generation atomic absorption spectrometry with on-line ultraviolet photooxidation.

A coupled system for arsenic speciation determination based on high-performance liquid chromatography (HPLC), on-line UV photooxidation and continuous-flow hydride generation atomic absorption spectrometry (HGAAS) was built from commercially available modules with minor modifications to the electronic interface, the software and the gas-liquid separator. The best results were obtained with strong anion-exchange columns, Hamilton PRP X-100 and Supelcosil SAX 1, and gradient elution with phosphate buffers containing KH2PO4-K2HPO4. The on-line UV photooxidation with alkaline peroxodisulfate, 4% m/v K2S2O8-1 mol l-1 NaOH, in a PTFE knotted reactor for 93 s ensures the transformation of inorganic AsIII, monomethylarsonate, dimethylarsinate, arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium ion to arsenate. About 32-36 HPLC-UV-HGAAS runs could be performed within 8 h, with limits of detection between 2 and 6 micrograms l-1 As, depending on the species. The method was applied to the analysis of spot urine samples and certified urine reference materials (CRMs). Upon storage at 4 degrees C, reconstituted CRMs are stable for at least 2 weeks with respect to both their total arsenic content and the individual species distribution.

Arsenic↗
PubMed1992

Differential determination of chromium(VI) and total chromium in natural waters using flow injection on-line separation and preconcentration electrothermal atomic absorption spectrometry.

A rapid, sensitive and selective method for the differential determination of CrIII and CrVI in natural waters is described. Chromium(vi) can be determined directly by flow injection on-line sorbent extraction preconcentration coupled with electrothermal atomic absorption spectrometry using sodium diethyldithiocarbamate as the complexing agent and C18 bonded silica reversed-phase sorbent as the column material. Total Cr can be determined after oxidation of CrIII to CrVI by potassium peroxydisulfate. Chromium(III) can be calculated by difference. The optimum conditions for sorbent extraction of CrVI and oxidation of CrIII to CrVI are evaluated. A 12-fold enhancement in sensitivity compared with direct introduction of 40 microliters samples was achieved after preconcentration for 60 s, giving detection limits of 16 ng l-1 for CrVI and 18 ng l-1 for total Cr (based on 3 sigma). Results obtained for sea-water and river water reference materials were all within the certified range for total Cr with a precision of better than 10% relative standard deviation in the range 100-200 ng l-1. The selectivity of the determination of CrVI was evaluated by analysing spiked reference materials in the presence of CrIII, resulting in quantitative recovery of CrVI.

Chromium↗