Biomedical subjects

M Wortberg

Publications and source records attributed to M Wortberg.

4 recordsLinked to original sources

PubMed2005

Monitoring industrial wastewater by online GC-MS with direct aqueous injection.

An online GC-MS-system for automated monitoring of crude wastewater at a complex chemical production site is presented. The modular system is, in principal, based on commercial equipment, but utilizes a special, two-stage injector, which consists of a splitless vaporization chamber on top of a PTV injector filled with Tenax. This set-up enables direct injection of wastewater. Almost 140 volatile and semi-volatile compounds are calibrated down to 1 mg L(-1), which is sufficient for analysis of the influent of the wastewater-treatment plant. Two instruments analyze alternately, every 20 min, and the instrument cycle time is 40 min. The quantitative results are transferred to a database which is connected to a process-control system. Depending on the nature and concentration of a compound, an alarm can be generated and the wastewater stream can be diverted into an "off spec tank" if necessary. The GC-MS-system operates quasi-continuously with a system availability >98%. Data quality is automatically controlled in each run and by daily analysis of a quality-control sample. The development of a novel stacked PTV-PTV injector design to expand the range of analytes to selected basic compounds is described.

Gas Chromatography-Mass Spectrometry↗

PubMed1996

Application of the bootstrap to calibration experiments.

In calibration experiments, a number of samples of known concentration are used to establish the relationship between a measured response and sample concentration; this relationship is then used to estimate the unknown concentration of further samples from their measured responses. In addition to the estimates themselves, it is useful to have available some measure of their precision, usually given in the form of confidence limits. The standard method of inverting prediction limits is found to work well in simple situations, but in nonlinear multivariate calibration it becomes intractable. The bootstrap offers an alternative methodology, but in the calibration framework its application is not obvious. We describe some considerations in bootstrapping calibration data and compare our methods with a previous attempt and with the standard method in linear, nonlinear, and multivariate situations. The bootstrap is found to be a useful tool in those situations where the standard method is difficult to implement.

Calibration↗

PubMed1996

Rapid assays for environmental and biological monitoring.

Rapid, inexpensive, sensitive, and selective enzyme-linked immunosorbent assays (ELISAs) now are utilized in environmental science. In this laboratory, many ELISAs have been developed for pesticides and other toxic substances and also for their metabolites. Compounds for which ELISAs have recently been devised include insecticides (organophosphates, carbaryl, pyrethroids, and fenoxycarb), herbicides (s-triazines, arylureas, triclopyr, and bromacil), fungicides (myclobutanil), TCDD, and metabolites of naphthalene and toluene. New rapid assays have been developed for mercury.

Antifungal Agents↗

PubMed1994

Extension of the four-parameter logistic model for ELISA to multianalyte analysis.

The standard implementation of enzyme-linked immunosorbent assay (ELISA) for single analytes can lead to false conclusions if cross reacting compounds are present in the sample. This paper discusses the extension of the usual four-parameter logistic model for ELISA to the case of multiple cross-reacting analytes. The use of the extended model in multianalyte analysis (MELISA) is illustrated and compared with a more simplistic approach. Data on the analysis of a binary mixture of s-triazines suggests the superiority of the proposed model. This model is also suitable for other forms of immunoassay that use the four-parameter logistic curve.

Cross Reactions↗