Butyltin compounds in a sediment core from the old Tilbury basin, London, UK.

Sections from a sediment core taken from the River Thames were analysed for butyltin species using gas chromatography with species-specific isotope dilution mass spectrometry. Results demonstrated that in most samples tributyltin concentrations of 20-60 ng/g accounted for <10% of the total butyltin species present, which is in agreement with data from other sediment samples which were historically contaminated with tributyltin. Vertical distribution of the organotin residues with depth throughout the core, with data on organochlorine compounds and heavy metals allowed for the construction of a consistent hypothesis on historical deposition of contaminated sediments. From this it was possible to infer that the concentrations of tributyltin in sediments deposited during the early 1960s were in the order of 400-600 microg/g by using degradation rate constants derived by other workers. Such values fall well within the range quoted for harbour sediments in the literature.

High accuracy isotope dilution analysis for the determination of ethanol using gas chromatography-combustion-isotope ratio mass spectrometry.

A procedure was established for the determination of ethanol in water samples by isotope dilution analysis. After spiking the sample with labelled [13C2]ethanol, it was analysed by gas chromatography-combustion-isotope ratio mass spectrometry. Results are reported for two certified reference materials and also ethanol solutions prepared for a CITAC (Co-operation on International Traceability in Analytical Chemistry) interlaboratory comparison. The certified reference materials were certified using the dichromate titration method at nominal levels of 80 and 200 mg per 100 mL. The CITAC solutions were prepared gravimetrically at nominal levels of 50, 80 and 200 mg per 100 mL. The results of the analysis agree well to within 0.5% of the gravimetric values of the different samples. The relative expanded standard uncertainties (with a coverage factor equal to 2) associated with the results varied between 0.18 and 0.37%, a range that encompassed the gravimetric values for the different samples. A complete uncertainty budget was also drawn up so that the different contributions could be identified and quantified. The main contributions were due to variations in the measured isotope amount ratios and a 'between' blend component introduced to quantify the contribution of factors such as the degree of matching of the isotope amount ratios between standards and samples used in the isotope dilution analysis.

Determination of lysergide in urine by high-performance liquid chromatography combined with electrospray ionisation mass spectrometry.

A quantitative method which avoids derivatisation is described for the determination of lysergide (LSD) levels in urine. Sample preparation included addition of methysergide as an internal standard followed by solid-phase extraction. LSD was analysed on a system consisting of a C18 stationary phase and a mobile phase of 0.1 M acetate buffer pH 8.0-acetonitrile-triethylamine (75:25:0.25, v/v). LSD was detected by electrospray ionisation mass spectrometry with selected ion monitoring. The quantification limit was 0.5 ng/ml and the method was linear up to 10 ng/ml of LSD in urine.

The local reciprocal method for sizing DNA fragments: an obscure limitation.

The local reciprocal method, for sizing DNA fragments, has been found to fail when the experimental data produces a linear relationship. A simple solution for computerised systems is to test for this unexpected condition.

Assessment of a video system for scanning DNA autoradiographs.

A video based scanning system had been developed for processing DNA autoradiographs (T. Catterick and J.R. Russell, Lab. Microcomput. (1991), in press). Before the scanner was used in casework it was necessary to assess its performance. Test DNA samples containing fragments (alleles) of known kilobase size were run against the primary (Amersham, U.K.) calibration ladder. The resulting autoradiographs were processed with the new video scanner and also using manual, ruler based measurements. Comparisons were then made between these experimental results and also with the known kilobase values quoted by the supplier of the test samples.

A simple method for improving control of the time constant in recording transient signals in atomic-absorption spectrometry.

Significant improvements can be made in signal:noise ratios of transient signals arising in atomic-absorption spectroscopy by the use of resistor-capacitor damping. A suitable device is described and the effect it has on signals arising from instruments using analogue and digital forms of output is demonstrated.

Rapid analysis of small glass fragments by atomic-absorption spectroscopy.

A rapid method is described for the determination of magnesium, iron and manganese in small glass fragments (250-500 mug). The speed of the analytical procedure is made possible by the use of a convenient cold digestion stage allied to a discrete sampling method which permits the three elements of interest to be determined by flame atomic-absorption spectrophotometry.

The quantitative analysis of glass by atomic absorption spectroscopy.

An analytical procedure for the determination of manganese and magnesium in glass fragments of approximately 1 mg has been developed. The concentrations of these elements in glass are shown to have some potential value for classification and discrimination of glass.