Occupational and environmental laboratory medicine: A network of EQAS organisers

Most people in any community come into contact with chemicals that are potentially harmful to their health. Some elements are essential to health and inadequate amounts in food may also lead to ill health. Measurement of chemicals in blood, urine or other specimens is a fundamental feature of studies undertaken in the field of Occupational and Environmental Laboratory Medicine (OELM). Results are used to assess the risk for either overexposure or deficiency of essential nutrients. External Quality Assessment Schemes (EQAS) aid laboratories to achieve accurate and consistent data and 11 organisers of EQAS in Europe and North America are working to improve the effectiveness of their activities.The aims of the Network of EQAS Organisers in OELM are to stimulate improvements in analytical results, establish equivalence of assessment among Schemes, collaborate to enhance the practice of EQA including whenever possible to warrant traceability of EQAS to primary standards.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia.     

119Sn Mössbauer studies of glassy and crystalline compounds in the chalcogenide system SeSnAs

¹¹⁹Sn Mössbauer measurements have been carried out on 18 chalcogenide glasses of different composition in the system SeSnAs. In all cases tin is four-coordinated and appears to be tetrahedrally surrounded by selenium. Two of the glasses (Se₆₀Sn₃As₃₇ and Se₄₇Sn₃As₅₀) were crystallized by heat treatment, and their Mössbauer spectra have been measured as a function of crystallization temperature and annealing time. As a result of the heat treatment, crystalline SnSe and SnSe₂ are precipitated. The amount of each compound is determined by the composition of the original glass and the remaining glassy or crystalline phase (As₂Se₃ and As₄Se₄). The degree of the crystallization depends on the temperature and the annealing time, but not the mass ratio of the tin selenides formed.     

The interpretation of speech reception threshold data in normal-hearing and hearing-impaired listeners: steady-state noise

Speech-in-noise-measurements are important in clinical practice and have been the subject of research for a long time. The results of these measurements are often described in terms of the speech reception threshold (SRT) and SNR loss. Using the basic concepts that underlie several models of speech recognition in steady-state noise, the present study shows that these measures are ill-defined, most importantly because the slope of the speech recognition functions for hearing-impaired listeners always decreases with hearing loss. This slope can be determined from the slope of the normal-hearing speech recognition function when the SRT for the hearing-impaired listener is known. The SII-function (i.e., the speech intelligibility index (SII) against SNR) is important and provides insights into many potential pitfalls when interpreting SRT data. Standardized SNR loss, sSNR loss, is introduced as a universal measure of hearing loss for speech in steady-state noise. Experimental data demonstrates that, unlike the SRT or SNR loss, sSNR loss is invariant to the target point chosen, the scoring method or the type of speech material.     

Measurement error models and variance estimation in the presence of rounding error effects

An approach to estimating measurement error variances for any instrument having round-off effects that might also have instrument bias is presented. Recently finite instrument resolution effects on error variances have been studied, but negligible instrument bias was assumed and the contexts were different than considered here. Our intent is to use repeated measurements on several standards to estimate the instrument’s random and systematic error variances. Recognizing that rounding impacts item bias and variance in a manner that depends on the true value, an approach is presented to estimate random error variance and instrument systematic error variance. The key finding is that item-specific bias can interfere with the estimation of overall instrument bias unless appropriate error modeling and associated inference steps are taken.     

Microcalorimetric study of the growth of <Emphasis Type="Italic">Enterococcus faecalis</Emphasis> in an enriched culture medium

Enterococcus faecalis is a Gram-positive bacteria, considered one of the most common causes of nosocomial infections. Bacterial cultures produce an exchange of energy as a result of the bacteria metabolisms. The rate of heat production is an adequate measure of the metabolic activity of the organisms and their constituent parts. Microorganisms produce small amounts of heat: 1–3 pW per cell. Although the heat produced by bacteria is very small, their exponential reproduction in a culture medium permits heat detection through microcalorimetry. In this study, we analyzed the microcalorimetric behavior of Enterococcus faecalis. A thermal Calvet microcalorimeter was used. The inside of the calorimeter contains two stainless steel cells (experimental and reference). Experiments were carried out at final concentrations of 10⁶,10⁵,10³, and 10 CFU/mL and a constant temperature of 309.65 K was maintained within the microcalorimeter. Recording the difference in calorific potential over time we obtained E. faecalis’s growth curves. Thermograms were analyzed mathematically allowing us to calculate the constant growth, generation time and the amount of heat exchanged over the culture time.     

A time-resolved imaging study of Cr (I) emissions from a laserplasma formed on a sample at nonnormal incidence

The effect of sample orientation on atomic emission in laser-induced breakdown spectroscopy (LIBS) was studied using time-resolved imaging and spectroscopy. The purpose of this work was to determine the effect of sampling geometry on the analytical performance of the LIBS measurement. The results obtained indicate that atoms are ejected perpendicular to the sample surface independent of the angle-of-incidence of the laser pulse. This result is consistent with previous work by others. In addition, it was found that the observed LIBS atomic emission intensities were maximum for normal laser pulse incidence, reached a minimum at 50° angle-of-incidence, and then increased as the sample was rotated to higher angles-of-incidence     

Little exchange at the liquid/solid interface: defect-mediated equilibration of physisorbed porphyrin monolayers

The transition from low to high density 2D surface structures of copper porphyrins at a liquid/solid interface requires specific defects at which nearly all exchange of physisorbed molecules with those dissolved in the supernatant occurs.     

Picosecond dynamics of conformation changes in malachite green dye produced by photoionization of malachite green leucocyanide

The appearance of malachite green dye absorption following photoionization of malachite green leucocyanide has been examined using picosecond flash photolysis. The rate of absorption increase depends upon solvent viscosity and exhibits a two-step behavior in viscous glycerol solutions.