Wolfram Bremser

Temporal trend (1988-2008) of hexabromocyclododecane enantiomers in herring gull eggs from the german coastal region

Levels of α-, β-, and γ-hexabromocyclododecane (HBCD) were determined in pooled eggs from herring gulls (Larus argentatus) sampled on three bird sanctuaries near the German North Sea coast between 1988 and 2008 (Mellum and Trischen) and the German Baltic Sea coast between 1998 and 2008 (Heuwiese) and archived by the German Environmental Specimen Bank. Pressurized fluid extraction, gel permeation chromatography, and LC-MS/MS using (13)C(12)-labelled isotope standards and a chiral column were applied. α-HBCD was the dominating diastereomer and ranged between 3.7 and 107 ng g(-1)lw while β- and γ-HBCD were throughout close to LOQ. The highest α-HBCD concentration was found in eggs from Mellum sampled in the year 2000. Interestingly, HBCD in eggs from the three islands displayed similar time courses with levels increasing to a peak contamination around 2000 and decreasing levels ever since. Chiral signatures of α-HBCD in eggs differed among the islands but indicated a preferential enrichment of the first eluting enantiomer (-)-α-HBCD.

Ultra-trace analysis of 36 Cl by accelerator mass spectrometry: an interlaboratory study

A first international 36Cl interlaboratory comparison has been initiated. Evaluation of the final results of the eight participating accelerator mass spectrometry (AMS) laboratories on three synthetic AgCl samples with 36Cl/Cl ratios at the 10−11, 10−12, and 10−13 level shows no difference in the sense of simple statistical significance. However, more detailed statistical analyses demonstrate certain interlaboratory bias and underestimation of uncertainties by some laboratories. Following subsequent remeasurement and reanalysis of the data from some AMS facilities, the round-robin data indicate that 36Cl/Cl data from two individual AMS laboratories can differ by up to 17%. Thus, the demand for further work on harmonising the 36Cl-system on a worldwide scale and enlarging the improvement of measurements is obvious.

First international 26Al interlaboratory comparison – Part II

A first international 26Al interlaboratory comparison was initiated and evaluation of the results of the eight participating accelerator mass spectrometry (AMS) laboratories on four synthetic samples shows no difference in the sense of simple statistical significance. However, certain interlaboratory bias is observed with more detailed statistical analyses. Some laboratories seem to underestimate the uncertainties of their measurements, and others may overestimate measurement reproducibility.

State-of-the Art Comparability of Corrected Emission Spectra.1. Spectral Correction with Physical Transfer Standards and Spectral Fluorescence Standards by Expert Laboratories

The development of fluorescence applications in the life and material sciences has proceeded largely without sufficient concern for the measurement uncertainties related to the characterization of fluorescence instruments. In this first part of a two-part series on the state-of-the-art comparability of corrected emission spectra, four National Metrology Institutes active in high-precision steady-state fluorometry performed a first comparison of fluorescence measurement capabilities by evaluating physical transfer standard (PTS)-based and reference material (RM)-based calibration methods. To identify achievable comparability and sources of error in instrument calibration, the emission spectra of three test dyes in the wavelength region from 300 to 770 nm were corrected and compared using both calibration methods. The results, obtained for typical spectrofluorometric (0°/90° transmitting) and colorimetric (45°/0° front-face) measurement geometries, demonstrated a comparability of corrected emission spectra within a relative standard uncertainty of 4.2% for PTS- and 2.4% for RM-based spectral correction when measurements and calibrations were performed under identical conditions. Moreover, the emission spectra of RMs F001 to F005, certified by BAM, Federal Institute for Materials Research and Testing, were confirmed. These RMs were subsequently used for the assessment of the comparability of RM-based corrected emission spectra of field laboratories using common commercial spectrofluorometers and routine measurement conditions in part 2 of this series (subsequent paper in this issue).

Influence of correlation on the assessment of measurement result compatibility over a dynamic range

Comparison of measurement results obtained by different measuring equipment on the same reference object is a key element in equipment qualification. The paper discusses an approach for an integrated assessment of a series of comparison measurements taken on more than one (i.e. many) reference object(s). The approach accounts for the fact that measurements taken by one (and also by the other) instrument on a series of ideally independent objects are nevertheless partially correlated due to common uncertainty contributions arising from the measurement process. The approach is exemplified for international comparisons using a (travelling) transfer instrument for the comparison of national instrument standards with a reference standard over a range of measured ozone mole fractions.

HBCD Stereoisomer Pattern in Mirror Carps Following Dietary Exposure to Pure γ-HBCD Enantiomers

1,2,5,6,9,10-hexabromocyclododecane (HBCD) is a brominated flame retardant consisting of a mixture of diastereomeric pairs of enantiomers that is a known omnipresent, environmental contaminant. The present study investigated the possibility of bioisomerization of HBCD stereoisomers. Therefore, mirror carps (Cyprinus carpio morpha noblis) were exposed to pure (+)- and (-)-gamma-HBCD, randomly sampled biweekly over a period of three and a half months and the fillets were subjected to enantiomer-specific determination of HBCD. Considering the background contamination of the fish at the beginning of the feeding period, significant enrichment of the respectively fed gamma-enantiomer was already detectable after two weeks of exposure. However, no significant enrichment of the respectively expected alpha-enantiomer was observed within this period. Thus, no evidence for the isomerization of HBCD stereoisomers was found in mirror carp under the applied conditions.

Development of two certified reference materials for acrylamide determination in foods.

Certified reference materials (CRMs) are a versatile tool for quality assurance in the chemical laboratory. In the case of acrylamide analysis, the availability of appropriate materials was rather limited. This lack of acrylamide matrix CRMs has now been overcome by the development of two European reference materials (ERM) for the determination of acrylamide in food (crispbread, ERM-BD272, and rusk, ERM-BD274). This article describes the preparation of the materials, provides the results of the homogeneity and stability studies, and presents and discusses the outcome of the certification studies. Expert laboratories from different European countries took part in the certification studies using various analytical methods. The acrylamide mass fractions were certified to 980 microg kg(-1) for crispbread and 74 microg kg(-1) for rusk.

Quality assurance in immunoassay performance-temperature effects

Temperature is one factor that influences the performance of immunoassays. Most commonly all incubation steps of the immunoassay are performed at ambient temperature. To systematically study the influence of temperature deviations on assay parameters like signal variation coefficients, limit of detection and measurement range, direct competitive enzyme immunoassays for the determination of two anthropogenic markers, caffeine and carbamazepine, were run at different temperatures above and below room temperature during individual assay steps. The temperature during the competition step had the greatest impact on the assay sensitivity yielding changes in test midpoints by a factor of 10 to 15. For carbamazepine, the test midpoints varied from 36 ng L−1, 108 ng L−1 to 378 ng L−1 employing 4 °C, 21 °C, or 37 °C as incubation temperature, respectively. The edge effect can be minimized resulting in a good plate homogeneity with small variation coefficients, when the assay is performed at ambient temperature.

State-of-the Art Comparability of Corrected Emission Spectra. 2. Field Laboratory Assessment of Calibration Performance Using Spectral Fluorescence Standards

In the second part of this two-part series on the state-of-the-art comparability of corrected emission spectra, we have extended this assessment to the broader community of fluorescence spectroscopists by involving 12 field laboratories that were randomly selected on the basis of their fluorescence measuring equipment. These laboratories performed a reference material (RM)-based fluorometer calibration with commercially available spectral fluorescence standards following a standard operating procedure that involved routine measurement conditions and the data evaluation software LINKCORR developed and provided by the Federal Institute for Materials Research and Testing (BAM). This instrument-specific emission correction curve was subsequently used for the determination of the corrected emission spectra of three test dyes, X, QS, and Y, revealing an average accuracy of 6.8% for the corrected emission spectra. This compares well with the relative standard uncertainties of 4.2% for physical standard-based spectral corrections demonstrated in the first part of this study (previous paper in this issue) involving an international group of four expert laboratories. The excellent comparability of the measurements of the field laboratories also demonstrates the effectiveness of RM-based correction procedures.

Controlling uncertainty in calibration

Abstract A rigorous error-in-both variables procedure for linear and nonlinear curve fitting is described, including determination of the variance/covariance matrix of the fitted parameters. The curve parameters are determined by regression according to the maximum-likelihood functional relationship approach. The variance/covariance matrix is calculated by uncertainty propagation from the variances and covariances of the calibration data.