Development of a new cucumber reference material for pesticide residue analysis: feasibility study for material processing, homogeneity and stability assessment.

The feasibility of the production of a reference material for pesticide residue analysis in a cucumber matrix was investigated. Cucumber was spiked at 0.075 mg/kg with each of the 15 selected pesticides (acetamiprid, azoxystrobin, carbendazim, chlorpyrifos, cypermethrin, diazinon, (α + ß)-endosulfan, fenitrothion, imazalil, imidacloprid, iprodione, malathion, methomyl, tebuconazole and thiabendazole) respectively. Three different strategies were considered for processing the material, based on the physicochemical properties of the vegetable and the target pesticides. As a result, a frozen spiked slurry of fresh cucumber, a spiked freeze-dried cucumber powder and a freeze-dried cucumber powder spiked by spraying the powder were studied. The effects of processing and aspects related to the reconstitution of the material were evaluated by monitoring the pesticide levels in the three materials. Two separate analytical methods based on LC-MS/MS and GC-MS/MS were developed and validated in-house. The spiked freeze-dried cucumber powder was selected as the most feasible material and more exhaustive studies on homogeneity and stability of the pesticide residues in the matrix were carried out. The results suggested that the between-unit homogeneity was satisfactory with a sample intake of dried material as low as 0.1 g. A 9-week isochronous stability study was undertaken at -20 °C, 4 °C and 18 °C, with -70 °C designated as the reference temperature. The pesticides tested exhibited adequate stability at -20 °C during the 9-week period as well as at -70 °C for a period of 18 months. These results constitute a good basis for the development of a new candidate reference material for selected pesticides in a cucumber matrix.

PAHs in baby food: assessment of three different processing techniques for the preparation of reference materials.

A feasibility study for producing a matrix reference material for selected polycyclic aromatic hydrocarbons (PAHs) in baby food is reported. A commercially available baby food, containing carrots, potatoes, tomato, white beans and meat, was spiked with the so-called 15 + 1 PAHs included in the PAHs priority list for food of the EU, at a mass fraction level of 1 µg/kg. The contaminated baby food was further processed by autoclaving, freezing or freeze drying. The homogeneity of the three materials (bottle-to-bottle variation) and their short-term (4 weeks) and long-term (18 months) stability at different temperatures were assessed. To this end, an analytical method based on a solid-liquid extraction followed by cleaning up with gel permeation chromatography (GPC) and solid phase extraction (SPE) and GC-IDMS determination, was validated in-house. It could be demonstrated that the procedure fulfilled the demands for application to the homogeneity and isochronous stability studies for the candidate reference materials targeted here. All three materials proved to be sufficiently homogeneous for the intended use. Measurements on the autoclaved material provided the most promising results in terms of envisaged shelf life, although freeze drying was also found to be a suitable processing technique for most of the investigated PAHs. These results are an important step towards the development of a matrix reference material for PAHs in a processed food matrix in a presentation very similar to routine samples.

Empirical support for an evolutionary model of self-destructive motivation.

We tested predictions generated from an evolutionary account of self-destructive motivation in two survey studies of 18-24-year-old university students. As hypothesized, hierarchical regressions showed that the positive relationship between perceived burden to family and suicide ideation was amplified for participants with low measured health and romantic relationship satisfaction, and for participants with relatively young mothers. The moderating effect of maternal age was also observed in logistic regressions of suicide attempts. These effects occurred independently of depression, hopelessness, and other relevant extraneous variables. Results have implications for understanding self-destructive motivation, assessing suicide risk, and preventing suicidal thinking and behavior.

Infants' understanding of the link between visual perception and emotion: "If she can't see me doing it, she won't get angry.".

Two experiments investigated 18-month-olds' understanding of the link between visual perception and emotion. Infants watched an adult perform actions on objects. An emoter then expressed neutral affect or anger toward the adult in response to the adult's actions. Subsequently, infants were given 20 s to interact with each object. In Experiment 1, the emoter faced infants with a neutral expression during each 20-s response period but looked at either a magazine or the infant. In Experiment 2, the emoter faced infants with a neutral expression, and her eyes were either open or closed. When the emoter visually monitored infants' actions, the infants regulated their object-directed behavior on the basis of their memory of the emoter's affect. However, if the previously angry emoter read a magazine (Experiment 1) or closed her eyes (Experiment 2), infants were not governed by her prior emotion. Infants behaved as if they expected the emoter to get angry only if she could see them performing the actions. These findings suggest that infants appreciate how people's visual experiences influence their emotions and use this information to regulate their own behavior.

Feasibility study for producing a carrot/potato matrix reference material for 11 selected pesticides at EU MRL level: material processing, homogeneity and stability assessment.

The feasibility for producing a matrix reference material for selected pesticides in a carrot/potato matrix was investigated. A commercially available baby food (carrot/potato-based mash) was spiked with 11 pesticides at the respective EU maximum residue limits (MRLs), and further processed by either freezing or freeze-drying. Batches of some 150 units were produced per material type. First, the materials were assessed for the relative amount of pesticide recovered after processing (ratio of pesticide concentration in the processed material to the initially spiked pesticide concentration). In addition, the materials' homogeneity (bottle-to-bottle variation), and the short-term (1 month) and mid-term (5 months) stability at different temperatures were assessed. For this, an in-house validated GC-EI-MS method operated in the SIM mode with a sample preparation procedure based on the QuEChERS ("quick, easy, cheap, effective, rugged, and safe") principle was applied. Measurements on the frozen material provided the most promising results (smallest analyte losses during production), and also freeze-drying proved to be a suitable alternative processing technique for most of the investigated pesticides. Both the frozen and the freeze-dried material showed to be sufficiently homogeneous for the intended use, and storage at -20°C for 5 months did not reveal any detectable material degradation. The results constitute an important step towards the development of a pesticide matrix reference material.

Determination of tributyltin (TBT) in marine sediment using pressurised liquid extraction-gas chromatography-isotope dilution mass spectrometry (PLE-GC-IDMS) with a hexane-tropolone mixture.

Extraction conditions for the determination of tributyltin (TBT) in sediment samples have been developed further. The analytical procedure is based on spiking with isotopically labelled analyte, pressurised liquid extraction (PLE) with a hexane/tropolone mixture, Grignard derivatization and quantification by GC-MS. It was applied to two unknown sediment samples as part of an intercomparison exercise of the Comité Consultatif pour la Quantité de Matière (CCQM). The detection limit was approximately 1.5 ng/g TBT as Sn, while the repeatability and intermediate precision (as the coefficient of variation) were 1.9% and 3.2%, respectively. The expanded uncertainty was 6.2% (coverage factor k = 2), and the accuracy was confirmed by measurement of a certified reference material.

Intercomparison on measurements of PCBs in pork fat during the Belgian PCB-crisis.

During the Belgian PCB crisis (1999/2000) the quality of the data from the PCB monitoring were studied with a proficiency testing experiment. Pork fat that was spiked at the Institute for Reference Materials and Measurements (EC-JRC-IRMM) was sent out as unknown to all laboratories that participated in the monitoring. In parallel, the material was certified on the basis of the results of several leading PCB laboratories throughout Europe that did not participate in the monitoring. During the first round 15 to 25% deviation was experienced, while in the end of this multistep intercalibration procedure the average deviation for the respective PCBs was 10.9% (PCB 28), 13.1% (PCB 52), 10.1% (PCB 101), 10.7% (PCB 118), 10.7% (PCB 138), 9.1% (PCB 153), 8.1% (PCB 180) and 8.2% for the sum of the 7 PCBs. The concentrations measured for the higher volatile PCB 28 had a tendency to show lower levels, while for PCB 180 this was less pronounced. On the other hand, PCB 153 showed results rather to the higher side. During this exercise the material was also tested for stability by one of the certifying laboratories.