Analytical performance of an axial ICP-TOFMS, in terms of accuracy, precision, resolution, signal stability, repeatability, reproducibility, precision of isotope ratios and detection limits is reported. Cool plasma conditions (low power and high central gas ¯ow) allow the determination of K, Ca and Fe at trace levels. Detection limits for 64 elements are reported with typical values from 0.5±20 pg ml 21 (3 s criterion). The long-term stability over 4 h for the raw signal ranges between 1.0% RSD for 7 Li to 2.1% RSD for 40 Ca operating under cool plasma conditions. Under normal plasma conditions the corresponding values are 6.9% RSD for 208 Pb to 12.8% RSD for 59 Co. Accuracy for the determination of 16 different elements is assessed by measuring NIST 1643d (trace elements in water), yielding results in agreement with certi®ed values. Results for isotopic ratio determinations demonstrate that a precision of 0.07±0.7% RSD is obtained within a short data acquisition period.

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Validation of analytical methods for measurements of microplastics (MP) is severely hampered because of a general lack of reference materials, RM. There is a great need to develop such reference materials. This study presents a concept of three-component kit with immobilised MP in solid NaCl, a surfactant and clean water that can be applied for the production of many types of MP RMs. As proof of concept, an RM for polyethylene terephthalate (PET) particles in water was prepared and evaluated for its homogeneity. The particles ranged from 30 μm (Feretmin) to about 200 μm adapted by wet sieving. A specific number of PET particles were immobilized in about 0.29 g of solid NaCl by freeze-drying 1 mL of a NaCl suspension. By using manual and automated counting, twenty reconstituted 1-L water samples were evaluated for homogeneity with respect to number of PET particles from 30 μm to > 200 μm/L of water. The number of particles was 730 ± 120 (mean ± one standard deviation (SD); n = 10) and 865 ± 155 particles (n = 10) obtained by optical microscopy in two independent laboratories. This corresponded to relative SDs of 16.4 and 17.9% and a mean of 797 ± 151 particles (18.9% RSD, for n = 20). Homogeneity studies of the NaCl carrier without reconstitution resulted in 794 ± 60 particles (7.5% RSD). The homogeneity of PET in the salt carrier was also evaluated directly with respect to mass of PET per vial using an ultra-micro balance. An average mass of 293 ± 41 μg of PET was obtained (14, % RSD for n = 14). Micrographs were recorded to demonstrate the absence of major sources of contamination of the RM components. Information about the particle size distribution and particle shapes was obtained by laser diffraction (LD) and dynamic image analysis (DIA). In addition, the identity of the PET polymer was confirmed by Raman and FT-IR spectroscopy. The RM was developed for a large-scale inter-laboratory comparison of PET particles in water (ILC). Based on the homogeneity results, the material was found to be sufficiently homogeneous to be of meaningful use in the ILC. In a 3-day process, more than 500 samples of PET particles in the NaCl carrier were prepared with good potential for further upscaling with respect to the number of vials or with other kinds of polymers. The stability of PET was not evaluated but it was deemed to be stable for the duration of the ILC.

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A method for the simultaneous determination of mercury species at sub-ng I-' levels in natural waters is described. The detection limits are 0.05 ng I-1 for methyl-and ethylmercury and 0.15 ng I-' for inorganic mercury. Methyl-, ethyl-and inorganic mercury are first preconcentrated on a dithiocarbamate resin packed in a miniature 60 PI column incorporated in a closed and semi-automated flow injection system. The mercury species, which are quantitatively enriched on the resin, are completely eluted with an acidic thiourea solution, extracted into toluene as diethyldithiocarbamate complexes and butylated with a Grignard reagent. The butylated forms (2-40 pl) are injected into a gas chromatograph equipped with a retention gap, linked to a non-polar analytical column, and detected at 253.7 nm with an atomic emission detector after excitation in a microwave-induced plasma.

A set of four reference materials for the detection and quantification of silica nanoparticles (NPs) in food was produced as a proof of principle exercise. Neat silica suspensions were ampouled, tested for homogeneity and stability, and characterized for total silica content as well as particle diameter by dynamic light scattering (DLS), electron microscopy (EM), gas-phase electrophoretic molecular mobility analysis (GEMMA), and field-flow fractionation coupled with an inductively coupled mass spectrometer (FFF-ICPMS). Tomato soup was prepared from ingredients free of engineered nanoparticles and was spiked at two concentration levels with the silica NP suspension. Homogeneity of these materials was found sufficient to act as reference materials and the materials are sufficiently stable to allow long-term storage and distribution at ambient temperature, providing proof of principle of the feasibility of producing liquid food reference materials for the detection of nanoparticles. The spiked soups were characterized for particle diameter by EM and FFF-ICPMS (one material only), as well as for the total silica content. Although questions regarding the trueness of the results from EM and FFF-ICPMS procedures remain, the data obtained indicate that even assigning values should eventually be feasible. The materials can therefore be regarded as the first step towards certified reference materials for silica nanoparticles in a food matrix.

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