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 (Feret_min) 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.

A method employing supercritical fluid extraction (SFE) and GC coupled with microwave-induced plasma atomic emission spectrometry (MIP–AES) is presented for the determination of methylmercury in sediments. Butylmagnesium chloride was used to derivatize the target compound to butylmethylmercury which is amenable to GC. Using a commercially available reference sediment (PACS-1, National Research Council of Canada) as the model sample, a factorial design was utilized to investigate the effect of three variables; density, temperature and flow rate, on the extraction efficiency. An extraction efficiency of 49 ± 0.5% could be obtained for a 37.5 min dynamic extraction, corresponding to 25 thimble volumes of supercritical CO₂, and using purified support sand. Studies on the efficacy of SFE for another sediment matrix as a function of time have also been undertaken. Repeated pressure reductions in combination with support sand were found to increase the extraction efficiency of methylmercury from PACS-1 but not from a sediment issued by the Community Bureau of Reference (BCR) as part of an interlaboratory comparison. For PACS-1 this resulted in an increase in the average extraction efficiency to 96% for duplicate determinations following 50 thimble volume sweeps. Distillation was used as a reference method for isolation of methylmercury from sediments. Parallel extractions of the BCR sediment, using GC–MIP–AES for the final determination, gave results that were in good agreement and corresponded well with data submitted during the intercomparison exercise. The detection limit for the methylmercury in sediment using the described SFE GC–MIP–AES method is estimated to be 0.1 ng g^–1 based on a 20 µl injection, 0.5 g of sample and three times the blank level. It is proposed that the co-extracted sulfur from the sediment mediates the transport of methylmercury and, to some extent, inorganic mercury from the sediments. This is supported by the strong correlation between the concentrations of butylmethylmercury and dibutylsulfide found in the toluene extract. Using a stable isotope tracer, ¹⁹⁹Hg, and ICP-MS, evidence for the spurious formation of methylmercury during SFE under certain conditions is also presented.

A method for the simultaneous determination of mercury species at sub-ng l^–1 levels in natural waters is described. The detection limits are 0.05 ng l^–1 for methyl- and ethylmercury and 0.15 ng l^–1 for inorganic mercury. Methyl-, ethyl- and inorganic mercury are first preconcentrated on a dithiocarbamate resin packed in a miniature 60 µl 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 µl) 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.

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 flow) 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^–1 (3 s criterion). The long-term stability over 4 h for the raw signal ranges between 1.0% RSD for ⁷Li to 2.1% RSD for ⁴⁰Ca operating under cool plasma conditions. Under normal plasma conditions the corresponding values are 6.9% RSD for ²⁰⁸Pb to 12.8% RSD for ⁵⁹Co. Accuracy for the determination of 16 different elements is assessed by measuring NIST 1643d (trace elements in water), yielding results in agreement with certified values. Results for isotopic ratio determinations demonstrate that a precision of 0.07–0.7% RSD is obtained within a short data acquisition period.