The preparation of a certified reference material of polar pesticides in freeze-dried water (CRM 606)

From sea salt to seawater: a novel approach for the production of water CRMs

Natural water certified reference materials (CRMs) are mostly available in a liquid form, and they are produced starting from suitable environmental samples. Many precautions are usually needed to avoid biological or physical degradation, including filtration, acidification, and sterilization. In this study, the drawbacks associated with liquid-based seawater CRMs were tackled by developing a salt-based seawater proxy for nutrients that could be reconstituted in water solution just before use. Phosphate, silicate, and nitrate were chosen as target analytes. Sea salt mimicking the composition of seawater was spiked with an aqueous solution of the analytes and homogenized using a high-energy planetary ball mill (u_hom < 1.2%). The salt powder CRM SALT-1 ( https://doi.org/10.4224/crm.2022.salt-1 ) demonstrated good short- and long-term stability for nutrients. When the SALT-1 was reconstituted in water at the 4.0% w/w level, the resulting solution had similar properties with respect to typical seawater in terms of major constituents (± 20%), trace metals, density (1.023 g/mL), pH (8.8-9.0), and optical properties relevant to the photometric characterization. Phosphate and silicate were quantified by photometry (molybdenum blue method, batch mode), whereas nitrate was quantified by isotope dilution GC-MS (u_char < 1.2%). In the SALT-1 reconstituted seawater solution at the 4.0% w/w salt level, the nutrient amount concentration was w(phosphate, PO₄^3-) = 1.615 ± 0.030 μmol/L, w(silicate as SiO₂) = 8.89 ± 0.31 μmol/L, and w(nitrate, NO₃^-) = 18.98 ± 0.45 μmol/L at the 95% confidence (k = 2). Overall, the SALT-1 CRM exhibits similar nutrient profile and general analytical characteristics as the MOOS-3 CRM. However, the SALT-1 has much reduced preparation, storage, and distribution cost, likely much better long-term stability, and it could enable the production of lower cost and more accessible seawater reference materials.

Direct determination of monolinuron, linuron and chlorbromuron residues in potato samples by gas chromatography with nitrogen–phosphorus detection

A gas chromatography with nitrogen-phosphorus detection direct method for methoxyurea herbicide determination in powdered potato and fresh potato samples has been developed. A previous study of the thermal stability of the phenylurea herbicides seems to confirm that the ones containing the methoxy radical, i.e. monolinuron, linuron and chlorbromuron, were stable. The herbicides were extracted from the sample through liquid-liquid extraction with dichloromethane-light petroleum (1:1), followed by solid-phase extraction in a C8 cartridge. The recoveries were in the range 84-95% for powdered potato and 86-101% for fresh potato. The RSD values were less than 10%, at 0.1 microg g(-1) concentration level (n = 4) for both types of samples. Detection limits of the method were 7.0-30 ng g(-1) for powdered potato and 6.0-50 ng g(-1) for fresh potato.