Enea Pagliano

High-precision determination of inorganic nutrients (i.e., nitrite, nitrate, phosphate, and silicate) in seawater is paramount for understanding variations in marine biogeochemical cycles. Historically, the lack of consistency between nutrient data sets has been the Achilles’ heel for large-scale oceanographic studies and the regular use of certified reference materials (CRMs) was identified as a solution to improve data quality. In this study, the preparation and certification of NRC MOOS-4 nearshore seawater CRM for nutrients are presented. The discussion is focused on the optimization of the analytical methods that were developed in decade-long research. On the one hand, the classical spectrophotometric methods were studied with attention to potential systematic biases not normally considered in routine analysis. On the other hand, higher-order (isotope dilution) methods with better performance characteristics were developed for accurate quantitation of nitrite, nitrate, and silicate. This rigorous method development work resulted in exceptional agreement between nutrient data obtained by traditional and modern analytical methodologies and allowed improvement of measurement uncertainties with respect to previous MOOS-3 CRM. As a result, MOOS-4 could be certified with expanded (k = 2) uncertainties between 0.8% and 2.6%, consistent with the requirements of the oceanographic community (i.e., c(NO₂ ⁻) = 1.676 ± 0.013 µmol/L, c(NO₃ ⁻) = 17.14 ± 0.44 µmol/L, c(PO₄ ³⁻) = 2.835 ± 0.031 µmol/L, c(SiO₂) = 7.16 ± 0.13 µmol/L). In line with the FAIR principles for scientific data management, all measurement data for value assignment and software used for data analysis was made available in the Electronic Supporting Material. Graphical Abstract

Stable gas production from radical precursors during UV-C photolysis provides a tool for investigating transition metal-mediated PVG reactions. A tutorial approach supporting photocatalytic interactions with generated transition metals is presented.

Main text: Anions or nutrients in seawater are very important targets for oceanographic research and environmental monitoring of contaminations. Quantification of minor and trace anions in seawater has always been a challenge for the extremely high salinity, disparate levels of analyte and matrix ions, and even need to be measured at levels close to the detection limits of the method performance. Evidence of successful participation in formal, relevant international comparisons is needed to support calibration and measurement capability claims (CMCs) made by the national metrology institutes (NMIs) and designated institutes (DIs). The CCQM-K161 Anions in Seawater was organized by the Inorganic Analysis Working Group (IAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) to assess the abilities of the NMIs and DIs for the accurate determination of minor and trace anions in seawater. The measurands covered chloride (16 mg/g-25 mg/g), sulfate (1 mg/g-4 mg/g), bromide (30 mg/kg-100 mg/kg), nitrate (1 mg/kg-5 mg/kg) and phosphate (60 µg/kg-300 µg/kg). Twelve national metrology institutes and designated institutes participated in this key comparison. Participants were requested to evaluate the mass fractions, expressed in mg/g for chloride and sulfate, mg/kg for bromide and nitrate, and µg/kg for phosphate (as phosphorus) in a mixed natural seawater that was spiked with the phosphate. A variety of techniques including isotope dilution inductively coupled plasma mass spectrometry (IDMS), isotope dilution gas chromatography-mass spectrometry (ID-GC-MS), ion chromatography (IC), UV visible spectrophotometry (UV-Vis), flow injection analysis (FIA) was used by the participants for the determination. The NIST Decision Tree was used to assign the KCRV estimate and to calculate the degrees of equivalence of each participants following the IAWG Guidance on Using NIST Decision Tree for Comparison Reporting from 30 June 2023. Successful participation in CCQM-K161 demonstrates measurement capabilities for determination of anions in seawater. Considering the IAWG Core Capability Matrix, this material falls into the matrix challenge called 'High salts content', which corresponds to the CCQM amount-of-substance category sea water, and so will support CMCs for the anions in a mass fraction range from 60 µg/kg to 25 mg/g. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

In this study we demonstrate that the method of standard additions can provide unreliable results in chemical analysis when the linear calibration model is forced to fit the data. A well designed standard addition experiment can still yield results biased by 10% when the analyst relies only on the linear model. Recently, the Joint Committee for Guides in Metrology (GUM-6) has emphasized the need to address the uncertainty inherent to the choice of measurement models and here we show how model averaging can provide a practical way to account for model uncertainty in the method of standard additions.

Trace element determination and speciation at the part-per-trillion level (ng L−1) are challenging for most elemental detectors and become harder when complex samples are analyzed. Solid phase microextraction (SPME) can provide matrix separation along with analyte preconcentration which are essential steps to obtain interference free and measurable signals for quantitation of inorganics at these low levels. Fiber SPME was introduced first and it is still an indispensable tool for Hg and Sn speciation, and for the analysis of volatile organometallic metabolites. In recent years, several other SPME approaches have been employed for inorganic analysis, including in-tube SPME, capillary microextraction, hollow fiber SPME, micropipette tip SPME, SPME on a stir bar, SPME on a microfluidic device and dispersive SPME. A significant advancement in coatings has closely followed the developments of novel SPME formats: at this time a number of nanocomposites and polymers were available enabling the microextraction of most transition metal ions, directly in solution, without the need for derivatization.

The determination of inorganic anions in uranium ore concentrates (UOCs) is useful to nuclear forensics for establishing the provenance of sample materials. In this collaborative study, quantitation of inorganic anions was carried out on three UOC reference materials from the National Research Council Canada: UCLO-1 (https://doi.org/10.4224/crm.2020.uclo-1), UCHI-1 (https://doi.org/10.4224/crm.2020.uchi-1), and UPER-1 (https://doi.org/10.4224/crm.2020.uper-1). The analytes were extracted into water and characterized by ion chromatography with combined standard uncertainties (u_c) between 1.6 and 11%. The highest contributor to u_c was homogeneity. Sulfate was the most abundant anion (2000–12,000 mg/kg SO₄²⁻). Other anions were in the 15–500 mg/kg range.

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, PO₄³⁻) = 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. Graphical abstract

GC-MS identification of W(CO) ₆ and OsO ₄ confirms these products of photochemical vapor generation from W( vi ) and Os( iv ) in reductive and oxidative media, respectively.