PRODUCTION OF GASEOUS CERTIFIED REFERENCE MATERIALS AT INRiM FOR AMOUNT OF SUBSTANCE FRACTION OF CO2

Due to the involvement of carbon dioxide (CO2) in the global warming effects, INRiM is developing certified reference materials (CRMs) of CO2 in synthetic air. The mixtures are prepared by gravimetry, a primary method, and verified by NonDispersive Infrared spectroscopy. The CO2 amount fraction in the mixtures and its associated uncertainty are the certified properties of the CRMs. A corresponding stability study of the amount fraction of CO2 is also ongoing. Further work foresees the development of CRMs for the isotopic composition of CO2 in air, after the participation in specific international comparisons

Realisation of primary mixtures of CO2 in air at known isotopic composition

The monitoring of the increasing levels of CO2 in atmosphere, together with the discrimination between the natural and anthropogenic sources of CO2, is of utmost importance to support climate change studies and the reduction of the CO2 emissions from human activities in the close future. The involvement of the metrological community is essential to achieve the comparability of results over space and time, to assure accuracy and metrological traceability, linking all the individual measurement results to common and stable reference standards. The availability of sound and affordable reference materials for the measurement of the isotopic composition of CO2 at ambient amount fraction is foreseen to support the researchers operating in the isotope measurement field, by means of spectroscopic techniques, to assure the metrological traceability for the determination of the isotopic composition of CO2 in air. Reference gas mixtures at known isotopic composition produced by means of primary methods, such as gravimetry, represent a good opportunity for this purpose. At INRiM, the Italian National Metrology Institute, the realization of gaseous reference materials of CO2 in air at known δ13C-CO2 started within the European Joint Research Project (JRP) 16ENV06 SIRS, and continued with the JRP 19ENV05 STELLAR. The reference mixtures are realized by the gravimetric method, following the ISO standard 6142-1, in high-pressure cylinders of aluminum alloy, obtaining low preparation uncertainties of 0.33 % for the CO2 amount fraction at atmospheric level. These mixtures are prepared from parent mixtures at higher amount fraction, realized at INRiM from different pure CO2 sources. Non Dispersive Infrared Spectroscopy (NDIR ABB URAS 14, Switzerland) is used to verify the mixtures for their amount fraction values while Fourier Transform Infrared Spectroscopy (FTIR Thermo Scientific Nicolet iS50, USA) is used for the δ13C-CO2 value assignment. The δ13C-CO2 values of the gravimetric mixtures span in the range from +1.3 ‰ to -42 ‰. Recently, a Cavity Ring-Down Spectrometer (CRDS G2131i Picarro, USA) was acquired to double-check the isotopic composition of the prepared mixtures. Preliminary tests were carried out for the metrological characterization of the instrument, followed by the set-up of the analytical methodology for the confirmation of the isotopic composition of some mixtures prepared within the STELLAR project and sent to other project partners for analysis in the past two years. The results of the tests carried out are presented in this work, together with some future perspectives for the realization of primary reference mixtures of CO2 in air at know isotopic composition on a larger scale

Metrological challenges for the monitoring of the partial pressure of CO2 in the marine environment

The observed rising levels of carbon dioxide (CO2) in atmosphere, highly caused by anthropogenic emissions, are responsible for fundamental changes occurring also in seawater carbonate chemistry. The oceans are absorbing more CO2 from the atmosphere, which is decreasing seawater pH and leading to the acidification of marine waters, with important consequences for the global ecosystem. At present, the partial pressure of CO2 (pCO2) is one of the few variables of the marine carbon cycle directly measurable in situ. In order to achieve meaningful and significant measurement results, it is necessary to reach uncertainties small enough to discriminate observed variations due to natural fluctuations, from those due to real trends. In this framework, the development and validation of proper analytical methods and measurement standards is of utmost importance. Despite the availability of a variety of in situ sensors, currently used to monitor pCO2 in marine environment, there are several problems to be faced, such as the differences in adopted calibration methodologies and non-validated procedures, or the lack of metrological traceability and of operational harmonization for field measurements. In addition, the scarcity and expensiveness of suitable reference materials to calibrate instrumentation used for pCO2 monitoring represents an issue. A promising approach could be the provision, on a larger scale, of appropriate reference standards in gas phase to be used to calibrate pCO2 sensors, due to the stability of the CO2 in the gas mixtures. In addition, intermediate-level standards and working standards, could represent a more affordable and widespread traceability source. Concerning the analytical methods for pCO2 monitoring, Non Dispersive Infrared (NDIR) photometry is quite used, but its application could be potentiated. At INRiM, the Italian Metrology Institute, gaseous reference standards of CO2 at known amount fraction in synthetic air or nitrogen are produced by the gravimetric method. In the framework of the H2020 Project “MINKE - Metrology for Integrated Marine Management and Knowledge-Transfer Network”, feasibility studies are ongoing to extend the use of these primary mixtures to the calibration of sensors for pCO2 in seawater, in cooperation with the National Institute of Oceanography and Applied Geophysics (OGS). In the present work, some preliminary results of this activity will be presented

METROLOGICAL TRACEABILITY OF MOISTURE CONTENT MEASUREMENTS IN PLANT-ORIGIN BULK MATERIALS

This document explains advantages and disadvantages of the measurement methods for the moisture content determination of plant-based materials in order to identify the best one which can provide metrological traceability to SI units. The term “moisture” is generic and, to have proper Calibration and Measurement Capabilities (CMCs) and Certified Reference Materials (CRMs), a better specification of the measurand should be given. Currently, no CMCs for moisture content measurement in the plant-origin bulk materials, as well as respective CRMs, are available in the KCDB. Undoubtedly, those CMCs and CRMs are crucially needed to provide metrological traceability in this area

Generation of CO2 gas mixtures by dynamic dilution for the development of gaseous certified reference materials

The use of Certified Reference Materials (CRMs) is of utmost importance to achieve the comparability and traceability of data, which are essential features of measurement results in environmental and climate fields. The present paper focuses on the generation of gas mixtures at known composition of carbon dioxide at atmospheric amount-of-substance fraction in synthetic air by means of a dynamic dilution system, designed and implemented at the Istituto Nazionale di Ricerca Metrologica (INRiM). The validation of the dynamic system in terms of amount-of-substance fraction is presented. The system was also used to verify the carbon dioxide amount-ofsubstance fraction of a suite of gas mixtures gravimetrically prepared at INRiM in the framework of the EMPIR Joint Research Project 19ENV05 – STELLAR. Dynamic dilution proved to be an effective tool for the preparation and certification of CRMs for gaseous pollutants (i.e. carbon dioxide, nitrogen oxides) relevant for monitoring environmental pollution and climate changes

Metrology for marine monitoring: cooperation between INRiM and ENEA

The study of the status of the marine environment is typically carried out by monitoring several parameters, both chemical and physicochemical, classified as Essential Ocean Variables by the Global Climate Observing System. These variables are useful to obtain quantifiable indications to monitor the phenomena occurring in the oceans and to relate them to the changes occurring on the global scale in all the environmental compartments. In this framework, a research collaboration is ongoing between the Italian National Metrology Institute (INRiM) and the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), to support the collection, validation and maintenance of reliable and accurate databases, by applying the concepts of metrology from the laboratory to the field. Among the main Essential Ocean Variables, the dissolved oxygen and the partial pressure of carbon dioxide are key parameters to monitor the changing ocean and are largely measured in stations around the globe. INRiM and ENEA are collaborating in the measurement of these variables, focusing on the metrological traceability issues and the measurement uncertainty evaluation, also exploiting innovative Internet of Underwater Things (IoUT) in situ monitoring systems developed by WSense, spinoff of Sapienza University

A portable setup for the voltammetric determination of total mercury in fish with solid and nanostructured gold electrodes

A simple procedure for field fish sample pretreatment was developed. This treatment in combination with square wave anodic stripping voltammetry (SW-ASV) with solid gold electrodes (SGE) and gold nanoparticle-modified glassy carbon electrodes (AuNPs-GCE) was applied for the determination of total mercury content. A certified reference material (CRM, Tuna Fish BCR 463), ten freeze-dried samples of canned tuna and two fresh fish samples were analysed both with a bench-top voltammetric analyser after microwave digestion and with a portable potentiostat after mild eating using a small commercial food warmer. The results obtained by the two SW-ASV approaches and by a Direct Mercury Analyser (DMA), the official method for mercury determination, were in very good agreement. In particular, (i) the results obtained with in field procedure are consistent with those obtained with the conventional microwave digestion; (ii) the presence of gold nanoparticles on the active electrode surface permits an improvement of the analytical performance in comparison to the SGE: the Limit of Quantification (LOQ) for mercury in fish-matrix was 0.1 μg L−1 (Hg cell concentration), corresponding to 0.06 mg kg−1 wet fish, which is a performance comparable to that of DMA. The pretreatment proposed in this study is very easy and applicable to fresh fish; in combination with a portable potentiostat, it proved to be an interesting procedure for on-site mercury determination