1,720,983 research outputs found
Stability of a NDIR analyser for CO2 at atmospheric concentration
No full textCarbon dioxide monitoring is significant in the environmental field since this gas plays an important role in the greenhouse effect. In order to determine CO2 concentration and to develop simulation models, it is necessary to carry out measurements which are accurate and comparable in time and space, i.e. SI-traceable. Non-dispersive infrared (NDIR) analysers are employed for CO2 measurements, as they are precise and stable. In order to achieve traceability, such instruments have to be characterized and calibrated. At the Istituto di Metrologia "G. Colonnetti" - CNR, a procedure for calibrating NDIR analysers for CO2 at atmospheric level was developed, which enables to calculate a correction for the analyser output. In addition, a complete uncertainty analysis was carried out and a correct traceability chain was established. The goal of the present work is the study of the stability of a NDIR analyser by repeating calibrations during three years and comparing the correction curves obtained to identify a proper re-calibration interval for such analysers. The investigated instrument has good repeatability and reproducibility, hence satisfactory stability during time, as shown by the short-term and long-term compatibility of calibration curves
Determination of PCBs in organic solutions: an example of traceability chain
No full textPolychlorinated biphenyls (PCBs) are extremely persistent and widespread environmental pollutants. Because of their potential health impacts on a wide variety of biota, including human beings, they belong to the twelve classes of Persistent Organic Pollutants (POPs) selected by United Nations Environment Programme (UNEP) under the Stockholm Convention on POPs in 1997. For this reason, the European Community requires the development of measurement methods and standards in order to obtain comparable, consistent, reliable and high quality results for the measurements of these kinds of compounds. The present work deals with the establishment of a traceability chain for the analysis of various PCBs congeners in organic solutions. Traceability is the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparison all having stated uncertainties. The unbroken chain of comparisons is called traceability chain. A correct traceability chain needs to be established in order to obtain high quality reliable results and to compare results of measurements carried out in different places and by different laboratories. Traceable PCBs standards in iso-octane were prepared by accurate weighings from certified reference materials; an uncertainty budget was made, which took into account all the possible uncertainty sources, as the uncertainty of the reference materials and the uncertainty in the mass measurements. Various PCBs congeners were determined via gas-chromatography coupled with mass-spectrometry. The identification of the PCBs congeners in different organic solutions was made by means of the interpretation of the mass spectra obtained in the scan mode. The gas chromatograph coupled with an ion trap mass spectrometer was calibrated using the traceable standards prepared by weighing. The PCBs congeners amount was determined comparing the ion current of proper mass chromatograms of specific fragment ions, selected on the basis of the mass spectra of each congener
Uncertainty estimation in chemical measurements: carbon dioxide determination at atmospheric concentration
No full textThe present work deals with the evaluation of measurement uncertainty in the determination of carbon dioxide (CO2) concentration in atmosphere, given the high relevance of this greenhouse gas that influences earth climate. In order to carry out CO2 measurements, non dispersive infrared (NDIR) analysers are usually employed as they are stable and scarcely affected by interferences from other air components or pollutants. Typical uncertainty sources are the resolution of the analyser, its time drift and the contributions due to instrument calibration, which is required in order to produce traceable measurement results. The calibration uncertainty takes into account the uncertainty of the composition of the calibration gas mixtures, the instrument repeatability and the possible or residual lack of fit of the adopted mathematical model
Stability assessment of density reference liquids supported by GC–MS analysis (density reference liquids stability supported by GC–MS)
No full textDensity measurements are frequently associated to specific requirements to evaluate the quality of a process or to determine mass and/or volume of the material. Certified reference liquids can be used to assure metrological traceability of density measurements to the SI with uncertainty lower than 0.005%. This paper presents the new approach of INRIM to set density standards.
The procedure involved accurate density determinations of some reference liquids which were supported by gas-chromatography coupled with mass spectrometry (GC–MS) in order to assess their homogeneity and short-term stability. GC–MS analyses on tetrachloroethylene and trichloroethylene were carried out before and after density measurements. Samples that had undergone to variations in density value showed also different gas-chromatographic profiles. In the same time, samples that had not undergone to density variations kept similar gas-chromatographic profiles. The results support the approach of combining independent methods in order to set physico-chemical properties of reference materials
Facility for the preparation of primary gas mixtures by gravimetry
No full textPresso l’ I.N.RI.M. – Sezione Massa è stato progettato e realizzato un sistema per la preparazione, mediante il metodo gravimetrico, di miscele gassose campione primarie dato che la realizzazione di tali miscele rappresenta un obiettivo importante per l’Istituto.
Il presente prodotto descrive le caratteristiche della stazione per il riempimento e lo svuotamento di bombole le cui parti principali sono le linee di distribuzione per il gas, un sistema per il vuoto e una bilancia per la pesata preliminare delle bombole. Vi è inoltre un comparatore di massa per la pesata di precisione corredato di uno scambiatore meccanico per la movimentazione automatica delle bombole. Sono quindi riportati i risultati ottenuti nel primo Confronto Chiave Internazionale CCQM-K52 effettuato dall'INRIM (M. Sega: persona di riferimento per l'INRIM)utilizzando come campioni le miscele di CO2 in aria preparate mediante la suddetta stazione.A system for the gravimetrical preparation of primary reference gas mixtures was projected and set up at I.N.RI.M.. The realisation of such mixtures is an important goal for a national metrology institute. The features of the apparatus to fill and evacuate the cylinders station are described: its main parts are the lines for distributing the gases, a vacuum system and a balance for the preliminary weighing of the cylinders. The facility has, in addition, a mass comparator for high accuracy weighing and a system for exchanging the cylinder during the weighing process. The results obtained in the International Key Comparison "CCQM-K52" (INRIM contact: M. Sega)are presented. This is the first Key Comparoison carried out by INRIM in the chemical field using as measurement standards a set of primary mixtures of CO2 in air prepared at INRIM with the described facility
The use of GCMS to support stability assessment of density reference liquids
No full textDensity measurements are frequently associated to specific requirements in order to evaluate the quality of a process or to determine mass and/or volume of the material. Certified reference liquids can be used to assure metrological traceability of density measurements to the International System of Units - SI with uncertainty lower than 0.005 %. This paper presents the new approach of the Italian National Institute of Metrological Research (Istituto Nazionale di Ricerca Metrologica - INRIM) to set density standards.
The procedure has involved accurate density determinations of some liquid samples intended to be used as references with, in addition, analysis by means of gas-chromatography coupled with mass spectrometry (GC-MS) to support the short-time stability in addition to assess that any sample had not been polluted during the density investigation. In this exercise analyses on various liquid were carried out before and after density measurements. Changing in the composition of some tested samples has been observed as well as changing of the density values. The results show a good sensitivity in combining independent methods in order to set physico-chemical reference materials
Traceability in routine chemical measurements: an example of application in the determination of CO2 at atmospheric concentration
No full textIn routine chemical measurements traceability can be achieved by using analytical instruments calibrated against primary reference materials. In the present work the calibration of a CO2 nondispersive infrared (NDIR) analyzer with measuring range 0-2000 umol/mol of CO2 and a resolution of 5 umol/mol is reported. A procedure with working reference gas mixtures (WRMs) has been adopted, which requires seven calibration points. Primary reference gas mixtures (PRMs) are used to validate WRMs in a narrower range around the average atmospheric CO2 concentration value. In this range the relative uncertainty reached is of the order of some parts in 10(3) and the corrections are between 1 umol/mol and 5 umol/mo
Metrological traceability chain for PCBs: INRIM activity
No full textMetrology in chemistry has its own features, which distinguish it from classical metrology: due to the lack of primary methods applicable in routine measurements, metrological traceability of measurement results can be achieved by using in a proper way suitable certified reference materials (CRMs), which can assure a direct relation to a reference. This article deals with the activity of the Italian National Institute of Metrological Research (Istituto Nazionale di Ricerca Metrologica-I.N.Ri.M.) on the analysis of various polychlorinated biphenyls congeners in organic solution by means of gas-chromatography coupled with mass spectrometry. The metrological traceability approach in the quantification step is pursued via calibration solutions prepared by gravimetrically diluting a CRM. The uncertainty for the calibration solutions was evaluated taking into account all the relevant contributions
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