Open AccessMolar fraction stability in dynamic preparation of reference trace gas mixtures
Author(s) -
Demichelis Alessia,
Sassi Guido,
Lecuna Maricarmen,
Sassi Maria Paola
Publication year - 2016
Publication title -
iet science, measurement and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.418
H-Index - 49
eISSN - 1751-8830
pISSN - 1751-8822
DOI - 10.1049/iet-smt.2015.0051
Subject(s) - mole fraction , fraction (chemistry) , stability (learning theory) , chemistry , allan variance , molar , reproducibility , trace (psycholinguistics) , calibration , analytical chemistry (journal) , measurement uncertainty , environmental science , environmental chemistry , mathematics , chromatography , standard deviation , computer science , statistics , geology , paleontology , linguistics , philosophy , machine learning
Volatile Organic Compounds (VOC) at trace level are common indicators for climate change and ambient air quality. The calibration of detection systems at trace level needs VOC mixtures at nmol/mol level with 5% uncertainty, the dynamic preparation can fulfil it. A source of uncertainty for dynamic generation is the stability of the VOC molar fraction averaged on the sampling time. A general method for the calculation of the relevance of the stability contribution to the total uncertainty is here proposed. VOC molar fraction is here considered as a composed quantity. Threshold values for stability contribution were set to consider it either as negligible and relevant. The stability of the operative quantities of a device, for the dynamic preparation of accurate VOC reference mixtures, was measured at the working conditions by the Allan deviation algorithm. Stabilities of operative quantities were composed to calculate the VOC molar fraction stability and their contribution to total uncertainty of VOC molar fraction. The stability of the air inlet pressure gave the main stability contribution. The stability contribution to the total uncertainty resulted to be negligible for observation times below 60 min for VOC molar fraction uncertainty of 2% at 30 nmol/mol level.