Rhoderick, GC, et al. 2019. Stability of gaseous volatile organic compounds contained in gas cylinders with different internal wall treatments. Elem Sci Anth, 7: 28.Measurements of volatile organic compounds (VOCs) have been ongoing for decades to track growth rates and assist in curbing emissions of these compounds into the atmosphere. To accurately establish mole fraction trends and assess the role of these gas-phase compounds in atmospheric chemistry it is essential to have good calibration standards. A necessity and precursor to accurate VOC gas standards are the gas cylinders and the internal wall treatments that aid in maintaining the stability of the mixtures over long periods of time, measured in years. This paper will discuss the stability of VOC gas mixtures in different types of gas cylinders and internal wall treatments. Stability data will be given for 85 VOCs studied in gas mixtures by National Metrology Institutes and other agency laboratories. This evaluation of cylinder treatment materials is the outcome of an activity of the VOC Expert Group within the framework of the World Meteorological Organization (WMO) Global Atmospheric Watch (GAW) program.
We report a pilot study organized within the Consultative Committee for Amount of Substance (CCQM), in which the ozone reference standards of 23 institutes have been compared to one common reference, the BIPM ozone reference standard, in a series of bilateral comparisons carried out between July 2003 and February 2005. The BIPM, which maintains as its reference standard a standard reference photometer (SRP) developed by the National Institute of Standards and Technology (NIST, United States), served as pilot laboratory. A total of 25 instruments were compared to the common reference standard, either directly (16 comparisons) or via a transfer standard (9 comparisons). The comparisons were made over the ozone mole fraction range 0 nmol/mol to 500 nmol/mol.Two reference methods for measuring ozone mole fractions in synthetic air were compared, thanks to the participation of two institutes maintaining a gas-phase titration system with traceability of measurements to primary gas standards of NO and NO2, while the 23 other instruments were based on UV absorption.In the first instance, each comparison was characterized by the two parameters of a linear equation, as well as their related uncertainties, computed with generalized least-squares regression software. Analysis of these results using the Birge ratio indicated an underestimation of the uncertainties associated with the measurement results of some of the ozone standards, particularly the NIST SRPs.As a final result of the pilot study, the difference from the reference value (BIPM-SRP27 measurement result) and its related uncertainty were calculated for each ozone standard at the two nominal ozone mole fractions of 80 nmol/mol and 420 nmol/mol.Main text.
To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM.
Trimethylsilanol (TMSOH) can cause damage to surfaces of scanner lenses in the semiconductor industry, and there is a critical need to measure and control airborne TMSOH concentrations. This study develops a thermal desorption (TD)-gas chromatography (GC)-mass spectrometry (MS) method for measuring trace-level TMSOH in occupational indoor air. Laboratory method optimization obtained best performance when using dual-bed tube configuration (100 mg of Tenax TA followed by 100 mg of Carboxen 569), n-decane as a solvent, and a TD temperature of 300°C. The optimized method demonstrated high recovery (87%), satisfactory precision (<15% for spiked amounts exceeding 1 ng), good linearity (R
2 = 0.9999), a wide dynamic mass range (up to 500 ng), low method detection limit (2.8 ng m−3 for a 20-L sample), and negligible losses for 3-4-day storage. The field study showed performance comparable to that in laboratory and yielded first measurements of TMSOH, ranging from 1.02 to 27.30 μg/m3, in the semiconductor industry. We suggested future development of real-time monitoring techniques for TMSOH and other siloxanes for better maintenance and control of scanner lens in semiconductor wafer manufacturing.
Dimethyl sulphide (DMS) plays an important role in atmospheric chemistry and climate change. Ambient DMS is monitored in a global network and reported at sub-nanomole per mole (nmol/mol) levels. Developing traceable, accurate DMS standards at ambient levels is essential for tracking the long-term trends and understanding the role of DMS in the atmosphere. Gravimetrically prepared gas standards in cylinders are widely used for calibrating instruments. Therefore, a stable primary standard gas mixture (PSM) is required for traceable ambient DMS measurement at remote sites. In this study, to evaluate adsorption loss on the internal surface of the gas cylinder, 6 nmol mol−1 DMS gas mixtures were prepared in three types of aluminium cylinders: a cylinder without a special coating on its internal surface (AL), an Aculife IV + III-treated cylinder (AC), and an Experis-treated cylinder (EX). There was little adsorption loss on the EX cylinder, whereas there was substantial adsorption loss on the other two cylinders. The EX cylinder was used to prepare 0.5, 2, 5, and 7 nmol mol−1 DMS PSMs with relative expanded uncertainties of less than 0.4%. The DMS PSMs were analytically verified and consistent within a relative expanded uncertainty of less than 1.2%. The long-term stability of the 7 nmol mol−1 DMS PSM was assessed by tracking the ratio of the DMS to the internal standard, benzene. The results showed that the DMS was stable for about seven months and it was projected to be stable for more than 60 months within a relative expanded uncertainty of 3%.
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