Arul Murugan

Preparation and Validation of Fully Synthetic Standard Gas Mixtures with Atmospheric Isotopic Composition for Global CO2 and CH4 Monitoring

We report the preparation and validation of the first fully synthetic gaseous reference standards of CO2 and CH4 in a whole air matrix with an isotopic distribution matching that is in the ambient atmosphere. The mixtures are accurately representative of the ambient atmosphere and were prepared gravimetrically. The isotopic distribution of the CO2 was matched to the abundance in the ambient atmosphere by blending (12)C-enriched CO2 with (13)C-enriched CO2 in order to avoid measurement biases introduced by measurement instrumentation detecting only certain isotopologues. The reference standards developed here have been compared with standards developed by the National Institute of Standards and Technology and standards from the WMO scale. They demonstrate excellent comparability.

A novel method for measuring trace amounts of total sulphur-containing compounds in hydrogen

A novel method for the analysis of total sulphur-containing impurities in a hydrogen matrix has been developed. This method has a limit of detection (LoD) significantly lower than that maximum amount fraction for sulphur-containing compounds (4 nmol mol(-1)) specified by the international standard for hydrogen to be used in fuel cell vehicles (ISO 14687-2). To measure the LoD for this method, a novel gas standard containing five different sulphur-containing compounds at low nmol mol(-1) amount fractions has been gravimetrically prepared. Stable primary gas standards that are traceable to the SI were used to successfully validate the amount fractions of the sulphur-containing compounds in this gas standards using gas chromatography with flame ionisation detection (GC-FID) and sulphur chemiluminescence detection (GC-SCD).

Measurement of ‘total halogenated compounds’ in hydrogen: Is the ISO 14687 specification achievable?

A purity specification in an international standard (ISO 14687) for hydrogen for use in proton exchange membrane fuel cells is discussed. The specification, which is referenced in a recent EU directive, sets maximum limits for 14 impurities in hydrogen. We consider one entry in the specification, total halogenated compounds, and conclude that no currently available analytical method is able to measure total halogenated compounds in a robust, traceable and accurately quantifiable manner. Three suggestions for addressing this problem when the standard is revised are given, namely (1) replacing ‘total halogenated compounds’ with a list of key halogenated compounds that can be measured individually, (2) identifying compounds whose measurement is more routine to act as ‘canary species’ for hydrogen produced from different sources and (3) setting different specifications for hydrogen produced from different sources. Prior to the revision of ISO 14687, we propose that inductively coupled plasma mass spectroscopy provides the best currently available analytical solution to estimate the amount fraction of halogenated compounds in hydrogen.

Advancing the analysis of impurities in hydrogen by use of a novel tracer enrichment method

A novel tracer enrichment method for concentrating the impurities in hydrogen has been developed and validated. The method calculates the enrichment factor by spiking the gas mixture with krypton and measuring the change in amount fraction before and after enrichment. This method was compared against an existing non-ideal gas law enrichment method which calculates the enrichment factor by measuring the change in pressure and temperature of the hydrogen gas mixture. The comparison was achieved by performing tests where both methods were successfully used to calculate the amount fractions of nitrogen, carbon monoxide and methane in a mixture of hydrogen with a known composition. An uncertainty budget for both methods was also developed showing that the new tracer enrichment method gives a lower uncertainty of measurement compared to the non-ideal gas law enrichment method. An additional benefit to using the tracer enrichment method is that accurate measurements can be performed even during an air leak or membrane failure. It was concluded that a combination of both of the two enrichment techniques would form the ideal measurement tool for performing accurate measurement of impurities while being able to detect leaks and monitor the enrichment factor.