Atmospheric eye-opener: Illegal carbon disulphide levels found near pulp factory by sensitive GC/MS method

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  • Published: May 1, 2012
  • Author: Steve Down
  • Channels: Gas Chromatography
thumbnail image: Atmospheric eye-opener: Illegal carbon disulphide levels found near pulp factory by sensitive GC/MS method

Shifty carbon disulphide

Carbon disulphide has been measured in the air near an industrial pulp plant using a novel GC/MS procedure that eliminates interferences from other atmospheric pollutants and will allow routine airborne monitoring down to low levels.

The well-publicised benefits of tea are ascribed largely to the presence of a series of compounds known as polyphenols, which have antioxidative properties and mop up damaging free radicals in the body. They appear to provide protection against a number of conditions, including heart disease, atherosclerosis, liver disease and some cancers.

Carbon disulphide is a ubiquitous but elusive airborne pollutant. It is present in most air samples tested but can be very difficult to measure, due to the presence of other atmospheric chemicals like ozone, sulphur dioxide and nitrogen oxides, which can interfere in analytical procedures.

A team of scientists in Spain has now developed a new method for measuring CS2 in air, which eliminates these interferences and is sufficiently accurate and reliable to apply to routine monitoring for air pollution control. Luis Antonio Tortajada-Genaro from the Polytechnic University of Valencia, with co-researchers from the Center for Environmental Research (CIMA), Torrelavega, and the Centre for Environmental Studies of the Mediterranean (CEAM), Valencia, adopted a novel solid-phase sampling method before GC/MS analysis.

The desire to measure CS2 lies with its small but recognised influence on atmospheric chemistry and the climate, as well as its potential effects on human health. It targets the nervous system, increases the risk of heart disease and can cause brain damage, although these risks are generally associated with higher levels that might be encountered by industrial personnel or after a leakage incident.

There is also the social consequence of airborne CS2 due to its relatively high odour threshold. The sweet-smelling gas can be detected at levels above 0.1-0.5 ppm, which is only about 20-fold higher than that of hydrogen sulphide.

Although you might think that CS2 is a purely manmade pollutant, it has been estimated that 40-80% of air-bound releases are natural, originating from the seas and oceans, volcanoes, wildfires, aquatic microorganisms and vegetation. The industrial sources include oil and gas processing, the chemical industry, and the wood pulp industry, which was the focus of the current study.

Sorbent trapping

In order to trap CS2 from the air, the researchers tested two solid-phase sorbents based on activated coconut charcoal, Orbo-32 and SKC, the latter also containing sodium sulphate. Both devices were highly porous with large surface-to-volume ratios and small diffusion distances and they were compared for low-volume outdoor sampling using a pump to draw through the air.

Toluene and hexane were compared for extraction of CS2 from the cartridges. Both solvents gave statistically similar recoveries of 89-103% apart from the use of toluene with the Orbo-32.

The extracts were analysed directly by GC/MS using a 5% diphenyl-95% methyl polysiloxane column, with different temperature programs depending on the solvent. The mass spectrometer was operated in full-scan electron ionisation mode and CS2 was quantified by extracting the base ion chromatographic peak.

The team decided not to use selected ion monitoring, which would give a better detection limit, because this would lose the extra information provided in full-scan mode which would help to identify any potential interfering compounds in the samples. As it is, the detection limits were 0.3-0.9 pg/m3, which were well below the EU threshold limit of 10 µg/m3. The method also had acceptable inter-day and intra-day reproducibility.

EU limits exceeded in air near industrial plant

The procedure was validated using smog chamber experiments in a photoreactor in which measurements were also carried out by FTIR spectroscopy and differential optical absorption spectroscopy. There was excellent agreement between all three techniques over a wide range of CS2 concentrations from 7-3110 µg/m3. The best correlation was obtained with the SKC cartridge and hexane as solvent.

In addition, experiments with added excess H2S, O3 and SO2 confirmed that these three atmospheric gases did not interfere with the extraction process by interacting with the sorbent cartridges.

When real samples are analysed, there is the danger of influential matrix effects and unexpected interfering compounds. Both of these scenarios were ruled out after air from an industrial region in Paterna, Spain was sampled and added known amounts of CS2 for a standard addition experiment.

The main area of interest was the air near an industrial cellulose pulp plant in Torrelavega. Samples were collected over 13 days and the CS2 concentrations were found to vary from 1-141 µg/m3, with levels exceeding the EU limit of 10 µg/m3 in 75% of cases.

The highest concentrations correlated with the wind direction blowing from the factory to the sampling site and also matched the trends in the levels of SO2 and H2S. Conversely, the lowest concentrations were found when the wind was blowing away from the sampling site. All three chemicals are by-products of the pulping process and the correlation confirms that the analytical procedure can be used in this environment.

The new validated method emphasises the need for regular CS2 monitoring and will be useful for measuring the emission of CS2 from point sources with the ultimate aim of maintaining them at currently acceptable levels. This will help to prevent air pollution episodes, cut out malodours and minimise the effects on human health.

Related Links

Microchemical Journal 2012, 101, 37-42: "Development of a gas chromatography-mass spectrometry method for the determination of carbon disulfide in the atmosphere"

Article by Steve Down

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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