Careful chlorine measurements

Researchers in the US have reported a new robust system to measure accurately very low concentrations of chlorine in fossil fuels.

Chlorine is a significant pollution by-product of fossil fuel combustion, and it needs to be monitored carefully. As the environmental implications of chlorine bring tighter regulations into effect, many industries will be concerned with determining its content in fossil fuels, because the bulk of the chlorine present is emitted during combustion. Chlorine also affects mercury emission as it oxidises elemental mercury in fossil fuels to form mercury oxide.

By combining modified Carius combustion tubes - a simple technique in use since the 1940s to quantify combustion products - with negative ion thermal ionisation mass spectrometry, Maury Howard and the group at Southeastern Louisiana University have obtained accurate chlorine content measurements.

The researchers used Carius tubes to create a high-pressure, high-temperature closed system that overcomes difficulties previously associated with chlorine extraction, such as loss of sample. Evolved chlorine is trapped as silver chloride and is analysed by mass spectrometry after purification.

Howard expects the method will also be suitable for measuring chlorine isotope ratios in fossil fuels and chlorinated hydrocarbons.

Carolyn Ackers