Hydrogen helps hurry harmful dioxins through GC

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  • Published: Oct 15, 2017
  • Author: Ryan De Vooght-Johnson
  • Channels: Gas Chromatography
thumbnail image: Hydrogen helps hurry harmful dioxins through GC

Separation methods for PCDDs are lengthy

Trace amounts of the persistent pollutants PCDDs and PCDFs are widespread in the environment, and accurate measurements of the various related species are important since they vary in their toxicity. An EU standard, EN 1948-1,2,3.5, details official analysis methods for these compounds. The method requires clear separation of the 17 most toxic congeners (those with chlorines in the 2, 3, 7 and 8 positions) by GC, prior to high-resolution mass spectrometry. However, such a separation is not always possible on any one column, so two columns have to be used in many cases. The run times per column are also long, making it hard for laboratories to keep up with a large number of samples.

The Rome-based researchers have devised a new method for carrying out GC-MS on PCDDs and PCDFs, which uses hydrogen as the carrier gas, rather than helium. Hydrogen gives shorter run times than helium for the equivalent separation and is also much cheaper. Tandem mass spectrometry (MS/MS) was used to detect the products, two parent ions and their related transitions being examined for each group of isomers.

Quicker dioxin GC method uses hydrogen as a carrier gas

A standard mixture of PCDDs and PCDFs was separated by GC using a Thermo Fisher Trace GC Ultra instrument fitted with a Thermo Fisher TraceGOLD TG-XLBMS 60 m column, using hydrogen as the carrier gas. The flow rate was optimised to 3 mL/min, and the column temperature was taken from 150 to 320 °C in a series of ramps. Under these conditions, all the compounds with chlorines occupying the 2, 3, 7 and 8 positions were clearly separated. The new method using hydrogen gave a 35% run time reduction and slightly sharper peaks compared with that using helium with the same column.

A Thermo Fisher TSQ Quantum Triple Stage quadrupole mass spectrometer was used with electron ionisation (EI) and Thermo Fisher XCalibur software. The use of hydrogen instead of helium decreased the MS resolution by roughly 20%, as there was higher pressure in the spectrometer. However, clear precursor and product ions were still identified for each group of isomers.

Overall, the new method met the criteria of the EU standard, giving good linearity and reliability. The method was applied to various samples of fly ash, including three samples used in an inter-laboratory test. The fly ash samples were extracted with toluene and the extracts were concentrated to small volume. In order to remove impurities, the concentrated solutions were put through a column consisting of different layers: anhydrous sodium sulphate, activated silica, acidic activated silica, activated silica, activated silica with silver nitrate, activated silica and anhydrous sodium sulphate. The products were then absorbed onto an SPE (solid-phase extraction) cartridge, containing Super I basic alumina. The cartridge was washed with n-hexane to remove alkanes, then with n-hexane/dichloromethane (94:6) to remove polychlorinated biphenyls and finally with n-hexane/dichloromethane (50:50) to extract the desired PCDDs and PCDFs. The fly ash results were in line with those from other laboratories.

New GC method for dioxins meets EU standards

The new, quicker GC method gave accurate results and successfully met EU standards. It will be interesting to see how widely it will be used in the future. The use of hydrogen instead of helium as a carrier gas can speed up analysis and save money since hydrogen is much less expensive. However, appropriate safety precautions should be taken to minimise the risk of hydrogen fires and explosions.

Related Links

Journal of Separation Science, 2017, 40, 3469-3478. Benedetti et al. Analysis of polychlorodibenzo-p-dioxins and polychlorodibenzofurans in stationary source emissions in GC–MS/MS using hydrogen as the carrier gas.

LCGC North America, 2010, 28, 16-27. Heseltine. Hydrogen as a carrier gas for GC and GC-MS.

Wikipedia, Polychlorinated dibenzodioxins

Article by Ryan De Vooght-Johnson

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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