Thermal extraction coupled with gas chromatography-mass spectrometry as a tool for analysing dioxin surrogates and precursors in fly ash.

Thermal extraction-GC-MS (TE-GC-MS) is a relatively new analytical technique which demonstrates a large potential for the analysis of various solid matrices. This technique provides a rapid quantitative and simultaneous determination of a wide range of volatile and semi-volatile organic compounds without laborious sample preparation or any chemical pre-treatment. Its amenability to automation and coupling with on-line detection methods makes TE-GC-MS a promising technique, not only in laboratory analysis, but also for in situ emission monitoring. However, the number of studies dedicated to the application of TE-GC-MS to fly ashes, which are an unavoidable by-product of any thermal industrial process and also the sink of many environmental pollutants, is limited. The ability of TE-GC-MS to analyse a wide range of trace semi-volatile dioxin surrogate compounds in fly ash samples is investigated as an alternative to the well-established solvent extraction-GC-MS analysis (SE-GC-MS). Reproducibility, the effect of TE temperature, time, flow, and the influence of the analysed matrix are studied. Dedicated experiments demonstrate that the conversion (dechlorination and in situ formation) of target analytes and the decomposition of the fly ash matrix can take place at elevated TE temperatures and during prolonged TE times. Moreover, these effects are matrix-specific and vary from sample to sample. After optimizing the TE parameters, two fly ash samples of different origins are analysed and more than 50 individual analytes representing different classes of aromatic compounds are quantified and compared with those available from the SE-GC-MS analysis.

Thermogravimetric desorption and de novo tests I: method development and validation.

Thermogravimetric analysis (TGA) has been combined with evolved gas analysis (EGA) with the purpose of simulating the thermal behaviour of filter dust samples under inert (desorption) and de novo test oxidising conditions. Emphasis is on studying de novo formation of dioxins, surrogates and precursors arising from filter dust derived from thermal processes, such as municipal solid waste incineration and metallurgy. A new method is tested for sampling and analysing dioxin surrogates and precursors in the TGA effluent, which are collected on sampling tubes; the adsorbed compounds are eventually desorbed and quantified by TD-GC-MS. The major sources of error and losses are considered, including potential sorbent artefacts, possible breakthrough of volatiles through sampling tubes, or eventual losses of semi-volatiles due to their incomplete desorption or re-condensation inside the TG Analyser. The method is optimised and validated for di- to hexa-chlorinated benzenes in a range of 10-1000 ppb with average recovery exceeding 85%. The results are compared with data obtained in similar studies, performed by other research groups. As a result, the method provides the means for simulating de novo synthesis of dioxins in fly-ash and facilitates reliable and easy estimation of de novo activity, comparable with results of other studies, in combination with wide flexibility of testing conditions.