SPECTROSCOPY
Over the past decade, various field-based analytical technologies have been developed, expediting hydrocarbon determination on site and increasing the number of soil samples that can be analysed at lower cost. However, more data is needed before these can be widely adopted, such as their performance and accuracy for different soil types, different levels of contamination and different fuel types. Furthermore, comparison of their ability to quantify different hydrocarbon groups for risk assessment purposes and evaluation of whether they can offer a good alternative to lab-based technologies for remediation monitoring and validation is still limited.
FIELD-BASED NDIRS In analytical chemistry, extraction procedures aim to separate the analyte quickly, quantitatively and using as little solvent as possible. A recent report by Concawe outlined how solvent-based extraction field technologies, including NDIRS, performed well for the detection and quantification of TPH between 100 and 10,000mg kg-1, independent of soil type and fuel type. Te NDIRS instrument used
in Concawe’s study was the Infracal 2 ATR-SP TPH analyser, which can perform TPH determination of hydrocarbons in 5 to 10 minutes, considerably faster than lab-based GC-MS. For the
experiments covered in Concawe’s report, scientists used a hexane extraction
The Infracal 2 analyser
method, adding 1% v/w to soil samples and shaking them for two minutes. Tis extract was cleaned using activated silica gel and Whatman no. 40 filter paper. For level three spiked soils, the extracts were further diluted five times in accordance with the Infracal 2’s detection range. Before each measurement, the attenuated total reflectance (ATR) crystal was cleaned with 99.9% isopropanol and zeroed every hour. To measure a sample, 60 μL was deposited
into the ATR crystal and the solvent was given time to evaporate before the measurement was taken.
Te report
concluded that the NDIRS field test provides GC-MS comparable TPH recoveries and meets the performance requirements for many regulatory standards. Tis means scientists
can use the Infracal 2, which SciMed supplies, to conduct cost-effective petroleum hydrocarbon analysis on-site, without outsourcing to commercial analytical labs.
Paul Vanden Branden is director of SciMed.
www.scimed.co.uk
www.scientistlive.com 31
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