Application Note ReView: Method Validation of the Analysis of Organochlorine Pesticides and Polychlorinated Biphenyls Using DiLLME and GC-MS/MS
The use of pesticides, whilst being extremely effective at reducing crop destruction by pests, has caused considerable damage to wider ecosystems and the associated food chains. Although most organochlorine pesticides have been phased out of use due to their toxicity to organisms outside the original scope of application, they still persist in the environment due to their chemical stability. Therefore, this Application Note ReView takes a look back at AS230 – Organochlorine Pesticide Analysis – Method Validation of the Analysis of Organochlorine Pesticides and Polychlorinated Biphenyls Using DiLLME and GC-MS/MS:
Concentrations of organochlorine pesticides can be significantly increased within apex predators due to bioaccumulation – a problem which can also result in uptake of these compounds within humans. Polychlorinated biphenyls (PCBs) are one such class of organochlorine compounds that have been widely reported to accumulate in the body fat of organisms in the ecosystem.
Due to the longevity of these compounds and their extremely toxic nature, several of these compounds, for example dieldrin has a UK regulatory prescribed concentration or value (PCV) of 0.03 µg/L; far lower than 0.1 µg/L for most other organic pollutants. This makes low limits of quantification critical for methods that are employed in the analysis of these compounds.
Today’s well-established methodologies for these purposes require large sample and solvent volumes to reach these low limits and require many hours of analyst time to prepare samples. Whilst these procedures can still have their place, laboratories that are looking to the future to reduce unnecessary wastage, reduce preparation time, reduce costs associated with chemical and consumable usage and increase workflow throughput, can only improve existing methods by investing in newer improved technologies.
Automated dispersive liquid-liquid microextraction is a modified variant of solvent extraction. It is a technique used to extract analytes from an aqueous solution into a small solvent with the help of a dispersing solvent. This solvent, usually isopropyl alcohol, or other similarly polar solvent is added to the sample to aid in the mixing process between the two immiscible liquids; the sample and the extraction solvent, most often dichloromethane or chloroform.
With the addition of dispersing solvent, an emulsion is able to form during the agitation process so that extraction of analytes is quick and efficient. To separate the emulsion, the sample is centrifuged, after which a droplet of solvent forms at the bottom of the vial from which a portion is taken and injected into the instrument. Enrichment factors can be in the range of twenty to forty times depending on the volume of sample and solvent used.
In this Application Note, in collaboration with Thames Water, analysis of several organochlorine pesticides and PCBs in water was carried out with GERSTEL MultiPurpose Sampler capability involving a fully automated dispersive liquid-liquid microextraction (DiLLME) method, coupled with large volume injection (LVI) and analysis using Agilent’s 7010 triple quadrupole mass spectrometer with high efficiency source (HES) to reach the limits required resulting in all compounds being quantified to less than 0.01 µg/L. an NS30 style validation was performed with three duplicate batches to assess precision, bias in three water matrices, with a full eleven duplicate batches for a complete assessment of limit of quantitation.
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