Screening of Pollutants in Water Samples and Extracts from Passive Samplers using LC–MS and GC–MS

Aug 01, 2012

In December 2000, the European Union's Water Framework Directive (WFD) came into force with the aim of protecting and enhancing the quality of different water bodies within the community. The use of various passive sampling devices in conjunction with gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–mass spectrometry (LC–MS) techniques to screen pollutants has proved invaluable for investigative monitoring purposes within the remit of the directive. Used together, these new analytical approaches offer a robust solution to address specific future monitoring needs, particularly those prompted by legislative change.

The European Union's Water Framework Directive (WFD) became part of law in the United Kingdom in December 2003 with the objective of providing for the planning and delivery of better quality surface water, ground water and coastal waters (1). Various types of monitoring activities are described including: investigative, operational and surveillance. In particular, the WFD will help to deal with diffuse pollution that remains a serious environmental concern after most discharges from point sources have now either ceased or been remediated (2). Furthermore, the Marine Strategy Framework Directive came into force in June 2008, and its key aims are similar; to protect and enhance the environmental status of the marine waters by 2020 (3).

Most of the strategies currently used for the identification of pollutants in a body of water focus on the measurement of the concentrations of the priority substances (currently 33 priority chemicals and eight other pollutants). These are mainly organic compounds together with the metals cadmium, lead, mercury and nickel. The measured concentrations are compared to the proscribed environmental quality standards set by the European Commission for each of these pollutants (4). Each subset of pollutants, such as polyaromatic hydrocarbons (PAHs) or specific classes of pesticides, may require a separate water sample to be taken in the field and the combined cost of these analyses can prove labour intensive and expensive

In such surveillance monitoring campaigns, many compounds that could have a significant toxicological impact on the fauna and flora within the given aquatic environment will remain unidentified. This could result in the environmental objectives for a particular body of water not being met, and the causes of the failure need to be better understood. Further investigative monitoring may then be undertaken to gather further information on the likely reason for the failure. Additionally, within the WFD, the current monitoring practice of taking low volume (1–10 L) bottle, grab or spot samples of water followed by their laboratory analysis may not always provide a useful indication of the environmental status of a water course and alternative approaches, such as biomonitoring, sensors, passive sampling and others may be required.

Existing Approaches to Investigative Monitoring

For several years investigative monitoring within the remit of the WFD has involved the analysis of spot samples of water for unknown (non-target) organic chemical pollutants. This is usually accomplished by low resolution gas chromatographic–mass spectrometric (GC–MS) analytical methods using simple mass spectral library searching routines. GC–MS is a powerful technique for the separation and determination of volatile and semi-volatile compounds, but even with the use of high-resolution capillary columns, it is unable to resolve the multitude of compounds that can be present in complex environmental samples.

Screening of samples via low unit mass resolution GC–MS is also susceptible to interference from other compounds of a similar molecular mass. This implies that by using conventional single quadrupole GC–MS techniques many compounds can remain unidentified, which could have a significant aquatic toxicity (5). It is therefore desirable to introduce other instrumental techniques to improve the quality of environmental assessments and also to benefit from resource reduction as further analytical developments become available (6).