Site Investigation: Field Screening Techniques
The application of field screening techniques permits the fast determination of substances on site.
The on site analysis of solid, liquid and gaseous samples is a widespread problem in environmental science and technology. Very often, the composition and the spatial distribution of components, namely pollutants, have to be estimated for risk assessment and evaluation of remediation necessity and success. The direct measurement in the field avoids a number of measuring errors such as undesired transfer of volatile compounds into the gas phase, adsorption and reactions (e.g. oxidation) leading to non-quantifiable loss of the original substances. Another advantage of the application of on site techniques in comparison to conventional ex situ laboratory analysis is their suitability for long-term monitoring of soils, water quality in wells, natural waters, gaseous emissions and industrial processes. Due to the increasing relevance of low-invasive soil and water cleaning techniques such as natural attenuation and enhanced natural attenuation in remediation practice, low-cost on site systems attract growing interest. Another important aspect of on site analytical characterization is the inherent potential for process control especially for industrial purposes.
In contrast to laboratory methods, field screening techniques enables the concentrations and spatial distribution of chemical compounds in the environment to be quickly assessed without the need to take and transport samples to a laboratory (hence ruling out these sources of error). The results are available within a few minutes using field screening techniques. Furthermore, these techniques make analysis cheaper.
Typical applications are summarized in the Figure below.
The analysis of solid samples mostly requires a field sampling and a subsequent sample preparation. Only same spectroscopic techniques (fluorescence and near-infrared measurements) permit the direct investigation of soils and solid samples. The combination of direct-push sampling and sensor-based analyzers can be used for the fast investigation of soil gas.
For the determination of contaminations in water, in situ or on line techniques are mainly applied. In situ techniques permit the direct measurements within the sample matrix without sampling. Especially spectroscopic measurements are suitable as in situ technique for the determination of chemical substances in liquid media. On line techniques permit the continuous analysis of chemical substances within a sampling chamber.
Although the most of analytical techniques permit the direct analysis of gaseous samples, low concentration of gaseous analyst requires preconcentration techniques (e.g. thermodesorption tubes).
The most common field analytical techniques include:
Field able gas chromatography
Mobile GC-MS coupling (gas chromatography, mass spectrometry)
Ion mobility spectrometry
Non-dispersive IR spectroscopy
Energy dispersive X-ray fluorescence
Thin layer chromatography
Photo ionization detector
Electronic noises (e.g. Surface Acoustic Wave Devices)
Photo acoustic sensors
A lot of analytical techniques mentioned above are validated and part of EPA- and ISO standards.
3. Literature and Links
Gregory Bonito: An Ecological In Situ Sensor Resource: A Compilation of In situ Sensors, Sensor Array Projects and Sensor Manufacturers