Site Investigation:
Field Screening Techniques
1. Summary
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.
2. Methods
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
Fluorescence spectroscopy
Absorption spectroscopy
Near-infrared spectroscopy
Non-dispersive IR spectroscopy
Energy dispersive X-ray fluorescence
Thin layer chromatography
Photo ionization detector
Biosensors
Immunoassays
Test kits
Electronic noises (e.g. Surface Acoustic Wave
Devices)
Photo acoustic sensors
Electrochemical procedures
A lot of analytical techniques mentioned above are validated and part of
EPA- and ISO standards.
3. Literature and Links
http://fate.clu-in.org/immunoassay_index.asp?techtypeid=45
Gregory Bonito: An Ecological In Situ Sensor Resource: A Compilation
of In situ Sensors, Sensor
Array Projects and Sensor Manufacturers
http://www.lternet.edu/technology/sensors/
Environmental Sciences
Branch (ESB): Field-Screening Methods for TNT and RDX in Soil and Groundwater
http://www.crrel.usace.army.mil/es/research/field-screening.htm
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