Environmental monitoring — a flow–injection approach

(6) Long-term unattended operation. (7) Periodic recalibration. (8) Easy on-site maintenance. Water quality Water quality is a subject of increasing public interest and awareness. With regard to chemical parameters in particular it is also an area that has been the subject of increasingly stringent national and international legislation based on EC directives, for example, for the discharge of dangerous substances into the aquatic environment (EC/76/464) and water quality for human consumption (EC/80/778). This has necessitated the development of reliable analytical methodologies that meet specified requirements for accuracy, precision and limit of detection, and, if possible, can be automated tbr high sample throughputs. 'Fhe conventional approach is to combine periodic manual sampling with automated laboratory analysis. The most labour-intensive and rate-determining step in the procedure is sample collection, which can also introduce problems due to contamination and/or analyte loss during collection, pretreatment and storage. Field monitoring It is clear that there is a need tbr in silu analytical techniques tbr monitoring water quality. Not only would such systems overcome the problems stated above, they would also provide a more immediate response (usethl in the case of transient pollution incidents) and a more complete concentration versus time profile (useful tbr archiving and management purposes). The latter point is a particularly important one tbr thndamental environmental studies when other aspects of the local environment are also monitored pseudo-continuously in silu, tbr instance, flow rate, temperature and salinity. It is, however, very difficult to adapt laboratory instru-mentation for reliable field use. In addition to the analytical requirements specified above, a field monitor must also consider the following:. (1) Reagent stability. (2) Hardware and software flexibility. (3) Internal diagnostics. (4) Stay-clean properties. (5) Modular construction. Analytical approaches Ion-selective electrodes represent an analytical technology suited to in situ monitoring due to cost and size advantages but they are only available for a limited number of determinands, for example, nitrate and ammonia, and are prone to fouling of the sensor surface and base-line drift. Biological monitors, i.e. the use of living organisms such as fish and daphnia, present an interesting possibility tbr the future and function on the basis of increased movement or ventilatory frequency in the presence of pollutants. They are, however, not sufficiently selective to provide intbrmation on individual chemical species. Spectrophotometric detection is potentially very attractive for field use because there are well-documented methods for most organic and inorganic species that utilize a wide …

Water quality Water quality is a subject of increasing public interest and awareness. With regard to chemical parameters in particular it is also an area that has been the subject of increasingly stringent national and international legislation based on EC directives, for example, for the discharge of dangerous substances into the aquatic environment (EC/76/464) and water quality for human consumption (EC/80/778). This has necessitated the development of reliable analytical methodologies that meet specified requirements for accuracy, precision and limit of detection, and, if possible, can be automated tbr high sample throughputs. 'Fhe conventional approach is to combine periodic manual sampling with automated laboratory analysis. The most labour-intensive and rate-determining step in the procedure is sample collection, which can also introduce problems due to contamination and/or analyte loss during collection, pretreatment and storage.

Field monitoring
It is clear that there is a need tbr in silu analytical techniques tbr monitoring water quality. Not only would such systems overcome the problems stated above, they would also provide a more immediate response (usethl in the case of transient pollution incidents) and a more complete concentration versus time profile (useful tbr archiving and management purposes). The latter point is a particularly important one tbr thndamental environmental studies when other aspects of the local environment are also monitored pseudo-continuously in silu, tbr instance, flow rate, temperature and salinity. It is, however, very difficult to adapt laboratory instrumentation for reliable field use. In addition to the analytical requirements specified above, a field monitor must also consider the following:.

Analytical approaches
Ion-selective electrodes represent an analytical technology suited to in situ monitoring due to cost and size advantages but they are only available for a limited number of determinands, for example, nitrate and ammonia, and are prone to fouling of the sensor surface and base-line drift. Biological monitors, i.e. the use of living organisms such as fish and daphnia, present an interesting possibility tbr the future and function on the basis of increased movement or ventilatory frequency in the presence of pollutants. They are, however, not sufficiently selective to provide intbrmation on individual chemical species.
Spectrophotometric detection is potentially very attractive for field use because there are well-documented methods for most organic and inorganic species that utilize a wide range of selective and sensitive reagents. Conventional spectrophotometric detectors are too expensive, complex and heavy tbr remote deployment, but solid state detectors (SSDs) based on light-emitting diodes (LEDs) as sources and a photodiode as the detector provide a rugged, compact and low-cost alternative. A block diagram of an FI monitor suitable tbr remote deployment is shown in figure 1. A single board computer is used for control and data acquisition and a standard is available for regular recalibration via a switching valve.
Sample presentation to the monitor is a crucial aspect of the system and can range tiom a simple constant head device for treated waters to a sophisticated combination of filtration steps for high suspended solids waters. Biotbuling is another important factor that must be considered, particularly tbr long-term, i.e. greater than seven days, unattended operation. The importance of regular (short) maintenance visits cannot be over- Data transfer from the monitor must also be considered, but there is a range of options available including immediate transmission via telemetry links to a central facility and storage of data for periodic collection via a data logger. A local readout is also useful for diagnostic purposes.

Applications
A number of applications of FI-based instrumentation with SSD have been reported for in situ monitoring. These include the determination of nitrate [1][2][3], phosphate [4] and ammonia [5] in river water and the determination of aluminium [6] and iron [7] in treated waters. There is also considerable potential tbr the remote deployment ot" similar instrumentation in harsh industrial process environments [8].
Conclusions FI with spectrophotometric detection is well suited to remote deployment in environmental locations for the pseudo-continuous and selective monitoring of chemical species in natural and treated waters.