Chapter 16
Flow Injection Techniques for the in situ Monitoring
of Marine Processes
P. J. Worsfold . E. P. Achterberg . A. R. Bowie . R. Sandford· V. Cannizzaro . P. Gardolinski
16.1
Introduction
16.1.1
Flow Injection Techniques
Flow injection (PI) analysis has become established as an important tool for sample
presentation and on-line treatment in the laboratory environment. It is now being
increasingly considered for deployment outside of the laboratory, in both process and
environmental locations (Andrew et al. 1994).
FI has been described as an unsegmented flow technique in which a volume of liquid sample is inserted into a moving liquid carrier stream, whereupon it undergoes
physical dispersion as it is transported to a flow-through detector for measurement
(Ruzicka and Hansen 1981). The transient response is usually in the form of a peak,
with a sharp rising edge and a more gradual decay, the shape being due to axial dispersion and radial diffusion of the sample zone as it travels through the FI manifold. '
The height and area of the peak are usually directly related to analyte concentration,
but for convenience, peak height is usually the measured parameter. The degree of
sample dispersion is controlled by factors such as sample volume, carrier flow rate,
length and diameter of the manifold tubing and manifold geometry and under most
conditions is highly reproducible (relative standard deviations are typically less than
5%). The technique is now widely used in analytical laboratories for the automation
of wet chemical methods and has considerable potential for use on board ships
(Worsfold et al. 2000) and in submersible analysers (David et al. 1998)
A block diagram of a simple single channel PI manifold is shown in Fig. 16.1 and
typically consists of a means of propulsion (e.g. a peristaltic pump), a rotary injection valve for sample introduction (similar to HPLC valves but low pressure) and a
flow-through detector (e.g. a spectrophotometer). In this manifold, the carrier stream
transports the sample to the detector. PTFE tubing (typically 0.8 mm i.d.) is used
throughout the manifold for sample and reagent transport, with tightly-wound coils
often included to enhance mixing. If the method requires more than one reagent, additional streams can be merged with the carrier stream at suitable points in the manifold. Similarly, if in-line physical treatment of the sample is required, the necessary
components can easily be incorporated. These include:
• Solid phase chelating micro columns for matrix removal and analyte pre-concentration, e.g. 8-hydroxyquinoline for the removal of the major sea water ions and simultaneous preconcentration of trace metals;
Flow Injection Techniques for the in situ Monitoring
of Marine Processes
P. J. Worsfold . E. P. Achterberg . A. R. Bowie . R. Sandford· V. Cannizzaro . P. Gardolinski
16.1
Introduction
16.1.1
Flow Injection Techniques
Flow injection (PI) analysis has become established as an important tool for sample
presentation and on-line treatment in the laboratory environment. It is now being
increasingly considered for deployment outside of the laboratory, in both process and
environmental locations (Andrew et al. 1994).
FI has been described as an unsegmented flow technique in which a volume of liquid sample is inserted into a moving liquid carrier stream, whereupon it undergoes
physical dispersion as it is transported to a flow-through detector for measurement
(Ruzicka and Hansen 1981). The transient response is usually in the form of a peak,
with a sharp rising edge and a more gradual decay, the shape being due to axial dispersion and radial diffusion of the sample zone as it travels through the FI manifold. '
The height and area of the peak are usually directly related to analyte concentration,
but for convenience, peak height is usually the measured parameter. The degree of
sample dispersion is controlled by factors such as sample volume, carrier flow rate,
length and diameter of the manifold tubing and manifold geometry and under most
conditions is highly reproducible (relative standard deviations are typically less than
5%). The technique is now widely used in analytical laboratories for the automation
of wet chemical methods and has considerable potential for use on board ships
(Worsfold et al. 2000) and in submersible analysers (David et al. 1998)
A block diagram of a simple single channel PI manifold is shown in Fig. 16.1 and
typically consists of a means of propulsion (e.g. a peristaltic pump), a rotary injection valve for sample introduction (similar to HPLC valves but low pressure) and a
flow-through detector (e.g. a spectrophotometer). In this manifold, the carrier stream
transports the sample to the detector. PTFE tubing (typically 0.8 mm i.d.) is used
throughout the manifold for sample and reagent transport, with tightly-wound coils
often included to enhance mixing. If the method requires more than one reagent, additional streams can be merged with the carrier stream at suitable points in the manifold. Similarly, if in-line physical treatment of the sample is required, the necessary
components can easily be incorporated. These include:
• Solid phase chelating micro columns for matrix removal and analyte pre-concentration, e.g. 8-hydroxyquinoline for the removal of the major sea water ions and simultaneous preconcentration of trace metals;