Wet chemistry analyzers all work similarly. A sample-handling system extracts a clean sample from the process (to prevent plugging). The sample is injected into a chemically treated solution, and a chemical reaction takes place. The reaction can be a change in color, pH, or conductivity. The change is proportional to the concentration of a single component of interest in the process stream (Lang 1991).
The fastest wet chemistry technique is process flow injection analysis (PFIA). Here, a clean process sample flows continuously through a sample injection valve. At user-selected intervals, a fixed volume of sample, usually in microliters, is injected into a constantly flowing liquid carrier stream. Precise mixing generates a specific chemical reaction, and an appropriate detector (UV or visible, pH, or conductivity) gives a signal proportional to the concentration in the sample of the component of interest. The response time is usually fast so that one or two determinations can be made per minute.
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