Wet chemical analysers

A variety of wet chemical nutrient analysers exist on the market. These analysers draw in sample water and mix it with a reagent (or reagents). The resulting solution develops a characteristic property (e.g. colour complex or fluorescence) depending on the concentration of the target analyte, that is then measured in an absorption cell (colour complex) or by a light source and photodetector (fluorescence). In some cases heating of the solution is required to speed up development.
Depending on the chemical protocols followed (i.e. if heating and/or preconcentration steps are needed), the time response (time between independent measurements) is on the order of a few seconds to minutes.
Parameters limiting the deployment time of wet-chemical analysers are reagent consumption, reagent degradation time, available electrical energy (batteries) and biofouling.
A distinct advantage of wet-chemical analysers is the capability of conducting in situ calibrations by piping a blank or standard solution of known concentration into the analyser instead of the sample. Any instrument drift can be detected and the measurements corrected for the drift.
Nutrients that can be measured in situ include dissolved nitrate, nitrite, ammonia, phosphate and silicate (see "external links" to companies below for details).