Optical nitrate analysers use the property of dissolved nitrate that it absorbs ultraviolet light. The instrument consists of a light source (deuterium lamp of flash lamp), collimating optics, a light path through the sample water and a spectrometer with photodetector. The resulting absorption spectra have to be analysed (either by an on-board computer or after data recovery) as other constituents in the seawater also absorb ultraviolet light. (For details see Johnson & Colleti (2002[1]))
Optical nitrate analysers do not require any chemical reagents and have a very fast response (on the order of 1 s) and therefore are also suitable for measurements during profiling work, on towed vehicles and AUV's. The detection limits depend on the length of the optical absorption path, generally these instruments are not well suited for low nitrate concentrations (< 1 umol).
The deployment time of the optical instruments is limited by available electrical energy (batteries) and biofouling (though for some instruments anti-biofouling measures can be added).
Optical nitrate analysers do not require any chemical reagents and have a very fast response (on the order of 1 s) and therefore are also suitable for measurements during profiling work, on towed vehicles and AUV's. The detection limits depend on the length of the optical absorption path, generally these instruments are not well suited for low nitrate concentrations (< 1 umol).
The deployment time of the optical instruments is limited by available electrical energy (batteries) and biofouling (though for some instruments anti-biofouling measures can be added).
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