Nitrate sensors

Nitrate is an essential macronutrient for growth. Phytoplankton need nitrogen to build amino acids and proteins.

Recent advances have led to the development of low power In Situ Ultraviolet Spectrophotometers (ISUS), which are capable of making optical measurements of nitrate in seawater as deep as 4000 m.

Nitrate, amongst other compounds, can be identified based on its UV absorption spectrum. Spectral deconvolution techniques allow determination of nitrate in seawater with no interferences or chemical manipulations. This method allows high temporal resolution sampling (up to one measurement per second) to concentrations near 0.1 µM (Johnson and Coletti, 2002).

UV absorbance spectra for seawater.

UV absorbance spectra for seawater.

The figure above shows absorption spectra of compounds in seawater as collected with a Hewlett-Packard HP 8452 spectrophotometer (cell path length was 1 cm). Note that the left axis applies to bromide and the right axis to the other species. Taken from Johnson and Coletti (2002).

 

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