Thank you Sinica, Antonio and Ramón for taking time to reply my query. I have seen now that The most usual way to go for nutrient analysis in seawater is wet chemical, although some of your sugesstions included sensors. I was expecting to find nutrient sensors For long term online monitoring Of nitrates, phosphates, and silicates. I understand that fouling of sensors is a major problem.
http://www.wetlabs.com/products/nutrient-sensors - this can be deployed for a long time, but measures only phosphates. Systea products can either be deployed in the water (WIZ probe) or used to monitor the defined parameters in one certain location onshore (e.g. harbors, water treatment plants etc., water will be pumped in at defined time steps).
Satlantic makes an in situ optical nitrate analyzer that has been widely used. (http://satlantic.com/suna?qt-product_tabs=7). WETLabs has also developed a capability for ammonium, using the same technology as for the phosphate sensor.
Here's a link to a brochure from Hydrolab that summarizes their offerings, as well as Sea-Bird Electronics, WET Labs, and Satlantic. Good luck with your project! http://www.hachhydromet.com/web/ott_hach.nsf/gfx/B5829634DC3E8E6FC1257935005DD828/$file/Hydromet%20Coastal%20Brochure.pdf
Green Eyes LLC now offers wet chemistry instruments for the measurement of nutrients in fresh and salt water. We took over the product line from EnviroTech Instrument in Jan. 2014 and have made significant improvements since then. If interested, please contact us at [email protected]..
please i need a multiparameter probe that could suffice in physical, chemical and nutrient analysis of different water bodies considering salinity as a major factor in the aquatic environment