Dear Sir. Concerning your issue about the reliable nitrate quantification in algea cultures. The reference method for determination of nitrate in marine aqueous media, e.g. those used for microalgal cultures, requires a cadmium-copper column when nitrites are present; the use of this column brings about several problems, viz. need for periodic regeneration, due to the presence of chloride anions, as well as presence of poisoning iron and copper soluble cations, always present in this kind of samples. Furthermore, the method is time-consuming and cumbersome. The improved method proposed here is a good alternative in terms of accuracy and precision, as well as time required for its performance. In addition, our method is not affected by the high concentrations of chloride, which are typical of sea water. Its major drawback is the impossibility to determine either nitrate/nitrite when their concentrations are below the threshold of 0.05 mg L−1 . Although relative errors observed at lower concentrations are considerable, recall that nitrate concentration in microalgal culture media is often relatively high. Therefore, the improved method can be used as an alternative for determination of nitrate and nitrite in marine media. I think the following below link may help you in your analysis:

https://pdfs.semanticscholar.org/fc1e/fc0437642765e2dd622cdeffe69f9a9c6d37.pdf

Thanks

Thank you very much for your detailed and helpful answer! This does indeed give some more insight and might just be what I need. Concentrations below 0,05 mg/L are not of to much concern as you correctly pointed out...!

Thanks again!