It sounds me strange, the UV spectrophotometrical method is commonly used without major problems. The main issue is interference due to organic matter, as detailed in the paper you mention. I would recommend you to check for OM content and variability in your algal cultures. Sometimes, depending on culture and stress conditions, microalgae can excrete a lot of OM.

A good (and probably the most precise) option is also Ion-exchange HPLC assay.

Hi.

Actually the spectroscopic method using AFNOR norms works well with this.

Best wishes. Younes

Dear Mikhail Temnov ,

The error in the UV-VIS spectrophotometric method is mainly due to the calibration plot used for the calculation of the concentration. The calibration plot needs to be reconstructed after a certain period of time or to make it on the same day of estimation/analysis. Because the efficiency of the instrument changes with time.

You can follow this protocol

To 5 mL of wastewater sample, 2 mL brucine solution (4% w/v in chloroform) was added. 5 mL concentrated H 2 SO 4 was added drop by drop continuously to the solution. Absorbance of the resultant yellow colour was measured at 410 nm and nitrate present in the sample was calculated using a standard plot. The standard plot was prepared using NaNO 3 .

Y. Collos, F. Mornet, A. Sciandra, N. Waser, A. Larson, P.J. Harrison, An optical method for the rapid measurement of micromolar concentrations of nitrate in marine phytoplankton cultures, J. Appl. Phycol. 11 (1999) 179–184.

Thank you

Thank you very much!