MEASURING NITRATE CONCENTRATION IN NUTRIENT SOLUTIONS IN THE PRESENCE OF POLYETHYLENE GLYCOL THROUGH UV SPECTROMETRY [French]

摘要

A simple method has been devised for the determination of nitrate concentration in nutrient solution using UV spectrophotometry. it is suitable for an accurate determination of nitrate in the presence of iron chelates as well as polyethylene glycol (PEG), allowing the study of nitrate nutrition of plants in conditions of reduced water availability. Nitrate has a peak absorbance at 201 nm, independent of pH and ionic strength, and showing a linear relationship with concentration up to 0.20 x 10(-3) mol.L(-1). A comparison has been made between spectral properties of two iron chelates, Fe-EDDHA and Fe-EDTA. It is shown that the latter is more suitable for an accurate determination of nitrate concentration due to its lower specific absorbance and independence of pH conditions. The spectral properties of PEG are independent of pH and show a high absorbance in the 190-230 nm range. It is shown that nitrate concentration can be calculated with an accuracy better than 3%, by measuring absorbance at two or three wavelengths (without or with PEG respectively), provided that total absorbance is below 2 and nitrate concentration below 0.20 x 10(-3) mol.L(-1). in all cases, this can be reached simply by a mere dilution with water. Due to the non-linearity of PEG absorbance with concentration, a numerical method has been devised to solve the system of three equations.