Microfluorometric method to measure ammonium in natural waters1

Ammonium can be measured fluorometrically after a simple chromatographic separation from amino acids and reaction with o‐phthalaldehyde. The method (<0.5‐ml sample required) is sensitive down to 0.2 µm NH4+ in seawater. Fluorescence is proportional to concentration over the range of 0–100 µm NH4+ and analysis time is 6 min per sample.