Improvement of the Kjeldahl Method for Total Nitrogen Including Acid-Hydrolyzable Phosphorus Determinations in Freshwater Ecosystems

A simple, faster and accurate alternative procedure for the traditional Kjeldahl method is reported. Besides total nitrogen determinations it also allows the determination of acid-hydrolyzable phosphorus. The procedure does not distinguish N-NO2 and N-NO3. The method is sensitive at the μg level in samples containing 10 to 200μgN1−1 and 10 to 200μgP1−1. Nitrogen and phosphorus are determined colorimetrically. Reproducibility is better than ± 10%. P-PO4 and N-NH3 in water, sediments, macrophytes and terrestrial plants collected in central Chile have been determined using the method reported here.