Simultaneous determination of total nitrogen and total phosphorus in freshwater samples using persulfate digestion

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

“…9.7) at the start of the digestion process and becomes acidic (pH 4-5) as the sodium hydroxide decomposes [78,90,98]. Hosomi and Sudo also reported that pH change was important and in their method the pH decreased from 12.8 to 2.0-2.1 to ensure that even condensed polyphosphates were digested [92].…”

“…For example orchard leaves gave recoveries of 80-90% for TP and TN [91]. Higher recoveries can be obtained by decreasing the ratio of sample to peroxydisulfate [92]. Alkaline digestion of model phosphorus compounds has been found to be efficient for turbid water samples [125][126][127] although the concentration of suspended particulate material needs to be diluted to <150 mg L −1 and difficulties can arise when this material is of soil origin rather than biological origin, e.g.…”

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Evaluation of alkaline persulfate digestion as an alternative to Kjeldahl digestion for determination of total and dissolved nitrogen and phosphorus in water

“…2.2 Digest preparation protocols and reagent formulations were adapted from previously published procedures (Valderrama, 1981;Hosomi and Sudo, 1986;Ameel and others, 1993;D'Elia and others, 1997;American Public Health Association, 1998b). Two other reports (Nydahl, 1978;Cabrera and Beare, 1993) provided insight into the potential for low nitrogen recovery in samples containing high concentrations of dissolved and particulate organic carbon.…”

“…Second, nitrogen and phosphorus are recovered quantitatively from digests prepared by the method described in this report as explained in section 2.2. Furthermore, manual postdigestion pH adjustment prior to colorimetric determinations required by other previously published alkaline persulfate digestion methods (Valderrama, 1981;Hosomi and Sudo, 1986;D'Elia and others, 1987;Ameel and others, 1993;D'Elia and others, 1997) is not necessary in the method described in this report. This modification reduces digest preparation time substantially.…”

“…Alkaline persulfate digestion (Valderrama, 1981;Hosomi and Sudo, 1986;D'Elia and others, 1987;Ameel and others, 1993;D'Elia and others, 1997) provides a safer and more environmentally benign alternative to Kjeldahl digestion for routine, singledigest nitrogen and phosphorus determinations in water. Desirable characteristics of alkaline persulfate digestion compared to Kjeldahl digestion include:…”