SIMPLIFIED KJELDAHL NITROGEN DETERMINATION FOR SEAWATER BY A SEMIAUTOMATED PERSULFATE DIGESTION METHOD

Persulfate digestion in combination with indophenol colorimetry via a Technicon AutoAnalyzer II was used as an alternative to the standard Kjeldahl N method. Application of this method to the analysis of seawater samples demonstrated that a large quantity of samples can be rapidly processed with relative ease in a small environmental laboratory. A detection limit of 0.06 mg/l as N was calculated for the operating range 0-5.6 mg/l. Seawater samples spiked with 3.00 mg/l of ammonia N were analyzed with a precision of .+-.0.25 mg/l and a spike recovery of 105 .+-. 6.8%. Seawater samples spiked with 3.35 mg/l of Kjeldhal N contained in raw domestic waste were analyzed with a precision of .+-.0.30 mg/l and a spike recovery of 100 .+-. 8.1%. The persulfate method greatly simplifies the determination of Kjeldahl N in seawater while successfully maintaining low level requirements for sensitivity, precision and accuracy.