Abstract
A spectrophotometric measurement/PLS regression method and an anion chromatographic method for the determination of total nitrogen in seawater and brackish water were investigated. By oxidative digestion of seawater with potassium peroxodisulfate in alkaline borate buffer, nitrogen is oxidized to nitrate ion and bromide ion to bromate in seawater medium. No remaining bromide ion is present in the digested samples, while bromide ion does not fully oxidized to bromate in water not containing high concentration of salts. By using glass test tube with screw cap and aluminum block heater, digestion can be done simply and easily. After digestion, the absorption spectra were measured in the range of 220∼260 nm. Calibration standards were prepared by dissolving KNO3 and KBrO3 into simulated seawater without digestion. By spectrophotometric/PLS method, 0.2∼5.0 mg-N/l in seawater and brackish water could be determined without the interference from bromide/bromate. By IC method, 0.01∼10 mg-N/l could be determined with a DEAE column (weak anion exchange resin, 10 cm length glass column) and 0.2 M-NaCl eluent.
