DETERMINATION OF SEAWATER SALINITY BY ULTRAVIOLET SPECTROSCOPIC MEASUREMENTS

A method for the determination of seawater salinity by ultraviolet (UV ) spectroscopy is proposed. The effects of single salt concentrations and of salinity on UV absorption in the 190-250-nm range were investig ated. These studies revealed that the absorption spectrum of a solutio n with a given salinity is due mainly, in order, to KBr>MgCl2>NaCl. Th e influence of the temperature and salt concentration on UV spectra wa s studied by using synthetic seawater samples with the salinities rang ing from 1 to 50 parts per thousand (parts per thousand). Results show ed that, in the absence of interferences, the most sensitive and relia ble conditions for measuring the salinity are at 212 nm and al tempera tures in the range of 25-30 degrees C. Under these conditions this met hod shows quite linear calibration curves and allows us to perform sal inity determinations in seawater solutions at concentrations as low as 4 parts per thousand. Moreover, it requires no sample pretreatment an d offers a precision of 0.20 parts per thousand. The proposed method i s very simple and rapid for laboratory and on-board analysis. Finally, the interference of organic matter, nitrite, and, nitrate species wit h the salinity determinations was investigated. These studies show tha t organic matter does not interfere at concentrations of carbon lower than 1 mg/L and at 210 nm. Interferences due to NOx- species can be ig nored if these species are dissolved in solution at concentrations low er than approximate to 0.2 mg/L and the analyses are carried out at wa velengths lower than 212 nm.