The apparent dissociation constants of carbonic acid in seawater were determined as functions of temperature (2-35°C) and salinity ( 19-43%) at atmospheric pressure by measurement of K'1 and the product K', K',. At 35sa salinity and 25°C the measured values were pE1 = 6.600 and pK'2 = 9.115; at 35% and 2°C the measured values were pK'1 = 6.177 and pKPz = 9.431.

The apparent (stoichiometric) association constants for the formation of ion-pairs between bicarbonate and carbonate and the major cations of seawater at 25°C were dctcrmined experimentally.The results wcrc used, in conjunction with earlier data on sulfate ion-pairs, to calculate the concentrations of the major species present in scawatcr.Here we measured the apparent (stoichiometric) association constants for the formation of bicarbonate and carbonate ion-pairs with sodium, calcium, and magnesium ions at 25°C and 0.72 ionic strength. The results were used, in conjunction with the sulfate association constants determined by Kester and Pytkowicz ( 1969)) to detcrmine the major ionic species present in seawater at 25°C and 34.8z0 salinity. We will show later that the proportions of ion-paired and free species are insensitive to the salinity.Activity coefficients are lower and solubility products higher in some mixed elcc-.trolyte solutions such as seawater than in chloride solutions ( Kester and Pytkowicz 1969). This is usually attributed to ionic interactions, which can range from the formation of ion-pairs (outer sphere interactions due to electrostatic attraction) to that of true complexes (inner sphere bonds with loss of water of hydration).Partial molal volume data (Kestcr 1969) and results from Raman spectra (Daly et al. 1972) suggest that the major ions of seawater may form ion-pairs, although the potentiometric method we used does not distinguish between ion-pairs and complexes.

Modifications to the normal apparatus used for the cold vapor atomic absorption determination of mercury have been made by reducing the dead volume of the apparatus, by Increasing the efficiency of diffusion of elemental mercury into the carrier gas, and by optimizing the instrumental parameters. The time of analysis, the sample volume, and the detection limit have been greatly reduced. For a 1-ml sample, the concentration detection limit is 1 ppt of Hg(ll). The relative standard deviation for 0.05-10 ppb of Hg(ll) is approximately 3%. At concentrations below 0.05 ppb Hg(ll), imprecision is due mainly to the fluctuations from the radiation source; and, at concentrations above 0.05 ppb Hg(ll), sampling imprecision is limiting. To prevent mercury losses, an oxidizing agent and acid should be used as a preservative and, to prevent contamination, all glassware must be adequately cleaned with the oxidizing solution.

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