Standard output - seawater analysis

By means of the example of the seawater analysis already discussed in chapter 2.2.1.1 it is shown what results can be taken from the standard output. 

General information can be taken from the paragraphs solution composition and description of solution . Looking at the molarities of the solution composition it is obvious that the water is of Na-Cl-type (Cl = 0.55 mol/L, Na = 0.47 mol/L seawater). 

The ratio N(5)/N(-3) is approximately 3 1. The Fe(3)/Fe(2) ratio is 4 1. Thereby it is important to see that Fe(2) exists in form of the free cations Fe2+ or as positively charges complex FeCl+ and thus is subject to cation exchange, while Fe(3) occurring mainly in form of the zero charged complex Fe(OH)3° is not. U(6) clearly dominates compared to U(5) and U(4). In contrast to U(4), U(6) is considerably soluble and thus more mobile. But the predominant U(6) species are the negatively charged complexes (U02(C03)34, U02(C03)22 ), which are subject to interactions with e.g. iron hydroxides and thus mobility may be limited. The different proportions of the reduced form of the total concentration for N, Fe, and U are in accordance with the theoretical oxidation/reduction succession (see also Fig. 20). The oxidation of Fe(2) to Fe(3) already starts at pE values of 0, the oxidation of N(-3) to N(5) only at pE= 6, while the oxidation of uranium is already finished at a pE value of 8.451, which was determined in the seawater sample. 

Hints for super- or undersaturation of minerals can be found in the last paragraph of the initial solution calculations entitled saturation indices . Graphical representation of saturation proportions is often done by means of bar charts, whereas SI = 0 marks the point of intersection between the x-axis and the y-axis, and the bars of super-saturated phases point upwards and those for undersaturated phases downwards (example Fe-bearing mineral phases Fig. 37). 

It is important to note that not all mineral phases with an SI 0 necessarily will be precipitated because low reaction rates and prevailing boundary conditions may lead to the preservation of disequilibria over long periods. Therefore, dolomite will not precipitate from seawater despite its distinctly positive SI of 2.37 (or 1.82 

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The classic work of Dawson and Pritchard [264] on the determination of a-amino acids in seawater uses a standard amino acid analyser modified to incorporate a fluorometric detection system. In this method the seawater samples are desalinated on cation exchange resins and concentrated prior to analysis. The output of the fluorometer is fed through a potential divider and low-pass filter to a comparison recorder. 

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