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common organic solvent (e.g. with 4-methylpentan-2-one), and calibration performed using special
organic standards. It is not always possible to introduce organic solvents directly, as will be seen.

1.6.3 Agricultural Samples

In soil analysis, the sample pretreatment varies depending on whether a total elemental analysis or an
exchangeable cation analysis is required. In the former, a silicate analysis method (see below) is
appropriate. In the latter, the soil is shaken with an extractant solution, e.g. 1 M ammonium acetate,
ammonium chloride or disodium EDTA. After filtration, the extractant solution is analysed. Fertilizers
and crops can be treated as chemical and food samples, respectively.

1.6.4 Waters and Effluents

Where the analyte is present in sufficient concentration, it may be determined directly. Otherwise it
may need to be concentrated by evaporation before determination. Methods of concentration include
evaporation, solvent extraction and preconcentration using ion exchange or chelating resins.

If information on total metals is required, the sample must be acidified before analysis. If information
on dissolved metals only is required, the sample may be filtered (using a specified pore size) before
analysis. Losses may occur however, by adsorption during filtration.

1.6.5 Geochemical and Mineralogical Samples

Silicate analysis is not without problems. If measurement of silicon is not required, it may be
volatilized off as silicon tetrafluoride, using hydrofluoric acid, although some calcium may be lost as
calcium fluoride. Alternatively, sodium carbonate-boric acid fusions may be employed. Where
possible, final solutions are made up in hydrochloric acid.

1.6.6 Metals.

Where possible, hydrochloric acid-nitric acid is used to dissolve the sample. The standards may be
prepared by dissolving the trace metal in an appropriate solution of the matrix metal [e.g. iron(III)
chloride solution for steel].