Soil solution metal exchange Table

Some of the more commonly used reagents are listed in Table 1-6 together with an indication of which chemical fraction they are thought to extract. The order in the table is one of increasing vigour of attack on the soil so that a solution which extracts, say, metals from the humus in soil will also extract from the soil solution and from the exchangeable pool. All are empirical and, while the fractions proposed are based on much research, the fractions as measured are usually operationally defined in the sense that an individual fraction is presumed to attack a certain chemical reservoir. Shuman (1991) should be consulted for a recent critical review of the chemical forms of micronutrients in soils. Fig. 1-3 uses data from Shuman (1985) to illustrate the results from a typical fractionation study. 

Atomic absorption spectrometry is one of the most widely used techniques for the determination of metals at trace levels in solution. Its popularity as compared with that of flame emission is due to its relative freedom from interferences by inter-element effects and its relative insensitivity to variations in flame temperature. Only for the routine determination of alkali and alkaline earth metals, is flame photometry usually preferred. Over sixty elements can be determined in almost any matrix by atomic absorption. Examples include heavy metals in body fluids, polluted waters, foodstuffs, soft drinks and beer, the analysis of metallurgical and geochemical samples and the determination of many metals in soils, crude oils, petroleum products and plastics. Detection limits generally lie in the range 100-0.1 ppb (Table 8.4) but these can be improved by chemical pre-concentration procedures involving solvent extraction or ion exchange. 

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