Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 3/12)
Character Range: 745046–748024

entire sample may be homogenised; however, it is advisable to keep a portion in the 'as received' state to check, if necessary, that no contamination has occurred during the homogenising process. Described below are the pre-treatment procedures to obtain homogenised field-moist and dry analysis portions.

    4.2.3         Preparation of field-moist ('as received') analysis portions
In general, soils to be tested for organic analytes, especially rapidly degradable or otherwise labile contaminants, should not be dried but should be analysed in a field-moist state. If an excess of moisture would affect the extraction efficiency, the sample may be 'dried' by mixing the analysis portion with anhydrous sodium sulfate or magnesium sulfate prior to extraction (US EPA SW-846, Method 3540C).

Field-moist samples will often not be amenable to mechanical grinding or sieving. For those samples that are suitable, the process involves taking at least 25% by weight or 200 g of the laboratory sample, whichever is the smaller (or other sub-sample that can provide a well-mixed portion representative of the whole sample), and thoroughly grinding and mixing by hand in a mortar and pestle, or using other appropriate techniques, to obtain a homogeneous sub-sample. Equipment should be thoroughly cleaned between samples, or other systems put in place to ensure no cross-contamination.

For most metals and inorganics, better analytical reproducibility is obtained using air-dried soil (see Section 4.2.4 below). However, if the sample is to be analysed for these analytes in the field-moist state and if it is amenable to sieving (for example, sandy loam), it should be passed through a 2 mm plastic sieve to remove large soil particles and other extraneous particles—ensure that the sample contains no solid particles distinctly different from the soil, such as fragments of metal or other unusual particles.

Note: Do not grind samples being analysed for metal contaminants, as this can release natural metals from the interior of soil grains that are not normally available.
Store the treated sample in a suitable container.

Clean all equipment to minimise sample cross-contamination; this can be confirmed by analysing equipment rinsates and/or control samples.

    4.2.4         Preparation of dry analysis portions (non-volatiles only)
Air-drying helps to give a representative analysis portion by producing samples amenable to grinding, sieving and splitting. However, air-drying may modify the chemical form of some species and hence affect the results obtained (Adam & Anderson 1983, Bartlett & James 1980, Harry & Alston 1981, Khan & Soltanpour 1978, Leggett & Argyle 1985, Specklin & Baliteau 1989).

The effect of air-drying temperature on analyte modification is not completely understood but in some cases it seems to change the bioavailability or extractability of the analyte. The impact of air-drying on analysis may be more pronounced in certain soil types and