Method 713a Determination of trace elements in plants and feeds

Reagents.

• Hydrochloric acid, approximately 36% m/m (for AAS)

Procedure. Weigh 2.0000 g of the dried and milled (to 1 mm) sample into a silica crucible and place in a cold muffle furnace with the chimney vent open, and allow to heat up to 450°C. Close the vent and maintain at this temperature overnight. Remove from the furnace and allow to cool, then add 15 drops HCl from a polythene Pasteur pipette, being careful to moisten all the sample. Using a fume cupboard, gently evaporate off all the HCl on a hotplate at moderate heat, then remove and cool. Dissolve the residue in 0.1 M HCl, and transfer quantitatively to a 10-ml volumetric flask. Make up trace element standards in 0.1 M HCl covering the expected ranges in the sample solutions and analyse by AAS (or ICP) according to the instrument manufacturer's instructions.

Calculation. The sample solution is of 2 g in 10 ml, therefore the concentrations in pg ml-1 of the trace element should be multiplied by 5 to give the concentration in pg g-1 of the trace element in the dried sample.

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