Method 101c Preparation of ytterbium marked feed for analysis

Reagent.

• Nitric acid solution, approximately 5% (v/v) - add 100 ml nitric acid (approximately 70% m/m HNO3) to 2 l distilled water and mix.

Procedure. Weigh 2 g of the oven dried sample ground to 1 mm into a porcelain or glass crucible and place in a cool muffle furnace. Increase the temperature to 550°C and ash for 2 h. Cool and dissolve in nitric acid solution, make up to 20 ml and store in a polythene capped tube. Allow to settle before transferring to another clean sample tube by decanting or using a polythene Pasteur pipette. Analyse the solution by AAS or ICP according to the manufacturer's recommendations.

Note: A typical ICP analysis requires making a solution of 9.6 ml ultrapure water, 0.2 ml nitric acid (approximately 70% m/m HNO3), 0.1 ml marked feed sample solution (or 1 ml faecal sample solution) and 0.1 ml rhodium internal standard solution (10 pg ml-1 in 5% v/v nitric acid solution). This is contained in a sample tube sealed with clingfilm. The sample probe is inserted through the clingfilm. A pick-up time of 35 s, and a scan time of 35 s proved satisfactory. The probe is rinsed in the 5% v/v nitric acid solution between samples.

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