Procedure. The AOAC and the SI 1996 No. 1342 methods differ, and both are outlined below.
1. AOAC (Method 977.01 Preparation of solution) extraction: Weigh 1.000 g of the ground sample and transfer into a 9-cm filter paper in a funnel. Wash with successive small portions of water by directing a jet of water from a wash bottle around the entire periphery of the paper and into the residue, which should be well mixed up with each washing, and drain through completely before the next addition. Continue until the filtrate amounts to about 250 ml. Use suction only if the process would take longer than 1 h. Any turbidity should be removed by the addition of 1-2 ml HNO3 to the filtrate. Make up to 250 ml with water and mix. A sample of triple superphosphate should give a solution of approximately 800 pg P ml-1. 2. SI 1996 No. 1342 extraction: Weigh 5 g prepared sample to the nearest 0.001 g, and place in a 500-ml volumetric flask. Add 450 ml water at 20-25°C and shake for 30 min on a rotary shaker at 35-40 turns per minute. Make up to the mark with water and mix. Filter through a dry fluted filter paper into a dry container. A sample of triple superphosphate should give a solution of approximately 2000 pg P ml-1.
Was this article helpful?