The Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991

9h. EXTRACTION OF PHOSPHORUS BY WATER

1.    SCOPE

This method is for the determination of water-soluble phosphorus.

2.    FIELD OF APPLICATION

All fertilisers, including compound fertilisers, where water-soluble phosphorus is to be determined.

3.    PRINCIPLE

Extraction in water by shaking under specific conditions.

4.    APPARATUS

500 ml graduated flask (for example Stohmann).

Rotary shaker, 35 — 40 turns per minute.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

Extraction

6.1  Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a 500 ml graduated flask (4.1). Add to the flask 450 ml of water, the temperature of which must be between 20° and 25°C. Shake on the rotary shaker (4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly by shaking and filter through a dry fluted filter, into a dry container.

6.2  Determination

Determine the phosphorus according to Method 10, on an aliquot part of the clear filtrate.