The Fertilisers (Sampling and Analysis) Regulations 1996

26b. EXTRACTION OF WATER — SOLUBLE TRACE ELEMENTS

“1.    SCOPE

This method defines the procedure for extracting water-soluble forms of the following trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc. The aim is to carry out the minimum number of extractions, making use wherever possible of the same extract to determine the level of each of the elements listed above.

“2.    FIELD OF APPLICATION

This procedure concerns fertilisers containing one or more of the following trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc. It is applicable to each trace element, the declared content of which is more than 10%.

“3.    PRINCIPLE

The trace elements are extracted by shaking the fertiliser in water at 20±°C.

Note: The extraction is empirical and may not be quantitative.

“4.    REAGENTS

Diluted hydrochloric acid (HCI) solution, about 6 M

Mix 1 volume of hydrochloric acid (ρ = 1.18 g/ml) with 1 volume of water.

“5.    APPARATUS

Rotary shaker set at about 35 to 40 rpm.

Note: Where the boron content of the extract is to be determined, do not use borosilicate glassware. Teflon or silica is preferable for this extraction. Rinse the glassware thoroughly if it has been washed in detergents containing borates.

“6.    PREPARATION OF THE SAMPLE

See Method 1.

“7.    PROCEDURE

Test sample

Take a quantity of fertiliser weighing 1 or 2g depending on the declared content of the product. The following table shall be used to obtain a final solution which, after appropriate dilution, will be within the measuring range for each method. The samples should be weighed to within 1mg.

Declared content of trace element in the fertiliser (%)	<10 –<25	<25
Mass of test sample (g)	2	1
Mass of element in the sample (mg)	<200 –<500	<250
Volume of extract V (ml)	500	500
Concentration of element in extract (mg/l)	<400 –<1000	<500

Place the sample in a 500 ml flask.

Preparation of the solution

Add about 400 ml of water.

Stopper the flask well. Shake vigorously by hand to disperse the sample, then place the flask on the shaker and shake for 30 minutes.

Make up to volume with water and mix thoroughly.

Preparation of the test solution

Filter immediately into a clean, dry flask. Stopper the flask. Carry out the determination immediately after filtering.

Note: If the filtrate gradually becomes cloudy, make another extraction following 7.1 and 7.2 in a flask of volume Ve. Filter into a calibrated flask of volume W which has previously been dried and has received 5 ml of dilute hydrochloric acid (4.1). Stop the filtration at the exact moment when the calibration mark is reached. Mix thoroughly.

Under these conditions the value of V in the expression of results is:

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The dilutions in the expression of results depend on this value of V.

“8.    DETERMINATION

The determination of each trace element is carried out on the aliquot portions indicated in the method for each individual trace element.

Methods 26e, 26f, 26g, 26i and 26j cannot be used to determine elements present in a chelated or complexed form. In such cases Method 26c must be used prior to the determination.

In the case of determinations by atomic absorption spectrometry (Methods 26h and 26k) such treatment may not be necessary.