# Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996, Paragraph 7: PROCEDURE


Preparation of the blank solution
7.1 Prepare a blank solution by repeating the whole procedure from the extraction stage, omitting only the test sample of fertiliser.
Preparation of the series of calibration solutions
7.2 Prepare a series of at least six calibration solutions of increasing concentration corresponding to the optimum response range of the spectrometer.
For the interval 0-12.5 μg molybdenum, place 0, 1, 2, 3, 4 and 5 ml, respectively, of the working solution (4.7.3) in the separating funnels (5.2). Make up to 50 ml with 6 M hydrochloric acid (4.1). The funnels contain, respectively, 0, 2.5, 5, 7.5, 10 and 12.5 mg molybdenum.
Development and separation of the complex
7.3 To each separating funnel (6.2, 7.1 and 7.2), add in the following order:
— 10 ml of the copper solution (4.2);
— 20 ml of the ascorbic acid solution (4.3);
mix thoroughly and wait for two or three minutes. Then add:
— 10 ml of n-butyl acetate (4.4), using a precision pipette;
— 20 ml of the thiocyanate solution (4.5).
Shake for one minute to extract the complex into the organic phase; allow to separate; after the separation of the two phases, draw off the entire aqueous phase and discard it; then wash the organic phase with:
— 10 ml of the stannous chloride solution (4.6).
Shake for one minute. Allow to separate and draw off the entire aqueous phase. Remove the organic phase in a test tube; this will make it possible to collect the drops of water in suspension.
Determination
7.4 Measure the absorbencies of the solutions obtained at 7.3 at a wavelength of 470 nm using the 0 mg/ml molybdenum calibration solution (7.2) as a reference.

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Source: https://www.legislation.gov.uk/nisr/1996/513/schedule/2/part/I/chapter/25j./paragraph/7 (the official version)
Page: https://openlegislation.uk/fertilisers-sampling-and-analysis-regulations-northern-ireland-1996/schedule-2/part-I/chapter-25j./paragraph-7
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.