SCHEDULE 2 Methods of analysis

Part I

25j. DETERMINATION OF MOLYBDENUM IN FERTILISER EXTRACTS BY SPECTROMETRY OF A COMPLEX WITH AMMONIUM THIOCYANATE

EXPRESSION OF RESULTS

8.  Construct the calibration curve by plotting the corresponding masses of molybdenum in the calibration solutions (7.2) expressed in mg along the abscissa and the corresponding values of the absorbencies (7.4) given by the spectrometer reading along the ordinate.

From this curve determine the mass of molybdenum in the test solution (6.2) and the blank solution (7.1). These masses are designated (x_s) and (x_b) respectively.

The percentage of molybdenum in the fertiliser is:

If Method 25c has been used:

where:

• Mo is the quantity of molybdenum expressed as a percentage of the fertiliser;

• a is the volume in ml of the aliquot taken from the last dilute solution (6.2);

• x_s is the mass in μg of Mo in the test solution (6.2);

• x_b is the mass in μg of Mo in the blank solution (7.1) the volume of which corresponds to the volume (a) of the aliquot of the test solution (6.2);

• V is the volume in ml of the extract solution obtained in accordance with Method 25a or 25b;

• D is the factor corresponding to the dilution performed in 6.2;

• M is the mass in g of the test sample taken in accordance with Method 25a or 25b.

Calculation of the dilution factor D: where (a₁), (a₂) are successive aliquot portions and (v₁), (v₂) are the volumes corresponding to their respective dilutions, the dilution factor D will be: