Paragraph 8 EXPRESSION OF RESULTS

Calculate the amount of magnesium (Mg) or magnesium oxide (MgO) in the sample by reference to the calibration solutions and taking into consideration the blank.

The percentage of magnesium (Mg) in the fertiliser is equal to:

$$\mathrm{Mg}\left(\mathrm{\%}\right)=\genfrac{}{}{0.1ex}{}{\left(\mathrm{x}\mathrm{s}-\mathrm{x}\mathrm{b}\right)\times \mathrm{D}1\times \left(200/10\right)\times \mathrm{D}2\times 500\times 100}{1000\times 1000\mathrm{M}}$$

where:

• x_s = the concentration of the solution as calculated from the calibration curve, in μg/ml.

• x_b = the concentration of the blank solution as calculated from the calibration curve, in μg/ml.

• D₁ = the dilution factor if the solution is diluted (7.1). It is equal to four if 25 millilitres are taken. It is equal to one when the solution is not diluted.

• D₂ = the dilution factor in 7.3.

• M = the mass of the test sample taken for the extraction.

• MgO (%) = Mg (%)/0.6.