Paragraph 9 CALCULATION OF RESULTS

Draw a calibration curve by plotting the average response for each calibration solution along the ordinate and the corresponding concentrations, expressed in μg per ml on the abscissa. Determine from this the sodium concentration of the test solution. Calculate the quantity of sodium from the standard solutions taking account of the levels of dilution. Express the results as a percentage of the sample.

The percentage sodium (Na) content of the fertiliser is as follows:

$$\mathrm{Na}\left(\mathrm{\%}\right)=\mathrm{X}\times \genfrac{}{}{0.1ex}{}{\mathrm{v}3}{\mathrm{v}4}\times \genfrac{}{}{0.1ex}{}{\mathrm{v}1}{\mathrm{v}2}\times \genfrac{}{}{0.1ex}{}{10-2}{\mathrm{m}}$$ $$\mathrm{Na}2\mathrm{O}\left(\mathrm{\%}\right)=\mathrm{Na}\left(\mathrm{\%}\right)\times 1.348$$

where:

• X = the concentration of the solution introduced into the spectrometer in μg/ml,

• v₁ = the volume of the extraction solution in millilitres,

• v₂ = the aliquot volume in the intermediate dilution in millilitres,

• v₃ = the volume of intermediate dilution in millilitres,

• v₄ = the aliquot volume in ml of the final dilution (in 100 millilitres),

• m = the mass of the test sample in grams.