Paragraph 8 EXPRESSION OF RESULTS

Plot a calibration curve of the concentration of the calibration solutions (7.2) along the abscissa and the absorbance given by the spectrophotometer (7.4) along the ordinate.

Read off the calibration curve the concentration of boron in the blank (7.1), the concentration of boron in the test solution (6.2) and, if the test solution is coloured, the corrected concentration of the test solution. To calculate the latter, subtract the absorbance of the correction solution (6.3) from the absorbance of the test solution (6.2) and determine the corrected concentration of the test solution. Note the concentration of the test solution (6.2), with or without correction, (x_s) and of the blank (x_b).

The percentage of boron in the fertiliser is given by:

$$\mathrm{B\%}=\mathrm{[}\left(\mathrm{x}\mathrm{s}-\mathrm{x}\mathrm{b}\right)\times \mathrm{V}\times \mathrm{D]}/\left(\mathrm{M}\times 104\right)$$

If Method 25c is used:

$$\mathrm{B\%}=\mathrm{[}\left(\mathrm{x}\mathrm{s}-\mathrm{x}\mathrm{b}\right)\times \mathrm{V}\times \mathrm{2D]}/\left(\mathrm{M}\times 104\right)$$

where:

• B is the quantity of boron expressed as a percentage of the fertiliser;

• x_s is the concentration (μg/ml) in the test solution (6.2) with or without correction;

• x_b is the concentration (μg/ml) in the blank (7.1);

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

• D is the factor corresponding to the dilution carried out in 6.2;

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

Calculation of the dilution factor D: if (a₁) and (a₂) are successive aliquot portions and (v₁) and (v₂) are the volumes corresponding to their respective dilutions, the dilution factor is given by:

$$\mathrm{D}=\left(\mathrm{v}1/\mathrm{a}1\right)\times \left(\mathrm{v}2/\mathrm{a}2\right)\mathrm{.}$$