12. Procedure for Insoluble Solids
12.1 In case the sample is insoluble in the solvent or solvent mixture used, one of two modifications may be applied. The entire sample-solvent slurry may be titrated, or after stirring and standing, an aliquot of the clear supernatant liquid may be withdrawn and titrated. The latter modification is particularly useful for alkaline samples which are relatively insoluble in the solvent used (8).
12.2 Weigh the sample into a clean and dry titration cell, add 25 to 50 mL of the selected solvent (Section 7) and stopper the cell. Extract the water by stirring with a magnetic stirrer for 15 min or longer, or warming if indicated. Titrate the mixture at room temperature with KF reagent as described in 11.2 (Note 17). Also titrate the same volume of solvent as a blank.
NOTE 17 - If desired, a known excess of KF reagent may be added to the cell, allowed to stand, and then back-titrated with standard water-in-methanol reagent, as described in Test Methods D1348.
12.3 Calculation - Calculate the water content of the sample as follows:
where:
A = millilitres of reagent required to titrate the sample mixture,
B = millilitres of reagent required to titrate the solvent blank,
F = water equivalent, in milligrams of water per millilitre of KF reagent, and
W = grams of sample.
12.4 Alternatively, add 50 to 100 mL of the solvent to the sample in a volumetric flask, stopper, and extract as before. Make up to the mark with solvent, mix, and allow to stand until clear. Transfer a suitable aliquot of the supernatant liquid to a titration cell, and titrate with KF reagent as described in 11.2. Also titrate the same volume of the solvent, as a blank.
12.5 Calculation - Calculate the water content of the sample as follows:
where:
A = millilitres of reagent required to titrate the sample,
B = millilitres of reagent required to titrate the solvent blank,
F = water equivalent, in milligrams of water per millilitre of KF reagent,
W = grams of sample, and
R = aliquot factor.