ASTM D1744 method for determination of water in liquid petroleum products
ASTM D1744 standard test method for determination of water in liquid petroleum products by Karl Fischer reagent
9. Standardization of Karl Fischer Reagent
9.1 The dilute Karl Fischer reagent should be standardized at least daily in accordance with either 9.1.1 to 9.1.3 or 9.1.4 to 9.1.8.
9.1.1 Add 50 mL of the sample solvent to a clean, dry titration flask. Insert the stopper and adjust the magnetic stirrer to give a smooth stirring action. Turn on the indicating circuit and adjust the potentiometer to give a reference point with approximately 1 µA of current flowing. Add Karl Fischer reagent in suitable amounts to the solvent to cause the needle to deflect from the reference point. At first the needle will deflect due to local concentration of the unreacted reagent about the electrodes but will fall back to near the reference point. As the end point is approached, the needle will fall back more slowly after each addition of Karl Fischer reagent. The end point is reached when, after the addition of a single drop of reagent, the needle remains deflected at least 1 µA from the reference point for at least 30 s.
9.1.2 To the solution in the titration flask add carefully, from a weighing pipet previously weighed to the nearest 0.1 mg, 1 drop of distilled water. Stopper the flask. Reweigh the weighing pipet. Titrate to the end point as described in 9.1.1.
9.1.3 Calculate the water equivalence of the Karl Fischer reagent as follows:
F = W/T
where:
F = water equivalence of Karl Fischer reagent, mg/mL,
W = milligrams of water added, and
T = millilitres of reagent required for titration of the added water.
9.1.4 Alternatively, add 50 mL of methanol as the titration solvent to the titration flask and titrate to the end point as described in 9.1.1.
9.1.5 From a tared weighing bottle, by means of a clean, dry spatula, transfer approximately 250 mg of sodium tartrate dihydrate to the pretitrated alcohol in the titration flask. Record the mass.
9.1.6 Dip the spatula into the solvent to ensure the removal of any adhering tartrate (Note 3). Stopper the flask and titrate to the end point as described in 9.1.1.
NOTE 5 - To facilitate transferal of the tartrate to vessels having constricted openings or narrow necks, a spatula with the tip bent at a right angle to the handle is satisfactory.
9.1.7 Determine the total water content of the sodium tartrate dihydrate by drying a preweighed sample to a constant mass in an oven at 150 more or less 5°C.
9.1.8 Calculate the water equivalence of the Karl Fischer reagent as follows:
F = (A x B )/100T
where:
F = the water equivalence of Karl Fischer reagent, mg/ mL,
A = milligrams of sodium tartrate dihydrate used,
B = percentage of water in the sodium tartrate dihydrate, and
T = millilitres of reagent required for titration of the water in the sodium tartrate dihydrate.
