ASTM D1533 for water in insulating liquids by Coulometric KF Titration
ASTM D1533 standard test method water in insulating liquids by Coulometric Karl Fischer Titration
6. Apparatus
6.1 Coulometric Titrator, consisting of a detector electrode, generator electrode, titration vessel, magnetic stirrer, and control unit.
6.1.1 Detector Electrodes - This electrode pair amperometrically determines the end point of titration by measuring a sharp change in cell resistance.
6.1.2 Generator Electrodes - This electrode pair performs the cathodic reduction of iodide, which allows the Karl Fischer reaction to take place. It may consist of two platinum meshes or wires separated by a diaphragm within a glass assembly or two platinum meshes or wires not separated by a diaphragm.
6.2 Titration Flask - The titration flask will be of suitable capacity and will be protected against atmospheric moisture. A bottom drain cock is desirable but not necessary for removing reagents.
6.3 Stirrers - Means for agitation during titration will consist of a magnetic stirrer with a glass or TFE-fluorocarbon-covered stirring bar about 2 to 5 cm long or appropriate to the titration vessel. The bar should be cleaned thoroughly, rinsed with methanol, dried in an oven for 1 h at 100°C, and stored in a desiccator until used. In a sealed system, recleaning and redrying are not necessary for routine use.
6.4 Transfer Syringes - Syringes shall be used of a suitable size to accommodate instrument manufacturers' recommendation of sample size. Syringes may be glass or plastic. Glass syringes shall be cleaned and dried for 1 h at 100°C prior to use. Plastic syringes shall be disposed of following each sample use.
6.5 Needles - Needles that are to be fitted to the transfer syringes shall be long enough to inject samples directly below the surface of the Karl Fischer reagent. They should be of a large enough gauge to allow for easy transfer of the sample.
6.6 Septums, used to seal sample port, allowing the introduction of test specimens with a minimum amount of contamination from atmospheric moisture.
6.7 Sealing Grease - If the apparatus does not have a gasket seal, use a sealing grease to seal the titration chamber against atmospheric moisture.
6.8 Drying Oven, vacuum or air circulating.
6.9 Desiccator, standard laboratory type with color change indicator.
6.10 Analytical Balance, capable of weighing to more or less 0.001 g.
7. Reagents
7.1 Purity of Reagents - Unless otherwise indicated, all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available.
7.2 Coulometric Karl Fischer Reagent, can be obtained commercially. Refer to Annex A1 for information on alternative solvent systems.
7.2.1 Anode Reagent, frequently referred to as vessel solution.
7.2.2 Cathode Reagent, frequently referred to as generator solution.
7.3 Verification Solutions - Verification solutions are available commercially. Verification solutions may be formulated in-house from long chain alcohols.
7.3.1 The moisture content of water-saturated octanol is:
Water-saturated 1-Octanol 39.2 ± 0.85 mg/mL of solution
7.3.2 The water-saturated alcohol can be prepared by adding deionized water to the alcohol (ACS reagent grade) at 25°C such that the final mixture consists of a two-phase system in which the lower water phase is at least 2 cm high. Initially, this solution should be mixed thoroughly and allowed to stand at room temperature for at least three days to achieve complete equilibration.
NOTE 1 - For the best accuracy the solution should not be mixed or shaken after standing. Remove the sample aliquot from the top phase and inject it immediately into the titration cell. The degree of saturation of the water-saturated 1-Octanol varies <1 % between 10 and 30°C.
7.3.3 The response of the instrument shall be verified with 1 to 2 µL of water; this can give a response value of 1000 to 2000 µg within the specified precision of the instrument.
