6. Apparatus
6.1 Coulometric Karl Fischer Apparatus (using electrometric end point) - A number of automatic coulometric Karl Fischer titration assemblies consisting of titration cell, platinum electrodes, magnetic stirrer, and a control unit are available on the market. Instructions for operation of these devices are provided by the manufacturers and are not described herein.
6.1.1 Water Vaporizer Accessory - A number of automatic water vaporizer accessories are available on the market. Instructions for the operation of these devices are provided by the manufacturers and are not described herein.
6.2 Syringes - Samples are most easily added to the titration vessel by means of accurate glass or disposable plastic syringes with luer fittings and hypodermic needles of suitable length to dip below the surface of the anode solution in the cell when inserted through the inlet port septum. The bores of the needles used shall be kept as small as possible, but large enough to avoid problems arising from back pressure or blocking while sampling. Suggested syringe sizes are as follows:
6.2.1 Ten microlitres, with a needle long enough to dip below the surface of the anode solution in the cell when inserted through the inlet port septum and graduated for readings to the nearest 0.1 µL or better. This syringe can be used to accurately inject a small quantity of water to check reagent performance as described in Section 10.
6.2.2 As identified in Table 1, syringes of the following capacities: 250 µL accurate to the nearest 10 µL; 500 µL accurate to the nearest 10 µL; 1 mL accurate to the nearest 0.01 mL; 2 mL accurate to the nearest 0.01 mL; and 3 mL accurate to the nearest 0.01 mL. A quality gas-tight glass syringe with a TFE-fluorocarbon plunger and luer fitting is recommended.
7. Reagents and Materials
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society3, where such specifications are available. Use other grades, provided the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
7.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water as defined by Type II of Specification D 1193.
7.3 Xylene, Reagent Grade, less than 100 to 200 mg/kg water, dried over a molecular sieve (Warning - Flammable. Vapor harmful).
7.4 Karl Fischer Reagent, standard commercially available reagents for coulometric Karl Fischer titrations.
7.4.1 Anode Solution - Mix six parts of commercial Karl Fischer anode solution with four parts of reagent grade xylene on a volume basis. Newly made Karl Fischer anode solution shall be used. Other proportions of anode solution and xylene may be used and determined for a particular reagent, apparatus, and sample tested. Some samples may not require any xylene, whereas others will require the solvent effect of the xylene (Warning - Flammable, toxic if inhaled, swallowed, or absorbed through skin).
NOTE 1 - Toluene may be used in place of xylene. However, the precision data in Section 17 were obtained using xylene.
7.4.2 Cathode Solution - Use standard commercially available cathode Karl Fischer solution. Newly made solution shall be used (Warning - Flammable, may be fatal if inhaled, swallowed, or absorbed through skin. Possible cancer hazard).
7.4.3 If the sample to be analyzed contains ketone, use commercially available reagents that have been specially modified for use with ketones.
NOTE 2 - Some laboratories add the ketone suppressing reagent as part of their standard analytical procedure since often the laboratory does not know whether the sample contains ketone.
7.5 Hexane, Reagent Grade, less than 100 to 200 mg/kg water (Warning - Flammable. Vapor harmful). Dried over molecular sieve.
7.6 White Mineral Oil - Also called paraffin oil or mineral oil. Reagent grade.
7.7 Molecular Sieve 5Å - 8 to 12 mesh.
