ASTM D1364 for Water in Volatile Solvents (Karl Fischer Reagent Titration Method)
6. Apparatus
6.1 Titration Vessel - For color end point titrations, use a 100 or 250-mL volumetric flask, which need not be calibrated; a 250-mL flask fitted with interchangeable electrodes (Fig. 1) may also be used for the instrumental end point and is particularly suitable for titrations at ice temperatures. For permanently mounted assemblies, the vessel should have a capacity about equal to that of a 300-mL tall-form beaker; and be provided with a tight-fitting closure to protect the sample and reagent from atmospheric moisture, a stirrer, and a means of adding sample and reagents and removing spent reaction mixture. It is desirable to have a means for cooling the titration vessel to ice temperature.
6.2 Instrument Electrodes - Platinum with a surface equivalent to two No. 26 wires 5 mm long. The wires should be 3 to 8 mm apart and so inserted in the vessel that 25 mL of liquid will cover them.
6.3 Instrument Depolarization Indicator, having an internal resistance of less than 5000 Ω and consisting of a means of impressing and showing a voltage of 20 to 50 mV across the electrodes and capable of indicating a current flow of 10 to 20 µA by means of a galvanometer or radiotuning eye circuit.
6.4 Buret Assembly for Karl Fischer reagent, consisting of a 25 or 50-mL buret connected by means of glass (not rubber) connectors to a source of reagent; several types of automatic dispensing burets may be used. Since the reagent loses strength when exposed to moist air, all vents must be protected against atmospheric moisture by adequate drying tubes containing indicating calcium sulfate drying agent. All stopcocks and joints should be lubricated with a lubricant not particularly reactive with the reagent.
6.5 Weighing Bottle, of the Lunge or Grethen Type, or equivalent.
7. Reagents
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without decreasing the accuracy of the determination.
7.1.1 Karl Fischer Reagent (equivalent to 6 mg of H2O per mL) - For each liter of solution, dissolve 133 more or less 1 g of I2 in 425 more or less 2 mL of anhydrous (less than 0.1 % H2O) pyridine in a dry glass-stoppered bottle. Add 425 more or less 2 mL of anhydrous (less than 0.1 % H2O) 2-methoxyethanol. Cool to below 4°C in an ice bath and add gaseous SO2, dried by bubbling through concentrated H2SO4(sp gr 1.84); determine the amount of SO2 added by measuring the change in weight of the SO2 cylinder (102 more or less 1 g) or the increase in volume (70 more or less 1 mL) of the reagent mixture. Alternatively, add 70 mL of freshly drawn liquid SO2 in small increments.
7.1.2 Solvent Mixture - Mix 1 volume of anhydrous (less than 0.1 % H2O) pyridine with 4 volumes of anhydrous (less than 0.1 % H2O) ethylene glycol.
NOTE 3 - Pyridine, ethylene glycol, and 2-methoxyethanol, each containing less than 0.1 % water, are available and should be used.
NOTE 4 - If adequately dry reagents cannot be procured, they can each be dried by distillation through a multiple-plate column, discarding the first 5 % of material distilling overhead and using the 95 % remaining. Drying may also be accomplished by the addition of 1 volume of toluene or cyclohexane to 19 volumes of the pyridine-glycol, or of the pyridine ethylene glycol monomethyl ether mixture, followed by distillation; the first 5 % distilled is discarded and the residual 95 % is used.
