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
6. Apparatus
6.1 Assemble the apparatus as described in the Annex A1. (See Note 1.)
NOTE 1 - Any apparatus that will give equal or better precision is acceptable.
7. Reagents and Materials
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 can be used, provided it is first ascertained that 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 distilled water or water of equal purity. The solvents used must have low-water content, for example, less than 500 mg/kg mass.
7.3 Karl Fischer Reagent, Solution (Note 2), Stock - (Warning - Toxic.) For each litre of solution, dissolve 85 more or less 1 g of iodine in 270 more or less 2 mL of pyridine in a dry, glass-stoppered bottle. Add 670 more or less 2 mL of methanol (99.9 %) (Note 3). Cool the mixture in an ice bath to below 3.9°C. Bubble gaseous sulfur dioxide (SO2) (Note 4) through concentrated sulfuric acid (H2SO4, rel dens 1.84) (see warning information below) into the cooled mixture. Continue the addition of SO2 until the volume is increased 50 more or less 1 mL. Alternatively, add 50 more or less 1 mL of freshly drawn liquid SO2 in small increments to the precooled mixture in an ice bath. Mix well and set aside for at least 12 h before using. (Warning - Poison. Corrosive. Strong oxidizer. Contact with organic material can cause fire. Can be fatal if swallowed. Liquid and vapor can cause severe burns. Harmful if inhaled. Contact with water liberates large amounts of heat. Spillage can cause fire.)
NOTE 2 - Commercially prepared Karl Fischer Reagent may be used.
NOTE 3 - If 99.9 % methanol is not commercially available, it can be prepared by dissolving 24 g of magnesium metal turnings in 200 mL of methanol. Caution, the reaction is vigorous. When the reaction is complete, add 3 L of methanol. Reflux for 5 h and distill directly into the container in which the 99.9 % methanol is to be kept. Vent the system through a drying tube during the distillation.
NOTE 4 - Follow standard safety precautions for handling toxic gases.
7.4 Karl Fischer Reagent, Dilute Solution - Adjust the strength of the stock solution to a water equivalence of 2 to 3 mg of water per mL by dilution with pyridine.
7.5 Sample Solvent - Mix 1 volume of methanol (Note 4) with 3 volumes of chloroform. (Warning - Can be fatal if swallowed. Harmful if inhaled. Can produce toxic vapors if burned.)
8. Sampling
8.1 Take samples in accordance with the instructions in Practice D4057.
