ISO 3733 Petroleum products and bituminous materials - Determination of water - Distillation method
8 Procedure
8.1 Homogenize the sample in accordance with 7.3 before taking the test portion.
8.2 Measure the required test portion to an accuracy of +/- 1 % and transfer it to the still in accordance with 8.3 or 8.4, depending on the sample type.
8.3 Measure mobile liquid samples in a graduated cylinder of an appropriate size. Rinse the material adhering to the cylinder with one 50 ml and two 25 ml portions of the solvent-carrier liquid (see clause 4 and Table 3). Drain the cylinder thoroughly after the sample transfer and each rinsing.
8.4 Weigh solid or viscous materials directly into the still and add 100 ml of the selected solvent-carrier liquid (see Table 3). When testing material of low water content where large test portions are necessary, a solvent-carrier liquid volume in excess of 100 ml may be used.
8.5 A magnetic stirrer has been found to be most effective, but glass beads or other boiling aids may be added, if necessary, to reduce bumping.
8.6 Assemble the components of the apparatus as illustrated in Figures 1 and 2, choosing the trap in accordance with the expected water content of the sample and making all connections vapour- and liquid-tight. If a metal still with a removable cover is used, insert a gasket of heavy paper, moistened with solvent, between the body and the cover of the still. The condenser tube and trap shall be chemically clean to assure free drainage of water into the bottom of the trap. Insert a loose cotton plug in the top of the condenser to prevent condensation of atmospheric moisture inside it. Circulate cold water through the jacket of the condenser.
8.7 Apply heat to the still, adjusting the rate of boiling so that condensed distillate discharges from the condenser at a rate of 2 drops per second to 9 drops per second. If the metal still is used, start heating with the ring burner approximately 75 mm above the bottom of the still and gradually lower the burner as the distillation proceeds. Continue the distillation until no water is visible in any part of the apparatus except in the trap, and the volume of water in the trap remains constant for 5 min. If there is a persistent ring of water in the condenser tube, carefully increase or cut off the condenser water for a few minutes.
8.8 When the evolution of water is complete, allow the trap and contents to cool to room temperature. Dislodge any drops of water adhering to the sides of the trap with a glass rod, or by other suitable means, and transfer them to the water layer. Read the volume of the water in the trap to the nearest scale division.
8.9 Whenever a new solvent batch is used, a solvent blank shall be established by placing the volume of the solvent to be used during the actual determinations in the distillation flask and testing as outlined in 8.5 to 8.8.
9 Calculation
Calculate the water in the sample, φ as a percentage (volume/volume), or w as a percentage (mass/mass), in accordance with the basis on which the sample was taken as follows:
φ = (V1 - V2)/Vo x 100
φ = (V1 - V2)/(m/ρ) x 100
w = (V1 -V2)/m x 100
where
V0 is the volume of the test portion, in millilitres;
V1 is the volume of water, in millilitres, in the trap when the measurement is made on the unknown sample;
V2 is the volume of water, in millilitres, in the trap when the measurement is made on the solvent blank;
m is the mass of test sample, in grams;
ρ is the density of sample, in grams per millilitre at 15 °C.
It is assumed that the density of water is 1 g/ml.
NOTE Volatile water-soluble material, if present, is measured as water.
