ISO 3733 Petroleum products and bituminous materials - Determination of water - Distillation method
6 Verification and recovery test
6.1 General
Before initial use, verify the accuracy of the trap in accordance with 6.2. Before using the apparatus, carry out a recovery test in accordance with 6.3.
6.2 Verification
Before initial use, verify the accuracy of the graduation marks on the trap by adding 0.05 ml increments of distilled water from a 5 ml microburette or a precision micropipette readable to the nearest 0.01 ml. If there is a deviation of more than 0.05 ml between the water added and water observed, reject the trap or recalibrate.
6.3 Recovery test
Before using the apparatus for a water determination, test the overall recovery of water in the entire apparatus by introducing 250 ml to 1000 ml of dry (0.02 % water maximum) xylene, according to the size of the vessel, to the apparatus (500 ml to 2000 ml vessel as specified in 5.2) and proceed as described in clause 8. When complete, discard the contents of the trap, allow the contents of the still to cool and add the appropriate quantity of distilled water from a burette directly to the distillation flask in accordance with Table 2, and proceed as described in clause 8. The readings shall be judged accurate if the permissible limits given in Table 2 for graduated traps of different sizes are not exceeded.
A reading outside the permissible limits indicates malfunction due to vapour leaks, too rapid boiling, or ingress of extraneous moisture. Eliminate these factors and repeat the recovery test.
7 Sampling (see annex A)
7.1 General
Sampling is defined as all steps required to obtain a representative sample of the contents of any pipe, tank or other system and to place the sample in the laboratory test container.
7.2 Laboratory sample
Only representative samples obtained as specified in ISO 3170 and ISO 3171 shall be used in this International Standard.
The size of the test portion shall be based on the expected water content of the sample, such that the water yield does not exceed the capacity of the trap, unless a trap with a stopcock is used, since excess water can then be withdrawn into a graduated cylinder.
7.3 Preparation of the test samples
The following sample-handling procedures shall apply in addition to those covered in ISO 3170 and ISO 3171.
7.3.1 Solid samples which are sufficiently brittle shall be crushed and mixed thoroughly. A representative test portion shall be drawn from the crushed and mixed samples.
7.3.2 Liquid samples shall be mixed, after warming, if necessary, in the original container. The mixing time, mixing power (speed) and height above the bottom of the container shall be satisfactory for the product being analysed as established in the procedure given in annex A. The volume and water content of the sample shall not exceed the maximum validated in annex A.
NOTE If there is any doubt about the homogeneity of the mixed samples prepared in 7.3.1 or 7.3.2, determinations should be made on the total volume of the sample if the sample size is compatible with the expected water content. If this is not possible, a determination should be made on at least three test portions. All these results should be included in the test report and their average should be recorded as the water content of the sample.
