8. Sampling
8.1 Sampling is defined as all the steps required to obtain an aliquot representative of the contents of any pipe, tank, or other system and to place the sample into a container for analysis by a laboratory or test facility.
8.2 Laboratory Sample - The sample of petroleum product presented to the laboratory or test facility for analysis by this test method. Only representative samples obtained as specified in Practices D 4057 and D 4177 and handled and mixed in accordance with Practice D 5854 shall be used to obtain the laboratory sample.
NOTE 3 - Examples of laboratory samples include bottles from a manual sampling, receptacles from automatic samplers, and storage containers holding a product from a previous analysis.
8.3 Test Specimen - The aliquot obtained from the laboratory sample for analysis by this test method. Once drawn, use the entire portion of the test specimen in the analysis.
8.4 Select the test specimen size as indicated in Table 1 based on the expected water concentration.
9. Preparation of Apparatus
9.1 Follow the manufacturer's directions for preparation and operation of the titration apparatus.
9.2 Seal all joints and connections to the vessel to prevent atmospheric moisture from entering the apparatus.
9.3 Add the Karl Fischer anode solution to the anode (outer) compartment. Add the solution to the level recommended by the manufacturer.
9.4 Add the Karl Fischer cathode solution to the cathode (inner) compartment. Add the solution to a level 2 to 3 mm below the level of the solution in the anode compartment.
9.5 Turn on the apparatus and start the magnetic stirrer for a smooth stirring action. Allow the residual moisture in the titration vessel to be titrated until the end point is reached. Do not proceed beyond this stage until the background current (or background titration rate) is constant and less than the maximum recommended by the manufacturer of the instrument.
NOTE 4 - High background current for a prolonged period may be due to moisture on the inside walls of the titration vessel. Gentle shaking of the vessel (or more rigorous stirring action) will wash the inside with electrolyte. Keep the titrator on to allow stabilization to a low background current.
10. Calibration and Standardization
10.1 In principle, standardization is not necessary since the water titrated is a direct function of the coulombs of electricity consumed. However, reagent performance deteriorates with use and shall be regularly monitored by accurately injecting a known quantity of water (see 7.2) that is representative of the typical range of water concentrations being determined in samples. As an example, one may accurately inject 10 000 µg or 10 µL of water to check reagent performance. Suggested intervals are initially with fresh reagent and then after every ten determinations (see 11.3).
