11. Procedure A (by Mass)
11.1 Add newly made solvents to the anode and cathode compartments of the titration vessel and bring the solvent to end-point conditions as described in Section 9.
11.2 Add the petroleum product test specimen to the titration vessel using the following method:
11.2.1 Starting with a clean, dry syringe of suitable capacity (see Table 1 and Note 5), withdraw and discard to waste at least three portions of the sample. Immediately withdraw a further portion of sample, clean the needle with a paper tissue, and weigh the syringe and contents to the nearest 0.1 mg. Insert the needle through the inlet port septum, start the titration, and with the tip of the needle just below the liquid surface, inject the test specimen. Withdraw the syringe, wipe clean with a paper tissue, and reweigh the syringe to the nearest 0.1 mg. After the end point is reached, record the micrograms of water titrated.
NOTE 5 - If the concentration of water in the sample is completely unknown, it is advisable to start with a small trial portion of sample to avoid excessive titration time and depletion of the reagents. Further adjustment of the aliquot size may then be made as necessary.
11.2.2 When the background current or titration rate returns to a stable reading at the end of the titration as discussed in 9.5, additional specimens may be added as per 11.2.1.
11.3 Replace the solutions when one of the following occurs and then repeat the preparation of the apparatus as in Section 9.
11.3.1 Persistently high and unstable background current.
11.3.2 Phase separation in the anode compartment or oil coating the electrodes.
11.3.3 The total oil content added to the titration vessel exceeds one quarter of the volume of solution in the anode compartment.
11.3.4 The solutions in the titration vessel are greater than one week old.
11.3.5 The instrument displays error messages that directly or indirectly suggest replacement of the electrolytes - see instrument operating manual.
11.3.6 The result of a 10 µL injection of water is outside 10 000 more or less 200 µg.
11.4 Thoroughly clean the anode and cathode compartment with xylene if the vessel becomes contaminated with product. Never use acetone or similar ketones. Clogging of the frit separating the vessel compartments will cause instrument malfunction.
11.5 For products too viscous to draw into a syringe, add the sample to a clean, dry bottle and weigh the bottle and product. Quickly transfer the required amount of sample to the titration vessel by suitable means, such as with a dropper. Reweigh the bottle. Titrate the sample as in 11.2.
12. Procedure B (by Volume)
12.1 Follow steps 11.2.1 through 11.5 from Procedure A, taking sample by volume instead of mass.
NOTE 6 - A volume aliquot of the product is titrated to an electrometric end point using a coulometric Karl Fischer apparatus. The steps described in Procedure A are followed except as noted. The volume injection method is applicable only when the vapor pressure and viscosity of the sample permit an accurate determination of the volume of the sample.
NOTE 7 - The referee procedure for determination of water in liquid petroleum products by coulometric Karl Fischer titration is Procedure A, which uses a mass measurement of the product test specimen.
NOTE 8 - The presence of gas bubbles in the syringe can be a source of uncertainly. The tendency of product to form gas bubbles is a function of product type and corresponding vapor pressure. Viscous products can prove to be difficult to measure volumetrically with a precision syringe.
NOTE 9 - Helpful hints in obtaining reliable results are given in Appendix X1.
13. Procedure C (Water Evaporator Accessory)
13.1 If using the water evaporator accessory for samples difficult to analyze by Procedure A or B due to sample viscosity, matrix interference, or extremely small concentrations of water (for example, <100 mg/kg), add 10 mL of white oil to the evaporator accessory. Bubble dry nitrogen gas at about 300 mL/min through the oil. Heat the oil to the temperature suggested by the instrument manufacturer for a particular product type.
13.2 Dissolve 5 more or less 0.01 g of accurately weighed viscous sample in a 10 mL volumetric flask. Make up to volume with dried hexane. Shake the sample until it is completely dissolved in the solvent.
NOTE 10 - All parts of the glass assembly must be thoroughly dry before use. The smallest amount of contamination by moisture will cause erroneous results. Perform several preliminary runs with known content standards to determine that the system is operating correctly. Water-in-alcohol standards must be capped with rubber septa rather than rubber stoppers.
13.3 Inject 1 mL of dissolved sample into the evaporator assembly. Start the operating sequence. Follow steps 11.1 through 11.5 in Procedure A. After the end point is reached, record the micrograms of water titrated from the digital readout on the instrument.
