1.1 Following precautions are suggested to obtain accurate and precise results by this test method. Some of these suggestions are also described in the text of the test method, but are compiled here for easy reference.
1.1.1 A number of chemicals interfere in this titration: mercaptans, sulfides, amines, ketones, aldehydes, oxidizing and reducing agents, and so forth. Some of the interferences can be eliminated by addition of suitable reagents, for example, addition of benzoic or succinic acid for aldehyde and ketone interference.
1.1.2 At low water concentrations (<0.02 mass %), the interference by mercaptan and sulfide (>500 mg/kg as sulfur) may be significant (see Test Method E 203).
1.1.3 All equipment should be scrupulously clean of moisture. Rinse all syringes, needles, and weighing bottles with anhydrous acetone after cleaning. Then dry in an oven at 100°C for at least an hour and store immediately in a desiccator.
1.1.4 Fill the dry cooled sample bottle as rapidly as possible with the sample within 15 mm of the top and immediately seal.
1.1.5 After removing a sample aliquot from the bottle with a dry hypodermic syringe, inject dry nitrogen into the sample bottle with the syringe to displace the removed sample void.
1.1.6 The presence of gas bubbles in the syringe may be a source of uncertainty. Viscous samples may be difficult to measure with a precision syringe. In such cases, taking the sample aliquot by mass is preferred to volume measurement.
1.1.7 Although standardization is not necessary in coulometric titrations, reagent performance deteriorates with use and must be regularly monitored by accurately injecting 10 000 µg or 10 µL of pure water. Suggested intervals are initially with fresh reagent, and then after every ten determinations.
1.1.8 Rinse the clean dry syringe at least three times with the sample and discard the aliquots before taking an aliquot for injecting into the titration vessel.
1.1.9 During the blank measurement instrument preparation, high background current for a prolonged period may be due to moisture on the inside walls of the titration vessel. Wash the inside with the electrolyte by gently shaking the vessel or by more vigorously stirring.
1.1.10 The frit separating the vessel compartments may get clogged with sample residues; Disassemble the apparatus in such cases and acid clean the frit.
1.1.11 Any time one of the following situations occurs, replace the anode and the cathode solutions and then repeat the preparation of the apparatus as in Section 9.
1.1.11.1 Persistently high and unstable background current.
1.1.11.2 Phase separation in the anode compartment or the sample coating the electrodes.
1.1.11.3 The total amount of sample added to the titration vessel exceeds one fourth of the volume of solution in the anode compartment.
1.1.11.4 The solutions in the titration vessel are over one week old.
1.1.11.5 The instrument displays error messages that suggest replacement of the electrodes.
1.1.11.6 The results of a 10 µL injection of water is outside 10 000 more or less 200 µg.
1.1.12 If the titration vessel gets contaminated with the sample, thoroughly clean the anode and cathode compartments with xylene. Never use acetone or similar ketones.
