ASTM D1533 for water in insulating liquids by Coulometric KF Titration
ASTM D1533 standard test method water in insulating liquids by Coulometric Karl Fischer Titration
9. Sampling
9.1 The preferred method for sampling insulating liquids is Practice D923. If the test specimen is cloudy or contains free water, it may be difficult to obtain a representative specimen.
10. Preparation of Apparatus
10.1 Thoroughly clean and dry the titration vessel and then reassemble according to the manufacturer's recommendations. Follow the instructions provided in Annex A2 for detailed instructions on cleaning.
10.2 Fill reagent reservoirs with appropriate reagents according to the manufacturer's instructions.
10.3 Turn the instrument on and allow to stabilize.
11. Verification of System Operation
11.1 The accuracy of titration of the instrument and reagents shall be verified prior to beginning of testing by use of a suitable verification solution (see 7.3) containing a known quantity of moisture. It is desirable to verify the system operation using a solution that approximates the same range of water expected to be in the samples. Verification solutions shall be run with new reagents prior to testing. If verification solution results lie outside parameters established by the manufacturer for acceptable moisture content of the solution, reagents shall be changed and reverified.
12. Procedure
12.1 After verifying the system is operating properly, allow the instrument to restabilize prior to use.
12.2 Follow the manufacturer's instructions for suggested specimen size for an expected range of moisture content.
12.3 Using an appropriate syringe and needle (see 6.4 and 6.5) sample the insulating fluid to be tested. Prior to sampling, rinse the syringe and needle with the liquid to be tested one time.
12.4 Determine the sample mass by difference to three significant figures by weighing the test specimen before and after injection. Alternately, inject a known volume of a sample whose density is known at the test temperature to determine sample size.
12.5 Reagent solutions can be used until verification solutions no longer test accurately. See Section 11 for instructions on the use of verification solutions.
13. Calculation
13.1 Most commercially available coulometric Karl Fischer instruments automatically calculate the water content in ppm or percent. If not, calculate the amount of water in the sample as follows:
Water Content, mg/kg (ppm) = A/B
where:
A = mass of water, (µg) (instrument readout), and
B = mass of test specimen, g.
