BS ISO 03771:2011 pdf download
BS ISO 03771:2011 pdf download.Petroleum products —Determination of base number —Perchloric acid potentiometric titration method.
8 Preparation of electrode system
8.1 Preparation of electrodes
Remove the cap from the electrode filling neck. Ensure that the ground glass sleeve is securely in place by pushing it firmly up or down (depending on the electrode type). Turn the ground glass sleeve slightly and gently push it in again. Aftow a lew drops of electrolyte to flush through (to wash the diaptwagm) and allow the electrolyte to spread out between the ground glass surface and the core inner cell. Top the electrolyte up to the top of the electrolyte filling neck. In addition to its basic function, the electrolyte provides an electrical shield agarnst outside interference. pH electrodes are particuLarly sensitive to interference when used with non-aqueous solvents. For this reason, it is very important that the level of the electrolyte is as hgh as possible Only conduct measurements and titrations with the plug removed.
Precondition new electrodes. It has been found that submerging the new electrodes in the solvent mixture for 12 h is effective. The same applies for electrodes which are used in water (see 8,3).
8.2 Maintenance of electrodes
Thoroughly clean the electrode before long-term storage and then keep in the same electrolyte that will be used to fill it. Close the electrode filling plug during storage.
8.3 Testing of electrodes
If there ate any doubts about the performance of the electrode, for example when adjusting the tltre, test the electrode using a buffer solution, for example with a standard pH buffer (pH 4 and pH 7), As the electrode is a pH electrode for acidlbase titrations, the testing is different to a standard electrode test. Measure the potential difference (use the mV range) of the titrator (or a pH meter) between two buffer solutions with pH 4 and pH 7. Proper performance ves a difference of at least 150 my (50 mVIdpH).
Condition the electrode after this test (see 8.1).
8.4 Cleaning of electrodes
Thoroughly wash the electrode with the solvent between titrations (washing with toluene then petroleum ether, then toluene again has been found to be effective). The electrode may not be coated with an oil film after washing. Both dipping the electrode and automatic deaning have proved effective with the various automatic samplers on the market,
9 Performance
9,1 Sample amounts
Select the sample mass so that approximately 5 ml of perchloric acid solution are used up at the inflection Table 2 shows the test sample mass based on total base number (3.1).
9.4.2 Incremental titration
See the manufacturer’s recommendations.
9.5 Cleaning of apparatus
See the manufacturer’s recommendations for cleaning and storing the apparatus for long periods of time (see also 8.4).
9.6 Blank test
For each series 01 test samples, the blank volume Is found with the recommended amount of titration solvent (59). This conditions the electrode system. A blank test is mandatory for each new batch of solvent. Normally the blank is so low that it does not need to be taken into account.
10 Calculation of base number
10.1 The end point of a potentionietnc titration lies at the mid pornt of the inflection of the resulting titration curve Modem titration apparatus finds the inflection automahcelly Follow the manufacturer’s recommendations regarding the sensitivity and parameters. As the total base number titration records the sum of the base components, it is not necessary to differentiate between potential multiple endpoints. In order to avoid stopping the titration too earty It Is recommended only to stop the titration after a predefined maximum volume.
