When performing a TAN or TBN titration, each sample gets slower and slower and the curves get flatter and flatter until I don get a result. What could be wrong?
The TAN and TBN titrations are non-aqueous acid/base titrations performed using a glass pH sensor. For a glass pH sensor to work it is necessary that the electrode has a microscopic hydrated ‘gel’ layer on the bulb of the electrode. This hydration is achieved by soaking the electrode in water for some time. During the course of any non-aqueous acid/base titration the gel layer is slowly dehydrated resulting in a weaker and less stable signal. The loss in stability of the signal can cause an automatic titrator to slow down in an attempt to match the rate of addition to the electrode response. The weaker signal means that the size of any jumps is smaller and, depending on instrument settings, can result in the instrument no longer recognizing the jump. The solution to the problem is to rehydrate the electrode between every sample, and this is in fact specified by the ASTM methods for TAN/TBN determination.
