The adjustment of the pH value of the sample solution is crucial for the acquisition of NMR spectra. Slight pH variations of just 0.005 units can change the chemical shift of NMR spectra, the pH value should be adjusted to more than +/- 0.04 tolerance, but this necessitates careful pH adjustment. A problem arises from the fact that the totally available sample volumes are only in the order of 1-2ml. Currently, this adjustment is done manually, by adding reagents in the low µl range. pH adjustment under these conditions is relatively tedious, time consuming work and requires an experienced person.
Buffer solution, with an optional internal standard, is added to the sample and mixed. The pH is measured and, depending on the predefined pH value, small amounts of acid/base are automatically added and mixed. Additional cycles of pH measurement, acid/base addition and mixing are executed until the target pH is reached. Automating this procedure saves time and delivers higher reproducibility of results.