pH Titration Unit
Motivation
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.
Solution
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.
One-Step pH Adjustment
The specialized pH-electrode with integrated capillares for buffer, acid and base, enables treatment of small sample volumes down to 300 µl in a One-Step pH-endpoint titration.
The One-Step procedure requires the calibrated pH electrode to be placed into the sample just once. With predefined values for buffer volume, mixing frequency and final pH, the pH adjustment will run without the need for further manual interaction and lists the total volume added. This is needed for precise quantification.
Integration into complete automation is a further step to be realized in the future.
