Improvement of conductivity measurement in liquid chromatography

In liquid chromatography the ability to measure the conductivity is essential toreach a good result. This is done by applying a current through the electrolyte ofinterest and measuring the voltage drop over the electrolyte. The conductivity isthen calculated with the known current and the measured voltage. It is of highimportance that it is an AC-current to avoid polarization at the electrodes of thesensor. With the AC-current a frequency must be chosen to reach the most accurateresult. This is hypothetically done where the phase is as low as possible. An electricequivalent circuit and previous work was used as a starting point in the work offinding the best frequency algorithms that would give the lowest phase. Afterseveral measurements with different frequency algorithms it could be seen that thecurrent algorithm is plenty good and that at the moment it is not worth it to improveit further. The sensor in this thesis, chip LFS155 from IST AG, Switzerland, wassaid to have an linear cell constant between 0.1-200 mS/cm. So after multiplemeasurements on five different LFS155 sensors it could be seen that in the regions oflower conductivity as well as higher conductivity the cell constant could be adjustedfora better result. The adjustments were done by excels curve fitting function andimplemented witha good result. The demands on the accuracy for the sensor tomeasure conductivity could be improved. In the lower part of conductivity spectra(<0.1 mS/cm) the promised accuracy went from±0.02 mS/cm to±0.005 mS/cm.In the higher end of the conductivity spectra (>100 mS/cm) itwas changed from±4 % to±2