We've run into a problem at my lab where we are trying to analyse calcium and magnesium with ion chromatography and conductivity detector. We're using a Waters Spherisorb SCX 150x4.6 mm and 5µm, flowrate 1.5 ml mobile phase consisting of 75% H2O/20% buffer and 5% acetone. Buffer is citric acid, tartaric acid and ethylene diamine in water.

What we're having trouble with is a peak which co-elutes completely with our calcium peak. We've run all the components in the buffer by themself and we can see this peak with every injection when running either the blank(0.1 M HCl), the citric acid or the tartaric acid. It is not in our water, ethylene diamine or the acetone. We've tried cleaning our column with 20% Methanol in water over night and also rinsed the entire LC-system with 0.1 N nitric acid without any improvement.

Any ideas at all will be very welcome!