Negative peaks in my dialysates interfere with my analysis

Applies to

Electrochemical detection

Summary

Negative peaks appear in the chromatograms of brain dialysates. They overlap with relevant analyte peaks.

Cause

Dialysates usually contain relatively high concentrations of ions such as potassium, sodium, chloride, magnesium. These ions may appear as negative peaks in a chromatogram.

Other causes of (negative) peaks can come from certain contaminants that are introduced with the sample. Compare with standards in clean solvent, or injection of some mobile phase. By systematically adding the steps toward injection of real samples, the cause can be found. For example, we have learned that certain sample filters, or vials, or other materials used in sample prep can cause negative peaks.

Remedy

Adding a chelating agent such as EDTA affects the chromatographic behavior of some of these ions. Alternatively, the ion pair (OSA) concentration or pH can be changed to get rid of shouldering or overlapping peaks. In case a certain material used in the sample prep appears to be the cause, look for alternatives or optimize the analysis so that peaks no longer interfere.