A „negative intercept“ looks similar to the standard addition technique, where the “negative concentration” is the analytical result. The reason in your case might be a reagent blank not compensated for or some interfering compound not sufficiently separated from your analyte.

You can prepare more standard solutions with lower concentrations, and run the calibration curve again, to see the linearity. You can read :

Paul King HPLC METHOD DEVELOPMENT AND VALIDATION: A Direct P rocedure For Determining An HPLC Method’s “Linear Through Zero” Range. LC GC 1999 January;

17 (1): 46, 48, 50.

you might need to adjust the std concentration range. The negative intercept indicates that the au of std solutions with higher concentration of std material is bit off (positive), or the measurements for std solution with low concentration of std material is not accurate (lower than theoretical value). Not sure how much vol you injected into the column, increase the vol some times helps. You can also check the connections of the whole system to reduce the dead volume and the consitency of the ID of the tubing form injector to column. clean the flow cell, check the lamp of UV light et al, might also help.

A „negative intercept“ looks similar to the standard addition technique, where the “negative concentration” is the analytical result. The reason in your case might be a reagent blank not compensated for or some interfering compound not sufficiently separated from your analyte.