We have been conducting specificity analysis and have been finding a reduction in the peak area of 4-AP in the samples containing an erythrosine dye. The samples have a conc of 0.0004 mg/ml of 4-AP and are made up in sample solvent (25:75 Acetonitrile:0.02M Phosphate Buffer)

Mobile Phase: 0.02M Phosphate Buffer
Column : Zorbax Eclipse XBD-C18 150x4.6, 5 micron, with security guard c18 4 x 3mm
Wavelength: 245

Does anyone know of any reason/any potential interaction that could be causing this to occur?