Selective and simultaneous determination of indigo carmine and allura red in candy samples at the nano-concentration...

A novel, unique electroanalytical method was developed for the simultaneous quantification of the dyes indigo carmine (IC) and allura red (AR) in candies by coupling flow injection analysis and multiple pulse amperometry with a cathodically pretreated boron-doped diamond electrode, using 0.30 mol L^-1 H₂SO₄ as supporting electrolyte. A dual-potential waveform was employed, causing the electrooxidation of either IC solely or IC and AR simultaneously. Thence, subtraction of current signals was used to quantify IC and AR in the concentration ranges of 70.0-1000 nmol L^-1 and 40.0-770 nmol L^-1, with limits of detection of 40.0 nmol L^-1 and 7.0 nmol L^-1, respectively. The proposed method, which permits up to 153 determinations per hour with good precision, was successfully applied in the quantification of these dyes in samples of commercial candies; their obtained contents were similar (at a 95% confidence level) to those from a comparative HPLC method.