Qualitative and quantitative analysis of some co-existing colorants in some hard candies

•Simplify quantitative work through qualitative analysis.•Quantitative comes from qualitative.•No or little spectral overlap is the condition for separate determination.•Realize the separation-free measurement of coexisting pigments.•The method is simple, rapid, accurate, sensitive and selective. Based on the results of qualitative analysis, a simple and accurate acidity-controlled absorption spectroscopy method for the determination of certain coexisting pigments in commercial candies is established. Using a Tris−HCl (pH 3.6) reaction medium, brilliant blue (BRI) and tartrazine (TAR) react with malachite green (MAG); tartrazine and sunset yellow (SUN) react with brilliant green (BRG); and curcumin (CUR) and sunset yellow react with crystal violet (CRY). They all form binary ion association complexes. Their linear range are 0.06–21.4 mg/L (BRI-MAG, 628 nm), 0.06–11.8 mg/L (TAR-MAG, 436 nm), 0.04–11.8 mg/L (TAR-BRG, 425 nm), 0.04–9.1 mg/L (SUN-BRG, 502 nm), 0.03–10.0 mg/L (SUN-CRY, 484 nm), and 0.03–11.1 mg /L (CUR-CRY, 390 nm), respectively. The detection limit and quantification limit of each system are 0.041 mg/L and 0.71 mg/kg (MAG system), 0.035 mg/L and 0.61 mg/kg (BRG system), and 0.030 mg/L and 0.52 mg/kg (CRY violet system), respectively. This method is simple, rapid, accurate, sensitive and selective. The coexisting pigments curcumin, tartrazine, sunset yellow, and brilliant blue can be determined without pigment separation and complex mathematical model. It has been used in the determination of actual candies with satisfactory results.