Optimisation of a CE method for caffeine analysis in decaffeinated coffee

Multiple response simultaneous optimisation was used to develop a micellar electrokinetic chromatography method for caffeine determination in decaffeinated coffees. Buffer composition and voltage were optimised using a central composite design. Six responses were evaluated and each set of response values was regressed on the factor levels of the experimental design using linear and quadratic models. The regression models, correlation coefficients and a principal component analysis (PCA) were used to determine the optimum conditions. Successful results were obtained using a buffer containing 10 mmol L−1 sodium carbonate and 50 mmol L−1 sodium dodecylsulfate, 15 kV voltage, 25 °C temperature, 48 cm × 50 μm fused-silica capillary, hydrodynamic injection of 50 mBar during 7 s and detection at 206 nm. This optimised method was applied for caffeine analysis in 45 samples of commercial decaffeinated coffee.