Reduction of the environmental impact of the determination of l-carnitine and acetyl-l-carnitine in milk products by microchip electrophoresis

A novel miniaturized analytical method for the simultaneous determination of l-carnitine and its ester, acetyl-l-carnitine in fresh milk and milk products by microchip electrophoresis (MCE) with conductivity detection was developed. Under optimized separation conditions, separation voltage of 4 kV and 50 mmol L⁻¹ acetic acid and 0.1 % methylhydroxyethylcellulose at pH 3.0 as background electrolyte, carnitines were sufficiently separated in less than 10 min. An elimination of adsorption of the cationically migrated analytes on a poly(methyl methacrylate) microchip was achieved by addition of 1 mmol L⁻¹ triethylenetetramine to all analyzed samples. The detector response was linear in the range 0.2–1.5 µg mL⁻¹ for l-carnitine and 0.4–2.0 µg mL⁻¹ for acetyl-l-carnitine. The LOQ values were 0.1 µg mL⁻¹ and 0.4 µg mL⁻¹ for l-carnitine and acetyl-l-carnitine, respectively. Recoveries of the analytes in the analyzed samples were in the range 87.5–97.8 %. The developed MCE method has been successfully applied to the analysis of carnitines in eight milk products after a sample pretreatment which included precipitation, centrifugation, and filtration. The developed MCE method has a low hazardous impact on human health and the environment.