Highly integrated microfluidic chip coupled to mass spectrometry for on-line analysis of residual quinolones in milk.

In this work, a highly integrated microfluidic chip with multifunction coupled to mass spectrometry (MS) was developed for online analysis of seven different regulated quinolones (QNs) in milk samples. Procedures of sample extraction, immunoaffinity enrichment, magnetic separation, and online elution were performed simultaneously on the specifically designed device. Based on the specificity of antibodies, direct (electrospray ionization) ESI-MS at full scan mode without liquid chromatography (LC) separation and further tandem mass spectrometry (MS/MS) analysis was developed for the identification of target QNs. One single isotope internal standard (IS) method was presented for quantitative analysis of seven QNs. Upon targeted online extraction and enrichment by antibody conjugated magnetic beads, seven QNs were quantitatively determined by the IS method with the linear range of 0.2/0.5-10 ng/mL (R-2 > 0.991). The limits of detection (LODs) for the seven QNs were in the range of 0.047-0.490 ng/mL. This system permits automated on-chip immunoaffinity enrichment and accurate MS detection without additional off-line cleanup procedures.