In-line coupling SPE and CE for DNA preconcentration and separation

An in‐line SPE method coupled to CE was developed for the analysis of DNA. The amino silica monolith was prepared in situ by polymerization of tetraethoxysilane and N‐(β‐aminoethyl)‐γ‐aminopropyltriethoxysilane in ethanol aqueous solution at the inlet end of a 100 μm id fused‐silica capillary, and the remaining part of the capillary was used as separation channel. The procedure for this in‐line SPE‐CE method was constructed on the basis of investigation on operational conditions such as the introduction mode of sieving matrix, the composition of elution solvent and the elution time. Twenty millimolar ammonium hydroxide was demonstrated to be effective for DNA desorption from the monolith, and linear poly(N‐isopropylacrylamide) was used as the separation matrix. The proposed method could achieve limits of detection of 0.065–0.123 ng/mL for six DNA fragments ranging 100–2000 bp. Compared with conventional CE, preconcentration factors of over 100 times were obtained. The applicability of the in‐line SPE‐CE method was further demonstrated by analyzing plasmid DNA from Escherichia coli crude lysate.