Nano-high-performance liquid chromatography–electron ionization mass spectrometry approach for environmental analysis

We describe a method, based on a new nano-HPLC gradient generator coupled to a modified direct electron ionization (EI) LC–MS interface, for the analysis of several compounds of environmental interest. The gradient generator was installed on a conventional HPLC system and the nano-flow rate was achieved using a double splitter. Reproducible gradients of different shapes (i.e. linear, convex, concave) can be generated at micro- and nano-flow rates. This attribute makes this device particularly appropriate for coupling with direct-EI LC–MS interface. The combination of the gradient generator with the direct-EI interface optimizes the analytical conditions for the generation of good quality EI spectra for trace level analytes. The performance of this new system was tested at a flow rate of 250 nl min−1, evaluating linearity, intra-day reproducibility and limits of detection of several compounds of environmental interest belonging to three different classes: nitro-polycyclic aromatic hydrocarbons, pesticides and human hormones. Excellent signal stability and low detection limits were obtained in most cases. Enhanced performance was observed for critical separations due to the possibility to run gradients of different shapes.