Combining chip-ESI with APLI (cESILI) as a multimode source for analysis of complex mixtures with ultrahigh-resolution mass spectrometry.

Recently we have established atmospheric-pressure laser ionisation (APLI) as a method for coupling time-of-flight mass spectrometric detectors (TOF MS) with chromatographic systems (HPLC and GC) to allow two-photon ionisation of non-polar aromatic compounds. Here we demonstrate that APLI can be combined with chip-electrospray ionisation (cESI) coupled to Fourier-transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) for ultrahigh-resolution analysis of complex samples. With the laser turned off, the analytes are ionised only by ESI, whereas when the laser is switched on non-polar aromatic substances also are ionised. In combination with the extremely high mass resolution of an FT-ICR MS, simultaneous qualitative analysis of polar and non-polar analytes is possible in both positive and negative modes, as is exemplified with a crude oil sample. Nevertheless, ion suppression was observed (up to ca. 70% for D(10)-pyrene) and thus sample preparation with chromatographic or electrophoretic pre-separation is necessary for quantitative analysis of targets. In addition, for the first time, the dopant-assisted APLI method in combination with cESI (DA-cESILI) was used for determination of 1-nitrocoronene.