Non-target analysis has become an important tool in the field of water analysis since a broad variety of pollutants from different sources are released to the water cycle. For identification of compounds in such complex samples, liquid chromatography coupled to high resolution mass spectrometry are often used. The introduction of ion mobility spectrometry provides an additional separation dimension and allows determining collision cross sections (CCS) of the analytes as a further physicochemical constant supporting the identification. A CCS database with more than 500 standard substances including drug-like compounds and pesticides was used for CCS data base search in this work. A non-target analysis of a wastewater sample was initially performed with high performance liquid chromatography (HPLC) coupled to an ion mobility-quadrupole-time of flight mass spectrometer (IM-qTOF-MS). A database search including exact mass (±5 ppm) and CCS (±1 %) delivered 22 different compounds. Furthermore, the same sample was analyzed with a two-dimensional LC method, called LC+LC, developed in our group for the coupling to IM-qTOF-MS. This four dimensional separation platform revealed 53 different compounds, identified over exact mass and CCS, in the examined wastewater sample. It is demonstrated that the CCS database can also help to distinguish between isobaric structures exemplified for cyclophosphamide and ifosfamide. Graphical Abstract Scheme of sample analysis and database screening.
A two-dimensional LC (2D-LC) method was coupled to an ion mobility-high-resolution mass spectrometer (IM-MS), which enables the separation of complex samples in four dimensions [2D-LC, ion mobility (IM) and mass spectrometry (MS)]. This approach works as a continuous multiheart-cutting LC-system, using a long modulation time of four minutes, in comparison to comprehensive two-dimensional liquid chromatography, which allows the complete transfer of most of the first dimension peaks to the second dimension column without fractionation. Hence, each compound delivers only one peak in the second dimension, which simplifies the data handling even when ion mobility as a third and mass spectrometry as a fourth dimension are introduced. The analysis of different complex samples, such as a plant extract from Hediotys diffusa and Scutellaria barbata, a waste water inflow, and a biocoal sample, was shown. The results of the four-dimensional separation method demonstrate that with the same column combination and the same solvents and gradients, that means without method optimization, totally different samples can be separated with outstanding separation power. Each sample was spiked with cyclophosphamide and ifosfamide and the ion suppression was determined by comparison of the peak area in the complex samples and in pure water after analysis of these samples with a 1D-LC and a 2D-LC approach. It is shown that the 2D-LC method allows an external calibration for the spiked compounds in the plant and waste water sample because of the higher separation power in comparison with 1D-LC.
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