Multidimensional liquid chromatography separations with mass spectrometry as a generic method to study the degradation of environmentally relevant micropollutants

The contamination of natural water resources with emerging pollutants is of growing interest since potentially harmful chemicals can reach the environment through wastewater produced by human activities. Different treatment technologies can be employed to degrade contaminants in wastewater. One such treatment technology, overall termed Advanced Oxidation Processes (AOP), effectively degrades hazardous pollutants and produces a large spectrum of degradation products showing a wide variety in physicochemical properties, such as polarity, ionizability and molecular size. Before these degradation products can be identified, adequate chromatographic techniques are required to separate all compounds. Due to the broad variety in compound characteristics, adequate chromatographic resolution is usually challenging to achieve under a single set of separation conditions. Furthermore, signal suppression in the electrospray (ESI) interface because of matrix impurities leads to a loss of sensitivity. The use of high–end mass spectrometry (MS) such as triple–quadrupole (QQQ) MS under multiple reaction monitoring (MRM) mode, may compensate for inadequate chromatographic resolution. However, this technique is difficult to optimize, time–consuming and expensive. To greatly enhance separation performance, a comprehensive two–dimensional liquid chromatography (LC x LC) hyphened to quadrupole time–of–flight (Q–TOF) MS method will be explored. In LC x LC, different orthogonal separations can be used in the 1st and 2nd dimensions to separate compounds with diverse properties. The major advantage of LC × LC compared to one–dimensional LC is a greater peak capacity, multi–selectivity and, therefore, reduced matrix effects. Different combinations of separation modes will be evaluated in terms of separation capacity, robustness and ease of hyphenation with MS for subsequent identification and quantification of the degradation products. Active Solvent Modulation (ASM) will be used to address the solvent compatibility issue between two different dimensions, e.g. when hydrophilic interaction liquid chromatography (HILIC) and reversed–phase liquid chromatography (RPLC) are combined. If the method is proven successful, a software tool that can suggest a good standard for comprehensive LC x LC in terms of selectivity and kinetics for the analysis of environmentally relevant molecules will be suggested, in order to expand the use of two–dimensional LC techniques in routine environments.