Determination of several fullerenes in sewage water by LC HR-MS using atmospheric pressure photoionisation

Abstract

The main challenge in the mass spectrometric analysis of fullerenes in complex matrices is to prove unambiguously their presence or absence. Usually, this can be done by fragmentation, but due to the atmospheric interface and solvents commonly used, complex adduct formation will hinder quantification and qualification by distorting the isotopic cluster. In the present study, contrary to other methods in the literature, a 100% toluene isocratic mobile phase is used, employing an atmospheric pressure photoionisation (APPI) interface. In this manner, the adducts that are formed when methanol is present in the system are almost completely eliminated, thus avoiding higher than expected abundance for the isotopic cluster ions. The expected relative abundance of the isotopic clusters correlates well with the ones observed and was shown to be an effective tool for qualifying the presence of fullerenes even at low concentrations. For the analysis of suspended matter for the presence of fullerenes in sewage water, an optimised procedure was proposed. Filters with different mesh sizes (8.0, 0.7 and 0.45 μm) were used and the filtrate was analysed by means of solid phase extraction. For a 100 mL influent wastewater sample, limits of quantitation for the functionalised fullerenes were between 0.22 and 0.28 ng L⁻¹ and for the pristine fullerenes between 0.7 and 1.4 ng L⁻¹. The method used to analyse sewage water from six different wastewater treatment plants proved to be highly sensitive, able to unambiguously identify and quantify C₆₀ in sewage water.