Determination of aqueous fullerene aggregates in water by ultrasound-assisted dispersive liquid-liquid microextraction with liquid chromatography-atmospheric pressure photoionization-tandem mass spectrometry

A simple and solvent-minimized method for the determination of three aqueous fullerene aggregates (nC ₆₀, nC ₇₀, and aqueous [6,6]-phenyl C ₆₁ butyric acid methyl ester (nPCBM)) in water samples is described. The method involves the use of ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) coupled liquid chromatography-tandem mass spectrometry with atmospheric pressure photoionization (LC-APPI-MS/MS). The parameters affecting the extraction efficiency of the analytes from water samples were systematically investigated and the conditions optimized. The best extraction conditions involved the rapid injection of a mixture of 1.0mL of 2-propanol (as a disperser solvent) and 10μL of benzyl bromide (as an extraction solvent) into 10mL of an aqueous solution (pH 10.0) containing 1% sodium chloride in a conical bottom glass tube. After ultrasonication for 1.0min and centrifugation at 5000rpm (10min), the sedimented phase 5.0μL was directly injected into the LC-APPI-MS/MS system. The limits of quantification (LOQs) were 150, 60 and 8ngL ^-1 for nPCBM, nC ₆₀ and nC ₇₀, respectively. The precision for these analytes, as indicated by relative standard deviations (RSDs), were less than 12% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 70 and 86%. A standard addition method was used to quantitate three aqueous fullerene aggregates, and the concentrations of these aqueous fullerene aggregates were determined to be in the range from n.d. to 130ngL ^-1 in various environmental samples including municipal influent and effluent samples, industrial wastewater samples, and surface water samples.