Identification of ubiquinones and menaquinones in activated sludge by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

A sensitive analytical method has been developed for identification of ubiquinones (UQ-n(Hx)) and menaquinones (MK-n(Hx)) in activated sludge by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry in negative mode (LC-NI-APCI-MS). Extraction and clean-up of samples were carried out on Sep-Pak Plus Silica solid-phase extraction cartridges. Complete separation of quinones was achieved with an ODS analytical column and using isopropyl ether-methanol (17:83, v/v) as the mobile phase. The compositions of ubiquinones and menaquinones were determined directly using combined information on retention time, the molecular ion mass and fragment ion masses. The lowest instrument quantitative detection limits (LODinst) for UQ-6, UQ-10, and Vitamin K1 were estimated to be 0.4, 4 and 0.12 ng (S/N = 10) using LC-NI-APCI-MS in SIM mode, and the lowest method detection limits (LODmeth) achieved by spiking experiment were estimated to be 0.2, 2 and 0.06 microg/g for UQ-6, UQ-10 and Vitamin K1, respectively. On the other hand, the LODinst for UQ-6, UQ-10, and Vitamin K1 were estimated to be 10, 100 and 2 ng (S/N = 10) using LC-NI-APCI-MS in full-scan mode, and the LODmeth were estimated to be 7, 60 and 1.2 microg/g for UQ-6, UQ-10, and Vitamin K1, respectively. Both LC-NI-APCI-MS and LC-UV/DAD were applied in the analysis of an activated sludge extract. UQ-n (n = 6-10), MK-n (n = 6-10), MK-n(H2) (n = 7-10), MK-n(H4) (n = 8-9) and MK-8(H6) were detected by LC-NI-APCI-MS, while UQ-6, UQ-7, MK-7(H), MK-9 and MK-10(H2) were not found by LC-UV/DAD. These results suggest that LC-NI-APCI-MS is more sensitive than LC-UV/DAD for the analysis of quinones in environmental samples such as sediment, activated sludge and bio-film in biological processes and other aquatic environments.