Heterogeneous photocatalysis of moxifloxacin: Identification of degradation products and determination of residual antibacterial activity

Abstract

TiO2-mediated heterogeneous photocatalysis of the fluoroquinolone antibiotic moxifloxacin in water is investigated with respect to both the formation of degradation products and the evaluation of residual antibacterial activity after photocatalytic treatment. High-resolution magnetic sector mass spectrometry coupled to high performance liquid chromatograph is used to determine the accurate mass of the measured degradation products. Eight main photoproducts are identified at both acidic, neutral and alkaline pH. A molecular structure is proposed by using the accurate mass, the double bond equivalent and by taking into account the structural formula of the parent compound. The photocatalytic degradation does not take place at the quinolone core and defluorination was not observed. A general initial photocatalytic pathway for moxifloxacin is proposed. Time profiles of the different degradation products reveal that the solution pH influences their relative abundance during reaction but the observed degradation products show no pH dependency. Residual antibacterial activity of the photocatalytic reaction solutions against Escherichia coli (G−), Staphylococcus carnosus (G+), Streptococcus mutans (G+) and Klebsiella pneumoniae (G−) is evaluated by means of agar diffusion tests. A reduction in antibacterial activity is noticed for all investigated pH levels with a complete inactivation at neutral pH after 12min of photocatalytic treatment.