Detection, occurrence and fate of indirubin in municipal sewage treatment plants

Indirubin which has been isolated from human urine is an extremely potent AhR agonist. This paper first established an analytical method based on liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) for indirubin in complex environmental waters, and then applied this method to investigate its occurrence and fate in sewage treatment plants (STPs). For the various types of aqueous matrices considered, the absolute recoveries were from 64 to 81%, and the limits of quantification were below 0.05 ng/L Among the seven STPs studied, the average concentrations of indirubin in influents ranged from 8.3 to 29.7 ng/L, and their aqueous-phase removal rates were 72-91%. In the receiving waters, the Tonghui and Qinghe Rivers, the concentrations of indirubin (0.65-3.7 ng/L) in some samples were much higher than those in their corresponding STP effluents, suggesting that there is random discharging of untreated sewage. The fate of indirubin was investigated in mechanical and biological sewage treatment as well as in sewage-sludge treatment at a STP consisting of anoxic, anaerobic, and aerobic tanks. The indirubin was largely removed in the anoxic tank and the secondary clarifier mainly due to the biodegradation and sorption on sludge, respectively. An increase of indirubin was observed in the aerobic tank, which was due to the cleavage of indirubin conjugates.

Determination of indican, isatin, indirubin and indigotin in Isatis indigotica by liquid chromatography/electrospray ionization tandem mass spectrometry

The roots and leaves of Isatis indigotica, named 'Ban-Lan-Gen' and 'Da-Qing-Ye', respectively, are widely used for the treatment of influenza, viral pneumonia, mumps, pharyngitis, and hepatitis. The indoxyl derivatives detected in the roots and leaves of I. indigotica have been reported to be biologically active. In the present study, a liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed to determine indican, isatin, indirubin and indigotin in the roots and leaves of I. indigotica. The method has been validated for linearity, precision and accuracy. Using multiple reaction monitoring (MRM), the limits of detection (LODs) were determined as 0.004 ng for indican, 0.01 ng for isatin, 0.01 ng for indrubin and 0.03 ng for indigotin, while the limits of quantitation (LOQs) were 0.015 ng for indican, 0.04 ng for isatin, 0.04 ng for indirubin and 0.1 ng for indigotin. Compared with previously reported methods, the current method is more rapid, selective and sensitive. This is the first report of the LC/MS/MS determination of indican, isatin, indirubin and indigotin.