Selective determination of sulphide based on photoluminescence quenching of MPA-capped CdTe nanocrystals by exploiting a gas-diffusion multi-pumping flow method

In this study an automated flow-based methodology for the fluorometric determination of sulphide was reported. It relies on the utilization of CdTe nanocrystals as photoluminescent probes, which upon reaction with S2- are subject to a noteworthy concentration-related photoluminescence decrease. For lower S2- concentrations the photoluminescence quenching was based on dynamic processes while for higher concentrations the quenching mechanism was ascribed to the depassivation of the surface ligands, replaced by S2-, resulting in the aggregation of QDs. The developed approach was automated by resorting to a pulsed stream multi-pumping flow system guaranteeing a high versatility in terms of sample and reagent manipulation and reaction zone formation. The selectivity was ensured by means of the utilization of a gas-diffusion unit relying on a hydrophobic PTFE membrane that facilitated sulphide isolation from sample matrix interferences. Under optimal conditions, a good linear relationship between the photoluminescence quenching magnitude (Delta F) and the logarithmic of the S2- concentration within the range of 0.25-5.0 mmol L-1 were verified (R = 0.998, n = 5). The limit of detection (LOD) was found to be 0.19 mmol L-1. The sampling rate was of about 13 h(-1).