Hydrogen peroxide detection with quartz-enhanced photoacoustic spectroscopy using a distributed-feedback quantum cascade laser

A quartz-enhanced photoacoustic spectroscopy sensor system was developed for the sensitive detection of hydrogen peroxide (H2O2) using its absorption transitions in the v6 fundamental band at ∼7.73 μm. The recent availability of distributed-feedback quantum cascade lasers provides convenient access to a strong H2O2 absorption line located at 1295.55 cm−1. Sensor calibration was performed by means of a water bubbler that generated titrated average H2O2vapor concentrations. A minimum detection limit of 12 parts per billion (ppb) corresponding to a normalized noise equivalent absorption coefficient of 4.6 × 10−9 cm−1W/Hz1/2 was achieved with an averaging time of 100 s

Spatial and temporal variations in pollution indicator bacteria in the lower Vaal River, South Africa

The aim of this study was to evaluate the spatial and temporal variation of microbiological parameters of the Lower Vaal River, with emphasis on the Staphylococci population. River water concentrations of Staphylococci, heterotrophic, total coliforms, fecal coliforms and Streptococci groups of sanitary indicator bacteria were monitored. Results indicated significant contamination from agricultural land use inputs and municipal waste applications. Significant temporal and spatial variation was observed in response to the varying river discharge. Higher microbial concentrations were detected during high river discharge whereas during low river discharge both low and high microbial concentrations were detected. The varying responses associated with river discharge helped to identify the importance of different sources of contamination in the catchment and the mechanisms transferring them. The overall impact of contamination on the water quality of the Vaal River could have potentially serious public health risks but also provide valuable data for integrated water resource managemen