Development of a LowCost UVVis Spectrophotometer and Its Application for the Detection of Mercuric Ions Assisted by Chemosensors. Detection of an environmental contaminant requires the use of expensive measurement equipment, which limits the realization of in situ tests because of their high cost, their limited portability, or the extended time duration of the tests. This paper presents in detail the development of a portable lowcost spectrophotometer which, by using a specialized chemosensor, allows detection of mercuric ions (Hg2), providing effective and accurate results. Design specifications for all the stages assembling the spectrophotometer and the elements selected to build them are presented along with the process to synthesize the chemosensor and the tests developed to validate its performance in comparison with a highprecision commercial laboratory spectrophotometer.

Diurnal Patterns in Solute Concentrations Measured with In Situ UVVis Sensors: Natural Fluctuations or Artefacts? In situ spectrophotometers measuring in the UVvisible spectrum are increasingly used to collect highresolution data on stream water quality. This provides the opportunity to investigate shortterm solute dynamics, including diurnal cycling. This study reports unusual changes in diurnal patterns observed when such sensors were deployed in four tropical headwater streams in Kenya. The analysis of a 5year dataset revealed sensorspecific diurnal patterns in nitrate and dissolved organic carbon concentrations and different patterns measured by different sensors when installed at the same site. To verify these patterns, a second mobile sensor was installed at three sites for more than 3 weeks. Agreement between the measurements performed by these sensors was higher for dissolved organic carbon (r u003e 0.98) than for nitrate (r  0.43xe2x80x930.81) at all sites. Higher concentrations and larger amplitudes generally led to higher agreement between patterns measured by the two sensors. However, changing the position or level of shading of the mobile sensor resulted in inconsistent changes in the patterns. The results of this study show that diurnal patterns measured with UVVis spectrophotometers should be interpreted with caution. Further work is required to understand how these measurements are influenced by environmental conditions and sensorspecific properties.