Characterization and field test of an in situ multi‐platform optical sensor

Abstract

The characterization and field testing of a compact in situ optical instrument using fluorescence, absorbance, and scattering to identify and quantify contaminants and natural substances in water bodies are described. The instrument, based on a technology named LEDIF (LED-Induced Fluorescence) developed by Ng et al. (2012a) was configured for in situ long-term continuous monitoring at a fixed location. The optical performance and sensing capabilities of the instrument were assessed by calibrating against laboratory-prepared and commercial standards, and compared with several commercial sensors and published values. The effects on sensor response of temperature, pressure, and particle interference due to turbidity and total suspended solids were assessed and reported. Instrumental baseline shift over time, instrument detection limits, and the capability of LEDIF to determine characteristics such as quantum yield and intramolecular deactivation of fluorescence response, were also assessed. Experimental results match well with results from commercial instruments and published data. To demonstrate field deployment, the LEDIF instrument was installed at Chinese Garden of Singapore for longterm continuous monitoring of chlorophyll a (Chl a) and turbidity at a management-selected location. The analytes were chosen based on management's needs in recording temporal trends of algal biomass and water cloudiness to develop effective controls of inflow and outflow water quality. A monitoring record showing the temporal response of algal biomass to ambient conditions and turbidity variations is presented and discussed.

Functional Analysis in Long-Term Operation of High Power UV-LEDs in Continuous Fluoro-Sensing Systems for Hydrocarbon Pollution

“…The choice of a non-contact system instead of the peristaltic system employed in the other applications to identify diluted materials [ 3 , 4 ], was because of the future integration of the present workbench instrumentation in the analysis-sink with open fluent water, as shown in Figure 1 b. This method is advantageous because it is clean and the LED light analyzes fluent water; however, the drawback is that it requires a higher optical output power because the HP UV-LED needs to be separated from the water in order to avoid the fluent water staining the LED lens.…”

“…, and the associated traffic generated implies a relevant/critical hazard for inland water. In the case of inland water pollution by hydrocarbons and other pollutants which emit fluorescence under high energy light, new developments and analyses are being conducted [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. The conventional methods used in recognizing a hydrocarbon pollutant involves transporting a sample from the area of water pollution and identifying the pollutant in the laboratory, most often using the fluorescence spectroscopic method [ 13 , 14 ].While this is an accurate method, it involves too much time for a rapid, and in some cases, programmable automatic action, to mitigate the pollution effect.…”

“…The UV-LEDs emits in a narrow band of wavelength [ 18 , 19 , 20 ]. To obtain the fluorescence signature at different wavelengths sources the use of several LEDs are needed [ 2 , 3 , 4 ], or the combination with other light sources [ 21 ]. The classical spectrometer laboratory equipment [ 14 ], has been used for decades in the identification of pollutants by fluorescence in a wide wavelength range.…”

“…The classical spectrometer laboratory equipment [ 14 ], has been used for decades in the identification of pollutants by fluorescence in a wide wavelength range. However, the employment of LED or UV-LED has enjoyed only a short field experience in the fluoro-sensing applications in real-time [ 2 , 3 , 4 , 7 , 8 , 10 ]. This work proposes to move a step further from the occasional real-time measurements to continuous real-time detection and pollutant identification.…”

“…Furthermore, the spectroscopy workbench instrumentation developed for this HP UV-LED work analysis is in accordance with the new generation of compact, real-time, low cost [ 7 , 8 ], low and easy power, fixed [ 9 ] or portable [ 2 , 3 , 12 ], autonomous systems [ 4 ], that connect to a PC or single-board computer. The experiments over the last few years dealt with the detection of substances such as chlorophyll and phytoplankton [ 2 , 3 , 4 , 7 , 8 , 9 ], besides pollutant detection [ 6 , 20 ].…”