In Situ Water Quality Monitoring Using an Optical Multiparameter Sensor Probe

Abstract

Optical methods such as ultraviolet/visible (UV/Vis) and fluorescence spectroscopy are well-established analytical techniques for in situ water quality monitoring. A broad range of bio-logical and chemical contaminants in different concentration ranges can be detected using these methods. The availability of results in real time allows a quick response to water quality changes. The measuring devices are configured as portable multi-parameter probes. However, their specification and data processing typically cannot be changed by users, or only with difficulties. Therefore, we developed a submersible sensor probe, which combines UV/Vis and fluorescence spectroscopy together with a flexible data processing platform. Due to its modular design in the hardware and software, the sensing system can be modified to the specific application. The dimension of the waterproof enclosure with a diameter of 100 mm permits also its application in groundwater monitoring wells. As a light source for fluorescence spectroscopy, we constructed an LED array that can be equipped with four different LEDs. A miniaturized deuterium–tungsten light source (200–1100 nm) was used for UV/Vis spectroscopy. A miniaturized spectrometer with a spectral range between 225 and 1000 nm permits the detection of complete spectra for both methods.

Comparing Sensor Fusion and Multimodal Chemometric Models for Monitoring U(VI) in Complex Environments Representative of Irradiated Nuclear Fuel

“…Combining absorption, fluorescence, and Raman spectral features and simultaneous chemometric analysis can be highly useful for characterizing and monitoring various chemical species in multiple fields. ,,,, The absorption, fluorescence, and Raman spectra of the chemical species characterized in this study are shown in Figure with labeled dominant fluorescence emissions and absorption peaks. Molecular species such as the free uranyl ion (UO 2 2+ ) and uranyl nitrate complexes (UO 2 (NO 3 ) n (2– n )+ , n = 1 or 2) can be quantified by LIFS .…”

In-situ optical water quality monitoring sensors—applications, challenges, and future opportunities

“…However, PMTs and photodiodes have no spatial discrimination, i.e., they convert the intensity of light into an electrical signal and cannot differentiate them according to wavelengths, which limits their applicability to broad spectrum (UV-VIS) sensing (Spring, 2001;Yokota et al, 2021). Miniaturizing traditional benchtop spectrometers into mini and microspectrometers provides new opportunities for developing fielddeployable UV-VIS OWQM probes (Bouyé et al, 2016;Shi et al, 2022;Goblirsch et al, 2023). The mini/micro-spectrometers use a linear CCD or CMOS imaging sensor in a Czerny-Turner design or micrograting to achieve smaller form factors (Bouyé et al, 2016;Chen et al, 2022).…”

“…The LED-photodiode specificity allows for precise measurements of specific variables such as nitrate and reduces the scope of interference by other contaminants. However, the specificity limits the potential to account for background interferents, which full spectrum light source and detector combinations can observe and account for in a single measurement (Goblirsch et al, 2023). Current mini-spectrometers in the market are the size of a fingertip (C12880MA and C16767MA, Hamamatsu Pvt.…”

“…They use highly-sensitive image sensors such as CCD and CMOS and direct the incident light through optical slits and gratings. Depending on the type of applications, the mini-spectrometers can be tuned to maximum sensitivity at desired blaze angles and are likely to replace the photodiode arrays in future probes aimed at broad-spectrum sensing (Goblirsch et al, 2023). However, only one commercial product (Opus, Trios) is currently mentioned to use a minispectrometer (200-360 nm) as the detector, with most probes relying on an array of photodiodes, sensitive to wavelengths of interest as an alternative way of broad-spectrum sensing.…”

“…In-situ optical sensors measuring fluorescence, absorbance, and scattering have become particularly important for aquatic monitoring. Advancements in optical components, i.e., light emitting diode (LED) technology, and miniaturization of sensing elements such as photodiodes, photomultiplier tubes, charge-coupled device (CCD), and complementary metal-oxide-semiconductor (CMOS) sensors, etc., have made the optical sensors, such as fluorimeter, absorbance and turbidity sensors, smaller in form-factor, lowered their power requirements and improved their field usability (Mukunda et al, 2022;Zainurin et al, 2022;Goblirsch et al, 2023). Fluorescence spectroscopy relies on the principle of Stokes shift, which is the spectral shift between incident (excitation, ex) light and emitted (em) light (detected orthogonally to incident light) from shorter to longer wavelengths (Figure 1).…”