Current Optics and Photonics

Optical Society of Korea (한국광학회)
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Real-time Spectroscopic Methods for Analysis of Organic Compounds in Water

  • Kim, Chihoon (Laboratory of Semiconductor Device Research, School of Electronics and Computer Engineering, Chonnam National University) ;
  • Ji, Taeksoo (Laboratory of Semiconductor Device Research, School of Electronics and Computer Engineering, Chonnam National University)
  • Received : 2019.04.26
  • Accepted : 2019.06.28
  • Published : 2019.08.25
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Abstract

This paper proposes an optical system where the organic compound content in water is determined by using an ultraviolet (UV) LED (280 nm) and photodetector. The results obtained by the proposed prototype LED spectroscopy system, which includes a single photodetector and two parallel sample holders, are calculated by applying partial least square regression; the values are highly correlated with the actual concentrations of potassium hydrogen phthalate solutions, with an adjusted coefficient of determination about 0.996. Moreover, the total organic carbon values derived from the UV-Vis spectrometer of real samples (lake, river and sea water) differed little from those obtained by the LED spectroscopy. We confirm that the fast, sensitive, and compact LED sensor system can be readily configured for real-time monitoring of organic compounds in water.

Keywords

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FIG. 1. Schematic of a prototype of the proposed LED spectroscopy system.

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FIG. 2. Transmittance spectra of solutions with different reference situations (a) and absorbance spectra of the solution with different KHP concentrations measured by (b) a UV-NIR spectrometer (Bayspec Inc) using a UV-LED light source at a wavelength of 280 nm. The transmittance intensities are normalized with respect to the highest intensity value.

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FIG. 3. Relationship between the prepared KHP concentrations (standard solution prepared) and concentrations calculated by PLS analysis for (a) low to high KHP concentrations ($R_{adj}^{2}$: 0.952; R2: 0.953) before averaging and (b) after averaging KHP concentrations ($R_{adj}^{2}$: 0.976; R2: 0.977).

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FIG. 4. Absorbance values measured by a single photodetector (Si avalanche photodetector) for (a) low KHP concentrations, (b) medium KHP concentrations, (c) high KHP concentrations, and (d) calculated by analysis for low to high KHP concentrations ( $R_{adj}^{2}$ : 0.996). The signal before signal processing can be seen on the insets and based on a 500 sample rate for the program.

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FIG. 5. (a) Absorbance spectra including 5% error bar for three samples by the prototype LED spectroscopy system (A: lake water, B: river water, and C: sea water). The signal before signal processing can be seen on the insets. (b) Comparison of the TOC values calculated from the LED spectroscopy with those measured by the spectrometer detector. B and C were collected from the Gwangju stream and South Sea in Korea, respectively.

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