# Advances on Water Quality Detection by UV-Vis Spectroscopy
## 4 Research Status and Progress of Main Water Quality Parameters
### Research on the Detection of DOC in Water  
DOC is a universal part of the freshwater carbon cycle. It can weaken ultraviolet radiation and affect the function of aquatic ecosystems. As a by-product of water disinfection, DOC has an impact on human health [66].  
The 0.22 \(\upmu\)m membrane is hydrophilic microporous membrane. The 0.45 \(\upmu\)m filter membrane is hydrophobic microporous membrane. DOC is the fraction of organics that pass through a 0.45 \(\upmu\)m membrane. The type of wastewater plays an important role in the quality of DOC and it has been shown that DOC may be related to aquatic humic substances, hydrophobic bases, hydrophobic neutrals, hydrophilic acids, hydrophilic bases, and hydrophilic neutrals [67].  
DOC is commonly measured directly using two laboratory methods. DOC can be measured as 'non-purgeable' organic carbon by converting inorganic carbon into carbon dioxide (CO\({}_{2}\)) and purging this CO\({}_{2}\). The remaining organic carbon is then converted to CO\({}_{2}\) through thermal oxidation and measured by using the absorbance of infrared radiation [68]. The second method involves measuring total carbon (TC) and inorganic carbon (IC) and deriving the DOC by subtracting the IC from TC. The water sample and oxygen are respectively introduced into the high temperature combustion tube and the low temperature reaction tube. The water sample passing through the high temperature combustion tube is converted into carbon dioxide under the action of the catalyst and oxygen. The water sample passing through the low temperature reaction tube is acidified to decompose the inorganic carbonate into carbon dioxide. The generated carbon dioxide enters the non-dispersive infrared detector in turn. Since the intensity of infrared absorption of carbon dioxide is directly proportional to the concentration of carbon dioxide, the TC and IC in water samples can be quantitatively determined [69]. Both these methods require access to relatively expensive analytical equipment.  
In the water treatment industry, absorbance at 254 nm is often used as a proxy for DOC because aromatic humic substances are the dominant source of DOC in natural waters, and these absorb light in the UV region of the electromagnetic spectrum. [PERSON] et al. [70] studied the applicability of UV-Vis spectroscopy for tropical DOC water samples from any tropical peatland. First, the applicability of single-wavelength and dual-wavelength proxies for tropical DOC determination was explored; then calibration data sets and parameter sets were established to indirectly calculate DOC concentrations, providing researchers with guidance on the best spectrophotometric method.  
The aim of [PERSON]'s study was to test the performance of a portable, submersible UV-Vis spectrophotometer during the snowmelt period in a boreal mire-forest catchment. A conceptual understanding of the spatial and temporal dynamics of DOC concentrations was provided during and after snowmelt. Based on PLSR, the local calibration showed good agreement with the results obtained from the high-resolution absorption measurements and the wet persulfate oxidation method [71].  
[PERSON] et al. [72] investigated the appropriateness of different wavelengths (230 nm, 254 nm, and 263 nm) as proxies for DOC concentration. These findings should enable the use of UV-Vis spectroscopy as a tool to analyze DOC concentration and quality in natural waters.