Based on usage scenarios, rapid COD analyzers can be categorized into portable field analyzers, benchtop laboratory analyzers, and online automatic monitoring instruments. Portable field analyzers, such as the pHotoFlex portable rapid COD analyzer, consist of a photometer, digester, and accompanying COD reagents, suitable for rapid testing in the field or on-site. The SH-8 handheld rapid COD analyzer uses ultraviolet absorption spectroscopy, requires no reagents, and is easy to carry. Benchtop laboratory analyzers, such as the DR1010 rapid COD analyzer, have a built-in standard curve, support dual power supplies, and are suitable for laboratory environments. Domestic models such as the JH-TC201C and JH-TD401C typically feature a touchscreen and an integrated digestion and colorimetric tube.
Based on measurement principles, they mainly include instruments based on rapid digestion spectrophotometry and instruments based on ultraviolet absorption spectroscopy. The rapid digestion spectrophotometric method was invented in 1982 by the Lanzhou Refining & Chemical Environmental Protection Instrument Research Institute. Its principle is based on the oxidation of organic matter in water samples by potassium dichromate under strong acid and catalyst conditions. The COD value is determined by measuring the color change caused by the reduction of Cr6+ to Cr3+ at a specific wavelength, conforming to the national standard HJ/T 399-2007. Ultraviolet absorption spectroscopy, such as the technology used in the SH-8 handheld rapid COD analyzer, requires no chemical reagents and directly correlates COD concentration by measuring the absorption of water samples in the ultraviolet band.
Based on functional expandability, water quality analyzers can be divided into single-parameter COD analyzers and multi-parameter water quality analyzers. Multi-parameter water quality analyzers can be expanded to measure various water quality parameters such as total phosphorus, total nitrogen, ammonia nitrogen, and heavy metals through preset programs or modular design.
