Development of an online analyzer for determination of total phosphorus in industrial circulating cooling water with UV photooxidation digestion and spectrophotometric detection

Abstract A simple, effective and automatic analyzer was developed for rapid determination of total phosphorus and the presence of phosphonates in industrial circulating cooling water monitored. The key components of the analyzer were an ultraviolet (UV) photooxidation digester and a spectrophotometer. The total phosphorus was first converted to orthophosphate using the UV digester, and then its content was measured using the vanadomolybdophosphoric acid method. A bus topology and distributed control system were used. Industrial standard communication Modbus protocol was used for communication between the main controller and a computer. The online analyzer automatically processed the determination steps such as sample injection, reagent mixing, online digestion, signal detection, data acquiring and analysis. The detection linear range was 0.2–50 mgP L −1 , and detection limit of 0.04 mgP L −1 . The relative standard deviations of the method for 1 mgP L −1 and 20 mgP L −1 phosphate samples were 2.6% and 2.1% (n = 11), respectively. The recoveries of several real samples at various concentrations ranged from 91.5% to 103.8%. The total phosphorus of a certified reference material (GSBZ50033-95) was 1.50 ± 0.04 mgP L −1 (n = 3), consistent with the certified value (1.51 ± 0.02 mgP L −1 ). The analyzer had been used successfully in a circulating cooling water workshop; its integrated software-hardware not only demonstrated to be versatile but also suitable for monitoring total phosphorus in industrial or other water bodies.