Potassium Persulfate Oxidation vs. Photo Oxidation: Determining and Optimizing the Most Accurate Method in Evaluating the Total Dissolved Nitrogen and the Total Dissolved Phosphorus in Various Water Matrices

Chemical and photo oxidation methods have been used in water quality labs to determine the concentrations of total dissolved nutrients in water samples. Most studies compare the results of the chemical and the photo oxidation methods in fresh water systems. The purpose of our research conducted at the Natural Energy Lab of Hawaii Authority (NELHA) is to determine and optimize the most accurate and efficient method in evaluating the total dissolved nitrogen (TDN) and the total dissolved phosphorous (TDP) in brackish groundwater and marine samples. We performed a comparison between Standard Method’s SM 4500- N C, the potassium persulfate (K₂S₂O₈) chemical oxidation method, and NELHA’s historical photo oxidation method. In both methods, the TDN/TDP of the oxidized glutamic acid and glycophosphate gravimetric standards were compared. In the SM 4500- N C chemical oxidation method, we prepared the K₂S₂O₈ reagent using the North Temperate Lake Ecological Research recrystallization procedure to remove the NH₃ contaminant. The standard samples were then autoclaved for 1 hour in the presence of ammonia-free K₂S₂O₈. In the photo oxidation method, using a UV 1200W mercury vapor lamp, samples were oxidized in the presence of hydrogen peroxide at 254 nm for 2.5 hours. TDN and TDP were determined by an Astoria Pacific A2 segmented flow auto-analyzer. This iterative study will determine whether NELHA should transition from the photo oxidation method to the chemical oxidation method in their water quality testing.