Determination of total nitrogen in wastewater

This post was last edited by sunshineda_VGMP on 2018-9-7 at 15:21. The determination of total nitrogen in wastewater generally involves the alkaline potassium persulfate digestion followed by ultraviolet spectrophotometry; total nitrogen meters also operate on this principle. Besides issues related to drugs and reagents, the reasons for the failure in curve plotting as mentioned by the poster also suggest considering the equipment – was the instrument properly adjusted/calibrated before sample injection? A standard sample can be used to check whether the readings are too high or too low, and then to determine the specific reason for it.

This post was last edited by qugd on 2018-9-7 at 10:24. In the determination of total nitrogen, all nitrogen compounds are oxidized and converted into nitrate ions. Due to the strong oxidizing properties of persulfate, organic substances and low-valent compounds are transformed into their high-valent inorganic forms. There are two main factors that can affect the determination of total nitrogen: 1. Reagent blank: Residual nitrate ions or nitrogen compounds in the reagents can cause issues; this can be addressed by purifying the reagents through recrystallization to eliminate or reduce the impact of such blanks. The water used for recrystallization must be ammonia-free pure water. 2. Substandard quality of water used in experiments: Water containing ammonia or nitrogen-containing organic substances may end up in the pure water produced. At this point, the water should be redistilled, preferably using a quartz or stainless steel distiller. During distillation, alkali and potassium permanganate are added to the water; the first 10% of the distillate is discarded as it may contain ammonia. Throughout the distillation process, it is necessary to ensure that the color of potassium permanganate does not fade. When about 70–80% of the distillate has been collected, the water and reagents are replaced and the distillation process is repeated for another batch. Purifying the reagents with ammonia- and organic-free water, and preparing the reagents using ammonia-free water, will certainly yield satisfactory results. When I worked in the laboratory before, for such experiments I would prepare the water required according to the experimental specifications. The so-called pure water in products sometimes fails to meet the requirements of analytical chemistry. Currently, some laboratory staff have limited knowledge and are unwilling to use their hands or brains. What I mentioned above is discussed in many chemical handbooks or monographs on analytical experiments.