What is a Kjeldahl digestion for phosphorus determination?
This digestion is used when the same samples are being analyzed for Kjeldahl nitrogen as well. Samples are digested in a solution of sulfuric acid, potassium sulfate and a catalyst (mercuric oxide). Polyphosphates and organic phosphorus are converted into orthophosphate. Lachat Instruments typically refers to the resulting analyte as Total Kjeldahl Phosphorus (TKP) in order to specify the procedure used for digesting the samples. The resulting orthophosphate can be determined by using an FIA system, where the orthophosphate ion reacts with reagents in order to form a colored complex. The absorption of which is directly proportional to the TKP concentration.
