Quality control of NPK fertilizers – Rapid and reliable analysis by thermometric titration
30-07-2019

Analyzing sulfate, ammonium, potassium, and phosphate in NPK fertilizers
Metrohm is pleased to present several titrimetric applications for the fast and straightforward determination of macronutrients such as sulfate, ammonium, potassium, and phosphate in NPK fertilizers. The reaction endpoint is determined using a thermometric sensor. Unlike competing methods such as gravimetric analysis or flame photometry, thermometric titration usually requires no sample preparation at all, and it is also faster, more robust, and easier to use.

Application Note H-145 describes thermometric titration of sulfate in liquid and solid NPK fertilizers. The determination takes only about 3 minutes.

Application Note H-146 describes the determination of ammonium (nitrogen) in NPK fertilizers. Usually, the ammoniacal nitrogen is determined by Kjeldahl digestion followed by titration. In the method presented in AN-H-146, the nitrogen is determined by a redox titration with sodium hypochlorite; no sample preparation is required for liquid fertilizers. The endpoint is registered by a thermometric sensor; the complete analysis takes about 2 minutes only.

Potassium is traditionally determined gravimetrically or by flame photometry. Application Note H-147 describes a robust titration method, where the endpoint of the precipitation titration of the potassium is determined thermometrically; the complete analysis takes about 5 minutes.

Application Note H-035 describes the determination of phosphate in NPK fertilizers. Gravimetric determination is time consuming while mass spectrometry requires expensive instrumentation. In the method presented in AN-H-035, the phosphate content is determined by precipitation titration with magnesium. No sample preparation is required, as the reaction endpoint is determined using a robust thermometric sensor (thermometric titration).

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