Method F-007A The Determination of Potassium in Fertilisers

Equipment Required:

1. Sherwood Model 410 Flame Photometer
2. Balance weighing to +/-0.0005g
3. Potassium Standard (Sherwood part 00156621)

Method:

1. Prepare a series of Potassium standards range 0-10 ppm
2. Weigh out accurately 10g fertilizer and add 300 ml distilled water. Shake for 30 minutes.
3. Transfer the solution to a 500 ml volumetric flask and dilute to the mark using distilled water.
4. Filter the solution.
5. If necessary dilute the filtrate to produce an expected concentration within the 0 – 10 ppm range.
6. Aspirate the 10ppm standard into the flame photometer and adjust the controls to give a suitable display reading. Aspirate each of the other standards in turn, record their readings and plot a curve of intensity against concentration of Potassium.
7. Aspirate the sample into the flame photometer and record the reading.
8. From the graph obtain the concentration of the Potassium.
9. The percentage Potassium contained in the fertilizer can be determined taking into account the dilution factors used in step 3 and, if applicable, step 5.