Aim : to determine the contain of element e.g. K, Mg, P,
Ca in the fertilizer followed by the specification.
Inductively Coupled Plasma(ICP)- determine all
element at one time include heavy metal if necessary.
Atomic Absorption Spectrophotometer(AAS) & UV
Spectrophotometer - one element at a time.
of pH value
DETERMINATION OF POTASSIUM AND MAGNESIUM
Why we need potassium and magnesium?
POTASSIUM - provide the ionic environment for metabolic
process in cytosol.(growth regulation)
- potassium ions (K+) for protein synthesis and
opening and closing of stomata.
MAGNESIUM - part of chlorophyll in plant for photosynthesis
• Method for the determination of magnesium
Determination of water-soluble magnesium content (MgO)
Magnesium in magnesium sulphate fertilizers is extracted in
boiling water and the magnesium content determined by
atomic absorption spectrophotometer.
• Reference: MS 417: Part 6: 1994
•Weigh the sample
•Add distilled water and HCl
• Digest the solution using hot plate at boiling
point around 20minutes
• Leave to cool
• Transfer into volumetric flask and dilute to
the mark (250ml)
• Mixed the solution and filter in plastic vial
• Further dilution(100ml)
• Add strontium nitrate(5ml) and dilute to the
• To remove phosphate from magnesium and
calcium and prevent interference from other
• Preparation for Atomic Absorption
• Standard stock solution
- Potassium dihydrogen sulphate solution
- Magnesium sulphate solution
• For 1000ppm,weigh 4.3928g.
• Dry in oven for 2 hours
• Undergo further dilution(m1v1=m2v2)
• 0, 0.25, 0.5, 0.75, 1.00 and 1.25 ppm
• Pre-calibrate the AAS with standard stock
• Run the AAS
• Then, we can determine the concentration of
DETERMINATION OF PHOSPHORUS
Why phosphorus important to plant?
• Essential to stimulate early plant growth and hastens the
• Development of root health.
• Classified as macronutrient.
• molybdovanadate method (yellow method).
•MS 417: Part 4: 1994
•Amount of light transmitted (yellow colour) dependent on the
concentration of phosphorus.
•Spectophotometric absorption curve from known standard
phosphorus solutions determined in unknown solution.
Standard stock solution:
Potassium dihydrogen phosphate (4.3928g in 1L)
1000ppm 100ppm 0ppm 2ppm 4ppm 8ppm 10ppm
Molybdovanadate reagent: Ammonium molybdate (100ml) mixed together
Mixing the HCl & HNO3 together.
• Sample preparation and
weigh the samples (fertilizer)
• Add distilled water.
• Add 10ml HCl and 5ml HNO3 and boil.
• transfer into volumetric flask.
• Mark-up with distilled water then filter.
• 1ml of sample solution is pipette into 100ml volumetric flask.
• Add Molybdovanadate reagent and diluted to the mark with
• Prepare calibration standard (0,2,4,6 & 8 ppm) from the stock
solution (1000ppm) and take reading after 30 minutes.
Determine phosphate at acidic colour at pH ±
Double acid method is used.
We put HCl and HNO3 to convert all
polyphosphate (P2O7) to orthophosphate
phosphate + metavanadate =
phosphomolybdate acid + water. (yellow