In general, Ca is analyzed by Titration method in feeds. Find the procedure below.
ESTIMATION OF TOTAL CALCIUM
Principle
Calcium was precipitated as calcium oxalate by ammonium oxalate, when it reacts with ammonia solution oxalate gets released, then calcium alone precipitate and was titrated against potassium permanganate.
Reagents
Potassium permanganate (0.1N)
Sulphuric acid (1N)
Ammonia solution (2%)
Ammonium oxalate (4%)
Procedure
1g of sample was weigh and digest with di-acid (3ml of conc. HNoз & 1ml of Perchloric acid) at 150 ºc for 21/2hrs or ignite the sample at 540 ºc for 6 h and dissolve using diluted acid combination.
Make up known with distilled water then filter
Take 2ml of aliquots in a centrifuge tube
Add 5ml of ammonium oxalate and mix thoroughly
Keep it at overnight
Mix and centrifuge at 2500 rpm for 15mins
Discard the supernatant without disturbing precipitate
Add 3ml of 2% ammonia solution
Mix and centrifuge at 2500 rpm for 15mins
Discard the supernatant without disturbing precipitate
Process was repeat 2 - 3 times for the complete removal of oxalate
Discard the supernatant without disturbing precipitate
Dissolve the precipitate with 5ml of 1N sulphuric acid
Heat the solution and titrate against 0.1N Potassium permanganate
End point is appearance of pale pink colour
Calculation
Total calcium (%) = Volume of KMnO4 Х2 (Volume make up / Volume of aliquots) / Sample weight X 100