Potentiometric Titration of the Calcium/Mg in Milk Products

Potentiometric Titration of the Calcium/Mg in Milk Products

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0502.140 Cu2+ sensitive indicator electrode; input 1
6.0726.100 Ag/AgCl double junction reference electrode (KNO3 sat.)

Reagents
c(EGTA) = 0.1 mol/L; D0
c(Cu complex) = 0.100 mol/L; D1
Buffer solution pH = 10; D2

Sample
app. 10 g milk

Remarks
· Calculations:

Calcium=C70*C01*C02*C03/C00;3;%

Calcium = content of calcium in %
C01 = concentration of titrating agent (0.1 mol/L)
C02 = molecular mass of calcium (40.08 g/mol)
C03 = factor for % (0.1)
C70 = EP1 from submethod Milk-Ca3

. Answer

Calcium = 3.008 x 0.1 x 40.08 x 0.1 / 10.0516 = 0.12%

C70 = 3.008

· Reagents:
c(EGTA) = 0.100 mol/L:
38.04 g EGTA - ethylene glycol-0,0’-bis-(2-aminoethyl)-N,N,N’,N’-
tetraacetic acid are added to a 1 liter volumetric flask, dissolved in
250 mL c(NaOH) = 1 mol/L and the solution made up to the mark
with dist. water.
Cu complex:
EGTA titrant (100 mL) is mixed with 100 mL of a solution containing
0.2 mol/L NH4Cl and exactly 0.100 mol/L Cu(II)nitrate. Titration can
used to check that this solution contains no excess of Cu(II) or EGTA.

Buffer solution pH = 10:
54 g NH4Cl is dissolved in ca. 400 mL dist. water in a volumetric
flask, 300 mL w(NH3) = 0.25 (25%) added and the solution made up
to 1 liter with dist. water.
· The method „Milk-Ca3“ can also be used as work-alone method
(without TIP). Add the Cu complex-solution and the buffer solution
manually.

Literature
· Metrohm Application Bulletin No. 235: Potentiometric titration of Ca
(Mg) in milk products

Method documentation

'pa

751 GPD Titrino 15215 751.0010
TIP Milk…-Ca
parameters
>sequence
1.stirrer: N
2.method:… Milk-Ca1
3.pause …40 s
4.method:… Milk-Ca2
5.pause …10 s
6.method:… Milk-Ca3
>statistics
status: …OFF
>preselections
req.ident:… OFF
req.smpl size: value
meas.mode:… OFF
temperature …25.0 °C
------------
'fm
751 GPD Titrino 15215 751.0010
TIP Milk…-Ca
>calculations

Calcium=C70*C01*C02*C03/C00;3;%

C00= 10.0516
C01= 0.1
C02= 40.08
C03= 0.1
C70= 3.008
------------'fr
751 GPD Titrino 15215 751.0010
TIP Milk…-Ca
smpl size 10.0516 g
C70 3.008
Calcium 0.120 %
TIP terminated
============