Potentiometric Determination of EDTA/NTA in Detergents

Potentiometric Determination of EDTA/NTA in Detergents

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(Cu²⁺) = 0.01 mol/L; D0

Sample
10 mL sample solution
10 mL buffer pH = 9.6 [c(NH₃/NH₄NO₃) = 1 mol/L]
2 mL c(Na₂EDTA) = 0.01 mol/L
30 mL dist. Water

Remarks
Calculations:

EDTA=(EP1-C01)*C02*C03/C00;2;%
NTA=(EP1-C01)*C02*C04/C00;2;%

EDTA = content of EDTA in %
NTA = content of NTA in %
C01 = amount of EDTA/NTA added (2 mL)
C02 = factor for % (100)
C03 = 1 mL c(Cu²⁺) = 0.01 mol/L = 2.9225 mg EDTA
C04 = 1 mL c(Cu²⁺) = 0.01 mol/L = 1.9114 mg NTA

Answer

EDTA = (3.004-2.00) x 100 x 2.9225 / 82.63 = 3.55 %
NTA = (3.004-2.00) x 100 x 1.9114 / 82.63 = 2.32 %

EP1 = 3.004 mL
C00 = 82.63 mg

Sample preparation:

Dissolve 0.5 ... 1 g detergent in 50 mL dist. water at 40 °C. Allow solution to cool and add up to 100 mL. Select the appropriate formula. The other may be deleted. Na2EDTA is added to get a greater break. Treat the amount of Na2EDTA added like a blank value.

Literature
Metrohm Application Bulletin No. 143: Potentiometric determination of nitrilotriacetic acid (NTA) and/or ethylenediaminetetracetic acid (EDTA) in detergents.

Method documentation

'pa
751 GPD Titrino 15215 751.0010
DET U…... EDTA-NTA
parameters
>titration parameters
meas.pt.density…. 4
min.incr. ….10.0 ml
dos.rate max…. ml/min
signal drift ….50 mV/min
equilibr.time ….26 s
start V: ….OFF
pause …0 s
dos.element:… internal D0
meas.input: …1
temperature …25.0 °C
>stop conditions
stop V: …abs.
stop V ….10 ml
stop U ….OFF mV
stop EP ….9
filling rate max…. ml/min
>statistics
status: ….OFF
>evaluation
EPC ….5
EP recognition:… all
fix EP1 at U ….OFF mV
pK/HNP:…. OFF
>preselections
req.ident: ….OFF
req.smpl size:…. all
activate pulse: ….OFF
------------
'fm
751 GPD Titrino 15215 751.0010
DET U…. EDTA-NTA
>calculations

EDTA=(EP1-C01)*C02*C03/C00;2;%
NTA=(EP1-C01)*C02*C04/C00;2;%

C00= 82.63
C01= 2
C02= 100
C03= 2.9225
C04= 1.9114
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) -26 mV DET U.... EDTA-NTA
smpl size ….82.63 mg id#1 Total
id#2 Futura id#3 MIFA
EP1 ….3.004 ml 6 mV
NTA …..2.32 %
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U EDTA-NTA
1.0 ml/div dU=20.0 mV/div
============