Estimation of Nitrilotriacetates in Detergents as per ASTM D4954

Nitrilotriacetate (NTA) is mainly used in detergents to reduce the hardness of water and as a chelating agent. Included in various functions of NTA are inhibition of calcification and limestone formation by complexation with metal ions like Fe3+, Cu2+, and Ca2+. Thus, NTA content is a crucial parameter for assessment of the quality of detergents. It is estimated using back-titration with excess cupric nitrate.


Detergent powder spiked with 6 % NTA.

Sample Preparation

Detergent is solvated in deionized water, followed by adjustment of the pH to 7.0 with concentrated HNO3.


100 mL of the sample prepared using above method is taken in a beaker with the use of a pipette. 3 mL of concentrated HNO3 is added while stirring the mixture continuously, post which it is allowed to settle for nearly 5 minutes.

Concentrated HNO3 is further added until the mixture reaches the pH of 0. 25 mL of Cu(NO3)2 with 0.1 mol/L concentration is then added, and the pH is adjusted to 1.05 with 20% NaOH. Further to that, 25 mL of acetate buffer is added, and pH is adjusted to 4.65 with 20% NaOH.

Titration is then carried out using the indicator Cu-ISE and the titrant NTA with 0.3 mol/L concentration until after the equivalence point is reached.


. .
Main module Pick&Place S 2.1010.0010
Pick&Place module 2.1014.0010
"Peristaltic" (2-channel) pump module 2.1016.0010
Gripper fingers 42.8 - 65 mm 6.02601.010
Dummy panel for module plate 6.02600.000
OMNIS Rod Stirrer "Sample Robot" 2.1006.0010
Titration head 6xNS14 / 3xNS9 (P&P) 6.01403.000
Stirring propeller 30 mm ETFE 6.01900.010
OMNIS sample rack 9 x 250 mL, 2x 6.02041.010
Sample beaker (10x) PP 250 mL (P&P), 2x 6.01400.100
OMNIS Titrator (Advanced) 2.1001.0210
Cable MDL PL/SO 1 m, 4x 6.02102.020
OMNIS Dosing Module, 4x 2.1003.0010
OMNIS 5 mL cylinder unit, (nitric acid) 6.03001.150
OMNIS 10 mL cylinder unit, (titrant) 6.03001.210
OMNIS 20 mL cylinder unit, (sodium hydroxide) 6.03001.220
OMNIS 50 mL cylinder unit, 3x (acetate buffer, cupric nitrate solution, EDTA) 6.03001.250
Analog measuring module 6.02101.010
Cu-ISE 6.0502.140
Unitrode with Pt1000 (Head U) 6.0258.600
Electrode cable plug-in head G / plug P, 1.5 m for Cu-ISE 6.02104.010
Electrode cable plug-in head U / plug P, 1.5 m for Unitrode 6.02104.610
OMNIS Stand-alone license (including one instrument license) 6.06003.010
OMNIS instrument license, 1x 6.06002.010


. .
Titrant c(NTA) = 0.3 mol/L
Cupric nitrate solution c(Cu(NO3)2) = 0.1 mol/L
Acetate buffer Acetate buffer with pH = 4.65
EDTA solution c(Na2EDTA) = 0.1 mol/L
HNO3 w(HNO3) = 65 %
NaOH w(NaOH) = 20 %


. .
Mode MET U
Pause 30 seconds
Volume Increment 0.05 mL
Stirring rate 8
Signal drift 30 mV/min
Max. waiting time 32 seconds
Min. waiting time 5 seconds
Dosing rate Maximum
Stop volume 10 mL
Stop EP 1
Volume after EP 1.0 mL
EP criterion 5 mV
EP recognition Greatest


. .
Content wNTA / (%) (n = 5) S(rel) / %
t8.41 0.49

About Metrohm

At Metrohm is one of the world’s most trusted manufacturers of high-precision instruments for chemical analysis. Metrohm was founded in 1943 by engineer Bertold Suhner in Herisau, Switzerland. Today, Metrohm is represented in 120 countries by subsidiaries and exclusive distributors. The global Metrohm Group also includes the Dutch companies Metrohm Applikon and Metrohm Autolab, manufacturers of online analyzers and instruments for electrochemical research, respectively. Recently, the Metrohm Group was joined by Metrohm Raman, a leading manufacturer of handheld Raman spectrometers.

Metrohm is the global market leader in analytical instruments for titration. Instruments for ion chromatography, voltammetry, conductivity, and stability measurement make the Metrohm portfolio for ion analysis complete. Instruments for Near-infrared and Raman spectroscopy are another, strongly growing segment of the Metrohm portfolio.

Metrohm is a problem solver, both in the laboratory and within the industrial process. To this end, the company offers their customers complete solutions, including dedicated analytical instrumentation as well as comprehensive application know-how. More than 30% of the company’s employees at the Metrohm international headquarters in Herisau work in R&D.

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Last updated: May 15, 2020 at 11:34 AM


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