Estimation of Citrate in Detergents as per ASTM D4608

Citrate is mainly used as a component of detergents to prevent calcification and to reduce hardness of water. Therefore, while determining the quality of detergents, citrate content is considered as an important parameter. The method utilizes cupric sulfate as the titrant.


Liquid hand soap

Sample Preparation

No sample preparation is required.


5 to 10 grams of detergent sample is pipetted into a beaker and 150 mL of water is added by an automatic program. pH is then adjusted to nearly 8.5 using HCl with 0.1 mol/L concentration, followed by addition of 25 mL borate buffer.

The pH of the mixture is further adjusted to around 8.5 using NaOH with 0.1 mol/L concentration. The titration is then carried out using Cu-ISE as the indicator and CuSO4 with 0.05 mol/L concentration as the titrant until after the equivalence point is achieved.


. .
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, (EDTA solution) 6.03001.150
OMNIS 10 mL cylinder unit, 3x (hydrochloric acid, sodium hydroxide, titrant) 6.03001.210
OMNIS 50 mL cylinder unit, (borate buffer) 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(CuSO4) = 0.05 mol/L
Borate buffer Borate buffer with pH = 8.5
EDTA solution c(Na2EDTA) = 0.05 mol/L
HCl c(HCl) = 0.1 mol/L
NaOH c(NaOH) = 0.1 mol/L


. .
Mode DET U
Pause 30 seconds
Start volume (Sample size / 2) – 1.5 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 10 mV
EP recognition Greatest


. .
Content wCitric acid / (%) (n = 5) S(rel) / %
0.40 1.77

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.

Metrohm has been owned 100% by the non-profit Metrohm Foundation since 1982. The Metrohm Foundation, which does not exert any influence on the company’s business operations, sponsors gifted students in the natural sciences, supports charitable and philanthropic purposes and, above all, ensures the independence of the company.

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Last updated: Feb 1, 2020 at 7:53 PM


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