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.
Sample
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.
Analysis
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.
Configuration
| . |
. |
| 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 |
Solutions
| . |
. |
| 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 % |
Parameters
| . |
. |
| 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 |
Results
| . |
. |
| 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.
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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