Redox Titration of Vitamin C of Milk Powder Employing the Double Au-ring Electrode

Milk powder is supplemented by a vital antioxidant, Vitamin C. With the help of 2,6-dichlorophenolindophenol (DPIP) as the titrant, the double Au-ring electrode gives an excellent titration curve, and easy to clean.

Using a bi-voltametric titration with the OMNIS system, a quick and reliable determination method of Vitamin C in milk powder is established.

Samples

Milk powder (with 709 mg/kg ascorbic acid)

Sample Preparation

16.4 grams of milk powder is weighed using the balance, and taken in a 1 L volumetric flask. It is then dissolved in around 500 mL of deionized water. The quantity of deionized water sufficient to fill the flask up to the mark is then added.

Analysis

50 mL of milk powder solution is taken in the titration vessel using a pipette. Titration is then carried out using DPIP with 0.25 g/L concentration until after the equivalence point is achieved.

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
Stirring propeller 30 mm ETFE 6.01900.010
Titration head 3xNS14 / 4x6.4 mm (P&P) 6.01403.030
OMNIS Advanced Titrator 2.1001.0210
OMNIS 20 mL cylinder unit (titrant) 6.03001.220
Analog measuring module 6.02101.010
Electrode cable plug-in head G (pol.) / plug P, 1.5 m 6.02104.050
OMNIS Stand-alone license (including one instrument license) 6.06003.010
OMNIS instrument license, 1x 6.06002.010
Double Au-ring electrode 6.00353.100

 

Solutions

. .
Titrant β(DPIP) = 0.25 g/L

 

Parameters

. .
Mode MET Ipol
I(pol) 1.0 μA
Pause 30 seconds
Stirring rate 8
Volume increment 50 μL
Signal drift 30 mV/min
Max. waiting time 32 seconds
Min. waiting time 0 seconds
Dosing rate Maximum
Stop volume 20 mL
Stop EP 1
Volume after EP 1.0 mL
EP criterion 30 mV
EP recognition Greatest

 

Results

. . .
Sample Ascorbic acid S(rel) / %
Milk powder 0.086% (n = 5) 0.89

 

About Metrohm

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: Jul 14, 2018 at 7:02 PM

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