Determination of ascorbic acid (vitamin C) and its compounds

Significance of the Topic

The accurate determination of ascorbic acid (vitamin C) is essential in food, beverage and pharmaceutical industries for quality control, nutritional labeling and regulatory compliance.

Objectives and Study Overview

This bulletin presents a suite of analytical protocols—titrimetric, photometric and polarographic—for the quantification of ascorbic acid and its derivatives in diverse matrices.

Applied Methodology and Instrumentation

Several complementary approaches are described:

• Bi-voltammetric titration with iodine: Automated MET-mode titrator, double Pt-sheet electrode, 0.01 M I2 titrant, glyoxal pretreatment to eliminate SO2 interference.
• Bi-voltammetric titration with 2,6-dichlorophenol-indophenol (DPIP): MET-mode titrator, double Pt electrode, ~0.001 M DPIP titrant in oxalic acid medium, daily titer calibration.
• Photometric titration with DPIP: Optrode at 520 nm endpoint detection, tolerant to colored or turbid samples.
• Polarographic determination: Differential pulse voltammetry using a mercury drop electrode, Ag/AgCl reference, acetate buffer pH 4.6, standard addition for quantification.

Main Results and Discussion

• Iodometric bi-voltammetry yields clear endpoints independent of sample color but may co-determine other oxidizable species.
• DPIP-based titrations enhance selectivity for vitamin C in complex food or pharmaceutical preparations.
• Photometric detection extends applicability to strongly colored or particulate samples without pre-clarification.
• Polarography provides the highest selectivity; common interferences are effectively excluded, achieving reproducibility within ±0.5 % in juice samples.

Benefits and Practical Applications

• Automated endpoint detection reduces operator bias and increases throughput.
• Method flexibility allows adaptation to beverages, foods, supplements and biological fluids.
• Choice of titrimetric, photometric or voltammetric endpoints accommodates diverse sample interferences and optical properties.

Future Trends and Potential Applications

• Integration of flow-injection analysis and microelectrodes for rapid online monitoring of vitamin C.
• Development of mercury-free polarographic sensors and greener reagent systems.
• Coupling with chromatographic or spectrometric techniques for detailed speciation of ascorbic acid derivatives.

Conclusion

This bulletin consolidates robust titrimetric and voltammetric methods for precise quantitation of vitamin C in a wide range of matrices, enabling laboratories to select the optimal analytical strategy based on selectivity, sensitivity and sample characteristics.

Reference

• Swiss Federal Food Codex – Method 703.1 Iodometric determination of ascorbic acid in juices.
• ISO 6557/2 Fruits, vegetables and derived products – Determination of ascorbic acid content – Part 2: routine methods.
• Schweizerisches Lebensmittelbuch – Method 1560.1 Titrimetric determination of ascorbic acid in food and cosmetics.
• Erdey L., Svehla G., Ascorbinometric Titrations, Akademiai Kiado, 1973.
• Pongracz G., Neue potentiometrische Bestimmungsmethoden für Ascorbinsäure, Fresenius Z. Anal. Chem., 1971, 253, 271–274.
• Amin D., Application of differential pulse polarography to the assay of ascorbic acid, Microchem. J., 1983, 28, 174–179.
• Kozar S. et al., Determination of L-ascorbic acid in fruit and vegetables by differential pulse polarography, Fresenius Z. Anal. Chem., 1988, 329, 760–763.