The Determination of Sugars in Molasses by High-Performance Anion Exchange with Pulsed Amperometric Detection

Importance of the Topic

Accurate quantification of sugars in final molasses is critical for sugar mills because the economic value of molasses is directly tied to its sugar content. Traditional methods like gas chromatography require time-consuming derivatization and may suffer from coelution interferences. High-performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) offers a rapid, sensitive, and selective alternative for routine analysis.

Objectives and Overview of the Study

This application note describes the implementation and validation of an HPAE-PAD method to determine glucose, fructose, sucrose and raffinose in cane and beet molasses. Key goals include establishing calibration protocols using lactose as an internal standard, defining sample preparation and dilution strategies, and demonstrating method precision and accuracy compared with existing approaches.

Methodology and Instrumentation

Sample preparation involves dissolving measured molasses in deionized water with a fixed amount of lactose internal standard, followed by appropriate dilutions and filtration. Sugars are separated on a CarboPac PA1 analytical column using 150 mM NaOH eluent at 1 mL/min. Pulsed amperometric detection with gold working electrode potentials above pH 12 ensures selective carbohydrate measurement.

Applied Instrumentation

• High-performance pump
• Liquid chromatography module
• Pulsed electrochemical detector
• Eluent degasser or organizer
• Dionex PeakNet or AI-450 workstation

Main Results and Discussion

The CarboPac PA1 column achieved baseline resolution of glucose, fructose, lactose (internal standard), sucrose and raffinose. Relative response factors (RRF) were calculated from bracketing calibration standards. Precision for sucrose duplicates was better than 1% RSD; for glucose and fructose under 2%; and for raffinose under 6%. Example analyses yielded 4.39% glucose, 6.67% fructose and 30.8% sucrose in cane molasses, and 47.7% sucrose with 2.10% raffinose in beet molasses, all within expected ranges.

Benefits and Practical Applications of the Method

• No derivatization step and minimal sample cleanup
• High specificity via pulsed amperometric detection
• Rapid throughput with reproducible chromatography
• Compatibility with existing chromatography workstations

Future Trends and Potential Uses

Advancements may include automated sample handling, integration with multianalyte workflows, and expansion to oligosaccharide profiling. Further development of resin chemistries and pulse sequences could improve sensitivity for trace carbohydrates in complex matrices.

Conclusion

HPAE-PAD using CarboPac PA1 columns and NaOH eluent provides a robust, accurate, and efficient method for routine determination of major sugars in cane and beet molasses. The approach meets industry precision and accuracy requirements and streamlines analytical workflows.

Reference

1. Kort, M.J. High-Pressure Liquid Chromatography, SMRI Annual Report 1979–1980.
2. Day-Lewis, C.M.J.; Schäffler, K.J. HPLC of Sugars, Fourth African Sugar Technologists Association, 1990.
3. Day-Lewis, C.M.J.; Schäffler, K.J. Analysis of Sugars in Final Molasses by IC, South African Sugar Technologists Association, 1992.
4. Morel du Boil, P.G.; Schäffler, K.J. Comparison of Anion and Cation Exchange HPLC, Sugar Processing Research Conference, 1990.
5. Thompson, J.C. Methods for Carbohydrates by IC, Sugar Processing Research Conference, 1990.
6. Dionex Technical Note 20, Analysis of Carbohydrates by AEC with PAD.
7. Dionex Technical Note 21, Optimal PAD Settings for Carbohydrates.