Fast analyses of additives in soft drinks by minimal sample preparation

Importance of the Topic

A reliable, fast and minimal-preparation technique for quantifying both sweeteners and preservatives in soft drinks addresses growing consumer demand for low-calorie beverages with safe shelf lives. Direct injection HPLC methods reduce sample handling errors, solvent use and analysis time while maintaining sensitivity for polar additives.

Objectives and Study Overview

This study demonstrates a direct-injection HPLC protocol to separate and quantify seven common soft-drink additives—ascorbic acid, acesulfame K, saccharin, caffeine, aspartame, sorbic acid and benzoic acid—using a polar-embedded reversed-phase column.

Methodology

Sample Preparation:

• Degas soft-drink samples by 2-minute ultrasonic treatment.
• Filter through a 0.45 µm syringe filter; inject directly (5 µl).

Chromatographic Conditions:

• Column: ProntoSIL 120-3 C18 ace EPS (100 × 2 mm, 3 µm).
• Mobile phase A: 20 mM KH2PO4 buffer, pH 3; B: acetonitrile.
• Gradient: 100 % A (0–1.5 min), to 65 % A/35 % B (5.0 min), hold (8.5 min), re-equilibrate to 100 % A by 16 min.
• Flow rate: 0.40 ml/min, increasing to 0.70 ml/min during column regeneration.
• Column temperature: 40 °C; UV detection at 220 nm.

Used Instrumentation

• Binary gradient HPLC system with low-pressure or high-pressure mixing, degasser, autosampler and column oven.
• UV detector for multi-wavelength monitoring.
• Software control for gradient programming and data acquisition.

Main Results and Discussion

The method achieved baseline separation of target analytes within an 8.5 min runtime. Retention times ranged from 0.87 min for ascorbic acid to 8.22 min for benzoic acid. Limits of detection (LOD) were in the low µg/L range (e.g., 0.00013 mg/L for ascorbic acid). Direct injection chromatograms of a lemon-flavored soft drink revealed additional matrix peaks (citric acid and unknowns) without interference of analyte peaks.

Benefits and Practical Applications

• Minimal sample preparation reduces analysis time and risk of compound loss.
• High throughput: under 12 min total cycle time including re-equilibration.
• Applicability to quality control laboratories for routine monitoring of sweeteners and preservatives.

Future Trends and Applications

Advances may include coupling to mass spectrometry for improved specificity, further reduction of cycle times with sub-2 µm particles or core-shell columns, and expansion to additional polar additives in beverage matrices. Integration with automated sample handling platforms will enhance laboratory efficiency.

Conclusion

A direct-injection reversed-phase HPLC method using a polar-embedded C18 column provides rapid, sensitive and reproducible analysis of key soft-drink additives. The approach streamlines workflow and meets quality control requirements with minimal resource consumption.

References

• [1] Pressemitteilung Landesbetrieb Hessisches Landeslabor, 4 April 2008
• [2] Ron Lewis, Varian Application Note No. 23