Negative Mode Detection of Sulfonated Azo Colourants in Sweets/Candies using the MALDI-8030 Dual Polarity Benchtop MALDI-TOF Mass Spectrometer

Importance of the Topic

Sulfonated azo dyes are common food additives valued for their stability, water solubility and low cost. They impart attractive colors but are regulated due to potential health risks such as links to ADHD in children. Reliable analytical methods are essential for quality control and regulatory compliance in the food industry.

Objectives and Study Overview

This study demonstrates the application of a dual polarity benchtop MALDI-TOF mass spectrometer for qualitative detection of regulated sulfonated azo colorants in commercial sweets. It aims to develop a simple workflow combining selective extraction with negative-mode MALDI analysis to confirm the presence of dyes such as Sunset Yellow, Tartrazine, Allura Red and Brilliant Blue in candy samples.

Methodology

The workflow involves three main steps:

• Dye dissolution: Individual candies were vortexed in water to release soluble colorants.
• Ion-pair extraction: Benzyltributylammonium bromide (10 mM) and NaOH (pH>8) were added, followed by chloroform to form an organic phase containing extracted dye–ion pairs.
• Sample preparation: The organic extract was spotted with 9-aminoacridine matrix (10 mg/mL in methanol) for MALDI analysis in negative ion mode.

Used Instrumentation

MALDI-8030 dual polarization linear MALDI-TOF mass spectrometer operating in negative ion mode. The benchtop system provides high resolution and accurate mass measurements for monoisotopic species after sodium removal.

Main Results and Discussion

Standards analysis delivered clear deprotonated ion signals with mass errors below 0.07 Da for all four dyes:

• Sunset Yellow FCF (m/z 407.071, Δ –0.07 Da)
• Allura Red AC (m/z 451.008, Δ +0.019 Da)
• Tartrazine (m/z 467.017, Δ –0.02 Da)
• Brilliant Blue FCF (m/z 747.152, Δ –0.001 Da)

Candy extracts produced MALDI spectra consistent with expected dye compositions based on candy color:

• Orange: Sunset Yellow FCF
• Pink: Allura Red AC
• Purple: Allura Red AC, Indigo Carmine, Brilliant Blue FCF
• Yellow: Tartrazine
• Green: Tartrazine and Brilliant Blue FCF

The high resolution and selective extraction enabled unambiguous qualitative identification of regulated colorants in complex food matrices.

Benefits and Practical Applications

The proposed method offers:

• Rapid qualitative screening without extensive cleanup
• Cost-effective analysis on an affordable benchtop instrument
• Compliance verification for regulated food colorants

This workflow is suitable for QA/QC laboratories, regulatory agencies and research settings focused on food safety and authenticity.

Future Trends and Potential Applications

Advancements may include quantitative MALDI approaches, automation of sample preparation to increase throughput, expansion to other classes of food additives, and integration with complementary techniques such as LC-MS for comprehensive profiling of food contaminants.

Conclusion

The dual polarity MALDI-8030 system combined with ion-pair extraction in negative ion mode provides a straightforward and reliable approach for detecting sulfonated azo dyes in confectionery. This method enhances food safety screening by delivering high-quality spectra and rapid results on a benchtop platform.

References

[1] Arroyo Negrete MA et al. Anal Bioanal Chem 411:5833–5843 (2019).