Best Practice for the Use of Xevo TQ-S cronos for Residue Analysis in Food – Determination of Triphenylmethane Dyes in Shrimps

Importance of the Topic

Triphenylmethane dyes such as malachite green and crystal violet are illegal in food-producing animals but persist as toxic metabolites in seafood. Regulatory bodies set reference points for action (RPA) at low µg/kg levels, driving the need for highly sensitive, precise methods to ensure compliance and protect consumer health.

Objectives and Overview

This study aimed to optimize the electrospray ionization (ESI) source parameters of the Xevo TQ-S cronos tandem quadrupole mass spectrometer for the analysis of triphenylmethane dyes in shrimp extracts. Key goals included determining ideal probe position and cone gas flow to maximize sensitivity and repeatability, and evaluating method performance in terms of linearity, matrix effects, precision, and detection limits.

Methodology and Instrumentation

Sample Preparation

• Modified QuEChERS extraction of 10 g shrimp with acidified acetonitrile and cleanup using PSA and MgSO4 cartridges.
• Stable isotope–labelled analogues added post-extraction as internal standards; antioxidants added to stabilize dyes.

Chromatography and Detection

• UPLC: ACQUITY UPLC I-Class PLUS with BEH C18 column (2.1×100 mm, 1.7 µm), gradient elution with ammonium formate (pH 4.5) and formic acid in acetonitrile, flow 0.25 mL/min.
• MS/MS: Xevo TQ-S cronos, positive-mode ESI, desolvation 600 °C, source 150 °C, capillary voltage 0.3 kV, cone gas optimized to 0 L/hr, StepWave off-axis ion guide, travelling-wave collision cell, MRM transitions with auto-dwell.

Main Results and Discussion

ESI Probe and Cone Gas Optimization

• Probe Position: Two horizontal settings compared; the farther position (position 1) gave lowest %RSD (<6 %) and robust sensitivity across all dyes.
• Cone Gas Flow: Zero gas flow minimized signal variability, especially for leucomalachite green and leucocrystal violet, without compromising response.

Linearity and Matrix Effects

• Calibration over 0.05–10 µg/kg yielded R² > 0.99; residuals <20 %.
• Matrix effects evaluated by slope ratios; only leucocrystal violet showed significant enhancement, addressed by matrix-matched calibration and isotope-labelled internal standards.

Precision and Sensitivity

• Repeat injections (n = 10) at 0.5 and 5 µg/kg showed %RSD for peak area within acceptable limits for all analytes.
• Detection at the RPA level (0.5 µg/kg) confirmed suitability for regulatory screening.

Benefits and Practical Applications

• Rapid QuEChERS sample prep paired with robust UPLC-MS/MS workflow supports high-throughput residue monitoring in seafood.
• Optimized orthogonal ESI geometry and adjustable probe deliver consistent sensitivity in complex matrices.
• Isotope dilution quantitation ensures accuracy despite matrix variability.

Future Trends and Opportunities

• Integration of automated sample handling to further increase throughput.
• Adoption of high-resolution MS for broader screening of emerging dyes and metabolites.
• Development of real-time data analysis and remote monitoring for decentralized laboratories.
• Expansion of validated methods to other aquaculture species and food matrices.

Conclusion

By fine-tuning ESI probe placement and eliminating cone gas flow, the Xevo TQ-S cronos platform achieves reliable detection of banned triphenylmethane dyes in shrimp at regulatory levels. Combined with QuEChERS extraction and isotope-labelled standards, this method provides a powerful tool for routine compliance testing in food safety laboratories.

References

• Penninks A et al. EFSA Journal 2017;15(7):4920.
• EU Commission Regulation 2019/1871 on reference points for action.
• Verdon E et al. J AOAC Int. 2015;98(3):649–657.
• Waters Application Note: QuEChERS extraction and Xevo TQD analysis.
• Waters Application Note: Robustness for acrylamide determination.
• Waters Blog: Determining matrix effects in complex food samples.