Determination of Thiosulfate and Pyrophosphate in Crayfish Wash Powder

Importance of the Topic

This method addresses the food safety concern of residual thiosulfate and pyrophosphate in crayfish wash powder, compounds associated with adverse effects such as rhabdomyolysis.
Accurate quantification of these anions is essential for consumer protection and regulatory compliance.

Objectives and Study Overview

• Develop a simple and sensitive capillary ion chromatography (IC) approach for thiosulfate and pyrophosphate determination in wash powders.
• Integrate suppressed conductivity detection with mass spectrometric (MS) confirmation for reliable identification.
• Validate method performance: reproducibility, linearity, detection limits, and application to real samples.

Used Instrumentation

• Dionex ICS-4000 Integrated Capillary HPIC System with eluent generation and 0.4 µL sample loop.
• Dionex IonPac AG19 Capillary Guard (0.4 × 50 mm) and AS19 Capillary (0.4 × 250 mm) columns.
• Dionex EGC-KOH Capillary Eluent Generator Cartridge and ACES 300 Anion Capillary Electrolytic Suppressor.
• Thermo Scientific TSQ Vantage Triple Stage Quadrupole Mass Spectrometer with ESI in negative ion mode.
• Chromeleon CDS and Xcalibur software for data acquisition and processing.

Methodology

• Sample pretreatment: Dissolve 100 mg powder in water, filter and cleanup with OnGuard RP and OnGuard II Na cartridges to remove organics and metals.
• Eluent: KOH gradient (6.5–67 mM) at 0.012 mL/min; column temperature 30 °C.
• Detection: Suppressed conductivity (14 mA) and ESI-MS for peak confirmation.
• Calibration: Mixed standards of 14 anions; working standards for thiosulfate and pyrophosphate (0.02–7.5 mg/L).

Main Results and Discussion

• Baseline separation of 14 anions achieved in a single 46-minute run with the capillary AS19 column, reducing eluent consumption.
• MS confirmation of thiosulfate (m/z 112.9) and pyrophosphate (m/z 176.9) in wash powder samples.
• Calibration linearity: r2 = 0.9993 for thiosulfate, r2 = 0.9991 for pyrophosphate.
• Detection limits: 6 µg/L for thiosulfate and 11 µg/L for pyrophosphate (S/N = 3).
• Reproducibility: RSDs <1% for retention time and peak area (intra- and inter-day).
• Sample analysis: Thiosulfate at 27.2 mg/kg (Sample 1) and 4.6 mg/kg (Sample 2); pyrophosphate at 16 mg/kg (Sample 2) with recoveries of 80–110%.
• An additional unknown peak was observed, indicating potential impurities.

Benefits and Practical Applications

This capillary IC–MS method combines high sensitivity, selectivity, and low reagent consumption, making it ideal for routine food safety monitoring and quality control in complex matrices.

Future Trends and Potential Applications

• Extension to other phosphate-related modifiers and trace anions in food and environmental samples.
• Coupling with high-resolution MS for enhanced structural elucidation.
• Automation and miniaturization of sample preparation and analysis for high-throughput screening.

Conclusion

The developed capillary IC method with suppressed conductivity and MS detection offers a reliable and efficient tool for quantifying thiosulfate and pyrophosphate in crayfish wash powders, supporting food safety assurance.

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