Compound-specific carbon and hydrogen isotope analysis of volatile organic compounds using headspace solid-phase...

Area of Science:

• Analytical Chemistry
• Food Science
• Isotope Ratio Mass Spectrometry

Background:

• Natural flavourings command high prices, increasing vulnerability to adulteration.
• Compound-specific isotope analysis (CSIA) is a sophisticated tool for verifying flavour authenticity but has limited application.
• Current methods are restricted to common volatile organic compounds (VOCs).

Purpose of the Study:

• To develop and validate a robust protocol for on-line measurement of δ13C and δ2H in fruit VOCs.
• To improve the accuracy and reproducibility of CSIA for flavour authenticity.
• To assess the impact of analytical parameters on isotopic measurements.

Main Methods:

• Utilized headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) and gas chromatography-high-temperature conversion-isotope ratio mass spectrometry (GC-HTC-IRMS).
• Implemented peak size/linearity and drift corrections, with results normalized using multiple-point linear regression against reference materials.
• Investigated and controlled isotopic fractionation effects from equilibration, adsorption, and desorption parameters.

Main Results:

• Achieved an average combined measurement uncertainty (MU) of 0.42‰ for δ13C values, consistently below ±3*MU across various analytical conditions.
• Identified specific conditions (low temperature, optimized equilibration and adsorption times) crucial for minimizing δ2H measurement uncertainty (<10‰).
• Demonstrated the necessity of method optimization, data normalization, and validation for reliable flavour authenticity studies.

Conclusions:

• The developed protocol offers a reliable method for on-line CSIA of fruit VOCs, enhancing flavour authenticity assessment.
• Careful control of analytical parameters and rigorous validation are essential for accurate isotopic analysis.
• This method can expand the application of CSIA in combating natural flavour fraud.