Calibration and data processing in gas chromatography combustion isotope ratio mass spectrometry

Abstract

Compound-specific isotope analysis (CSIA) by gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) is a powerful technique for the sourcing of substances, such as determination of the geographic or chemical origin of drugs and food adulteration, and it is especially invaluable as a confirmatory tool for detection of the use of synthetic steroids in competitive sport. We review here principles and practices for data processing and calibration of GCC-IRMS data with consideration to anti-doping analyses, with a focus on carbon isotopic analysis (13C/12C). After a brief review of peak definition, the isotopologue signal reduction methods of summation, curve-fitting, and linear regression are described and reviewed. Principles for isotopic calibration are considered in the context of the Δ13C = δ13CM – δ13CE difference measurements required for establishing adverse analytical findings for metabolites relative to endogenous reference compounds. Considerations for the anti-doping analyst are reviewed.

Gas Chromatography‐Combustion‐Isotope Ratio Mass Spectrometry for Traceability and Authenticity in Foods and Beverages

“…The 1st step in data processing is that of peak detection whereby peak start and stop parameters are defined (Zhang and others ). From there, ion current ratios can be calculated for the detected peaks via summation, curve fitting, or linear regression.…”

Complementary approach for accurate determination of carbon isotopic compositions in γ‐hydroxybutyric acid using gas chromatography/combustion‐isotope ratio mass spectrometry

“…This isotopic drift could be due to the kinetic isotope effect caused by derivatization over a wide range of GHB concentrations (10 ppm and 500 ppm). Another possibility of isotopic drift in our setting could be inferred from the properties of instrumental performance that are dependent on the quantity of analyte applied . For instance, after sample injection, several factors (e.g., injector, carrier gas flow rate, and combustion) could lead to drift of the isotopic signal due to relative variations of the m/z 44 to 45 signal intensities depending on CO 2 quantities in the GC/C‐IRMS system .…”

“…Furthermore, sample quantities can modify the δ 13 C values of C‐containing compounds such as amino acids and phenols . Such issues have been evaluated by (1) measuring samples and standard compounds of interest under identical set‐up conditions, (2) using quantities of standards similar to those of samples, and (3) calibrating samples relative to standards . However, studies that involve the matching of standard quantities to sample quantities are tedious and costly .…”

Gas Source Isotope Ratio Mass Spectrometry (IRMS)

“…78 As in EA/IRMS, the analyte gas is admitted to the IRMS ion source via a low-flow open split, thereby carefully optimising the split efficiency for sensitive detection from capillary chromatography. For more detailed descriptions we refer to the vast amount of specialised and review literature [79][80][81][82] and citations therein.…”