Utilizing the third order advantage with isotope dilution mass spectrometry.

Akin to the standard addition method requiring only a single chromatographic injection, a robust isotope dilution mass spectrometry method is described. The (13)C labeled analyte at known concentration serves as the standard to quantify the unlabeled target analyte. Two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOFMS) provides a combined (12)C and (13)C analyte peak as part of the third order data cube. This combined peak can be isolated from interfering compounds and noise based on the "third order advantage" with parallel factor analysis (PARAFAC). The combined mass spectra are then mathematically resolved using classical least squares (CLS) providing a (12)C/(13)C ratio, thus absolute amounts of (12)C and (13)C. Good agreement between the prepared and determined concentration ratios for test analytes was achieved with further demonstration to real-world samples.