Reducing variation in decomposition odour profiling using comprehensive two-dimensional gas chromatography

Abstract

Challenges in decomposition odour profiling have led to variation in the documented odour profile by different research groups worldwide. Background subtraction and use of controls are important considerations given the variation introduced by decomposition studies conducted in different geographical environments. The collection of volatile organic compounds (VOCs) from soil beneath decomposing remains is challenging due to the high levels of inherent soil VOCs, further confounded by the use of highly sensitive instrumentation. This study presents a method that provides suitable chromatographic resolution for profiling decomposition odour in soil by comprehensive two‐dimensional gas chromatography coupled with time‐of‐flight mass spectrometry using appropriate controls and field blanks. Logarithmic transformation and t‐testing of compounds permitted the generation of a compound list of decomposition VOCs in soil. Principal component analysis demonstrated the improved discrimination between experimental and control soil, verifying the value of the data handling method. Data handling procedures have not been well documented in this field and standardisation would thereby reduce misidentification of VOCs present in the surrounding environment as decomposition byproducts. Uniformity of data handling and instrumental procedures will reduce analytical variation, increasing confidence in the future when investigating the effect of taphonomic variables on the decomposition VOC profile.

A Comparison of One-Dimensional and Comprehensive Two-Dimensional Gas Chromatography for Decomposition Odour Profiling Using Inter-Year Replicate Field Trials

“…Library matches were generated using the NIST 2011 mass spectral library. The test mixture used to assess column suitability in [23] was also used in this study to verify separation quality and allow retention index matching in order to increase confidence of analyte identification. Alignment of samples was performed using the Statistical Compare feature within the ChromaTOF ® software (LECO) using unique mass.…”

“…Statistical significance for criterion 2 was determined by logarithmic transformation of the data and the use of an independent student's t-test, as this has been previously shown to target compounds that can be attributed to the decomposition process for GC×GC-TOFMS data [23]. Following data processing, the decomposition VOCs were sorted into compound classes for further analysis.…”

“…This column set was recommended for optimal volatile analysis by GC×GC-TOFMS and column suitability has been assessed in previous work [23]. The 1 D column was joined to the TD transfer line using an Ultimate Union kit (Agilent Technologies) and to the 2 D column using a SilTite™ µ-Union (SGE Analytical Science).…”

“…More recent studies have highlighted the value of employing comprehensive two-dimensional gas chromatography (GC×GC) coupled with TOFMS for the chemical profiling of decomposition odour [4,17,18,[20][21][22][23][24][25]. In GC×GC, the coupling of two columns in series with different stationary phases allows the sample to be subjected to two independent separation processes (i.e.…”

“…Furthermore, the chromatographic peaks are compressed into highly focused pulses, as a result of zone compression occurring at the modulator, enhancing peak detectability. Overall, GC×GC is a particularly valuable technique for separating complex mixtures and has been applied in many fields where conventional 1D separations are used, such as food and flavour [27,28], environmental studies [29], metabolomics [30], petroleum products [31][32][33], and forensic science [34,35], including decomposition odour profiling [4,17,18,[20][21][22][23][24][25].…”