Gas Chromatography (GC) Analysis

Scope

Gas chromatography covers the separation and quantification of volatile and semi-volatile compounds in gas, liquid, and (via headspace or thermal desorption) solid samples. The configuration – injection mode, column, detector, and method conditions – is selected based on the analytes and the matrix.

Key aspects of the technique include:

• Detectors – flame ionization detection (FID) for organic compounds, thermal conductivity detection (TCD) for general use and fixed gases, electron capture detection (ECD) for halogenated compounds, and mass spectrometry (GC-MS) for compound identification, among others
• Injection and sampling modes – direct liquid injection, headspace sampling for volatiles in complex matrices, purge-and-trap, and thermal desorption depending on the sample
• Column types – capillary columns of various stationary-phase chemistries selected to resolve the target compounds
• Analyte classes – VOCs, residual solvents, hydrocarbons, fatty acid methyl esters (FAMEs), residual monomers, fragrance and flavor compounds, and other volatile/semi-volatile species
• Quantification – external standard, internal standard, and standard addition approaches against calibration standards
• Applicable methods – numerous ASTM, USP, EPA, and ISO methods specify GC for particular analytes and matrices

Applications

• Purity and composition analysis – determining the purity of chemicals and solvents and quantifying the components of a mixture for quality control and specification verification
• Residual solvent analysis – measuring residual solvents in pharmaceuticals, polymers, and finished products, often by headspace GC (e.g., per USP <467>)
• Volatile organic compound (VOC) analysis – identifying and quantifying VOCs in materials, products, environmental samples, and emissions
• Petrochemical and fuel analysis – composition, hydrocarbon profiling, and purity determination of fuels, solvents, and petrochemical streams
• Polymer and plastics analysis – residual monomer determination, additive analysis, and outgassing/volatile content studies on polymer materials
• Food, flavor, and fragrance analysis – characterization of flavor and aroma compounds, fatty acid profiles, and volatile contaminants in food and consumer products
• Environmental testing – analysis of organic contaminants in water, soil, and air following established EPA and ISO GC methods
• Impurity and unknown identification – using GC-MS to identify unknown volatile compounds and characterize impurity profiles

Benefits

• High separation power for complex mixtures – GC resolves many components in a single run, making it well suited to samples containing numerous volatile compounds that other techniques cannot separate as cleanly
• High sensitivity and low detection limits – depending on the detector, GC can quantify analytes down to trace (ppb) levels, suitable for residual solvent, VOC, and contaminant analysis
• Flexible detector and sampling options – the technique can be tailored to the analyte and matrix by selecting the appropriate detector (FID, TCD, ECD, MS) and sampling mode (direct, headspace, purge-and-trap)
• Compound identification with GC-MS – coupling GC with mass spectrometry allows not just quantification but confident identification of unknown compounds, which is essential for impurity and contaminant investigations
• Backed by established standard methods – a large body of ASTM, USP, EPA, and ISO methods specify GC, so analyses can be run to recognized methods appropriate to the industry and application