**1. Definition and short history of gas chromatography**

Gas chromatography (GC) is a type of chromatography. According to the International Union of Pure and Applied Chemistry (IUPAC) recommendation, gas chromatography is defined as a separation technique in which the mobile phase is a gas. Gas chromatography is always carried out in a column [1]. GC is a separation and detection method for sample mixtures, whose components can be volatilized without thermal decomposition. The analytical procedure is used for the determination of organic substances; usually molecules have a molecular mass of less than 500 g/mol and a boiling point of less than 400°C. GC is a technique used to separate mixtures of gaseous chemical compounds based on differences in the compounds' relative affinities for a solid (gas-solid chromatography) or liquid (gas-liquid chromatography) stationary phase held within a column.

Gas-liquid partition chromatography was invented by Martin and James from the National Institute for Medical Research, London, in 1952. The invention of this technique is generally attributed to the inventors in their 1952 published paper in the *Biochemical Journal* [2]. In this publication the theory of the partition column has been extended to cover a compressible mobile phase, and gas-liquid partition columns were described for the separation of volatile fatty acids. In the same year, the *Nobel Prize* in chemistry was awarded jointly to Martin and Synge for their *invention of partition chromatography*. Starting from this time, gas chromatography has become one of the most important and widely applied analytical techniques in modern chemistry. The first commercial gas chromatograph was introduced in 1955 by Perkin-Elmer (USA). Subsequently, this method was used to study petrochemical products. Today, gas chromatography is one of the most widespread investigation methods of instrumental analysis. This technique is used in the laboratories of the chemical, petrochemical, and pharmaceutical industries, in the research institutes and also in the clinical and environmental and food and beverage analyses. Recent developments in GC have resulted in the introduction of better and selective fused silica capillary columns and methods for sample preparation. Newer separation and detection solutions, such as fast GC, multidimensional separation GC techniques (GC × GC), and hyphenation of GC and GC × GC with mass spectrometry (MS), with triple quadrupole mass spectrometry and with time-of-flight mass spectrometry (TOF-MS), have been developed and become industrial routine. Analytical pyrolysis (Py) technique hyphenated to GC and GC/MS has extended the range of possible tools for the characterization of synthetic polymers and copolymers. This technique has been

used extensively over the last 30 years as a complementary analytical tool used to characterize the structure of synthetic organic polymers and copolymers, polymer blends, biopolymers, and natural resins [3].
