From the used oil analysis laboratory, gas chromatography is becoming increasingly essential for correctly determining the concentrations of contaminants – especially fuel and glycol – in used oil samples. In transformer oil analysis, the method is used to determine the concentrations of dissolved gases inside the oil sample, which is used with gas analysis and other procedures to assess electrical faults within a transformer or petroleum insulated electric components. Gas chromatography is among the most widely used methods in modern analytical chemistry. In its fundamental form, gas chromatography is used to separate complex mixtures of different molecules based on their physical attributes, such as polarity and boiling point. It is the best tool to analyse liquid and gas samples containing many hundreds or even thousands of different molecules, allowing the analyst to identify both the types of molecular species present and their concentrations.
Molecular Speciation Using Gas Chromatography
Gas chromatography can be divided into two classes, gas-liquid chromatography and gas-solid chromatography. In both cases, the technique requires the separation of components of a gaseous sample, with a stationary stage, either a typical liquid in the event of gas-liquid chromatography, or a typical solid in the event of gas-solid chromatography. Since the overwhelming majority of test criteria used for hydrocarbon Analysis rely on gas chromatography, this guide will concentrate exclusively on this system, although the same basic principles apply to both approaches.
In gas-liquid chromatography, it is the interaction between the Gaseous sample the mobile phase and a normal liquid the stationary phase, which leads to the separation of distinct molecular components. The stationary phase is either a polar or nonpolar liquid, which, in the case of capillary column, coats the interior of the column, or is impregnated onto an inert solid that is then packaged into the gas chromatography column. A schematic design of a gas chromatography instrument is shown in Figure 2. The basic elements are an inert carrier gas, most commonly helium, hydrogen or nitrogen, a gas chromatography column packed or coated with a suitable stationary phase, an oven which allows for precise temperature control of this column and some kind of sensor capable of detecting the sample because it exits or elutes from the column. Gas-liquid chromatography works since the molecules at the Samples are transported along the pillar in the carrier gas, but partition between the gas phase and the liquid phase.