Gas chromatography-mass spectrometry (GC-MS) is a powerful technique for separating and detecting molecules. It is a widely-used method across different industries like forensics, pharmaceuticals, environmental analysis, and petrochemicals to detect for volatile organic molecules or gases. In this article, we will discuss the operating mechanism of GC-MS, followed by its applications in the petrochemical field.
How GC-MS works
GC-MS consists of a gas chromatograph and mass spectrometer. Once a sample is introduced into a gas chromatograph instrument, its various components are vaporized. Analyte properties such as volatility and polarity determine their affinity to the liquid stationary phase in the analytical columns. For instance, non-polar stationary liquid phase is better at retaining and, hence, separating non-polar analytes. The physical dimensions of the column also affect how long the analytes are retained in the column and eventually eluted.
Once the analytes are eluted from the analytical column, they are then ionized, fragmented, separated, and captured as a function or spectrum of their mass-to-charge ratios by the mass spectrometer. The analytes’ identity is verified by comparing them to libraries of mass spectra of known compounds. The peak areas of the mass-to-charge functions also inform users of the relative quantity of the analytes.
Useful features of GC-MS for the petrochemical field
GC-MS is a very sensitive technique to detect for compounds in petroleum products. Petrochemical companies have exploited this feature of GC-MS to assess the commercial value of oil reserves by characterizing the types of hydrocarbons and their relative concentrations without having to go through expensive drilling operations. This is made possible with modern-day GC-MS instruments that are sensitive enough to detect analytes in the microgram range.
The speed and throughput at which GC-MS is able to provide analytical data also helps petrochemical companies maintain quality control throughout production. Close to 100 million barrels of petroleum products are generated daily, and it is important for companies to be able to detect the slightest abnormalities in huge volumes of products quickly and accurately.
Crude oil contains a complex mixture of hydrocarbons with a wide range in boiling points and molecular weights. Petroleum products derived from crude oil are highly purified, and GC-MS is used to detect contaminants, and determine if the refining process was effective. Many compounds found in crude oil may also have similar column retention times or mass-to-charge ratios. When mass-to-charge ratio spectra overlap, column retention times can be used to identify different compounds, and vice versa. The detection limit of GC-MS can be as sensitive as parts per billion, and some GC-MS models are able to provide analysis in as short as a few minutes. This enables petrochemical companies to perform high throughput quality control.
The ability to fine tune or optimize GC-MS for detection and analysis also helps in developing product formulations. For example, oil additives are often added to petroleum products to improve lubrication and prolong the lifetime of the combustion engine, and prevent equipment fouling. Other types of additives are also commonly added to reduce corrosion and fuel line freezing. By adjusting parameters in the gas chromatograph such as the liquid stationary phase and size of the analytical column, different analytes in petroleum products can be separated and eluted, then detected. This allows companies to develop and improve proprietary recipes or formulations to suit the needs of their clients.
As a highly reproducible technique, GC-MS is helpful for regulators establishing emission guidelines. It also helps companies comply with environmental standards. Burning petroleum contributes many pollutants into the atmosphere, including organic molecules and gases. Regulators are interested in quantifying pollutant levels in petrochemical products to safeguard the interests of society. GC-MS is a reliable method for companies to quantify the levels of toxic gases like carbon monoxide and sulfur oxide emitted from their products, and comparing them to GC-MS standards set by regulators. Compounds in petroleum products can also affect living organisms with different levels of toxicity. In situations such as oil spills, GC-MS can determine the types and concentration of pollutants, inform intervention strategies for cleanup, and assess the adverse impact on marine life. For instance, the use of GC-MS has provided insights into how marine microbial populations were altered and the types of hydrocarbons that still lingered 15 years after the 1991 oil spill in the Saudi Arabian Gulf coast.
GC-MS is a powerful technique for identifying and analyzing molecules. Because of this, it has been widely adopted by the petrochemical industry throughout the entire production chain–from sourcing oil fields to formulating new products and complying with environmental standards.