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Mass Spectrometry in Trace Organic Analysis

Mass spectrometry is broadly used in analytical applications but does have some drawbacks

Aimee O’Driscoll

Trace organics are contaminants that exist in very low levels in a sample. Depending on the situation, these may be natural products, such as plant metabolites or hormones, or synthetic chemicals, such as pesticides or industrial pollutants. They can be difficult to detect, but their analysis is important in a variety of fields.  For example, some trace organics are toxic to humans while others can harm aquatic life or contribute to the formation of smog. As a result, monitoring of trace organics is carried out in areas such as food safety, drinking water monitoring, and wastewater management.

Trace organics can be analyzed using a variety of combinative techniques, including chromatography and mass spectrometry. These enable scientists to identify and quantify the different compounds present in a sample. Mass spectrometers are often used to identify and analyze trace organics because of their ability to detect very small amounts of material. This is particularly useful in areas such as human and environmental health. Of note, many countries around the world have signed or accepted the Stockholm Convention on Persistent Organic Pollutants (POPs), an environmental treaty that aims to restrict or eliminate the use and production of POPs. These include pesticides and insecticides such as aldrin, chlordecone, and lindane, and solvents including hexachlorobenzene and Polychlorinated biphenyls, among other chemicals.

While mass spectrometry is very well-suited for trace organic analysis, the technique doesn’t come without its challenges.

How mass spectrometers work

A mass spectrometer uses electric and magnetic fields to identify and analyze molecules based on their mass-to-charge ratio. These machines consist of three main components: an ionization source, a mass analyzer, and an ion detection system.

The ionization source is used to convert molecules into gas-phase ions. In this state, they can be moved and manipulated by electric and magnetic fields. One of the most common methods is electrospray ionization, in which high voltage is applied to a liquid sample to create an aerosol.

This information is critical for understanding the potential health hazards posed by these contaminants.

The mass analyzer is the component that separates the ions based on their charge-to-mass ratios. There are various types of mass analyzers, but one of the most common is the quadrupole mass analyzer, which consists of four parallel cylindrical rods. An electric field is applied within the analyzer, causing ions in the sample to oscillate as they travel through the field. The frequency of the oscillation is determined by the mass of the ion. The higher the mass of the ion, the lower the frequency of its oscillation.

The current of mass-separated ions must then be converted into a measurable signal by an ion detection system. This system measures the frequency of the oscillations and produces a corresponding mass spectrum. This chart shows the mass-to-charge ratio of ions against their relative abundance. By analyzing the signals on the mass spectrum, scientists can determine the masses of the ions in the sample.

The benefits and challenges of mass spectrometry

Mass spectrometry has numerous advantages over other methods of analysis. It is highly sensitive, so even very small amounts of a compound can be detected. This is especially useful in trace organic analysis, where contaminants are present in minute concentrations.

Additionally, since the technique is both qualitative and quantitative, it can be used to determine the structure and identity of unknown trace organic compounds, as well as their concentrations in samples. This information is critical for understanding the potential health hazards posed by these contaminants.

Another advantage of mass spectrometry is that it can be used in combination with other techniques. For example, various types of chromatography such as gas chromatography or high-performance liquid chromatography may be used to separate samples before running the eluted compounds through a mass spectrometer.

While mass spectrometry is a powerful tool, it does have some limitations. For example, because the technique relies on mass-to-charge ratio, it can be difficult to distinguish between similar ions, particularly optical or geometric isomers.

Applications for mass spectrometry in trace analysis

Due to the health and environmental concerns resulting from trace organics, mass spectrometry can play a vital role in various fields.

This technique is often used in environmental analysis to detect and quantify trace levels of pollutants such as pesticides and solvents in water and soil samples. This information can then be used to assess the risks posed by these pollutants and develop strategies for mitigating their impact on the environment.

Food safety is another field in which mass spectrometry can be used to detect trace organics. It can be leveraged to monitor levels of insecticides, hormones, veterinary drugs, and other contaminants in various types of food products.

Mass spectrometry can also be used in forensic applications. For example, trace levels of drugs or other chemicals present in a person’s body or possessions can be analyzed using this technique. This information can be used for various purposes, including identifying criminal activity and persons of interest or determining causes of illness or death. It may even be used as evidence in solving and prosecuting crimes.

Mass spectrometry is a sensitive and versatile tool often used to identify and quantify trace levels of organics. It’s broadly used in trace organic analysis in a variety of fields, including environmental analysis, food safety testing, and forensics. As the technology continues to evolve, the applications of mass spectrometry are likely to become even more diverse.