High-resolution mass spectrometry

What is HRMS and how does it work?

HRMS is an analytical technique that is used to determine the atomic masses of organic and inorganic molecules or monatomic ions present in different kinds of samples. High resolutions can be achieved through a variety of different mass spectrometers, yet the fundamental workings are similar.

HRMS analysis begins by passing a sample into the spectrometer, where it is ionized. The formed ions will travel along the spectrometer's length, separated by their relative charges and masses. Once the ions reach the end of the spectrometer, they are picked up by a detector, and the information is logged on a computer.

For every ionic species that passes through the mass spectrometer, a ratio of charge-to-mass is recorded, usually to four to six decimal places. This can be compared to theoretical values for the exact masses of different chemical species to determine which atoms and/or isotopes each detected ion contains.

What is HRMS used for?

HRMS is a technique that is used across a variety of fields due to its accuracy and ability to discern the presence of multiple chemical species, even at very low concentrations. It is used primarily for the detection and identification of these species. As such, it finds use across a wide range of sample types, from very small organic and inorganic compounds to much larger biomolecules and materials.

HRMS is very useful when it comes to identifying unknown compounds. This is because the results are far more accurate and precise when compared with a lower-resolution setup. HRMS can also be used for isotope analysis, as it can accurately show the differences in masses caused by the presence of different isotopes. The IRMS method is a more popular choice for isotope analysis, however.

LC-HRMS & additional applications

HRMS can be combined with liquid chromatography for LC-HRMS analysis, which enables the identification and quantification of various analytes with very high sensitivity. Examples include restricted biocides, such as isothiazolinones, which must not be present in certain product groups in concentrations above those defined in EU legislation. Other substances quantifiable with LC-HRMS in trace amounts include PFAS compounds and isocyanates.

What is the difference between HRMS and mass spectrometry?

The key difference between HRMS and standard mass spectrometry is the significantly increased resolution that HRMS offers. Here, the resolution describes the difference one would see between two peaks on a set of mass spectrum data. Essentially, the higher the resolution that a mass spectrometer can provide, the better it will be able to distinguish between different chemical species, even when they have very similar masses.

For example, two compounds may have different elemental makeups, yet very similar relative masses. With lower-resolution mass spectrometry, these would be indistinguishable, making it much more difficult to resolve what is present in a sample. HRMS, on the other hand, would be able to demonstrate the extremely slight difference in masses due to the different elemental makeups, making it far more suitable for distinguishing between the two compounds.

What are the limitations of HRMS?

In theory, every chemical component has a specific mass which, when properly resolved, can be determined through HRMS. This means that as a technique it is ideal for determining the elemental and isotopic makeup of a species or fragment present in the sample.

The main limitation, however, is that HRMS generally cannot determine the difference between geometric isomers of organic molecules with the same mass. While some samples will break into smaller fragments during ionization, and this will provide clues to the geometric layout of the molecule, it will not provide an exact answer in the same way that some more suitable techniques would. In such cases, HPLC-MS or NMR spectroscopy may be preferable analysis methods.

Sample requirements and preparation

HRMS can be used to analyze a wide range of different types of samples, which means that the preparation requirements depend on the sample and instrumentation. Depending on the setup, the sample may need to be dissolved in a solvent before ionization, though this is not always necessary. Regardless, only a very small amount of sample is generally required for HRMS measurements.

Looking for an HRMS analysis?

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