Targeted screening and quantitation workflows based on gas or liquid chromatography coupled with mass spectrometry (GC-MS or LC-MS) play a central role in the daily activities of analytical laboratories across a broad range of sectors, from food safety and forensic toxicology through to sports anti-doping and environmental analysis. While these workflows may differ depending on the individual application and specific analytical requirements, they are united by three common requirements. They must:
Deliver certainty in analyte identification and quantitation at ultra-low levels
Allow quick and easy method implementation and data analysis
Be reliable and robust for routine operation
Targeted quantitation workflows have traditionally been the domain of triple quadrupole (QQQ) instruments, which are capable of providing highly accurate analyses and are operationally robust. However, in recent years high-resolution accurate mass spectrometry (HRAM) approaches based on Thermo Scientific Orbitrap mas... have come to rival QQQ technologies in terms of selectivity, sensitivity, robustness and ease of use, enabling confident quantitation of targeted and non-targeted analytes in a single run. Consequently, many testing labs have deployed HRAM technology to improve cost and certainty of their analyses, as well as streamline screening and quantitation to a single step process, depending on regulatory constraints.
The exceptional resolving power of Orbitrap mass analyzer instruments
Targeted screening workflows typically involve complex samples that demand high resolution measurements for confident quantitation. Take food safety workflows as an example: high resolving power is particularly important for experiments involving food samples as solvent extracts of fruits, vegetables and other foodstuffs contain a wide range of matrix species in addition to the analytes of interest. Instrument resolving power can therefore make all the difference between detecting and not detecting analytes at low concentrations due to the masking effect of isobaric interferences.
Orbitrap mass analyzer instruments can achieve resolutions of up to 480,000 (FWHM) at m/z 200 (with the option of increasing this to up to 1,000,000 FWHM). This is far beyond the capabilities of other instrument designs such as quadrupole-time-of-flight (Q-TOF) systems. The exceptional mass resolution and sub-1 ppm mass accuracy offered by Orbitrap mass analyzer systems allows analysts to distinguish between analytes of interest and interfering ions over a wide mass range, including low molecular weight species that are often the focus of targeted quantitation workflows. High resolution is also critical for analyte confirmation based on fine isotopic structure.
Enhanced ease of use, throughput and retrospective data analysis
Quadrupole-Orbitrap mass analyzer instruments such as the Thermo Scientific Q Exactive series of mass analyzers combine the best of both worlds: the specificity of QQQ systems with the mass accuracy and resolution offered by the Orbitrap mass analyzer. Unlike QQQ-based quantitation alone, which can involve a large amount of tuning for each target analyte that must be screened for, implementing full scan HRAM methods is considerably more straightforward and requires very little in the way of optimization. What’s more, full scan approaches mean that multiple analyte workflows can be combined in a single run, saving time and boosting throughput.
This ease of use also extends to data analysis. Unlike QQQ instruments, which only collect data for compounds on predefined screening lists, full scan HRAM screening using Orbitrap mass analyzer instruments enables data collection on all compounds present in every sample. This offers quick and easy data mining, allowing users to retrospectively investigate new substances not on screening lists at the time of data collection. This capability can be extremely useful for novel psychoactive drugs of abuse substances, food safety testing, or emerging environmental contaminants, where new threats are constantly being identified.
Outstanding instrument robustness and consistent mass accuracy
Targeted screening and quantitation workflows operate day in, day out. Scan-to-scan reproducibility and instrument robustness are therefore essential for consistent and accurate data collection, especially for LC-MS applications, which are often used for multi-residue screening workflows in food safety, forensic toxicology, and environmental health applications.
Orbitrap mass analyzers have established an excellent reputation for mass stability. Once the instrument is calibrated, it maintains its exceptional analytical performance for several days within the low ppm range without the need for recalibration. Mass stability is even preserved when polarity switching is used for maximum compound coverage. This is unlike Q-TOF instruments, where the mass resolution needs seconds to recover after polarity switching, making it much less practical for LC-MS experiments.
But just how reproducible is Orbitrap mass analyzer HRAM? Well, we put the Thermo Scientific Q Exactive Focus hybrid quadrupole-Orbitrap mass spectrometer through its paces. Figure 1 shows the reproducible mass accuracy and peak area obtained for the fungal food contaminant Aflatoxin G2 in wheat matrix. These very consistent measurements, involving 900 continuous injections over a period of 120 hours without instrument recalibration, highlight the exceptional robustness of Orbitrap technology.
[caption id="attachment_20237" align="alignnone" width="979"] Click to enlarge -- Figure 1. Mass accuracy and peak area of Aflatoxin G2 in wheat matrix for 900 continuous injections without instrument recalibration.[/caption]
It’s this combination of robust scan-to-scan reproducibility, enhanced ease of use and exceptional mass accuracy and resolution that makes HRAM using Orbitrap mass analyzer technology so well suited to routine targeted screening and quantitation. But what about applications that require characterizing compounds that aren’t on target lists? Find out how Orbitrap mass analyzer technology packs a punch when it comes to characterizing unknown analytes in our next blog on non-targeted workflows.
Want to learn more about targeted quantitation using an Orbitrap mass analyzer?
To learn more about the power of Orbitrap technology for applied and research applications, check out the resources below: