Futuristic MS methods found feasible for forensics, pharma and food

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  • Published: Dec 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Laboratory Informatics / Chemometrics & Informatics
thumbnail image: Futuristic MS methods found feasible for forensics, pharma and food

Data revolution

Mass spectroscopy, particularly in the form of LC/MS or GC/MS, is a ubiquitous tool in analysis. It is particularly useful in proving the identity of compounds, including those in complex matrices like biological samples or foodstuffs. However, traditional MS sources, such as electron ionisation (EI) and chemical ionisation (CI), may not be sensitive enough to detect trace levels of compounds. For forensic scientists looking for tiny amounts of illegal drugs, medical researchers looking for low levels of biomarkers or food scientists looking for minute pesticide residues, lower limits of detection are key.

Newer, more sensitive variants of mass spectrometry have been developed in recent years. One is the surface-activated chemical ionisation/electrospray ionisation (SACI-ESI MS) method, which is a highly sensitive technique, particularly suitable for detecting low molecular weight compounds. Tandem mass spectrometry (MS/MS), with its different, distinct selection steps, is a useful modern method that can be used in conjunction with an SACI-ESI source.

Although new methods are more sensitive, the resulting fragmentation patterns are no longer compatible with conventional databases, which are often based on EI results. A new platform to compare output data, named SANIST (short for Surface Activated Chemical Ionization-Electrospray-National Institute of Standards and Technology Bayesian model database search), has recently been developed for SACI-ESI MS.

Use of SACI-ESI and SANIST for detection of trace compounds

The researchers from Italy, Peru and Switzerland set out to demonstrate that the SANIST system could match low levels of compounds in biological samples against standards according to EU regulations. Three types of samples were examined:

  1. Urine samples spiked with 11-nor-9-carboxytetrahydrocannabinol (a metabolite of THC, used in forensics to detect cannabis use).
  2. Serum samples spiked with the pharmaceutical tacrolimus (an immunosuppressant drug).
  3. Grapefruit juice samples spiked with the herbicide glyphosate.

In all three cases, 50 out of 100 samples were spiked at the low level of 1 ng/ml. In the case of the THC metabolite, such a level may be present many days after smoking cannabis (worrying for some). Levels of immunosuppressant drugs must be maintained in transplant patients, so the measurement of these in blood is important. Pesticide residues in food and drinks have long been a cause of concern; modern analytical methods mean that very low levels can be detected.

The samples were separated by LC and the analytes detected using SACI-ESI and tandem mass spectrometry under collision induced dissociation (CID) conditions with multiple reaction monitoring (MRM). The data was collected using the SANIST data elaboration platform. SANIST uses its own closed-source algorithm to compare spectra.

SANIST platform meets EU directive on compound identification

The researchers found that the system correctly identified the compounds in all the spiked samples, without giving any false positive results, thus demonstrating the sensitivity of the method. As required by the EU directive, fragments from different parts of each molecule were identified (this reduces the likelihood of error). Clear parent ions were noted, as mandated by the regulations. These regulations also require that the signal-to-noise ratio for each fragment should be >3:1 and the software was adjusted to reject fragments that failed to meet this limit.

The authors concluded that the SANIST system meets all the requirements of EU regulations. It is suitable for use in regulated sectors, such as forensics and the food industry. In the future, the authors intend to investigate its use on metabolites where interference from other compounds is common.

Related Links

J. Mass Spectrom. 2016, 2016, Early View Paper. Christoni et al. SANIST: Optimization of a technology for compound identification based on the European Union directive with applications in forensic, pharmaceutical and food analyses.

Rapid Comms Mass Spectrom., 2015, 29, 1703-1710. Albini et al. SANIST: a rapid mass spectrometric SACI/ESI data acquisition and elaboration platform for verifying potential candidate biomarkers.

Wikipedia, Tandem Mass Spectrometry

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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