Unlocking the power of DESI with IMS on the SYNAPT XS

DESI XS

Some ionization techniques involve significant sample preparation, taking valuable time away from scientific researchers. Desorption electrospray ionization (DESI) was developed by Graham Cooks’ group at Purdue University in 2004 as a mass spectrometry (MS) ionization method that does not require the sample to be inside of a vacuum. Ambient techniques such as DESI allow complex systems to be analyzed without significant sample preparation, and at high throughputs. [2]

Since its inception, the technique has further evolved to improve reproducibility. An example of this is the development of a new sprayer for DESI through a collaboration between Waters and academic scientists, which facilitated a jump in sensitivity. This allowed DESI MS imaging experiments to be run at an improved spatial resolution of 20-100 micron pixel size. [3]

By enhancing control of the sprayer’s geometry, the speed of acquisition was significantly increased, which is understandably a desirable analytical benefit. However, it is only by matching different ionization and separation techniques as required by the needs of the application that we can fully appreciate the power of the latest state-of-the-art imaging methods and how they can be used to drive pioneering research forward.

Read on to discover how combining the latest MS imaging technology with advanced separation and ionization techniques is opening up new possibilities for the research of tomorrow.

Combining the strengths of different techniques into one workflow

When the samples under investigation are highly complex, it is often beneficial to integrate multiple techniques into one workflow. For MS imaging experiments, in which an array of mass spectra are linked to coordinates on the surface of the sample, traditional techniques such as LC-MS are not suitable, as they can lose vital spatial information.

SYNAPT XS

Both MALDI and DESI can offer significant advantages. MALDI works on molecules of a wide mass range and does not remove the localization aspect of the experiment. However, sample preparation for MALDI can take anywhere from a few minutes to a few hours, depending on the nature of the sample. As DESI removes the necessity for this step, it can often be simpler to integrate it into a more complicated workflow.

For example, prior to ionization, thin layer chromatography (TLC) can be used to help separate complex mixtures. By combining TLC with DESI, a highly complex sample can become easier to analyze, without significantly affecting the timescale of the experiment.

In cases where the mixture of compounds under investigation is too complex for TLC alone, ion mobility spectrometry (IMS)  can add an additional dimension of resolution, increasing confidence in results by rapidly separating out isomers and isobars in the same timeframe as the experiment. As such, by performing TLC and subsequently interfacing DESI/IMS/MS into a workflow, scientists can obtain a more complete picture of their sample, speeding data analysis and ensuring that any conclusions drawn will withstand scrutiny.

It is clear that it is essential for researchers to have the flexibility to combine different techniques as necessary, and it is for this reason that we designed the SYNAPT XS, our high resolution IMS-MS instrument, to be compatible with both DESI and MALDI.

A pioneering method for plant ecdysteroid characterization

A study recently explored the advantages of hyphenating different techniques into a single workflow in order to obtain conclusive information on the nature of a complex sample. Claude et al., used high performance TLC in combination with time-of-flight (ToF) MS and IMS on the SYNAPT XS instrument to study the ecdysteroids, or insect moulting hormones, present in a variety of plant extracts. Through DESI, these polar polyhydroxylated steroids were separated on the silica gel of the high-performance thin layer chromatography (HPTLC) plate, allowing for subsequent MS imaging. By incorporating IMS into the workflow, scientists obtained additional data on drift times that enabled more confident identification.

Altogether, preliminary investigations indicate that the use of TLC followed by DESI/IMS/MS is highly effective for screening plant extracts, avoiding the need to remove the stationary phase and subsequent extraction. This is because with DESI, the sample could be analyzed directly from the TLC plate.

DESI XS

The use of DESI also conveniently avoided the additional sample preparation that would have been required for MALDI-MS imaging, and DESI-MS imaging was shown to produce richer images than those obtained using UV data. This helped the scientists to identify specific fingerprints for the plant samples investigated, and indicated the prevalence of contaminants. IMS brought an additional, orthogonal dimension to the overall separation, enabling co-migrating and isobaric compounds to be accurately resolved.

Through the use of these techniques in sync, researchers were able to conveniently detect and characterize a range of ecdysteroids in extracts of S. otitis, S nutans, S. maritime, S. viridiflora and S. fimbriata. Consequently, this intriguing study highlights the immense potential for this workflow to help researchers obtain a more complete picture of all molecules present in a variety of complex mixtures – from plant extracts to chemical samples.

The importance of flexibility

To extract all possible information from a complex sample, it is sometimes necessary to combine the power of different techniques into a single workflow incorporating the benefits of each. This must ideally be accomplished in a timely manner, to prevent lengthening project timelines. As such, it is vital that researchers have the flexibility to customize their workflows as needed, and that their instruments are compatible with a range of technologies.

The latest IMS-MS instruments were designed with this in mind. Learn more about the SYNAPT XS here.

Further reading

  1. Siuzdak, G. (2004). An Introduction to Mass Spectrometry Ionization: An Excerpt from The Expanding Role of Mass Spectrometry in Biotechnology, 2nd ed.; MCC Press: San Diego, 2005. JALA: Journal of the Association for Laboratory Automation9(2), 50–63. https://doi.org/10.1016/j.jala.2004.01.004
  2. Zoltán TAKÁTS, JUSTIN M. WISEMAN, BOGDAN GOLOGAN, R. GRAHAM COOKS (2004) Mass Spectrometry Sampling Under Ambient Conditions with Desorption Electrospray Ionization Vol. 306, Issue 5695, pp. 471-473. DOI: 10.1126/science.1104404
  3. Tillner, J., Wu, V., Jones, E.A. et al. Faster, More Reproducible DESI-MS for Biological Tissue Imaging. J. Am. Soc. Mass Spectrom. 28, 2090–2098 (2017). https://doi.org/10.1007/s13361-017-1714-z