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Experts Aaron Stella and Jacob McCabe from SCIEX answer 6 burning questions from customers about the Echo® MS system.
What applications are best suited for the Echo MS system and why?
Jacob: The Echo MS system is an acoustic ejection inlet with a triple quadrupole mass spectrometer detector. It is most suited for high-throughput screening where you’re monitoring the same multiple reaction monitoring (MRM) transition across the entire plate—for instance, if you’re looking at the conversion of substrate to the product in an enzymatic reaction in the presence of a drug target.
Aaron: The Echo MS system is best suited for high-throughput screening of various drug discovery assays in clean, neat solutions. The system is at its best when analyzing compounds in solutions containing mixtures of water, methanol and acetonitrile. Additionally, if buffers are needed for a conventional LC-MS experiment, ion suppression is likely to occur. The small ejection volume used by the Echo MS system helps counter this analytical challenge.
The Echo MS system can perform MRM scans, which increase an assay’s specificity. Although the platform will not separate isobaric species, it will detect the presence of compounds with specific MRM transitions, thus alerting the user about the presence of particular compounds in a sample—and it can do this at a rate of about 1 second per sample. Users can expect to build screening assays with high negative predictive values, which are ideal when performing screening tests.
For synthetic biology, how can the Echo MS system help me build a library?
Aaron: Users can place a unique solution of their pure compound in each individual well of an Echo MS system well plate and then infuse it with the acoustic ejector. An MS product ion scan and an MRM scan can be performed for each individual well. The user can also choose to ramp different voltages across each of the scans for method optimization.
For complex samples, it is common to use an LC separation before the mass spectrometer. The Echo MS system doesn’t have this separation prior to detection. Can it handle complex samples?
Jacob: The Echo MS system is not a complete substitute for LC-MS analysis. The Echo MS system allows for high-throughput results to help you make informed decisions rapidly. Subsequent LC-MS runs can be done to confirm hits as needed, but with a fewer number of runs needed.
Aaron: We have found that if the compound of interest is in high enough concentration, and is easily ionized, then the Echo MS system will be able to detect the compound in a complex matrix. However, this practice has caused unstable mobile phase flows. Therefore, I do not recommend using the Echo MS system for complex samples. If complex matrices need to be analyzed via the Echo MS system, I strongly recommend performing sample preparation prior to the analysis.
Is the Echo MS system quantitative?
Jacob: Yes! The Echo MS system allows the same quantitative workflows that are typically done on the SCIEX Triple Quad 6500+ system, but with less sample volume. The Echo MS system also allows for multiple droplets to be ejected over a linear range, which helps with additional sensitivity when samples have a low concentration—for example, if 4x the sensitivity is needed, we can eject the sample 4 times, changing the ejection volume from 2.5 nL to 10 nL.
How does the Echo MS system complete a contactless sample injection?
Aaron: Since the sample introduction takes place without contact, we refer to the sample introduction on the Echo MS system as an “ejection.” The acoustic ejector positions itself underneath the well to be ejected and sends acoustic energy upwards into the sample well. The result is a 2.5 nL-sized droplet (or multiple 2.5 nL-sized droplets if the user wishes to eject more sample) that gets ejected from the solution in the well up into the transfer line where the droplets are then carried to the mass spectrometer source by the carrier solvent (that is, mobile phase). This process is driven by the Venturi effect and requires the source gas 1 to be constantly run at 90 psi.
I have a low sample concentration. How would the Echo MS system cope with this? Or how would the Echo MS system cope if my samples were in complex matrices?
Jacob: Depending on the nature of the compound, the matrix containing the compound and how much sample is ejected, it is possible to detect concentrations in the single-digit ng/mL range with the Echo MS system. The best scenario for detecting low levels of compounds would be analyzing a compound that ionizes well with electrospray ionization (ESI) and is in a solution containing water and either methanol or acetonitrile. The user could reliably eject up to a total amount of about 200 nL to get the best signal. If the samples are in a complex matrix, I would recommend sample preparation. Derivatization may also be an option if the compound of interest does not ionize well with ESI.
Our experts
Jacob W. McCabe is a senior scientist at SCIEX specializing in the Echo® MS system. He is responsible for interacting with customers, providing technical support, running customer demonstrations, generating application notes and presenting on this innovative technology. He holds a bachelor’s degree in chemistry from Baylor University and a doctorate from Texas A&M University in analytical chemistry, studying under David Russell. He started his career as an R&D scientist at MOBILion Systems, Inc., outside of Philadelphia, PA. In his spare time, Jacob is a trombone player and enjoys spending time playing video games, watching motorsport racing and hanging out with his cat, dog and family.
Aaron Stella has been working for SCIEX for 6 years on the LC-MS Chemistries and Consumables R&D team. He specializes in developing sample preparation methods, LC methods, acoustic ejection methods and targeted mass spectrometry methods, particularly for drugs of abuse testing and other small molecule testing. Prior to working for SCIEX, he was an LC-MS/MS Technical Specialist for the Mayo Clinic: Mayo Medical Laboratories New England in Andover, MA. He currently teaches analytical chemistry to undergraduate and graduate students at the University of Massachusetts Lowell as an adjunct professor. Aaron earned a bachelor of science degree in medical technology, a master of science degree in clinical laboratory science and a doctorate in biomedical engineering and biotechnology, all from the University of Massachusetts Lowell.
