Authors

A Burton¹; C Tayler¹; 
¹ GSK, UK

Discussion

The Echo MS couples acoustic ejection sampling to a triple quadrupole mass spectrometer via an open port interface. The aim of this study was to redeploy a biochemical assay to detect acetylcholinesterase (AChE) inhibition activity onto the Echo MS. This study included method development and validation of the on the system and a comparison with data previously generated on a RapidFire MS (RFMS). Assessing the inhibition of AChE is important as irreversible inhibitors cause significant adverse effects including death. The Echo MS was successfully optimised with a significant sensitivity improvement compared to RFMS. The conditions obtained low limits of detection for both analytes (Acetylcholine and Choline), ~7nM, which provided a significant sensitivity improvement on the RFMS detection limit of ~1µM. To allow for correct % conversion to be obtained, a scaling factor was determined to compensate for the different ionisation efficiencies of the analytes. An enzyme titration and Km experiment were then performed to confirm suitable final assay conditions for the biochemical assay. Validation plates and subsequent routine screening provided an average Z’ of 0.68 and clear IC50 curves for standards. Overall, the Echo MS brought significant improvements to the assay. Echo MS had much faster plate reading speeds of around 10 mins compared to the RFMS time of ~90 minutes (including washes) and the issue of carryover was completely removed due to the acoustic ejection sampling. Future development of other biochemical assays will be undertaken to establish the Echo MS as a new capability for label-free mass spectrometry-based screening.