Authors

C Tayler¹; 
¹ GSK, UK

Discussion

An investigation into the effects of matrix dependent ion suppression across two MS-based screening platforms, the Agilent RapidFire and Sciex Echo® MS, was undertaken. RapidFire utilises on-line solid phase extraction (SPE) to provide efficient sample clean-up prior to MS injection, whereas the Echo® MS uses acoustic droplet ejection (ADE)-open port interface (OPI) technology to deliver nL droplets into the MS.

To simulate screening applications, MS response of two analytes of interest, acetylcholine and choline, were monitored on both platforms against 23 commonly used screening assay buffer components, with water as a control. For identification of ion suppression effects at typical buffer concentrations, aliquots of each were added to a known concentration of choline/acetylcholine 1:1 before reading on both platforms in parallel. Sensitivity experiments were subsequently conducted against the top five significantly suppressive buffer components. Here, serial dilutions of choline/acetylcholine were spiked into constant concentrations of assay buffer. Finally, serial dilutions of three suppressive components were prepared and spiked into a constant concentration of choline/acetylcholine to assess the impact of buffer concentration on limit of detection.

Results agreed with the widely accepted conclusion that ion suppression is analyte, matrix and instrument dependent. It was also discovered that most of the commonly utilised assay buffer components do cause significant ion suppression to varying degrees. This highlights the need to factor ion suppression studies into future assay development experiments. Furthermore, it was observed in this study that the Echo MS system is not immune to ion suppression, despite the significantly reduced sample volume.