Once a method has been developed, and good, consistent peak shapes have been obtained for an assay, the Echo® MS system is generally quite consistent. If peak quality deteriorates, consider the following points:
- The viscosity of the sample can affect the peak shape and cause broadening of the peaks. If your matrix does broaden your peak, decrease the sampling rate in the acoustic ejection method to ensure baseline separation between samples. Also, it is important to ensure that samples and standards are in in the same matrix for consistent peak shape across an analysis.
- Broadening of peaks can also be a result of interactions with the PEEKSil tubing material used in the electrode. If this is observed, you may need to adjust the mobile phase composition and/or add a delay time in between ejections to get back to baseline resolution.
If you see a previously smooth peak become jagged, look at the spray pattern using a small flashlight. If it is flickering, it could indicate plugging of the electrode. Remove the electrode assembly and view it under a magnifying glass. If precipitate is observed on the MS end of the electrode, it can affect the aspiration of the carrier solvent, which can in turn affect the carrier flow and vortex. Remove and clean the electrode in water (most likely to dissolve an organic insoluble precipitate). To clean the electrode, connect it to a high-flow LC pump, if available, for 10–15 minutes; otherwise, soak it in water for 30 minutes. This is more often needed when running high salt or plasma samples. For more information on maximizing the lifetime of the source electrode, please see this post.