Thu May 02, 2019 12:26 am by AdeebR
Mike - thanks for the suggestion regarding the Zirconium monitoring; definitely something to add to our wash QC.
Eric - I concur with Mike. We have seen instances of elevated background due to overstaining, but this tends to manifest as constant high background signal rather than a progressive increase in signal over the course of the acquistion.
David - yes, it does seem seem like certain channels are more predominantly and consistently affected. We also do generally run water for longer than 30s, so I agree that when this happens during routine operation it's due to some sort of persistence of wash solution in the system.
My current theory (disclaimer: lots of hand waving to follow) is that this may somehow be related to the tubing that connects the Helios PSI to the grounding nut. This is actually two layers of tubing - the interior fused silica line that carries the actual liquid, and the 1/16" exterior sheath tubing that pretty much serves to increase the outer diameter to accommodate the grounding port nut. Ideally, the ends of these tubes should be completely flush, the end of the fused silica tubing should mate exactly with the port in the grounding nut, and all liquid should pass directly through from the silica tubing into the grounding nut. In practice, this often does not seem to be the case - the little compression fitting at the end of the line does not seem to be sufficient to the keep the tube layers of tubing together, and the inner tubing can sometimes slide back and forth. Under these conditions, the end of the fused silica tubing may no longer flush with port in the grounding nut, and so instead of liquid going through the port, it instead goes into the void between the two layers of tubing (we can see visible evidence that this is happening by observing liquid between the lines, which really should be dry). So potentially, what could be happening is that the ends of the tubing are not well aligned with the grounding nut port, wash solution enters the space between the two tubes and is consequently not effectively flushed out when running water and therefore persists at levels sufficient to contaminate the sample.
Adeeb Rahman
Icahn School of Medicine at Mount Sinai, NYC