Intermittent System Peak on PA 800 Plus.

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Hi All,

My employer is relatively new to CE SDS (and I am completely new to it). An issue that they are yet to get to the bottom of is an intermittent system peak. This peak has a habit of rearing its ugly head at inopportune moments and invalidating assays.

Issue details:
- Product peaks have some variation in their retention times but this peak always comes off around 16.4min.
- It can appear in any injection, even blanks.
- It does not appear in every injection on a run. It is usually just one or two.
- It only occurs in reduced samples (containing Mercaptoethanol).

Assay details:
- Samples consist of liquid mAb drug substance, ultrapure water as diluent, SDS sample buffer from a kit and Mercaptoethanol. Blanks are simply ultrapure water, SDS sample buffer and Mercaptoethanol.
- The system is a standard PA 800 Plus with vendor recommended capillary and cartridge. Cleaning reagents are HCl and NaOH.

The main theory is that it is something to do with the Mercaptoethanol. We have tried a couple of vendors and batches with no joy. The peak still appears.

Does anyone with more experience in this method (or is a better chemist than me) have any ideas where this peak may be coming from? Has anybody had a similar issue?

Thanks in advance.
It would appear that the leading theory now is that this peak is contamination from the black rubber O-rings in the lids of the vials used to prepare the samples. Apparently the Mercaptoethanol is interacting with the rubber when it comes into contact with said O-rigns during prep. (either by inverting or accidental contact).

I will confirm if this is the true root cause when a little more times had passed :)
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