Tailing problem

[DeimerlyC]

I'm using an Na-exchange method. I have two instruments from different manufacturers and I am trying to transfer the methodology. I've got everything figured out save for one last nagging problem.

I've got tailing on the newer system and I'm trying to pin down its source. From what I've read I should look at the injector's rotary seal and tubing connections. I replaced all the manufacturer's tubing with 0.007" tubing from the injector to the detector and it has helped somewhat. I think I have a big unswept area but I'm not sure where to look. I'm fairly confident that the column is not at fault since it's brand-new, and my history with these columns has been very good.

My only other idea is to look for active sites in the tubing outside of the column. If this is happening I'm not sure how to fix this gremlin.

Any ideas on where best to look? Thanks in advance.

[Mark Tracy]

Double-check the fittings. At low flow rates a loose ferrule can result in an almost normal peak with a long, low tail. Also, check the detector flow cell; it may not be the optimum one for the flow rate you are using.

[DeimerlyC]

Thank you for the tips. Loose fittings, should I be looking for them outside the flow path from the injector to the detector? If so, that's a lot of extra tubing I'll need to check. I'm hoping the potential leaks is somewhere on the 6-port valve, if anywhere.

[Mark Tracy]

When I said loose, I did not mean leaky; I should have said mis-positioned. If it is a little too close to the end of the tubing, there will be a gap between the tubing and the fitting. This gap does not have to be large to cause tailing, especially at low flowrates. And yes, ferrules sometimes slip.