Chromatography Forum

I tried to reply to my earlier post but it appears to be locked. I hope this is a function of time since I've been working on my problem.

I've replaced every bit of tubing and connection from the injector to the detector and I'm running out of places where there could be a loose ferrule/connection. I doubt that it's my column since it was brand new when I put it on, and my instrument hasn't yet been validated.

I'm using an sodium-exchange method. Could my tailing be coming from a hang-up in the system???

Dear DeimerlyC:

I just looked at your previous post, at:
http://www.sepsci.com/chromforum/viewto ... highlight=
To avoid problem due to fittings, please use the one-piece universal fitting (cost more than two-piece, but you don't have to look for lost ferrule!). May be just replace them all!

As for tubing, you stated that it is 0.007'' ID. That is good. But make sure that you have cross-cut tubing! And push the tubing into the column's ends very tight before tightening the fitting (else you have a mini mixing chamber ->tailing).

One last thing I can think of (because this is a method transfer): check the detector's sampling rate, and/or detector time constant. Increase sampling rate (eg. 10 Hz), and reduce the time constant (eg. 0.5s). A very high time constant may give an apparent peak tail.

Good luck.

Alfred

Also, swap a good/known/trusted column for this 'new' column, and check for tailing!

Alfred

OK, here's where I'm at.

I took the column out of my new unvalidated machine and put it into my old trusty one. The column gives standard exceptional performance in the older one.

Using the new data point values, it seems that my tailing has been reduced quite a bit. My next problem is resolution. I am using the same buffers on both instruments and identical columns. My newer one is producing much smaller plate counts and the resolution is poor.

I know I can go through changing mobile phases, run conditions, blah blah and sorts, but much of what I am doing is pretty standard Moore/Stein stuff. While I have replaced all my tubing, there has got to be a place somewhere I've missed where there is a hang-up. I've got a call in to get the rotorseal exchanged out.

Anything I can do chemically to the system to make sure I don't have some odd passive retention?

Dear DeimerlyC:

Pls change at least the response time, to a lower value.

You did not describe the 'new' system. Is it a like-for-like system, or a completely different system? Can you change the sampling rate on it?

There is an excellent picture on p 143 of a book titled "Pitfalls and Errors of HPLC in Pictures" by Veronika Meyer (ISBN 978-3-527-31372-3). Look at that, and you will see the lag of the detector's response may cause apparent peak tailing. (Perhaps V Meyer can quote her book in this thread?)

Here is another article: "Effect of detector response time on the distortion of spectral peaks of Gaussian shape" and the link is below:
http://www.iop.org/EJ/abstract/0022-3735/1/12/305

Good luck in troubleshooting

Alfred

You misunderstood me; I did change it and it helped, thanks.

It's a similar system with a few plumbing differences.

I can't see the picture because I'm not a subscriber, but I appreciate you taking the time to find it, thanks.