By Dave Ellis on Thursday, March 16, 2000 - 06:51 am:
Hi folks. We have an interesting problem. It's a normal phase separation (silica column, 78:21.5:0.5 iso-octane:dioxan:acetonitrile). The flow is initially 2ml/min but is increased to 3ml/min, held and then lowered back to 2ml/min.
The method can be run on an Waters Alliance 2690 for so long before we have intermittent problems.
Basically, if we attempt to use the in-line degasser we get a massive, broad off-(upper) scale deflection during the flow gradient. The intermittent problem involves poor baselines comprising small "spikes". These can occur at any time during the separation and may (or may not!) continue into subsequent injections. We have been doing a variety of troubleshooting investigations that have removed some possibilities. We would welcome some input - someone out there may have a new lead for us. Many thanks in advance for any help.
Dave Ellis
By hinsbarlab on Thursday, March 16, 2000 - 08:34 am:
I'm not familiar with the Alliance 2690, but we had a similar problem with an HP 1100 system. We found that we could not use the in-line vacuum degasser with a flow gradient. As the flow was increased, the mobile phase spent less time in the degasser, was degassed less, and the absorbance increased. To get around this we switched to an isocratic flow method since flow programming really doesn't do much for the separation anyway.
Hope this helps.
Best Regards,
Michael Hinsberg
http://www.hinsbarlabs.com
By Anonymous on Thursday, March 16, 2000 - 11:49 am:
Your problem is almost certainly due to inadequate or variable degassing of the mobile phase. I believe the problem is called quenching. It probably is exaggerated at the lower wavelengths.
By Anonymous on Thursday, March 16, 2000 - 11:49 am:
if the flow is less degassed at higher flow you method will not be very robust. why not use an extra degaasiing (nitrogen, ultrasoon filtration, off-line vacuum filtration). if the inadequate degassing is the problem, this will solve it.
By Bill on Monday, April 10, 2000 - 07:49 am:
If you are premixing your mobile phase (i.e., not mixing in the pump) you could try splitting the mobile phase into two (or even three) bottles and "mixing" 50%/50% (or 33%/33%/34%) through two (or three) channels of the in-line degasser. That way you double (or triple) the efficiency of the degassing process.
By Anonymous on Friday, April 28, 2000 - 08:40 pm:
Try using your degasser in continuous mode.
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