Wyatt RI & LS detetor woes
Posted: Tue Jan 17, 2012 4:11 pm
Hi forum,
I came here because Wyatt (while an excellent resource!) has a slow turnover time for my feedback needs. I am the new instrument manager for our previously underused SEC system which utilizes an Agilent 1100 degasser/isocratic pump, Wyatt Dawn HELEOS II LS detector, and Wyatt OptilabREX RI detector. We are using columns from the American Polymer Standard (guard column, 100A, and 500A). Let's just say, since I've taking over the role, the instrument has picked up in popularity -- lucky me! I'll do my best to outline the turn of events.
(1) Originally, the system ran in HPLC grade THF (1.0 ml/min 25C) which seemed to work fine. I attempted to switch the system over to DMF (0.8 ml/min 25C) following Wyatt's manual. Upon injection of an Aldrich 31600 Da polystyrene standard, I observe no RI signal (fuzzy baseline) and a single sharp peak in the LS. Injection of a blank shows no signal.
(2) Not knowing if it was a hardware problem, I had the entire Wyatt portion serviced and repaired. The columns were new at the time as well. And the Agilent portion was serviced. So we're confident there are no hardware issues.
(3) Received the Wyatt portion back this month. Tried doing some injections of polysytrene and other user samples -- we have RI signal! However, the large peak we observed before in LS still appears at the same retention time for all injections. This peak does not appear in a blank.
(4) Switched over the system to THF and try to inject another PS standard -- we lose RI signal again (baseline is positive voltage), and the spike in LS is there again, same retention time. We switched out the column for THF so it's gotta be something to do with the solvent change in the detectors.... right?
What do you think is going on?
How can we get RI signal back consistently?
What is the proper technique for changing solvents?
What is that LS peak that always shows up whenever any sample is injected, but not the blank?
How do we clean up baseline noise, and make sure the baseline is zero?
Thanks for your help. This is sort of the main problem in a nut shell, but once I start getting feedback I can dive more into the details. Thanks!
I came here because Wyatt (while an excellent resource!) has a slow turnover time for my feedback needs. I am the new instrument manager for our previously underused SEC system which utilizes an Agilent 1100 degasser/isocratic pump, Wyatt Dawn HELEOS II LS detector, and Wyatt OptilabREX RI detector. We are using columns from the American Polymer Standard (guard column, 100A, and 500A). Let's just say, since I've taking over the role, the instrument has picked up in popularity -- lucky me! I'll do my best to outline the turn of events.
(1) Originally, the system ran in HPLC grade THF (1.0 ml/min 25C) which seemed to work fine. I attempted to switch the system over to DMF (0.8 ml/min 25C) following Wyatt's manual. Upon injection of an Aldrich 31600 Da polystyrene standard, I observe no RI signal (fuzzy baseline) and a single sharp peak in the LS. Injection of a blank shows no signal.
(2) Not knowing if it was a hardware problem, I had the entire Wyatt portion serviced and repaired. The columns were new at the time as well. And the Agilent portion was serviced. So we're confident there are no hardware issues.
(3) Received the Wyatt portion back this month. Tried doing some injections of polysytrene and other user samples -- we have RI signal! However, the large peak we observed before in LS still appears at the same retention time for all injections. This peak does not appear in a blank.
(4) Switched over the system to THF and try to inject another PS standard -- we lose RI signal again (baseline is positive voltage), and the spike in LS is there again, same retention time. We switched out the column for THF so it's gotta be something to do with the solvent change in the detectors.... right?
What do you think is going on?
How can we get RI signal back consistently?
What is the proper technique for changing solvents?
What is that LS peak that always shows up whenever any sample is injected, but not the blank?
How do we clean up baseline noise, and make sure the baseline is zero?
Thanks for your help. This is sort of the main problem in a nut shell, but once I start getting feedback I can dive more into the details. Thanks!