Chromatography Forum

Hey guys, trying to fix a bad baseline for Perchlorate on an Metrohm IC733 and I would appreciate any ideas. I've replaced most of the parts on the machine and can't figure out how to silence the baseline. I even tried connecting a Dionex CRD 200, which dropped the baseline by quite a bit but made the baseline jitter worse (super promising idea - wish it had worked, still planning to play with it more). We are using a 0.7mL/min flow, pressure is 1.4MPa. Eluent is 5mM 4-cyanophenol 12mM LiOh, which making inside the lab looks better then the eluent sold by metrohm and gives an approximate ~200mV higher baseline. The only part I can think of to change now is the pulse dampener, which works just fine for 300.1, but might not be good enough for Perchlorate. I tried chaining an extra pulse dampened into the mix and it didn't help and seemed to make things worse. Using a Metrosep Dual 4 -100 Column w/ Precolumn kit. Were also using a 1000uL loop. The Precolums make the method not even economical to run but we need to provide this testing for customers. Help? Everything looks GREAT for 300.1 with Standard Application but terrible when I run perchlorate. I've already thrown 2 x $2500, 4-5 GaurdColumn which need to be replaced WAY too often considering they cost about ~$400 each. And 3weeks plus. Your help is appreciated.

Thank you in advance

Dear aovaici

Please contact your Metrohm service person and send the raw data files to me (lae@metrohm.com).
On the first glance I do not expect the pulse dampner to be the problem, as the fluctuations are not related to pumpe frequecy.
See also newer perchlorate applications like AN-S-346

Markus, I've talked to support, they're really nice people but they haven't seemed to be able to help. Also I looked at the application note and it seemed that they mention two different columns in the method. Is this a type? They talk about the ASup7 250 in the initial write up then the ASup7 150 in the rest. Also I will email you the raw files in a bit.

Thanks,
Aovaici

Also 1.2ppb is too high Were aiming for 0.5ppb