Chromatography Forum

Don't know if this is a hardware problem, software, or both. We are using an Agilent 1200 HPLC interfaced with a LabLogic Model 5 radiometric detector (B-RAM) via an Agilent 35900 analog-digital converter, for analysis of 14C-labeled materials. While we've got the LabLogic Laura software installed, we are using ChemStation to control the runs and integrate the B-RAM peaks, via the ADC box. We have been getting some very strange results lately. With seemingly random samples we are getting radioactivity counts that are 2, 3, 4, or even 5 times higher than expected. In addition, the B-RAM peaks are distorted, with large "spikes", with heights that are many multiples of comparable samples, or even the same sample from a different injection. The UV peaks are consistent and well-shaped; the chromatograms from Laura show normally shaped peaks with expected and consistent counts, heights, areas. If anyone has any thoughts, I can send some pdfs of the chromatograms. Don't know how to insert an image here.

G'day,

Just a thought. If your UV and Laura looks goods, to me its a probable case of data transfer from B-RAM to your ADC/Agilent software.

What sort of wring do you have to connect B-RAM to the ADC box? Are they well insulated? Setup baseline monitor, jiggle the wires and watch for any spikes in your B-RAM baseline. Would suggest electrical interference from dodgy connections of wire insulation. Perhaps redo the actual wire connections at each end.

Do let us know how you go.

Peggsy

Peggsy - Thanks so much for the reply. We changed out the ADC box with one we knew to be working correctly and checked all wiring, but this didn't help. I had originally thought this phenomenon to be a random occurrence, but after many runs it seems to be related to the magnitude of the peak being distorted; that is, up to a certain amount of injected DPMs, everything is fine; after that, the ChemStation chromatography goes off the rails. I can take the same sample over to another system and using the same method, inject as much as I want, and the chromatography is always normal. I have tweaked every setting I can think of to tweak (even one that is suppose to be done by "...authorized personnel only...", to no avail. I'm beginning to think it's some sort of software glitch. Going to run it by the LabLogic and Agilent folks. If you think of anything else, please post. Thanks again!

Jim

Peggsy - Thanks so much for the reply. We changed out the ADC box with one we knew to be working correctly and checked all wiring, but this didn't help. I had originally thought this phenomenon to be a random occurrence, but after many runs it seems to be related to the magnitude of the peak being distorted; that is, up to a certain amount of injected DPMs, everything is fine; after that, the ChemStation chromatography goes off the rails. I can take the same sample over to another system and using the same method, inject as much as I want, and the chromatography is always normal. I have tweaked every setting I can think of to tweak (even one that is suppose to be done by "...authorized personnel only...", to no avail. I'm beginning to think it's some sort of software glitch. Going to run it by the LabLogic and Agilent folks. If you think of anything else, please post. Thanks again!

Jim

Not sure if you have scintillation detector. But if so - this may e PMT high-voltage problem. Larger the peak - the bigger PMT current. This my leak to electric breakdown.

Antonk - Thanks! That's an interesting possibility. Not sure if those B-RAM detectors have a PMT, but I'll definitely check into it.