Chromatography Forum

Hi all
I would like to know if anyone has noted increase frequency in source cleaning on 5975 msd compared to 5973 and older machine
We have a 5975 coupled with p&t with IS area problems: the 1,4 diclorobenzene-d4 has low recoveries on blank sample compared to cv (more than 50% less area) and source cleaning solve problem.
Even if tune ratio are perfect, source is bright and seems clean. The frequency is quite inacceptable, cause we need to clean source after 7-10 days of work, sometimes less (water sample).
Generally speaking, all the precaution possible was taken: desorb time 1min, spli ratio 60:1. purge e trap line cleaned/refurbed with new one, inj maintenace performed. No leak on system.
I suspect water is main problem, and I.m going to install water trap before rough pump, but I like to know if anyone has same issue on 5975 (and also newer models)
Thank you in advance.

Yes, when I run nasty (e.g. oily) samples. It gets much worse when running methanol extracts of soils. Normally a full source cleaning isn't required, just a methanol cleaning of the repeller.
I get a 1,2- vs 1,4- dichlorobenzene recovery problem when my transfer line gets dirty. You will see a difference related to the amount of methanol added to the sample. This frequently shows up when running samples with visible product / creosote.

It has been a problem with both the 5973 and 5975. One thing I found was it is also in the purge and trap. I had to bake the moisture trap only at 180C, just enough to remove the moisture but not char any organics that might be trapped there. I had another long thread where I discussed this problem in the past and it seems that the total mass of all analytes has an affect on the late internal standard recoveries. If the internal/surrogates are spiked at least at 50ppb it helps, higher is better.

I have upgraded all of our 5973 and 5975 mass specs to the Edwards E2M2 rough pumps and they have molecular sieve moisture traps at the inlet to the rough pump to reduce moisture problems.

We have to recalibrate a few times after a source cleaning until it becomes a little dirty, then it seems to stabilize and run for months or even a year before needing cleaning again, but when first cleaned it will drift for a few weeks until a little dirt accumulates on the source.

Thank you guys for reply. Next step I will install fl20k foreline trap to reduce moisture and see if it helps.
Source cleaning after one year is like a dream
I will report test results..