Chromatography Forum

Hi all
Recently when i clean my gc-ms ion source (according to agilent recommondation), the color of cotton swab (impregnated with alumina slurry) remains black even after 1 hour polishing. During the cleaning, i change cotton swab (more than 10) but the color of last swab is also changed to black after polishing.

All parts of ion source are clean visually.
I clean my ion source twic a month and I can't underestand where the problem comes from.

Any help would e appreciated.

The black is not dirt it is metal.

Peter

Peter is correct, the swabs will never stay clean.
Just give every metal part a good scrub, then I put them in a beaker and run hot tap water in to the beaker for 10-15 min. then I do 3 rinses with sonication using the following
DI water, MeOH, acetone, and sometimes one rinse with hexane if I want to get the ms up quickly.

Why do you need to clean your source so often?

Like Bigbear I'm also curious why you clean it twice a month. If we'd follow that frequency we'd be cleaning sources all day !

Once or twice a year max, if nothing unusual happens..

Thanks for your answer.

Thanks for your answer.
We determine pesticides residue in food samples and we analyze more than 20 samples in each day. After about two weeks, the intensity of ions decreased (intensity of m/z 69 in cal gas changes from 1,200,000 to lower than 700,000) and this is why we must clean the ion source so frequently. We use QuEChERS sample preparation method for food samples.

Any suggestion?

Do you need to use the full cleaning method each time?
I have a VOA analysis that dirties up my source fairly quickly. It usually only requires a light swabbing of the repeller with methanol to clean things up. This is much quicker and doesn't add wear and tear to the repeller surface.

What method and system do you use for VOA's, Steve?
We use 524.2 Agilent 6890/5973 with Agilent's water management kit. We see little source problems after switching to the large draw out plate and high split.
When we clean at about 6 months a full cleaning is done. Never occuured to me to just wipe the repeller with MEOH.

On our volatiles instruments we clean once every 12-18 months(or whenever both filaments burn out). We run over 600 drinking water THMs per quarter but the system stays clean. Our waste water instrument runs everything from monitoring wells to sludge samples, same source cleaning schedule, but the purge and trap requires frequent cleaning from all the crud.

Semivolatiles, like the Quechers Food methods, does require more often source cleaning since a lot of high boiling junk makes it through the column to the analyzer.

The worse I ever ran was Derivitized Melamine samples on pharma excipients, those killed the source on the 7000QQQ after about 40 samples. They were derivitized in the vials so the reagents were probably the source of the problem.

Another odd thing I have noticed on the 7000 is that when the source gets dirty, there will be a current across the filaments even when they are off. Go into manual tune and there is 25-30uA reading and when you turn on the filaments they read 35uA but barely glow, it is like a offset is placed on the circuit that monitors the filament current. Cleaned the source per Agilent's recommendation and the base current dropped to 1uA, which is still odd to me.