By Anonymous on Wednesday, January 7, 2004 - 02:04 pm:
I am unable to reproduce my area count from one standard to the next, with the same standard concentration. I have changed metering seals and rotor seals on the LC. My retention times are consistent, yet the areas are not. Any suggestions? Thanks
By Uwe Neue on Wednesday, January 7, 2004 - 06:13 pm:
Sounds like injection problems, including air bubbles, tight seals etc. Check previous discussions of similar issues!
By Anonymous on Wednesday, January 7, 2004 - 07:02 pm:
How bad are they, MS is not quite as reproducible as you might expect from UV.
By MG on Thursday, January 8, 2004 - 07:30 am:
I've never run an API-2000 as the original poster has, but if it's any help, our API-3000 usually had %RSD's ranging from 2% to 8% for reinjection of a solvent standard, depending on the method and signal-to-noise at the level being injected. When it started creeping up to 8% and above, it was time to clean the source. I recommend cleaning the atmospheric pressure side of your source if this hasn't been done in awhile. Are you using ESI or APCI?
If source cleaning doesn't help, I would also suspect a problem with the autosampler.
By Anonymous on Thursday, January 8, 2004 - 09:44 am:
As a quick+dirty check of reproducibility, make replicate injections and weigh the vials before + after, if you are injecting enough to weigh accurately. If your weight RSD is much lower than the area RSD, look at detector. If weight RSD matches the area RSD, look autosampler.