USP recently changed the assay limits on a compound from 98-102% to 99.0 to 100.5. They also introduced a new assay method that we haven't switched to because there was a mistake in the mobile phase ratios. This is being corrected in the next supplement. We probably made a mistake in switching to the new limits without switching to the new assay, because now we can't hit the new limits very often. We'll have one prep in and one prep out, or one injection in and one injection out. If we tighten up system suitability requirements, will that help? We specify plus/minus 2% but usually do better than that. What kind of RSD do we need to hit those limits? Or should we run precision on the old and new method and use that to justify an early method change or returning to the old specifications?
By M Emerick on Thursday, May 24, 2001 - 02:21 pm:
I saw your message on the LC board. Those are some tight specs. Tightening up the system suit. would correspond to the specs but it dosn't seem as though that will help you out. It appears the precision of the run needs to be tightened. Just tightening up the system suit. would give you more failed runs. Some suggestion: column heater, sample flush set at slow, replace rotor seal, change dilution.
By Anonymous on Thursday, December 27, 2001 - 11:10 pm:
I have a few doubts in the subject of GC-MS.
1. What is the principle of GC-MS?
2. How fragmentation of a molecule takes place in GC/MS and LC/MS?
3. Where the bond breaking takes in a perticular molecule?
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