two labs, same vial, 98.1 and 96.4. both right?
two labs, same vial, 98.1 and 96.4. both right. I am not trying to be the "source?" guy. I would just like a source.
Gave the same trace to two people I trust and got two integrations about a point apart. That was the most educational afternoon I have had here.
Retention time shifted 0.4 minutes and I assumed the worst. It was the column temperature.
Bought a second-hand instrument and learned more in six months of fixing it than in three years of reading traces.
Tell me where this is wrong. That is the useful part of posting it.
best — the order this archive was captured in
System suitability — repeat injections, tailing factor, plate count, RSD on area — is what tells you the instrument was fit for the measurement that day. Without it, the purity figure is unanchored.
Same method at both labs, or two different gradients?
A shoulder that does not baseline-resolve cannot be quantified honestly. You can report it as an unresolved shoulder, which is useful information, or you can develop the method until it resolves.
UV response is not uniform across species. At 214nm you are looking at the peptide bond, which is why it is the working wavelength for this class; at 280nm you only see tryptophan, tyrosine and phenylalanine.
Ran a blank after a high-concentration injection and found the carryover I had been calling an impurity.
Do you have the mass, or only the UV trace?
Carryover from a previous high-concentration injection looks exactly like a small impurity. The blank injection is four minutes and it removes the ambiguity entirely.
Right. And a blank between injections settles the carryover argument before it starts.
Left up. The integration disagreement in this thread is the most useful thing on the board this week.
LC-MS for identity, UV for relative quantity
That figure cannot be quoted to two decimals off that baseline. The precision is not in the data.