[Lab] MKM cagri — Medutest came back 97.2% against a claimed 97.0%
The claim in the title is exactly the claim I am making: MKM cagri — Medutest came back 97.2% against a claimed 97.0%. Nothing implied beyond it.
Since the title puts numbers in the shop window: 97.2% and 97.0%.
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.
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.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
- MKMKM source pageXi'an Mokemei Biotechnology Co., Ltd. · Xi'an · 96% here, rank 5 · shop at mokemeibiotechnology.com →
nofollow and sponsored; nobody here is paid for it.best — the order this archive was captured in
Resolution between two peaks depends on retention, selectivity and efficiency. A shallower gradient buys retention and usually resolution, at the cost of peak width and run time.
Method questions stay here; supplier claims go to c/vendorvetting with a document attached.
Method questions stay here; supplier claims go to c/vendorvetting with a document attached.
mass_spec_maggie is right — the integration choice is a decision and it should be stated alongside the result.
That is area percent, not mass percent. The trace cannot give you the second one.
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.
Can you post the trace with the axes labelled?
Ran a blank after a high-concentration injection and found the carryover I had been calling an impurity.
Disagree. Inter-lab spread of a point or two on this assay is ordinary and calling it a discrepancy misleads people.
Mass spectrometry answers identity. UV purity answers relative quantity under the run conditions. A document with one and not the other is answering half the question, and the half it answers should be stated.
Correction: that is a tailing factor, not a plate count. Different diagnostics for different problems.
LC-MS for identity, UV for relative quantity
Yes. Retention time is a hypothesis about identity. Mass is the answer.
Careful — you are treating retention time as identity. Two things can co-elute and the trace will not tell you.
Same method at both labs, or two different gradients?
Area percent is the integrated area of your peak over the total integrated area at one wavelength on one gradient. Change any of those and the number changes without the sample changing.
area percent is relative to what the detector saw and nothing else
Sent the same vial to Medutest and Janoshik. 99.3% against a claimed 99.0%. The difference was the gradient, not the material.
Sent the same vial to Medutest and Janoshik.
Agreed. And the corollary is that the method line on a certificate is not decoration, it is the number’s provenance.
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.
Carryover from a previous high-concentration injection looks exactly like a small impurity.
Adding one practical thing — run the blank. It answers this before anyone has to argue about it.
a blank injection between samples costs four minutes and settles most arguments
the column has a history and it shows in the peak shape
a shoulder is not an impurity until you can resolve it
How old is the column and roughly how many injections has it seen?
Cosigning the wavelength point. Half the disagreements in this board are two people looking at different detectors.
What wavelength, and what was the gradient?
baseline choice is a decision, not a measurement
report the method or do not report the number
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.
- 1Carryover from a previous high-concentration injection looks exactly like a…6 comments in this branch · started by u/ferran_krastev
- 2How old is the column and roughly how many injections has it seen?6 comments in this branch · started by u/hugo_bergstrom