This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.
An itemised related-substances table with retention times says considerably more about the synthesis than a single total. A total tells you how much is not the main peak and nothing about what it is.
The arithmetic on field-by-field walk through a certificate is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.
Post #153 is right about the mechanism and I think understates the practical bit.
Where two documents for the same lot disagree, the useful question is which was measured and which was transcribed. Most such disagreements are the second.
Worth checking against a second source before it gets quoted onward.
Worth separating two things that post #153 runs together.
I have three months of notes on field-by-field walk through a certificate and the honest summary is that the trend is real and the week-to-week numbers are noise. I nearly drew the opposite conclusion from the first fortnight.
Nothing to add, except that this is the answer I would give if asked.
Offering a way to settle field-by-field walk through a certificate rather than another opinion about it. Two measurements, taken the same way, a fortnight apart. If the difference is within the noise, the question was not answerable at this precision.
The arithmetic in post #157 is right; the assumption feeding it is the part to check.
"Not less than 98 per cent" is a specification. "98.3 per cent" is a result. A certificate carrying only the first has not told you what was measured.
The reasoning is more useful than the number, which is why I have shown it.
Adding the measurement that post #159 says would settle it.
The reason field-by-field walk through a certificate keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.
Post #160 describes the usual case. This is about the unusual one.
Endotoxin testing is separate: a certificate of purity says nothing about endotoxin. A chemically pure preparation can carry a clinically significant endotoxin load. If endotoxin matters, it needs to be tested and reported.
That is clearer than the version I had in my head. Thank you.
Nobody has said the unglamorous part of field-by-field walk through a certificate yet, so: most of the variation is explained by things that are boring to write about and easy to check.
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