Consumer Products Guy wrote:Philip01 wrote:
The USP method made no mention of a split ratio, the specific monograph was Benzyl Alcohol.
I found many USP Monograph methods to be poorly written and/or poorly-developed. Sad.
Of course our QA Director - who lacked hands-on knowledge and experience - felt USP was god. I had to fight with him about the recovery limit for our finished cGMP products to get him to OK 95-105% recovery as in FDA-ORA regulations.
I E-mailed USP "owners" of monographs a few times, like did "standardize frequently" under "Volumetric Solutions" mean every month, every day, or every 10 minutes? And I asked about how was content of pure alcohol tested, response was from specific gravity or refractive index, and not in the monograph.
Of course my own supervisor did not agree with allowable modifications detailed in <621> and in FDA-ORA, even though they were printed in black ink using the same 26 alphabet letters we learned in kindergarten. I never did get information as to if one could combine two of such changes (like decrease column from 4.6mm to 3.0mm and increase column temperature 5 degrees).
My first real encounter(and it wasn't actually a true encounter) was in a job interview for a QC chemist(not really my field, but they called me in for the interview when I hadn't applied for that specific job) and I was asked if I followed USP methods in any of my work. I was pretty well shot down and said "you can't do that" when I told them that in academia I never know what someone was going to bring me and that I developed a lot of my own methods or modified existing published ones. They were also less than impressed when I said that I do follow EPA methods both because I occasionally have environmental work and also because a lot of instrument comparison/testing seems to happen on EPA methods. They kept repeating in seeming disbelief that I'd never used a USP method.
Looking some up after that, I had much the same reaction. EPA methods can at times be annoyingly too detailed with things like DFTPP tunes. USP methods-like you said-are often a nightmare to try and figure out what instrument parameters you're supposed to use.
Of course, I also follow a fair few that have been journal published, and those can be hit or miss. Even in some good high-impact journals(JACS, Angewante, etc), it almost seems like the reviewers sometimes rubber-stamp chromatography methods without stopping to ask if they make sense. I seem to have better luck with good methods in lower impact but more focused journals like ACA. When you branch out of chemistry journals, it can be even more of a nightmare.
As a bit of an example, someone handed me a publication one time and asked if I could replicate the method/results in it. As it so happened, it was published on a 5890/5971 that I actually service and know fairly well...and have a copy of that lab's "universal" method on my 5890/5971 and 7820/5975. The published method said a "5% methylsiloxane column" which is fine and what I run as a standard column, but didn't give dimensions. I know it's a 20mx.20mm, which is a bit different from I run, but not a big deal as I run a larger diameter longer column that actually gives both similar retention times and a similar resolution. That was all good and well, but the paper claimed a 5mL/min flow rate. The pressure gauge on the front of a 5890 pegs at 30psi, and you need ~50psi to push helium through that column at 250ºC. Aside from that, I don't think the vacuum system on a 5971 is up to that kind of flow. That's not to mention that the peaks would probably look terrible moving that fast through that column. Fortunately, I know they keep their MS pressure set to 13psi, which is ~1mL/min depending on temperature, and I can replicate it decently well by using either my 5890 or 7820 set to constant flow at 1mL/min.