Earlier in my illlustrious career with Uncle Sam, I was a chemist with the Food & Drug Administration (FDA). This was in the ’60s, back when everything seemed possible. I worked for the New York office, which encompassed the New Jersey pharmaceutical industry. Some bright people far above my pay grade started a new program, where, instead of the traditional inspect-collect samples-slap on wrist approach, we would help troubled firms to clean up their act. We called it Intensified Drug Inspection Program (IDIP).
We descended on a firm which shall go nameless, since I’m not sure it is still in business 60 years or so later. One of its products was an opthalmic solution, a preparation listed in the United States Pharmacopeia (USP). The object of the game, so to speak, was to manufacture the substance so that it met the standards of the USP. Most of these firms had an in-house Quality Control lab which would test batches of the product to ensure it met these standards, one of which, for this stuff, was acidity.
I’m sure most of you are familiar with the term pH. (Full disclosure: there’s some chemistry coming……). Briefly, the pH scale for water (aqueous) solutions ranges from 1.0 (strongly acidic, think battery acid) to 7.0 (neutral, think drinking water) to 14.0 (strongly alkaline, think Drano). The USP requirement specifies a pH of about 6.0 (weakly acidic) for drops you are putting in your eye. The lab tested various batches over several months. Fresh ones met the standard, however, after a couple of weeks, the pH dropped to 1.5. Placed into the eye, that would smart! Big time! This was reported to Manufacturing, who, basically, did nothing. No wonder the firm was in trouble.
Since we were functioning as consultants and problem solvers, I checked out the formulation. Most water contains a small amount of dissolved oxygen. Seemed that it included a chemical called sodium hydrogen sulfite, (NaHSO3) which functioned to keep the product from turning brown. However, in solution, NaHSO3 combined with dissolved oxygen (in Jersey water) to form NaHSO4, which is strongly acidic. To prove this, I made up some material using water from Brooklyn which I deoxygenated by bubbling nitrogen through it for five minutes or so, and then put a cap on it. The pH held at about 6.0 for several weeks. Problem solved.
The Quality Assurance Program (QAP) attempted to answer that question. On a monthly basis, one of the 8 DEA labs provided a previously analyzed exhibit to all labs. The sample was quantitavely analyzed, and the average (mean) of the results was compared to the original analysis. The folks analyzing the QAP sample were (well) aware that this was part of the Program (did they tend to try harder?). If the original analysis (or any of the QAP results) fell outside of predetermined limits, lab management initiated corrective action.
It’s a fact of life, so to speak, that anytime you have a mixture of chemicals in a sample to analyze, you will get variation in results. There are numerous other factors which hinder accuracy (the deviation from the “real” answer), or precision (how closely the values in a series of assay of the same material are). I won’t bore you with any more of this mind-bending stuff. Just so you know.
Rogernarc 