Knowledge Base
Storage, shelf life and what a re-test date really means
A re-test date is a claim about a number, not about a chemical. Storage conditions, opening the vial, and why the freezer matters more than the label.
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Resources
Technical notes and regulatory updates on pharmaceutical impurity and reference standards, covering certificates of analysis, ICH M7 classification, nitrosamine method development, pharmacopoeial naming, purity versus assay, and standard storage.
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Technical Notes
Practical notes on working with impurity standards: what a certificate of analysis actually covers, and how nitrosamine methods are built, retained and defended.
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Regulatory Updates
Regulatory developments that change what you need from a reference standard: ICH M7 mutagenic impurity classification, nitrosamine acceptable intakes, and how USP and EP label the same related compound.
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Knowledge Base
Background reading on reference standards as material rather than paperwork: why purity and assay are different numbers, and how storage, shelf life and re-test dates decide whether a certificate still describes what you inject.
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Purity is not assay: reading HPLC figures correctly
Area percent purity and mass fraction assay answer different questions on different bases. How to read both without overstating what is in the vial.
Regulatory Updates
USP vs EP impurity naming, side by side
The same compound can carry an EP impurity letter, a USP related compound letter and a catalogue name. How to map them from structure rather than from the letter.
Regulatory Updates
ICH M7 in practice: classifying and controlling mutagenic impurities
How Class 1 to 5 assignment, the 1.5 microgram per day threshold and the four control options change what you need from a reference standard.
Technical Notes
Method development for nitrosamine impurities
Retention chemistry, deuterated internal standards and blank contamination control for nitrosamine methods, with a worked conversion from acceptable intake to working concentration.
Technical Notes
How to read a Certificate of Analysis
Which fields on a certificate of analysis decide whether an impurity or reference standard is fit for your method, and which ones get skipped.