Technical guides

Written for the people who have to defend a method — not for a search engine.

How to read a certificate of analysis A certificate is only useful if you can tell what it does and does not tell you. This is a field-by-field reading, with the points where certificates from different suppliers cannot be compared directly.How to choose a reference standard supplier Most supplier comparisons start with a catalogue and a price. The things that actually cause trouble later are documentation, lot-to-lot behaviour and how questions get answered. This is a checklist in that order.Stable isotope-labelled standards and when to use them A labelled internal standard is the most effective way to control for matrix effects, recovery and instrument drift in a quantitative method — provided it is chosen and specified correctly. These are the decisions that determine whether it helps.Nitrosamine and NDSRI standards: what to test for and what to buy Nitrosamine control moved from a recall response to a routine expectation. The practical consequence for a laboratory is that two different kinds of standard are now needed, and they are not interchangeable. This is what each one is for, and how to specify it.What is an impurity reference standard? The term is used loosely, and the looseness costs money: two suppliers can quote the same compound, the same purity figure and a very different material. This is what the term actually means, and which of its properties determine whether the standard will work in your method.