Choose the question before the instrument
A method name is useful only when connected to a question. The same instrument can support different procedures, and one impressive instrument name does not establish a complete testing panel.
| Question | Typical approach | Key limitation |
|---|---|---|
| What components are separated? | HPLC | Overlapping or weakly detected components can be missed. |
| Does the sample match the target? | LC-MS and other identifying evidence | Mass alone does not resolve every structural alternative. |
| How much is present? | Appropriately calibrated quantitative procedure | Needs a clear sample and dilution basis. |
| Which metals are present? | ICP-MS | Covers named elements, not peptide identity. |
| Is endotoxin present? | Endotoxin assay | Not a live microbial count. |
| How much microbial growth is recovered? | Enumeration | Not a sterility claim. |
| Is growth observed in sterility samples? | Sterility procedure | Selected samples cannot guarantee every vial. |
| Is a named unwanted drug detected? | Targeted screen | Targets outside the scope remain unanswered. |
| Does it dissolve or maintain its seal? | Defined physical or integrity test | Conditions and endpoints must be stated. |
An example of incomplete evidence
Accuracy and precision differ
Accuracy concerns agreement with an accepted reference. Precision concerns consistency among repeated measurements. A procedure can give closely grouped readings that are all biased in the same direction.
Compare limits on the same basis
A lower detection limit can answer a narrower “how little can be seen?” question. It does not automatically make a method better for every sample or purpose. The target, units, sample preparation and interference control must also match.
Coverage includes sampling
Ten different procedures on one submitted vial do not describe vial-to-vial variation. Several readings from one prepared sample do not become independent vial tests. Read which samples were examined as well as which techniques were used.
Sources
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