The physical characterisation bench, instrument by instrument: what a plastic moisture analyzer, a moisture analyzer balance and a microwave moisture analyzer each actually measure and why their numbers differ, what a plastic testing laboratory will run that an in house bench cannot, when an osmometer is the only honest way to confirm a formulation, what a titrator and an autotitrator automate that a burette does not and where a calorimeter instrument answers a stability question no assay can, and how to decide which of these belongs in house rather than at a testing laboratory

Choosing the instrument

1. Decide what moisture means for your sample. Loss on drying measures everything volatile at the chosen temperature; a specific chemical titration measures water alone. For a material that releases solvent or degrades on heating, the two differ substantially, and the specification has to name the method.
2. Use osmolality where tonicity matters. Osmolality is the property that decides whether a formulation is tolerated by cells or by a patient, and it is not calculable reliably from composition once excipients interact. Freezing point depression is the common method and it is fast, small volume and robust.
3. Automate titration where the volume justifies it. An automatic titrator removes endpoint judgement and produces a record. Below a few determinations a week the manual method is fine; above that the consistency and the audit trail usually pay for the instrument.
4. Match the calorimetric technique to the question. Thermal transitions, decomposition and interaction energetics are different measurements with different instruments. Buying a general purpose unit for a specific stability question frequently produces data that cannot answer it.
5. Decide in house against a testing laboratory. Occasional determinations, unusual methods and anything requiring accreditation are usually cheaper and more defensible bought in. Routine, high volume determinations belong in house where the method can be controlled and the turnaround is immediate.

The method is in the specification or the number is not comparable

For every measurement on this bench, the value depends on how it was obtained: the drying temperature and endpoint criterion, the titration reagent and detection, the osmometer principle, the calorimetric scan rate. Two laboratories quoting the same property without the method are not quoting the same number.

Write the method into the specification and into the certificate. It is the difference between a value someone can act on and a value someone will have to repeat.

Small instruments, real maintenance

These units are inexpensive to buy and easy to neglect. Balances drift, titration reagents change titre, osmometer probes foul and calorimeter cells contaminate. Each needs a check with a reference material on a defined schedule.

Assign each instrument an owner and a check interval at purchase. An uncalibrated small instrument produces numbers that look fine and are quietly wrong, which is worse than having no instrument.

Common questions

Why do two moisture results disagree?

Because they measure different things. A drying method reports total volatile loss at a temperature; a chemical titration reports water specifically. On a sample containing other volatiles, the drying figure will be higher and neither is wrong.

Can osmolality be calculated instead of measured?

Approximately, and the approximation degrades as formulations get more complex. Where tonicity affects cells or patients, measurement is the defensible route and the instrument is inexpensive relative to the risk.

What does an automatic titrator add?

Consistent endpoint detection, unattended operation and a record of every determination. The chemistry is unchanged; what improves is reproducibility between operators and the ability to show how a number was obtained.

Is calorimetry worth it for a small laboratory?

Only with a recurring question that it answers. These instruments need method development and a trained user, and for occasional stability questions a contract laboratory delivers better data for less.

Browse by service class

• Compare Gene synthesis on advertised prices