Getting a titration right once is one thing. Knowing it is still right next week, on another instrument, in someone else's hands, is another. That is the job of quality control. It sounds like paperwork, but done well it is just a handful of checks, each aimed at one of the few things a titration depends on.
What the chemicals use up on their own
Before your sample uses up any of the measuring liquid, the solvent, the indicator and everything else in the flask may use up a little on their own. So labs run the same titration with everything except the sample. That is called a blank, and its volume is subtracted. When a new batch of solvent arrives, the blank can change, so it gets measured again.
Keeping an eye on the measuring liquid
The strength of the measuring liquid is checked regularly, and every check is written down. Pharmacopoeias, the rulebooks for medicines, even set how closely repeated checks have to agree. But the most useful habit is simple: plot that strength over time. A liquid that slowly weakens, or jumps when a new bottle is opened, shows it on the chart long before it shows up in a result.
The simplest powerful check
Here is a check almost anyone can understand. Titrate the same material using different amounts: a little, a bit more, more again. If the titration is counting only what it should, twice the sample takes twice the liquid. Plot it, and the points fall on a straight line that passes through zero.
If the line misses zero, something is using up liquid that is not the sample, or the endpoint is off by a fixed amount. That offset matters most for small samples, which read consistently off in the same direction, high or low. A result that depends on how much sample you used is a result that is not counting cleanly.
Small samples have a second weakness. If the material is not perfectly uniform, a small scoop can differ from the whole. That shows up differently: small samples scatter both ways instead of drifting one way. The first points to the titration; the second points to the sample and how it was taken.
Charting the check sample
Labs also run a sample of known content alongside their routine work and plot each result. Results will always wander a little by chance. But in my experience, when the check sample clearly moves, something has usually changed: the liquid, the probe, the temperature, a new batch of solvent, or the way the sample was weighed or delivered. The chart's job is to tell you when to look. Knowing the titration tells you where.
Why this matters to you
Every result a lab sends out leans on checks like these. They are not about statistics for their own sake. They are about catching, early and cheaply, the day something changed, before it reaches a decision someone makes from the number.
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References
- European Pharmacopoeia 6.0, 4.2.2 Volumetric solutions.
- C. Walter, Validation of Titration Methods, Mettler Toledo application brochure.
- D. Harvey, Analytical Chemistry 2.1, 7.2 Designing a Sampling Plan (LibreTexts).