in-process control
A driver glances at the speedometer and dashboard constantly during a journey, correcting course before anything goes wrong — rather than waiting to arrive and only then asking whether the trip went well. In-process controls (IPCs) are those mid-journey checks for manufacturing: tests and observations performed during production to monitor, and if necessary adjust, the process so that the product will meet its specifications.
IPCs are carried out at key points along the chain of unit operations. On a tablet line they typically include blend uniformity before compression, then tablet weight, hardness, thickness, friability and disintegration sampled at intervals during the run; for capsules, fill weight; for liquids, pH and fill volume. Operators check these against in-process limits and can react immediately — adjusting compression force or refilling a hopper — long before the batch is finished.
The purpose is to catch drift early and steer the batch, supporting GMP's principle that quality is built in during processing, not inspected at the end. IPCs differ from finished-product release testing: they are about controlling the ongoing process, whereas release tests confirm the final product meets specification. Process analytical technology is, in effect, in-process control taken to its continuous, real-time, automated extreme. The caveat is that an IPC is only as useful as the sampling behind it — a check on too few or unrepresentative samples can give false comfort.
During a four-hour compression run, an operator pulls tablets every 30 minutes and checks weight and hardness; when average weight starts drifting low, the press feed is adjusted on the spot, keeping the whole batch within specification.
Periodic in-process checks let an operator correct a batch while it is still being made.
In-process limits are usually tighter than the final release specification, leaving a margin so that a batch trending toward an edge can be corrected before it ever produces out-of-spec product.