The Analytical Control Strategy: Which Parts of a Method Have to Stay Fixed

Two analysts follow the same written method and get different answers. Neither deviated from anything written down — which is the problem. What separates a method from a description of a method is knowing which details were doing work.

Quick answer

What is an analytical procedure control strategy? ICH Q14 defines it as a set of controls, derived from current understanding of the procedure including development data, risk assessment, robustness and prior knowledge, that ensures the procedure is fit for the intended purpose during routine use throughout its lifecycle. The guideline adds a sequencing rule worth noting: the control strategy should be defined before validation and confirmed after validation has been finalised.

It has two components: the procedure parameters that need controlling, and the system suitability test that is part of the procedure.

What the written procedure has to contain

ICH Q14 is unusually specific about this, and the list is a serviceable checklist for any method anyone intends to repeat. The procedure should describe the steps necessary to perform each analytical test, which can include:

• the sample, the reference materials and the reagents;
• sample and control preparations;
• use of the apparatus;
• generation of the calibration curve;
• the number of replicates;
• the formulae for calculating the reportable results;
• and other necessary steps.

The criterion the guideline sets for how much detail is enough is the useful part: the level of detail should enable a skilled analyst to perform the analysis and interpret the results.

Established conditions: what must stay fixed

ICH Q14 introduces the idea of established conditions (ECs) — the elements that must be held constant and whose change requires formal communication. The guideline says ECs could consist of:

The selection rule is conservative and worth quoting in substance: parameters which need to be controlled to ensure performance, as well as those where the need for control cannot be reasonably excluded, should be identified as ECs. Uncertainty counts as a reason to control something, not as a reason to leave it free.

The trade-off between fixing everything and understanding it

The guideline draws a direct relationship between how much is understood about a method and how much has to be nailed down.

• With a minimal development approach, the number of ECs may be extensive, with fixed parameters and set points. Little is known about which parameters matter, so everything is frozen.
• With an enhanced approach, there is increased understanding of the relationship between parameters and performance. ECs can be reduced and focused on performance — acceptable ranges rather than fixed points — when justified by procedure understanding and risk management.

The counter-intuitive consequence: a rigidly specified method is often the sign of a method nobody has characterised, not of a method held to a higher standard. Understanding buys flexibility, and the flexibility is the payoff for the work.

The guideline also closes an obvious loophole: use of the enhanced approach should not lead to a less detailed description of the procedure. Fewer fixed conditions does not mean a vaguer method.

How a parameter earns its way off the list

ICH Q14 gives a mechanism that is directly useful at the bench. If the application of performance criteria and/or the system suitability test demonstrates that a specific parameter is under control, that parameter may not necessarily need to be defined as an established condition.

In other words, a check that would catch a parameter drifting can substitute for freezing the parameter. This is why system suitability is not an administrative ritual: it is the thing that earns the method its freedom of movement. The definition and purpose of an SST — to increase the detectability of unacceptable performance — is covered in robustness and system suitability.

A control strategy for research work

Nobody outside a regulated setting is proposing established conditions to a regulator. The structure still answers a practical question: what do I have to keep the same for my results to remain comparable over time?

• The reference. Which lot, measured when, stored how. If this moves, every comparison built on it moves with it — see reference standards.
• The measurement principle. Switching from one physical basis to another is the largest change there is, and is treated as such.
• The acceptance check. A known sample with a written criterion, run before results are accepted.
• The preparation. Diluent, concentration, container type, and how long a prepared solution may stand — the duration question raised in how long a reconstituted peptide is stable.
• The arithmetic. The formula used to get from signal to reported result, written out once.

Five items. Anything not on the list is free to vary, which is the point: a control strategy is as much a statement of what does not matter as of what does.

Key takeaways

• ICH Q14 defines the analytical control strategy as the set of controls ensuring a procedure stays fit for purpose in routine use.
• It should be defined before validation and confirmed after validation is finalised.
• The written procedure should cover samples, reference materials, reagents, preparations, apparatus, calibration, replicates and formulae.
• The sufficiency test is whether a skilled analyst could perform the analysis and interpret the results from the description alone.
• Established conditions may include performance criteria, the procedure principle, suitability criteria, and parameter set points or ranges.
• Parameters where the need for control cannot reasonably be excluded are controlled — uncertainty argues for control, not against it.
• A system suitability check that would detect a parameter drifting can substitute for fixing that parameter.

Frequently asked questions

Is a detailed method the same as a controlled one?

No. Detail without knowing which details matter produces long documents and unreproducible results. The control strategy is the judgement about which parts are load-bearing.

Why define the strategy before validation?

Because validation demonstrates that a procedure performs — and a procedure is only defined once you have said what is fixed about it. Validating something whose boundaries are undecided leaves it unclear what was actually shown.

What if I do not know which parameters matter?

Then fix them all, and treat that as a statement about present knowledge rather than about rigour. The guideline's minimal approach is exactly this, and it is legitimate.

How does this relate to an analytical target profile?

The profile states what the measurement must achieve; the control strategy states what must be held constant to keep achieving it. The first is covered in the analytical target profile.

Does a research buyer ever see a supplier's control strategy?

Not directly. What it explains is why a supplier's results can stay consistent across lots while your own measurements of the same material wander: consistency is a property of controlled conditions, not of the material alone.

Sources

• International Council for Harmonisation. ICH Harmonised Guideline Q14: Analytical Procedure Development. Final version adopted 1 November 2023. ICH guideline
• International Council for Harmonisation. ICH Harmonised Guideline Q2(R2): Validation of Analytical Procedures. Final version adopted 1 November 2023. ICH guideline

Guideline text is quoted from the adopted ICH documents.

This article describes analytical methodology only. It contains no usage instructions, no dosing information and no protocols of any kind.

For laboratory and in-vitro research use only. Not for human or veterinary use.