Analytical valves control when the sample is loaded, when it is injected, and how flow is directed through different columns or analytical paths. Timing therefore affects both the amount of sample introduced and the way components separate.
Small timing errors can create large measurement effects.
Injection repeatability
For a repeatable result, the same amount of sample must enter the analytical path on every cycle. Timing of the sample valve, shut-off arrangement, and any atmospheric equalisation steps is critical to that consistency.
Unstable injection timing often shows up as unstable repeatability.
Separation performance
Timed switching is also used to move or redirect components through column trains. If a switching event happens too early or too late, peaks may shift, overlap, or disappear from the expected location.
That is why valve timing review is closely linked to chromatogram review.
When timing problems are suspected
Common symptoms include changing retention times, abnormal peak shapes, missing or split peaks, unstable repeatability, and unexplained response factor movement.
Timing should be reviewed alongside sample conditions and carrier stability, because several faults can produce similar symptoms.
Why timing should be handled carefully
Timing changes can improve one part of the chromatogram while degrading another. Adjustments should be controlled, documented, and checked against the complete analysis rather than one peak alone.
A good timing review always considers the whole method, not only one symptom.
