Spike Recovery & %RSD
Two everyday analytical-QC checks: spike recovery to test method accuracy against a known addition, and replicate precision (mean, standard deviation, and percent relative standard deviation) from a set of repeat measurements.
How to use this tool
Run the two routine QC checks behind a validated method: spike recovery for accuracy (does the method find a known addition?) and %RSD for precision (how tightly do repeats agree?). Pick the mode at the top.
What to enter
- Spike recovery: the unspiked result, the spiked result, and the amount added (all in the same units), plus your accept low/high window in %.
- Replicate precision: paste your replicate measurements, one value per line.
Reading the result
Recovery mode gives the recovery % with a pass/fail against your window (typically 80–120%). Precision mode gives %RSD plus n, mean, standard deviation and range. Lower %RSD is tighter; values outside your validated limit warrant investigation.
Worked example
An unspiked sample reads 2.0, the spiked one 11.0, with 10.0 added → recovery 90%, comfortably within an 80–120% window (pass).
Inputs
Result
Methodology
Spike recovery measures accuracy: recovery % = (spiked result − unspiked result) ÷ amount added × 100. A result near 100% means the method recovers the analyte without matrix bias; most methods accept 80–120% (tighten or loosen to your SOP). Precision is the sample standard deviation s = √[Σ(xᵢ − x̄)² / (n − 1)], and %RSD (coefficient of variation) = s ÷ x̄ × 100.
Reading the numbers
- Recovery outside your acceptance window points to matrix effects, losses, or calibration drift, investigate before reporting.
- %RSD targets are method-dependent: often ≤ 2% for instrumental assays, looser for trace or bioanalytical work. Compare to your validated limit.
- Keep the spike level and the sample in the same units, and small relative to saturating the method's linear range.