Use this free spike recovery calculator to turn your unspiked and spiked results into a percent recovery you can report. Work out the percent recovery of a matrix spike in seconds. Choose a simple calculation, correct for the volume your spike adds to a liquid sample, or spike a solid by mass. The calculator also shows the AOAC recovery range expected at your spike level.
How to use the Spike Recovery Calculator
- Choose the calculation type that matches how you spiked the sample.
- Enter the unspiked and spiked sample results and the result unit.
- Enter the concentration added, or the spike solution concentration with the spike volume and sample volume or mass.
- Press Calculate recovery and compare the result with the AOAC range for that level.
Record the spike recovery calculator result together with the spike level and matrix, so reviewers can trace it. For environmental testing, matrix spike QC requirements are set out in EPA SW-846.
How spike recovery is calculated
A matrix spike shows whether your method can find a known amount of analyte in a real sample. You analyse the sample with and without a known addition, then compare how much extra you found with how much you added.
AOAC expected recovery by concentration
| Analyte level | Expected recovery |
|---|---|
| 100% – 10% | 98–102% |
| 1% | 97–103% |
| 0.1% | 95–105% |
| 100 ppm | 90–107% |
| 10 ppm – 100 ppb | 80–110% |
| 10 ppb | 60–115% |
| 1 ppb | 40–120% |
Source: AOAC INTERNATIONAL, Guidelines for Standard Method Performance Requirements (Appendix F). Many environmental methods (for example US EPA methods) set their own matrix-spike windows, often 70–130% or 80–120%. Always use your method’s acceptance criteria when they exist.
Tips for reliable spikes
- Spike at 1–5 times the native concentration, or near the middle of the calibration range.
- Add the spike before extraction or digestion, so the recovery reflects the whole method.
- Keep spike volume small (≤ 1–2% of sample volume). Otherwise use the liquid option to correct for dilution.
- Record spike solution traceability (lot, certificate, preparation date) for your ISO/IEC 17025 records.
Frequently asked questions
What is an acceptable spike recovery?
It depends on concentration and method. AOAC guidance ranges from 98–102% at percent levels to 80–110% at ppm levels and 40–120% at 1 ppb. Environmental methods often use 70–130%.
Should I correct for the volume of spike added?
Yes, if the spike volume is more than about 1% of the sample volume. The liquid option applies the dilution correction to both the added amount and the native concentration.
What if my recovery is above 100%?
Recoveries slightly above 100% are normal because of measurement variability. Consistently high recoveries can point to matrix enhancement (common in ICP-MS and LC-MS), contamination, or an incorrect spike solution concentration.
What is the difference between a matrix spike and a spiked blank?
A spiked blank (laboratory control sample) tests the method with no matrix. A matrix spike tests the real sample, so it shows matrix effects such as suppression or interference.
What is the spike recovery formula?
% Recovery = (Cspiked − Cunspiked) ÷ Cadded × 100. If a sample reads 2.0 mg/L unspiked and 6.8 mg/L after a 5.0 mg/L spike, recovery is (6.8 − 2.0) ÷ 5.0 × 100 = 96%.
How do I calculate percent recovery for a solid sample?
First work out the amount added per gram: spike concentration × spike volume ÷ sample mass. For example, 10 mg/L × 0.5 mL ÷ 5 g = 1.0 mg/kg. Then use the same recovery formula with all results in mg/kg.
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Results are estimates for general information. Check critical decisions with a qualified professional.