What this tool does
Keep native analyte, known addition and measured spiked result on one clear basis before comparing recovery with your method's limits.
When to use it
When the unspiked/spiked measurements and known addition are available on a confirmed basis. Compare only with criteria from the applicable method/SOP and consider the rest of the batch QC.
Inputs and supported units
Use the labelled laboratory units and a consistent sample basis. Values are not silently interpreted as a regulatory method. Numeric input changes clear earlier results; CSV files are read locally, without uploading. The demonstration values only illustrate the arithmetic.
Calculation or decision method
Matched-basis mode
Recovery = 100 × (spiked − native) / known added concentration. All three concentrations must already refer to the same original-sample-equivalent reporting basis. This is not valid if one number is an instrument-diluted result and another is already back-calculated.
Physical-volume mode
For a simple aqueous aliquot, assume additive volumes. With original sample volume V, spike volume v, native concentration C0 and stock concentration Cs: native contribution in the mixture is C0×V/(V+v); added analyte is Cs×v/(V+v). Subtract the diluted native contribution from the measured final-mixture concentration, divide by the added contribution, and multiply by 100.
This mass-conservation form is explicitly derived for the stated inputs. It accounts for native dilution as well as added-analyte dilution. Do not also apply a prior original-sample correction to the final-mixture reading. The cited manufacturer's simplified recovery guidance is context, not a claim that every analytical method uses this exact reporting convention.
How to interpret the result
Read the breakdown, exclusions and input record before the headline. Meeting an entered numeric condition is not a complete analytical quality decision. Retain the original bench sheet and resolve differences with the laboratory reviewer.
Worked example
Matched basis: native 5 mg/L, measured spike 14.6 mg/L and addition 10 mg/L give 96% recovery. For a separate physical-volume example, native 2 mg/L in 100 mL plus 10 mL of 100 mg/L stock should give 10.9091 mg/L at full recovery; entering that final-mixture result gives 100%.
Assumptions
The entered measurements describe the same stated sample, method and basis. Inputs must already account for any upstream dilution not explicitly modeled. Criteria come from the governing SOP, not from this website.
Limitations
Physical-volume mode covers only the stated aqueous sample and spike addition. It does not reconcile extraction/digestion yields, dry-weight bases, extra reagents, evaporative loss or additional laboratory dilutions. Volume correction does not fix changes in matrix behavior caused by a large spike. Negative and above-100% recoveries remain visible for investigation; they are not clipped or used to automatically correct official results. The example recovery range is not a universal standard.
Sources
- USGS — Design, Analysis, and Interpretation of Field Quality-Control Data
- Thermo Fisher Scientific — Why and How to Matrix Spike