mgtomL.app
← Browse all tools

Laboratory concentration recovery check

Spike recovery calculator

Estimate how much added analyte is recovered in a spiked sample. Enter the original sample concentration and volume, the spike stock concentration and volume, and the measured final concentration on the same mg/mL basis.

Enter your values

Result

Results are based only on the inputs and assumptions shown here. Nothing you enter is sent or saved.

Formula: final mL = sample mL + spike mL; recovered spike mg = measured final mg/mL × final mL − original sample mg/mL × sample mL; recovery % = recovered spike mg ÷ (stock mg/mL × spike mL) × 100

Worked example

A 10 mL sample at 2 mg/mL contains 20 mg. A 1 mL spike at 10 mg/mL adds 10 mg. With an additive final volume of 11 mL, a measured 2.7 mg/mL implies 29.7 mg total, or 9.7 mg above the native 20 mg: 97% recovery.

Correct the background for spike volume

The original concentration is diluted when the spike is added. Subtracting the original mg/mL directly from the final mg/mL would ignore that change. EPA guidance defines background on the spiked mixture’s volume basis; this tool performs the equivalent mass balance.

Keep all measurements comparable

Use the same analyte and concentration basis throughout. Correct any instrument-side dilution before entering the measured final concentration. The model assumes homogeneous liquids, additive volumes and no separate evaporation or volume adjustment. If the actual final volume differs, this model is not appropriate.

Do not turn the percentage into an automatic verdict

Negative or above-100% apparent recovery can occur from inconsistent inputs, bias, matrix effects or measurement variation; these results are shown without clipping. Acceptance criteria depend on the validated method and sample. This tool is laboratory arithmetic, not a dosing, diagnosis or treatment tool.

Explore the related calculation

For a different starting point, try the standard-curve concentration calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

Found a problem? Email contact@mgtoml.app.