Enrichment · Passion Projects · Lab science

Of what you added,
how much did
the method find?

List each spiked sample with the result before and after spiking. The calculator gives the recovery for each, compares it with your acceptance window and tells you what a miss usually means.

Check the recoveryWhat you get

The spike recovery calculator

The worked example is made up: nitrate spikes in creek water for a student project. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
Each spike’s recovery, the mean and RSD, and which spikes fall outside the window. It prints for a lab report and downloads as a spreadsheet.
Who it is for
Chemistry and environmental science students, science teachers running water-quality labs, and research students.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Measure each sample as it is.
  2. Add a known amount of the analyte and measure again.
  3. Type the added amount as the concentration it adds to the sample.
  4. Choose the window your method uses.
  5. Look into any spike outside it.

Check the recovery

How recovery is worked out

The difference a spike makes, against what was added.

The worked example: nitrate spikes in creek waterUnspiked0.84 mg/Lupstream sampleSpiked2.71 mg/Lafter adding 2.00Found1.87 mg/L2.71 − 0.84Recovery93.5%1.87 ÷ 2.00 × 100The worked example: nitrate spikes in creek waterUnspiked0.84 mg/Lupstream sampleSpiked2.71 mg/Lafter adding 2.00Found1.87 mg/L2.71 − 0.84Recovery93.5%1.87 ÷ 2.00 × 100
A spike asks one question: of what you added, how much did the method find?

Why spike

A calibration with clean standards shows a method can measure pure analyte. Real samples carry other substances, the matrix, that can hide or mimic it. Adding a known amount to a real sample and measuring the increase shows whether the method still finds what is there.

Reading a miss

Recovery well below 100 percent suggests the matrix suppresses the signal or analyte is lost in preparation. Recovery well above suggests interference or contamination. A spike that is tiny next to the sample’s own level is hard to read, because small errors in either measurement swing the percent.

Sources

  1. U.S. Environmental Protection Agency. Guidance on matrix spikes and quality control in environmental methods, including Method 300.0 and SW-846 Chapter One (epa.gov).
  2. Harris, D. C. (2020). Quantitative Chemical Analysis (10th ed.). W. H. Freeman. Quality assurance and spike recovery.
  3. U.S. Geological Survey. National Field Manual for the Collection of Water-Quality Data, quality-control samples (usgs.gov).
  4. National Institute of Standards and Technology. NIST/SEMATECH e-Handbook of Statistical Methods (itl.nist.gov).

The worked example is made up. Use the acceptance limits your method or teacher sets. Your entries stay in this browser. Support: team@caveatacademic.com.