body {
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margin: 0 auto;
padding: 0;
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border: 1px solid #e9ecef;
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padding: 30px;
margin: 20px 0 40px 0;
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margin-bottom: 25px;
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.input-group {
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font-size: 16px;
box-sizing: border-box; /* Ensures padding doesn't affect width */
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button {
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.result-value {
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.status-indicator {
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.status-good { background-color: #d4edda; color: #155724; }
.status-warning { background-color: #fff3cd; color: #856404; }
.status-error { background-color: #f8d7da; color: #721c24; }
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function calculateRecovery() {
var measured = parseFloat(document.getElementById('measuredConc').value);
var background = parseFloat(document.getElementById('backgroundConc').value);
var spiked = parseFloat(document.getElementById('spikedAmount').value);
var resultBox = document.getElementById('result-box');
var statusMsg = document.getElementById('status-msg');
// Reset display
resultBox.style.display = 'none';
statusMsg.className = 'status-indicator';
// Validation
if (isNaN(measured) || isNaN(spiked)) {
alert("Please enter valid numbers for Measured Concentration and Spiked Amount.");
return;
}
if (isNaN(background)) {
background = 0; // Default to 0 if empty
}
if (spiked === 0) {
alert("Spiked amount cannot be zero.");
return;
}
// Calculation Logic
// Formula: ((Measured – Background) / Spiked) * 100
var netRecovered = measured – background;
var recoveryRate = (netRecovered / spiked) * 100;
// Display Results
document.getElementById('res-net').innerText = netRecovered.toFixed(4);
document.getElementById('res-percent').innerText = recoveryRate.toFixed(2) + '%';
resultBox.style.display = 'block';
// Interpretation (Standard EPA limits often 70-130% for many methods, though varies by method)
if (recoveryRate >= 70 && recoveryRate <= 130) {
statusMsg.innerHTML = "Status: ACCEPTABLE (Within 70-130% Range)";
statusMsg.classList.add('status-good');
} else if (recoveryRate < 10) {
statusMsg.innerHTML = "Status: CRITICAL FAILURE (Extremely Low)";
statusMsg.classList.add('status-error');
} else {
statusMsg.innerHTML = "Status: OUT OF RANGE (Check Method/Interference)";
statusMsg.classList.add('status-warning');
}
}
function resetCalculator() {
document.getElementById('measuredConc').value = '';
document.getElementById('backgroundConc').value = '';
document.getElementById('spikedAmount').value = '';
document.getElementById('result-box').style.display = 'none';
}
What is Contamination Recovery Rate?
In analytical chemistry and environmental testing, the Contamination Recovery Rate (often referred to as Matrix Spike Recovery) is a critical quality control metric. It measures the efficiency of an extraction or testing method by comparing the amount of a specific substance detected in a sample against a known amount that was added (spiked) to it.
This calculation helps laboratories determine if the sample matrix (soil, water, tissue, etc.) is interfering with the analysis. If the recovery rate is too low, the method may be failing to extract the contaminant. If it is too high, there may be interference causing a false positive or signal enhancement.
The Recovery Rate Formula
The standard formula used in this calculator is:
% Recovery = [ (Cmeasured – Cunspiked) / Cspike ] × 100
Where:
- Cmeasured: The concentration detected in the spiked sample.
- Cunspiked: The background concentration detected in the original, unspiked sample (also known as the background).
- Cspike: The theoretical concentration of analyte added to the sample.
Why is this calculation important?
Calculating recovery rates is mandatory for method validation and routine Quality Assurance/Quality Control (QA/QC) in laboratories governed by EPA, FDA, or ISO standards.
- Accuracy Assessment: It confirms the method calculates the correct concentration.
- Matrix Effects: It reveals if other components in the sample are suppressing or enhancing the signal.
- Equipment Validation: It ensures that loss of analyte during preparation (e.g., filtration, digestion) is within acceptable limits.
Interpreting the Results
While acceptable limits vary depending on the specific method (e.g., EPA Method 8270 vs. Method 200.8) and the analyte type, general guidelines often suggest:
- 70% to 130%: Generally considered acceptable for most environmental analyses.
- Below 70%: Indicates poor recovery. Possible causes include analyte loss during digestion, matrix suppression, or incomplete extraction.
- Above 130%: Indicates high recovery. Possible causes include matrix interference, contamination during prep, or calibration errors.
Frequently Asked Questions
What if my background concentration is zero?
If the unspiked sample does not contain the analyte (it is "non-detect"), you simply enter 0 for the Background Concentration. The formula then simplifies to (Measured / Spiked) × 100.
Can recovery be greater than 100%?
Yes. A recovery greater than 100% implies that the instrument detected more analyte than was actually added. This is often caused by positive interference from the sample matrix or evaporation of the solvent during processing which concentrates the sample.
What units should I use?
The calculation is a unitless percentage. However, you must ensure that the Measured, Background, and Spiked concentrations are all entered in the same units (e.g., all in mg/L, all in ppm, or all in µg/kg) for the math to be correct.