#protein-concentration-calculator {
max-width: 500px;
margin: 20px auto;
padding: 15px;
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@media (max-width: 500px) {
#protein-concentration-calculator {
margin: 10px;
padding: 10px;
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h2 {
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Protein Concentration Calculator
Calculate protein concentration using absorbance at 280 nm or other methods.
Absorbance at 280 nm
Bradford Assay
BCA Assay
Select method, enter values, then click “Calculate”.
Note: Assumes 1 cm path length for A280 method. Use standard curve slope for assay methods.
JavaScript is disabled. Please enable it to use the calculator. (function() { if (!document.getElementById(‘protein-concentration-calculator’)) return; const form = document.getElementById(‘calc-form’); const methodSelect = document.getElementById(‘method’); const absorbanceInput = document.getElementById(‘absorbance’); const extinctionCoefficientInput = document.getElementById(‘extinction-coefficient’); const molecularWeightInput = document.getElementById(‘molecular-weight’); const standardCurveInput = document.getElementById(‘standard-curve’); const extinctionCoefficientGroup = document.getElementById(‘extinction-coefficient-group’); const molecularWeightGroup = document.getElementById(‘molecular-weight-group’); const standardCurveGroup = document.getElementById(‘standard-curve-group’); const resultDiv = document.getElementById(‘result’); function toggleInputs() { const method = methodSelect.value; if (method === ‘A280’) { extinctionCoefficientGroup.style.display = ‘block’; molecularWeightGroup.style.display = ‘block’; standardCurveGroup.style.display = ‘none’; } else { extinctionCoefficientGroup.style.display = ‘none’; molecularWeightGroup.style.display = ‘none’; standardCurveGroup.style.display = ‘block’; } } methodSelect.addEventListener(‘change’, toggleInputs); toggleInputs(); function calculate() { resultDiv.className = ”; resultDiv.innerHTML = ”; try { const method = methodSelect.value; const absorbance = parseFloat(absorbanceInput.value); if (isNaN(absorbance) || absorbance < 0) throw new Error('Absorbance/Value must be a non-negative number.'); let concentration, units; if (method === 'A280') { const extinctionCoefficient = parseFloat(extinctionCoefficientInput.value); const molecularWeight = parseFloat(molecularWeightInput.value); if (isNaN(extinctionCoefficient) || extinctionCoefficient <= 0) throw new Error('Extinction coefficient must be a positive number.'); if (isNaN(molecularWeight) || molecularWeight <= 0) throw new Error('Molecular weight must be a positive number.'); // Concentration (mg/mL) = Absorbance / (Extinction Coefficient * Path Length) * Molecular Weight (in Da) // Path length = 1 cm, Molecular Weight in kDa needs conversion to Da (*1000) concentration = (absorbance / extinctionCoefficient * molecularWeight * 1000) * 1000; units = 'mg/mL'; } else { const standardCurve = parseFloat(standardCurveInput.value); if (isNaN(standardCurve) || standardCurve <= 0) throw new Error('Standard curve slope must be a positive number.'); // Concentration (μg/mL) = Absorbance * Standard Curve Slope concentration = absorbance * standardCurve; units = 'μg/mL'; } resultDiv.innerHTML = `Concentration: ${concentration.toFixed(2)} ${units}`; resultDiv.className = ‘success’; } catch (error) { resultDiv.innerHTML = `Error: ${error.message}`; resultDiv.className = ‘error’; } } function reset() { form.reset(); toggleInputs(); resultDiv.className = ”; resultDiv.innerHTML = ‘Select method, enter values, then click “Calculate”.’; methodSelect.focus(); } document.getElementById(‘calculate-btn’).addEventListener(‘click’, calculate); document.getElementById(‘reset-btn’).addEventListener(‘click’, reset); form.addEventListener(‘keypress’, function(e) { if (e.key === ‘Enter’ && e.target.tagName !== ‘BUTTON’) { e.preventDefault(); calculate(); } }); })();