The PEP (Principal, Enzyme, Product) calculator is a tool designed to help researchers and laboratory technicians quickly determine the required amount of a starting material (like a stock solution or enzyme) needed to achieve a desired final concentration of a product or component in a reaction or dilution. This is a fundamental calculation in many biological and chemical experiments.
The underlying principle is based on the conservation of the amount of substance. When you dilute a solution or add a reactant to a final volume, the total amount of that substance remains the same, only its concentration changes due to the change in volume. The formula used by this calculator is a rearrangement of the dilution equation, often represented as C1V1 = C2V2, or more generally, the amount of substance remains constant.
How it Works:
The PEP calculator utilizes the following logic:
Initial Volume (V1): This is the volume of the stock solution or reactant you are starting with.
Final Volume (V2): This is the total volume of the mixture after dilution or addition.
Initial Concentration (C1): This is the concentration of the substance in your stock solution or reactant.
Final Concentration (C2): This is the desired concentration of the substance in the final mixture.
The calculator determines the volume of the initial solution (V1) that needs to be taken to achieve the desired final concentration (C2) in the final volume (V2), given the initial concentration (C1). The formula derived is:
Amount of Substance (Initial) = C1 * V1
Amount of Substance (Final) = C2 * V2
Since the amount of substance is conserved:
C1 * V1 = C2 * V2
To find the volume of the initial solution (V1) required, we rearrange the formula:
V1 = (C2 * V2) / C1
In the context of this calculator, Initial Volume is the quantity we are trying to find, and the inputs are effectively:
Initial Concentration (C1)
Final Volume (V2)
Final Concentration (C2)
The calculator outputs the calculated Initial Volume (V1), which is the amount of the concentrated stock solution you need to pipette and add to bring the total volume up to Final Volume to achieve the Final Concentration.
Use Cases:
Enzyme Assays: Calculating the amount of enzyme stock needed to reach a specific working concentration in an assay buffer.
Reagent Preparation: Diluting stock solutions of chemicals, buffers, or reagents to a desired working concentration.
Media Preparation: Calculating the volume of a concentrated additive (e.g., antibiotic) required for a specific volume of cell culture media.
Molecular Biology: Preparing solutions for PCR, cloning, or other molecular techniques where precise concentrations are critical.
By using this PEP calculator, scientists can ensure accuracy and reproducibility in their experiments, saving time and valuable reagents.
function calculatePEP() {
var initialVolumeInput = document.getElementById("initialVolume");
var finalVolumeInput = document.getElementById("finalVolume");
var initialConcentrationInput = document.getElementById("initialConcentration");
var resultDiv = document.getElementById("result");
var initialVolume = parseFloat(initialVolumeInput.value);
var finalVolume = parseFloat(finalVolumeInput.value);
var initialConcentration = parseFloat(initialConcentrationInput.value);
if (isNaN(initialVolume) || initialVolume <= 0) {
resultDiv.innerHTML = "Please enter a valid positive Initial Volume.";
return;
}
if (isNaN(finalVolume) || finalVolume <= 0) {
resultDiv.innerHTML = "Please enter a valid positive Final Volume.";
return;
}
if (isNaN(initialConcentration) || initialConcentration Interpreted as Target Final Concentration (C2) in mM
// ID: finalVolume -> Interpreted as Target Final Volume (V2) in mL
// ID: initialConcentration -> Interpreted as Stock Concentration (C1) in mM
targetFinalConcentration = parseFloat(initialVolumeInput.value); // C2
var targetFinalVolume = parseFloat(finalVolumeInput.value); // V2
var stockConcentration = parseFloat(initialConcentrationInput.value); // C1
if (isNaN(targetFinalConcentration) || targetFinalConcentration <= 0) {
resultDiv.innerHTML = "Please enter a valid positive Target Final Concentration (mM).";
return;
}
if (isNaN(targetFinalVolume) || targetFinalVolume <= 0) {
resultDiv.innerHTML = "Please enter a valid positive Target Final Volume (mL).";
return;
}
if (isNaN(stockConcentration) || stockConcentration <= 0) {
resultDiv.innerHTML = "Please enter a valid positive Stock Concentration (mM).";
return;
}
if (stockConcentration < targetFinalConcentration) {
resultDiv.innerHTML = "Stock Concentration cannot be lower than Target Final Concentration.";
return;
}
// Calculate the volume of stock solution needed (V1)
// V1 = (C2 * V2) / C1
calculatedVolumeNeeded = (targetFinalConcentration * targetFinalVolume) / stockConcentration;
// Display the result
resultDiv.innerHTML = "You need to take: " + calculatedVolumeNeeded.toFixed(3) + " mL of the stock solution.Add this volume to a container and bring the total volume up to " + targetFinalVolume.toFixed(0) + " mL to achieve a final concentration of " + targetFinalConcentration.toFixed(3) + " mM.";
}