This calculator is designed to assist researchers in preparing solutions at specific concentrations. Specifically, it helps determine the amount of buffer needed to dilute a stock solution to a desired final concentration, or to calculate the final concentration achieved after adding a specific volume of buffer. This is a common task in molecular biology, biochemistry, and other laboratory settings, particularly when working with reagents like DNA/RNA oligonucleotides (often supplied by Integrated DNA Technologies, hence "IDT") or proteins.
The Math Behind the Calculation
The core principle used here is the conservation of mass (or in this case, the amount of solute). The amount of solute in the initial solution must equal the total amount of solute in the final, diluted solution. This is represented by the formula:
C1 * V1 = C2 * V2
Where:
C1 is the initial concentration of the stock solution.
V1 is the initial volume of the stock solution.
C2 is the target (final) concentration.
V2 is the final volume of the solution (initial volume + added buffer volume).
Scenario 1: Calculating Buffer Volume to Add
If the user provides the initial concentration (C1), initial volume (V1), and the target concentration (C2), the calculator will determine the volume of buffer (V_buffer) to add.
First, we calculate the final volume (V2) using the conservation formula rearranged:
V2 = (C1 * V1) / C2
Then, the volume of buffer to add is:
V_buffer = V2 - V1
Scenario 2: Calculating Final Concentration
If the user provides the initial concentration (C1), initial volume (V1), and the volume of buffer added (V_buffer), the calculator will determine the final concentration (C2).
First, calculate the final volume (V2):
V2 = V1 + V_buffer
Then, calculate the final concentration (C2):
C2 = (C1 * V1) / V2
How to Use the Calculator
Initial Concentration (mg/mL): Enter the concentration of your stock solution as provided by the manufacturer (e.g., 10 mg/mL).
Target Concentration (mg/mL): Enter the desired final concentration for your experiment (e.g., 1 mg/mL).
Initial Volume (µL): Enter the volume of the stock solution you are working with (e.g., 50 µL).
Buffer Volume to Add (µL):
If you know how much buffer you want to add and want to know the resulting concentration, enter that volume here. Leave the "Target Concentration" field blank (or set it to 0, the calculator will ignore it in this case).
If you know your desired target concentration and want to calculate how much buffer to add, leave this field blank (or enter 0).
Click the "Calculate" button.
The result will show either the required buffer volume to achieve the target concentration or the final concentration after adding the specified buffer volume.
Common Use Cases
Diluting synthetic DNA or RNA oligonucleotides (e.g., from IDT) to working concentrations.
Preparing protein solutions for assays.
Making serial dilutions for standard curves.
Adjusting the concentration of any liquid reagent in the lab.
function calculateResuspension() {
var initialConcentration = parseFloat(document.getElementById("initialConcentration").value);
var targetConcentration = parseFloat(document.getElementById("targetConcentration").value);
var initialVolume = parseFloat(document.getElementById("initialVolume").value);
var bufferVolumeToAddInput = document.getElementById("bufferVolume").value; // Keep as string to check if empty
var bufferVolumeToAdd = bufferVolumeToAddInput === "" ? 0 : parseFloat(bufferVolumeToAddInput);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "Your result will appear here."; // Reset previous result
// Input validation
if (isNaN(initialConcentration) || initialConcentration <= 0) {
resultDiv.innerHTML = "Error: Please enter a valid Initial Concentration (must be a positive number).";
return;
}
if (isNaN(initialVolume) || initialVolume <= 0) {
resultDiv.innerHTML = "Error: Please enter a valid Initial Volume (must be a positive number).";
return;
}
var finalConcentrationResult = "";
var requiredBufferVolumeResult = "";
var finalVolume = 0;
// Check if target concentration is provided and valid
var targetConcentrationProvided = !isNaN(targetConcentration) && targetConcentration > 0;
// Check if buffer volume is provided and valid (or if input was empty)
var bufferVolumeProvided = bufferVolumeToAddInput !== "" && !isNaN(bufferVolumeToAdd) && bufferVolumeToAdd >= 0;
if (targetConcentrationProvided && !bufferVolumeProvided) {
// Scenario 1: Calculate buffer volume to add for a target concentration
finalVolume = (initialConcentration * initialVolume) / targetConcentration;
if (finalVolume < initialVolume) {
resultDiv.innerHTML = "Error: Target concentration is higher than initial concentration. Cannot dilute.";
return;
}
var calculatedBufferVolume = finalVolume – initialVolume;
requiredBufferVolumeResult = "Add " + calculatedBufferVolume.toFixed(2) + " µL of buffer.";
finalConcentrationResult = "Final concentration will be " + targetConcentration.toFixed(2) + " mg/mL.";
finalVolume = initialVolume + calculatedBufferVolume; // Ensure finalVolume is calculated for context
} else if (bufferVolumeProvided && !targetConcentrationProvided) {
// Scenario 2: Calculate final concentration after adding a specific buffer volume
finalVolume = initialVolume + bufferVolumeToAdd;
if (finalVolume === 0) { // Should not happen if initialVolume > 0, but good to check
resultDiv.innerHTML = "Error: Final volume cannot be zero.";
return;
}
var calculatedFinalConcentration = (initialConcentration * initialVolume) / finalVolume;
finalConcentrationResult = "Final concentration will be " + calculatedFinalConcentration.toFixed(2) + " mg/mL.";
requiredBufferVolumeResult = "Buffer added: " + bufferVolumeToAdd.toFixed(2) + " µL.";
} else if (targetConcentrationProvided && bufferVolumeProvided) {
// Both provided – check for consistency or prioritize one calculation
finalVolume = initialVolume + bufferVolumeToAdd;
var calculatedFinalConcentration = (initialConcentration * initialVolume) / finalVolume;
var difference = Math.abs(calculatedFinalConcentration – targetConcentration);
var tolerance = 0.05; // Small tolerance for floating point comparisons
if (difference < tolerance) {
finalConcentrationResult = "Final concentration achieved is " + calculatedFinalConcentration.toFixed(2) + " mg/mL (matches target).";
requiredBufferVolumeResult = "Buffer added: " + bufferVolumeToAdd.toFixed(2) + " µL.";
} else {
resultDiv.innerHTML = "Note: Adding " + bufferVolumeToAdd.toFixed(2) + " µL of buffer results in a concentration of " + calculatedFinalConcentration.toFixed(2) + " mg/mL, which differs from the target of " + targetConcentration.toFixed(2) + " mg/mL.";
// Optionally, calculate the buffer needed for the target concentration
var neededFinalVolume = (initialConcentration * initialVolume) / targetConcentration;
var neededBuffer = neededFinalVolume – initialVolume;
resultDiv.innerHTML += "To reach the target concentration of " + targetConcentration.toFixed(2) + " mg/mL, you would need to add approximately " + neededBuffer.toFixed(2) + " µL of buffer.";
return; // Exit after providing detailed note
}
}
else {
resultDiv.innerHTML = "Error: Please provide either the Target Concentration or the Buffer Volume to Add, but not both simultaneously unless verifying.";
return;
}
resultDiv.innerHTML = "
" + finalConcentrationResult + "
" + requiredBufferVolumeResult + "
Total final volume: " + finalVolume.toFixed(2) + " µL.