PCR and qPCR master mix
PCR Master Mix Recipe
Bench-ready PCR master mix recipe for a standard 25 µL Taq reaction with worked component math, qPCR notes, and common pitfalls.
Standard 25 µL Taq reaction (per reaction)
- 10x Reaction Buffer
- 2.5 µLfinal 1x in 25 µL reaction
- dNTPs (10 mM each)
- 0.5 µLfinal 200 µM each
- Forward primer (10 µM)
- 1.25 µLfinal 500 nM
- Reverse primer (10 µM)
- 1.25 µLfinal 500 nM
- Taq polymerase (5 U/µL)
- 0.125 µL~0.625 U per reaction
- Template DNA
- 1 µL1–100 ng genomic typical
- Nuclease-free water
- ~18.4 µLto 25 µL final
Preparation steps
- 1Confirm reaction count, then multiply each per-reaction volume by reactions × (1 + excess). 10% excess is typical to cover pipette losses.
- 2Combine components on ice in this order: water, buffer, dNTPs, primers, then polymerase. Mix gently between additions.
- 3Dispense 24 µL aliquots (for a 25 µL reaction) into chilled tubes or wells, then add 1 µL of template last.
- 4Cap, spin briefly, and load the thermocycler with your validated cycling program.
Worked example
- For 12 reactions × 25 µL with 10% excess, the effective scale factor is 13.2.
- Buffer total = 2.5 µL × 13.2 = 33 µL. Forward primer total = 1.25 × 13.2 = 16.5 µL. Polymerase total = 0.125 × 13.2 = 1.65 µL. Total mix = 25 × 13.2 = 330 µL.
Safety and verification
- Keep enzymes on a cold block; even brief warming reduces activity.
- Use filter tips and a dedicated set of pipettes for PCR setup to prevent amplicon carryover.
- Decontaminate the bench with a fresh 10% bleach wipe before high-sensitivity assays.
Common mistakes
- Forgetting the excess factor — running out of master mix on the last reaction.
- Adding template into the master mix tube instead of dispensing aliquots first.
- Pipetting volumes below pipette accuracy (typically <0.5 µL) — use an intermediate dilution or smaller pipette.
- Mixing up final vs stock concentrations for primers (10 µM stock vs 500 nM final).
Frequently asked questions
How do you calculate a PCR master mix?
For each component, multiply (final concentration / stock concentration) × per-reaction volume to get the per-reaction volume. Then multiply by reactions × (1 + excess/100). Water fills the remainder up to the final reaction volume.
How much excess should a PCR master mix include?
10% excess is the bench standard. For small batches (≤6 reactions), use 15–20% because pipette losses are a larger fraction of the total.
What is a typical TaqMan qPCR master mix?
A 20 µL TaqMan reaction usually has 10 µL of 2x master mix, primers at 900 nM final each, probe at 250 nM final, 2 µL cDNA template, and water to volume. The LabTools master mix calculator includes a TaqMan preset.
Can the master mix go below 0.5 µL per reaction?
Yes, but most lab pipettes lose accuracy below 0.5 µL. Make an intermediate dilution of the stock, or batch by group of reactions, then add separately.
Scale this recipe without spreadsheet drift
Open LabTools for unit-aware solution prep, buffer presets, and protocol-style output.