Last updated: April 21, 2026

What QC Should I Request for Oligos? Vendor QC & Pool QC Guide

Q: When should I use PAGE vs HPLC purification?

PAGE (polyacrylamide gel electrophoresis): Best for separating full-length from truncation products, especially for oligos >40 nt. Resolution is length-dependent — excellent for removing n-1 deletions. HPLC (high-performance liquid chromatography): Best for removing failure sequences and chemical modifications. Provides higher purity (>95%) and is better for shorter oligos (15-30 nt). Also preserves chemical modifications (fluorophores, biotin).

Use this page when you need to decide whether vendor desalting is enough, how to read a QC report or COA, or how to QC an oligo pool before and after synthesis. It walks from single-primer QC decisions to pool-level representation checks, so you can match the QC request to the risk of your experiment instead of overpaying for generic upgrades. Use our Batch Sequence QC, Error Rate Calculator, and Uniformity Estimator for computational QC before and after synthesis.

High-tech Oligonucleotide Laboratory Quality Control

Key Takeaways

•Oligo QC verifies sequence identity, purity, and quantity. The three pillars: mass spectrometry (identity), HPLC/PAGE (purity), and UV absorbance (quantity).
•Coupling efficiency during synthesis determines full-length yield: 99% coupling for a 20-mer gives 83% full-length; 99.5% gives 90%.
•Purification method depends on application: desalting for standard PCR, PAGE for primers >40 nt, HPLC for probes and quantitative assays.
•The n-1 deletion product (missing one nucleotide) is the most common synthesis impurity, detectable by mass spectrometry as a -289 to -329 Da shift.
•Pool-specific QC requires NGS verification at 500-1000x coverage: check representation (>90%), uniformity (Gini <0.25), and dropout rate (<10%).
•Computational pre-synthesis QC (GC screening, homopolymer detection, structure prediction) prevents 40-60% of synthesis-related quality issues.

🔍 What QC question do you need answered?

→ What QC should I request from my vendor?→ How do I read my vendor's QC report?→ Desalting vs HPLC vs PAGE — which do I need?→ How do I QC an oligo pool?→ Screening oligos before I order → What coupling efficiency should I expect?

1. Why Oligo QC Matters

Oligonucleotide quality directly determines experimental success. A primer with incorrect sequence, truncation products, or inaccurate concentration can waste weeks of work and thousands of dollars in reagents and sequencing costs. Understanding QC metrics helps you choose the right purification level, interpret vendor QC data, and troubleshoot experimental failures.

Quality Issue	Cause	Experiment Impact	QC Detection
Wrong sequence	Synthesis error, ordering mistake	No amplification, wrong clone	Mass spectrometry
Truncation products	Low coupling efficiency	Non-specific bands, reduced yield	PAGE, HPLC, mass spec
Depurination	Acid exposure, old stock	Random cleavage during PCR	Mass spec (-136 Da for dA)
Inaccurate concentration	Wrong extinction coefficient	Suboptimal PCR, variable results	UV + sequence-based ε
Chemical impurities	Incomplete deprotection	Inhibit enzymatic reactions	HPLC, mass spec (+53 Da)
Pool representation bias	Synthesis or amplification bias	Missing targets in screen	NGS verification

2. QC Methods Overview

Method	What It Measures	Resolution	Throughput	Typical Cost
ESI-MS	Molecular weight (sequence identity)	±1-2 Da (single nucleotide)	Medium	$5-15/oligo
MALDI-TOF MS	Molecular weight	±5-10 Da	High (plates)	$3-10/oligo
Analytical HPLC	Purity, impurity profile	Separates n, n-1, n+1	Low	$10-20/oligo
Capillary Electrophoresis	Length and purity	1 nt resolution	High	$5-10/oligo
PAGE (analytical)	Length distribution	1 nt for short oligos	Low	$10-20/oligo
UV Spectroscopy	Concentration, purity ratios	A260/A280 ratio	Very high	<$1/oligo
NGS Sequencing	Exact sequence + representation	Single base accuracy	Very high (pools)	$200-500/pool

3. Purity Assessment & Coupling Efficiency

Synthesis purity is determined by coupling efficiency — the percentage of chains that successfully add each nucleotide during synthesis. Even small differences in coupling efficiency have dramatic effects on full-length yield as oligo length increases.

Full-Length Yield Formula

Full-length % = (Coupling Efficiency)^(N-1) × 100

Where N = oligo length in nucleotides. This exponential relationship is why coupling efficiency matters so much for longer oligos.

Oligo Length	98.5% CE	99.0% CE	99.5% CE	99.8% CE
20 nt	75%	83%	90%	96%
30 nt	65%	75%	87%	94%
50 nt	46%	61%	78%	90%
80 nt	30%	45%	67%	85%
100 nt	22%	37%	61%	82%
150 nt	10%	22%	47%	74%

CE = Coupling Efficiency. Values show % of chains that are full-length (no deletions). Use our Error Rate Calculator for custom calculations.

4. Purification Methods Compared

Method	Purity	Recovery	Best For	Cost
Desalting	75-85%	>90%	Standard PCR primers, sequencing	$
Cartridge (OPC)	85-90%	70-80%	Routine applications, short oligos	$$
PAGE	90-95%	40-60%	Cloning primers, oligos >40 nt, gene assembly	$$$
HPLC	>95%	50-70%	qPCR probes, labeled oligos, therapeutic oligos	$$$$
Dual HPLC	>98%	30-50%	Antisense therapeutics, diagnostic probes	$$$$$

When to Invest in Higher Purification

Standard PCR (desalting is fine): Truncation products are poor competitors for primer binding — they have lower Tm and anneal less efficiently. Full-length primers dominate the PCR reaction.

Cloning and gene assembly (PAGE/HPLC needed): Truncation products can ligate into vectors, creating mutant clones. For gene assembly, every deletion in an oligo creates a frameshift in the final gene.

qPCR probes (HPLC required): Truncated probes produce background signal with SYBR Green or reduce TaqMan probe efficiency by competing for binding site.

💡 Pro Tip: For PCR primers under 30 nt, desalting is almost always sufficient. The cost difference between desalting ($5) and HPLC ($25-40) per oligo adds up quickly when ordering dozens of primers. Reserve HPLC for probes and gene assembly oligos where purity directly affects results.

⚠️ Pitfall: PAGE purification has only 40-60% recovery yield. If you're ordering a small synthesis scale (10 nmol), PAGE purification may leave you with <5 nmol — barely enough for 10 PCR reactions. Order at 25 nmol or higher if you need PAGE purification.

⚠️ Pitfall: A CoA showing "95% purity by HPLC" does not guarantee your oligo is correct. HPLC measures length homogeneity but cannot distinguish a correct 20-mer from a 20-mer with a single base substitution. Always cross-check with mass spectrometry: if the observed mass deviates from the expected mass by >0.01%, you have a truncation or misincorporation that HPLC alone would miss.

5. Interpreting Your Vendor's QC Report

Most oligo vendors provide a Certificate of Analysis (CoA) with your order. Here's how to read the key metrics and spot potential problems before you waste reagents.

ESI-MS (Mass Spec)

✔ Good: Main peak matches expected MW within ±2 Da

△ Okay: Minor adducts (+Na: +22 Da, +K: +38 Da) present but main peak correct

✖ Problem: Main peak off by >5 Da → wrong sequence or failed deprotection

HPLC Purity %

✔ Good: >90% for standard; >95% for HPLC-purified oligos

△ Okay: 80-90% typical for desalting-only

✖ Problem: <75% suggests poor coupling or degradation

OD260 / Yield

✔ Good: Within vendor spec (typically 4-10 OD for 25 nmol scale)

△ Okay: Low yield may indicate synthesis difficulty (long or GC-rich)

✖ Problem: Very low yield (<2 OD) for standard 20-mer → request resynthesis

PAGE Analysis

✔ Good: Single band at expected position

△ Okay: Minor n-1 band visible but weak

✖ Problem: Significant truncation ladder → request PAGE or HPLC purification

💡 Pro Tip: If your experiment fails and the vendor CoA looks fine, the problem may be concentration measurement rather than purity. Most CoA yields are calculated from OD260 using a generic extinction coefficient. Use our Oligo Properties Calculator to calculate the sequence-specific extinction coefficient and re-measure your stock concentration.

6. Worked Example: Reading a 20-mer COA

You ordered a 20-mer PCR primer from IDT with desalting purification. The Certificate of Analysis arrives with your oligo. Here's how to interpret each section:

Primer Sequence

5'-ATCGATCGATCGTACGATCG-3'

Length: 20 nt | GC: 50% | Expected MW: 6,133.0 Da

✅ Mass Spec Check

Reported MW: 6,133.2 Da (±0.2 Da from expected). Pass — confirms correct sequence identity. Look for n-1 peak at ~6,133 - 304 = 5,829 Da (loss of dTMP). If n-1 peak is <15% of main peak area, purity is acceptable for PCR.

✅ Yield Check

Reported: 7.2 OD at 25 nmol scale. This translates to: nmol = (7.2 × 1000) / 195,800 = 36.8 nmol (using sequence-specific ε₂₆₀ = 195,800 L/mol·cm). This is above the 25 nmol ordered — normal for 20-mers.

📝 Resuspension Calculation

Target: 100 µM stock. Add 368 µL TE buffer (36.8 nmol / 100 µM = 0.368 mL). For 10 µM working solution: dilute 1:10 (10 µL stock + 90 µL water). Use our Dilution Calculator for complex multi-step dilutions.

🔍 Mass Spec Peak Interpretation Quick Reference▾

Peak Shift	Identity	Cause	Action
-289 Da	n-1 (lost dCMP)	Coupling failure at C	Acceptable if <15%
-304 Da	n-1 (lost dTMP)	Coupling failure at T	Acceptable if <15%
-313 Da	n-1 (lost dAMP)	Coupling failure at A	Acceptable if <15%
-329 Da	n-1 (lost dGMP)	Coupling failure at G	Acceptable if <15%
+22 Da	Na⁺ adduct	Insufficient desalting	Usually harmless for PCR
+38 Da	K⁺ adduct	Buffer contamination	Usually harmless for PCR
+53 Da	Cyanoethyl group	Incomplete deprotection	May inhibit enzymes — repurify
-136 Da	Depurination (lost A)	Acid exposure / old stock	Discard and reorder

💡 Pro Tip: Vendors report yield in OD units using a generic extinction coefficient (typically 33 µg/mL per OD for ssDNA). For accurate concentration, always recalculate using thesequence-specific ε₂₆₀ from our Oligo Properties Calculator. The difference can be 20-30%.

7. Pool-Specific QC (NGS Verification)

Oligo pools require entirely different QC approaches than individual oligos. Mass spectrometry and HPLC cannot resolve thousands of sequences; instead, next-generation sequencing (NGS) provides the gold standard for pool QC.

Metric	Definition	Excellent	Acceptable	Poor
Representation	% of designed oligos detected	>95%	>90%	<85%
Dropout Rate	% of oligos with <10 reads	<5%	<10%	>15%
Uniformity (CV)	90th/10th percentile ratio	<2-fold	<3-fold	>5-fold
Gini Coefficient	Inequality measure (0=perfect)	<0.15	<0.25	>0.35
Sequence Accuracy	% perfect-match reads	>90%	>85%	<80%
Skew (max/min)	Ratio of most to least abundant	<10x	<50x	>100x
NGS Depth	Average reads per oligo	>1000x	>500x	<200x

Use our Uniformity Estimator to predict expected pool quality before synthesis, and our Error Rate Calculator to interpret post-synthesis sequence accuracy data.

8. Computational QC Before Synthesis

Pre-synthesis computational screening is the most cost-effective QC step — it catches design problems before you spend money on synthesis. Screen all sequences through these checks:

GC Content Screening

Flag sequences with GC <30% or >70%. These are prone to synthesis failure and amplification bias.

Use GC Content Analyzer →

Homopolymer Detection

Flag sequences with ≥5 consecutive identical bases. Poly-G and poly-C are especially problematic for synthesis fidelity.

Use Batch Sequence QC →

Secondary Structure Analysis

Flag sequences with stable hairpins (ΔG < -3 kcal/mol). These impair synthesis and downstream amplification.

Use Structure Predictor →

Tm Uniformity Check

For pools: verify Tm range is within 5°C across all sequences. Large Tm variation causes amplification bias.

Use Tm Calculator (batch) →

Complexity & Repeat Analysis

Flag tandem repeats, palindromes >8 bp, and low-complexity sequences that cause synthesis slippage.

Use Batch Sequence QC →

9. Vendor QC Guarantees Compared

Not all vendors provide the same QC data or guarantees. Understanding what's included — and what's optional — helps you choose the right vendor and interpret results correctly.

QC Feature	IDT	Twist	GenScript	Eurofins
Mass Spec (ESI or MALDI)	✅ Standard	✅ Standard	✅ Standard	✅ Standard
COA with purity %	✅ Always	✅ Always	✅ Always	✅ Always
HPLC for purity	✅ If HPLC-purified	⚠️ On request	✅ If HPLC-purified	✅ If HPLC-purified
PAGE for purity	✅ If PAGE-purified	❌ Not offered	✅ If PAGE-purified	✅ If PAGE-purified
Coupling eff. reported	⚠️ Indirect (purity %)	✅ Direct	⚠️ Indirect	⚠️ Indirect
Pool NGS verification	✅ oPools™ included	✅ Included (10K+)	❌ Not standard	❌ Not standard
Guaranteed purity ≥85%	✅ Standard grade	✅ Standard	✅ Standard	✅ Standard
Guaranteed purity ≥95%	✅ HPLC purified	⚠️ On request	✅ HPLC purified	✅ HPLC purified
Re-synthesis policy	✅ Free if QC fails	✅ Free re-synth	✅ Free re-synth	✅ Free re-synth
Max oligo length	200 nt	300 nt (genes)	120 nt	110 nt

Specifications as of 2026. Policies may vary by order size and region. Always verify current terms with your vendor.

💡 Pro Tip: For critical experiments (therapeutic oligos, CRISPR libraries), always request HPLC purificationplus an independent mass spec check. The ~$2–5/oligo premium for HPLC is cheap insurance against a failed experiment that costs thousands in reagents and weeks of time.

10. Frequently Asked Questions

What QC should I request when ordering oligos?▾

For standard PCR primers: desalting purification + mass spec confirmation is sufficient ($5-15/oligo). For qPCR probes (TaqMan, molecular beacons): request HPLC purification + mass spec + analytical HPLC trace ($20-40/oligo). For cloning primers and gene synthesis oligos: PAGE purification removes n-1 truncations ($15-25/oligo). For genome-scale oligo pools: request NGS verification data showing representation and uniformity metrics.

How do I interpret an oligo mass spectrum?▾

The main peak should match the expected molecular weight (within ±2 Da for ESI-MS). Common impurity peaks: n-1 product (-289 to -329 Da, single deletion depending on which base is missing — dCMP 289 Da, dTMP 304 Da, dAMP 313 Da, dGMP 329 Da), n+1 product (+289-329 Da, single addition), cyanoethyl adduct (+53 Da, incomplete deprotection), and sodium adduct (+22 Da). If the main peak matches and impurities are <15% of signal, the oligo is acceptable for most applications.

When should I use PAGE vs HPLC purification?▾

PAGE (polyacrylamide gel electrophoresis): Best for separating full-length from truncation products, especially for oligos >40 nt. Resolution is length-dependent — excellent for removing n-1 deletions. HPLC (high-performance liquid chromatography): Best for removing failure sequences and chemical modifications. Provides higher purity (>95%) and is better for shorter oligos (15-30 nt). Also preserves chemical modifications (fluorophores, biotin).

What coupling efficiency should I expect from my vendor?▾

Standard column synthesis: 99.0-99.5% average stepwise yield is typical for major vendors (IDT, Sigma, Eurofins). Premium synthesis: 99.5-99.8% for critical applications. Array-based pool synthesis: 98.5-99.5% depending on platform. Ask your vendor for lot-specific coupling efficiency data. Use our Error Rate Calculator to convert coupling efficiency to expected full-length percentage for your oligo length.

How do I calculate the amount of oligo to reconstitute?▾

Vendors report quantity in either nmol or OD260 units. For nmol: directly convert using MW. For OD260: use the formula nmol = (OD260 × 1000) / extinction coefficient (L/mol·cm). Our Oligo Properties Calculator provides the extinction coefficient from your sequence, and our Dilution Calculator helps determine resuspension volumes for your target concentration.

How long can I store oligos?▾

Lyophilized oligos: 1-2 years at -20°C, 6-12 months at 4°C, and weeks at room temperature. Resuspended in TE (10 mM Tris, 0.1 mM EDTA, pH 8.0): 6-12 months at -20°C, weeks at 4°C. Avoid repeated freeze-thaw cycles — aliquot into single-use volumes. Modified oligos (fluorophores, biotin) degrade faster; store in the dark at -20°C. Water-only resuspension accelerates depurination; always use buffered solutions.

Related Tools

Batch Sequence QC

Screen sequences for synthesis-problematic features: homopolymers, repeats, GC extremes.

Error Rate Calculator

Calculate full-length yield from coupling efficiency. Interpret synthesis quality data.

Uniformity Estimator

Predict pool representation uniformity from pool size and sequencing depth.

GC Content Analyzer

Batch GC analysis with sliding-window distribution visualization.

Secondary Structure Predictor

Calculate hairpin and dimer ΔG. Identify synthesis-blocking structures.

Oligo Properties Calculator

MW, extinction coefficient, and concentration from OD260 measurements.

Next Pages to Open

Continue with the workflow, tutorial, or calculator that matches whether the next job is ordering, QC execution, or interpreting synthesis risk.