How to Evaluate a New Peptide Supplier: The Complete Checklist

Choosing a peptide supplier is one of the most consequential decisions a researcher makes. A reliable supplier delivers consistent, well-characterized compounds that form the foundation of reproducible science. An unreliable one introduces hidden variables that can waste months of work and thousands of dollars. Yet many researchers select suppliers based on price alone, or simply continue ordering from whichever company a colleague once recommended.

This guide presents a structured, 15-point evaluation checklist designed to help you assess any peptide supplier systematically. Whether you are sourcing peptides for the first time or considering a switch from your current vendor, working through these criteria will give you a comprehensive picture of a supplier's capabilities and trustworthiness.

The 15-Point Supplier Evaluation Checklist

1. Certificate of Analysis (COA) Quality

The COA is the most important document a supplier provides. It should be specific to the batch you are purchasing — not a generic template. Evaluate the COA for the following:

• Is it batch-specific with a unique lot number?
• Does it include the peptide sequence, molecular weight, and molecular formula?
• Are testing methods clearly identified (e.g., \"RP-HPLC\" rather than just \"HPLC\")?
• Does it report actual measured values, not just \"Pass/Fail\"?
• Is it dated, and does the date correspond to reasonable manufacturing timelines?

Red flag: Generic COAs that look identical across multiple batches or products, COAs without lot numbers, or documents that only state \"Purity: >98%\" without chromatographic data.

2. Third-Party Testing Availability

A confident supplier should be willing to provide samples for independent verification or supply documentation from accredited third-party laboratories. Ask whether:

• The supplier uses any external testing services
• They will provide a sample for your own independent analysis before placing a large order
• They can furnish raw analytical data files (not just summary reports)

3. HPLC Data and Chromatograms

High-performance liquid chromatography is the standard method for assessing peptide purity. A trustworthy supplier should provide actual chromatograms, not just purity percentages. When evaluating HPLC data:

• Look for a clearly defined main peak with good resolution from impurity peaks
• Check that the method parameters are stated (column type, mobile phase, gradient, detection wavelength)
• Verify that the integration parameters are reasonable (baseline drawn correctly, no obvious peak shaving)
• Confirm purity is calculated by area normalization at 220 nm (the standard for peptides)

4. Mass Spectrometry Confirmation

Mass spectrometry (MS) confirms that the peptide has the correct molecular identity. At minimum, a supplier should provide:

• An MS spectrum showing the observed molecular weight matches the theoretical value
• The ionization method used (ESI-MS or MALDI-TOF are most common)
• The mass accuracy — the observed mass should agree with the theoretical mass within the expected tolerance for the method (typically ±0.1% for ESI, ±0.05% for MALDI-TOF)

5. Manufacturing Transparency

Understanding how and where your peptides are made helps assess quality and consistency. Investigate the following:

• Does the supplier manufacture in-house or resell from third-party manufacturers?
• What synthesis method do they use (Fmoc solid-phase, Boc solid-phase, liquid-phase)?
• Can they describe their purification process?
• Are they willing to discuss their manufacturing facility and equipment?

Note: Many legitimate suppliers outsource manufacturing. This is not inherently problematic, but the supplier should be transparent about it and should still maintain quality oversight of their manufacturing partners.

6. Purity Grade Options

Different research applications require different purity levels. A well-established supplier should offer multiple purity grades:

Purity Grade	Typical Purity	Common Applications
Crude	~50–70%	Antibody production, initial screening
Desalted	~70–85%	ELISA standards, non-quantitative assays
Standard	>95%	Most in vitro research, binding assays
High purity	>98%	Quantitative studies, dose-response curves

7. Custom Synthesis Capabilities

Even if you are initially purchasing catalog peptides, custom synthesis capabilities indicate a supplier's technical depth. Evaluate whether they can handle:

• Long peptides (>40 amino acids)
• Peptides with post-translational modifications (phosphorylation, glycosylation, acetylation)
• Cyclic peptides
• Peptides containing non-natural amino acids
• Isotope-labeled peptides for mass spectrometry applications

8. Shipping and Packaging Practices

How a supplier ships its products reveals its commitment to product integrity. Ask about or observe:

• Are peptides shipped lyophilized (preferred) or in solution?
• Is appropriate cold-chain packaging used (dry ice, gel packs)?
• Are vials sealed properly with desiccant included?
• Is packaging adequate to prevent physical damage during transit?
• Are shipping days chosen to avoid weekend transit delays?

9. Pricing Structure and Transparency

While price should never be the sole criterion, pricing practices reveal a supplier's business ethics. Evaluate:

• Are prices clearly listed, or do you have to request a quote for every item?
• Is the pricing consistent with market rates? Dramatically low prices warrant suspicion
• Are there hidden fees for COAs, shipping, or handling?
• Does the supplier offer volume discounts for larger orders?
• Are custom synthesis quotes detailed, with clear deliverables and timelines?

Red flag: Suppliers offering peptides at 30–50% below market rates without a clear explanation. Quality synthesis, purification, and testing have real costs.

10. Customer Support and Technical Expertise

The quality of a supplier's technical support reflects the depth of their scientific knowledge. Test their support by:

• Asking a specific technical question about solubility or reconstitution of a peptide you are considering
• Requesting guidance on storage conditions for a particular compound
• Inquiring about potential sequence-related synthesis challenges
• Noting response time and the technical depth of the answer

11. Website and Documentation Quality

A supplier's public-facing materials indicate their professionalism and attention to detail:

• Is the website well-maintained and regularly updated?
• Are product descriptions scientifically accurate?
• Do they provide handling and storage instructions for their products?
• Are safety data sheets (SDS) readily available?
• Do they maintain a knowledge base or FAQ section?

12. Reputation and Track Record

Investigate the supplier's standing in the research community:

• How long have they been in business?
• Are their peptides cited in peer-reviewed publications?
• Can they provide references from other researchers or institutions?
• What do independent review platforms and forums say about them?
• Have they been involved in any regulatory actions or warnings?

13. Regulatory Compliance

Compliance with relevant regulations demonstrates a supplier's commitment to quality standards:

• Do they hold any quality certifications (ISO 9001, GMP certification)?
• Are they registered with appropriate regulatory bodies in their country of operation?
• Do they comply with import/export regulations for peptide compounds?
• Can they provide documentation needed for your institution's procurement processes?

14. Batch-to-Batch Consistency

Consistency across production runs is critical for reproducible research. Assess this by:

• Asking the supplier what their specifications are for batch-to-batch variability
• Requesting COAs from multiple batches of the same product to compare
• Asking whether they retain reference standards for each product
• Inquiring about their process validation and quality control procedures

15. Return and Resolution Policies

How a supplier handles problems tells you as much as how they handle routine orders:

• Do they have a clear return or replacement policy for defective products?
• How do they handle disputes over product quality?
• Will they re-test a product if you raise a concern about your analytical results?
• What is their process for investigating and resolving complaints?

Putting the Checklist Into Practice

We recommend using a scoring approach. For each of the 15 criteria, assign a score from 0 to 3:

Score	Meaning
0	Fails to meet the criterion or information is unavailable
1	Partially meets the criterion with notable gaps
2	Meets the criterion adequately
3	Exceeds expectations for this criterion

A perfect score would be 45. In practice, a score of 30 or above generally indicates a reliable supplier. Scores below 20 should prompt serious caution, regardless of pricing.

Weighted Priorities

Not all criteria carry equal weight. We suggest prioritizing as follows:

• Critical (must score 2+): COA quality, HPLC data, mass spectrometry confirmation, manufacturing transparency
• Important (should score 2+): Third-party testing, shipping practices, batch consistency, return policies
• Valuable (desirable at 2+): Custom capabilities, pricing structure, website quality, regulatory compliance

Bottom line: Investing time in supplier evaluation upfront saves far more time than troubleshooting failed experiments caused by substandard reagents. A thorough assessment protects both your research and your budget.

Frequently Asked Questions

How many suppliers should I evaluate before choosing one?

We recommend evaluating at least three suppliers using this checklist before making a decision. This gives you a reasonable comparison basis and helps calibrate your expectations for what constitutes standard industry practice versus exceptional quality. For critical research programs, maintaining relationships with two qualified suppliers provides a valuable backup option.

Should I always choose the supplier with the highest purity peptides?

Not necessarily. Higher purity comes at a higher cost and longer lead times. The appropriate purity level depends on your application. For initial screening or antibody production, 70–85% purity may be sufficient. For quantitative binding studies or dose-response experiments, 95% or higher is typically warranted. The key is matching purity to purpose and ensuring the stated purity is accurately measured and documented.

Is it a red flag if a supplier manufactures overseas?

Not inherently. Many high-quality peptides are manufactured in facilities around the world, including in China, India, and other countries with strong chemical manufacturing sectors. What matters is the quality management system, testing rigor, and transparency — not the geographic location. Apply the same evaluation criteria regardless of where the supplier is based, and pay particular attention to documentation quality and willingness to provide raw analytical data.

How often should I re-evaluate my current peptide supplier?

We recommend a formal re-evaluation annually or whenever you notice any quality issues. Additionally, re-evaluate if the supplier changes ownership, moves manufacturing facilities, or significantly changes their pricing structure. Keep a file of COAs from your orders over time to track batch-to-batch consistency — gradual drift in purity or the appearance of new impurity peaks can indicate process changes.