Buyers should require the analytical method that matches the compound they need to control: HPLC for individual non-volatile markers, GC or GC-MS for essential-oil composition, UV-Vis for suitable total-content methods, and GPC/SEC for molecular-weight distribution.
The wrong test method can create a misleading COA. For example, a total polyphenol result does not prove a specific EGCG or OPC percentage, and a visual colour check does not prove essential-oil authenticity.
1. Why the Assay Method Matters
An assay percentage has meaning only when the buyer knows what was measured and how it was measured.
The same product name may be used with different analytical definitions. For example:
- “Tea Polyphenols 98%” may refer to total polyphenols.
- “EGCG 98%” should refer specifically to EGCG content.
- “Grape Seed Extract 95%” may refer to OPC, proanthocyanidins or total polyphenols.
- “Curcumin 95%” may refer to total curcuminoids rather than pure curcumin alone.
- “Rosemary Oil” requires composition and identity testing rather than a simple purity percentage.
The test method should therefore be written into the product specification, COA and purchase order.
2. When Is UV-Vis Appropriate?
UV-Vis may be appropriate when the specification is designed to measure a total group of compounds and the method is clearly defined and validated for that purpose.
UV-Vis can be useful for selected total-polyphenol or colour-related measurements. It is generally faster and less complex than chromatographic testing, but the result may include interference from other absorbing compounds.
Questions to Ask About a UV-Vis Result
- What compound group does the method measure?
- Which reference standard is used?
- Is the result reported as total polyphenols, OPC or another parameter?
- Is the method validated for this botanical matrix?
- Can the supplier provide the method reference and batch result?
UV-Vis should not automatically be used to support a claim for an individual compound when other compounds may contribute to the measured absorbance.
3. When Should Buyers Require HPLC?
HPLC is generally preferred when the buyer needs to quantify a specific non-volatile compound or distinguish several related compounds.
HPLC may be requested for:
- EGCG and individual green-tea catechins.
- Curcumin, demethoxycurcumin and bisdemethoxycurcumin.
- Ellagic acid and other selected pomegranate markers.
- Withanolides and selected Ashwagandha markers.
- Specific phenolic or botanical compounds where individual quantification is required.
Questions to Ask About an HPLC Result
- What is the exact analyte being measured?
- What reference standard and calculation basis are used?
- Is the result reported on an as-is or dry basis?
- Does the chromatogram show separation from related compounds?
- Is the test method suitable for the target botanical matrix?
- Is the result from the actual batch being purchased?
An HPLC label alone does not prove that the method is suitable. The buyer should still ask what was measured, what standard was used and whether the result belongs to the current batch.
4. When Should Buyers Require GC or GC-MS?
GC or GC-MS is commonly used when the buyer needs to verify volatile compounds, essential-oil identity or chemotype composition.
Rosemary, lavender, peppermint and other essential oils contain volatile compounds that require a composition-based evaluation.
For rosemary essential oil, the buyer may request information about constituents such as:
- 1,8-Cineole.
- Camphor.
- Alpha-pinene.
- Borneol.
- Verbenone.
The acceptable composition range depends on the origin, chemotype, harvest, distillation method and product specification.
GC or GC-MS data can help identify composition deviation or possible adulteration, but buyers should review the complete chromatographic profile rather than focusing on one single compound.
5. When Is GPC or SEC Important?
GPC or SEC may be important when molecular-weight distribution affects the performance or specification of a peptide or polymer ingredient.
For fish or marine collagen peptides, buyers may need to review:
- Average molecular weight.
- Molecular-weight distribution.
- Percentage below or above a selected molecular-weight threshold.
- Protein content.
- Amino-acid profile.
- Solubility and sensory properties.
A statement such as “low molecular weight” is not a complete specification. Buyers should request the test method, distribution data and interpretation of the result.
6. Assay Method Selection by Ingredient
| Ingredient | Preferred Method to Discuss | Main Buyer Focus |
|---|---|---|
| Green Tea / EGCG | HPLC for individual catechins; UV-Vis for suitable total-polyphenol methods | EGCG, total catechins, total polyphenols and caffeine |
| Grape Seed Extract | UV-Vis or HPLC depending on the defined OPC or polyphenol specification | What does the stated percentage actually represent? |
| Turmeric / Curcumin | HPLC | Total curcuminoids and curcumin/DMC/BDMC breakdown |
| Pomegranate Peel Extract | HPLC or another defined method for ellagic acid or punicalagin-related specifications | Plant part, active marker and assay basis |
| Ashwagandha | HPLC or a clearly defined validated marker method | Root identity, Withanolides and selected marker profile |
| Rosemary Essential Oil | GC or GC-MS | Identity, chemotype and volatile composition |
| Fish Collagen Peptides | GPC/SEC for molecular weight, plus protein and amino-acid testing | Molecular-weight distribution, protein content and fish-origin information |
7. What a Method-Anchored COA Should Show
A useful COA should connect the product, batch, analyte, method, acceptance limit and actual result.
- Product name and botanical or chemical identity.
- Plant part or raw-material source.
- Batch or lot number.
- Manufacturing and test dates.
- Parameter being tested.
- Analytical method or method reference.
- Specification limit.
- Actual batch result.
- Unit and reporting basis.
- Laboratory or quality-control approval.
8. Buyer Checklist Before Approving an Analytical Result
- Does the method measure the compound I need to control?
- Is the method suitable for this botanical matrix?
- Is the result batch-specific?
- Is the reference standard identified?
- Is the result reported on an as-is or dry basis?
- Are related compounds separated or included in the result?
- Are contaminant tests performed separately?
- Does the COA match the product specification?
- Can an independent laboratory reproduce the result?
- Does the result support the intended finished-product specification?
Frequently Asked Questions
Is HPLC always better than UV-Vis?
Not always. HPLC is generally preferred for individual compounds, while UV-Vis may be suitable for certain validated total-content methods. The correct method depends on the specification and analyte.
Which method should be used for rosemary essential oil?
GC or GC-MS is commonly used to evaluate essential-oil identity and volatile composition. Buyers should review the complete composition profile and required chemotype rather than one single compound.
Can UV-Vis prove that grape seed extract contains 95% OPC?
It depends on the defined method and reference standard. Buyers should confirm whether the result refers to OPC, proanthocyanidins or total polyphenols and request the method details before approving the claim.
What test method is useful for collagen peptide molecular weight?
GPC or SEC may be used to characterize molecular-weight distribution. Buyers should request the method, distribution data and reporting basis rather than relying only on the phrase “low molecular weight.”
What should I do if a supplier gives me a generic COA?
Request a batch-specific COA that identifies the product, batch number, test method, specification limit and actual result. Additional independent testing may be appropriate for critical ingredients.
