High-Performance Liquid Chromatography (HPLC) is the most common analytical method you will see cited on a Certificate of Analysis (COA). It sounds intimidating, but the core idea is simple: HPLC separates a sample into its individual components so a laboratory can measure how much of the sample is the compound you actually want — and how much is something else.
How HPLC works, in plain terms
A liquid sample is pushed through a column packed with a special material. Different compounds travel through the column at different speeds, so they arrive at the detector at different times. The detector draws a graph called a chromatogram: a series of peaks along a time axis.
Each peak represents a component of the sample. The main peak should be the target compound; smaller peaks are impurities, degradation products, or residual solvents.
Where the purity percentage comes from
The purity figure on a COA is calculated from the area under the peaks. If the main peak accounts for 99.2% of the total peak area, the reported purity is 99.2%. This is why the chromatogram itself matters — a purity number without the underlying graph cannot be independently assessed.
Why ≥99% matters for reference standards
For reference-grade materials, a purity of 99% or higher is the widely accepted benchmark. At that level, impurities are present only in trace amounts, which means:
- Analytical results are reproducible and attributable to the target compound
- Unknown impurities are too small to meaningfully distort measurements
- Batch-to-batch comparisons remain valid over time
A material at 95% purity is not automatically unsafe — but 1 in every 20 parts is something other than what the label says, and the COA should identify what that something is.
What to check on any HPLC report
- The chromatogram is included, not just a summary number
- The batch number on the report matches the physical product label
- The testing laboratory is named and independent of the vendor
- The method and column conditions are documented, so the result can be reproduced
A vendor that publishes complete, batch-specific HPLC chromatograms is demonstrating the kind of transparency that third-party lab reports are meant to provide. You can see how listed vendors document their testing in our vendor directory.