It’s common to see “HPLC and MS tested” on a product label, but these two techniques answer fundamentally different questions, and conflating them can lead to a false sense of security about a sample’s quality.
HPLC: Measuring Purity
High-Performance Liquid Chromatography separates the components of a mixture based on how they interact with a stationary phase as they’re pushed through a column under pressure. The output is a chromatogram — a series of peaks, each representing a distinct compound, with peak area roughly proportional to concentration. This is how purity percentages are calculated.
Mass Spectrometry: Confirming Identity
Mass spectrometry ionizes a sample and measures the mass-to-charge ratio of the resulting fragments, producing a molecular weight signature. This is the step that confirms you actually have the peptide you think you have — HPLC alone can show a single clean peak that is nonetheless the wrong molecule entirely if the retention time happens to coincide with an impurity.
For sequence-specific confirmation, some labs go a step further with tandem MS/MS, fragmenting the peptide further to verify its amino acid sequence rather than just its overall mass.
Why Both Matter
A rigorous COA reports both: HPLC purity as a percentage, and MS confirmation that the detected mass matches the expected molecular weight of the target peptide within an acceptable margin. One without the other leaves a real gap in what you actually know about the vial in front of you.
