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HPLC and mass spectrometry, explained

By BioGenisys Research Team · 5 min read · Updated 2026-10-27

Most peptide lab reports rely on two instruments. HPLC tells you how pure a sample is. Mass spectrometry tells you whether it's the right molecule. You don't need to run either one to read a report, but knowing roughly how they work makes the results much easier to judge.

The short version

• HPLC separates a sample into its ingredients and measures how much of each there is. That gives the purity percentage.
• Mass spectrometry weighs the molecules. A weight that matches the expected one confirms it's the right compound.
• LC-MS on a report means both were done together, on the same sample.

HPLC: separating the sample

HPLC stands for high-performance liquid chromatography. The lab dissolves a tiny amount of the sample and pumps it through a narrow tube packed with very fine material. Different molecules cling to that material more or less strongly, so they come out the other end at different times, a bit like runners finishing a race at different times.

A light detector at the end of the tube spots each molecule as it comes out. Peptides absorb a particular kind of ultraviolet light, which is how the detector sees them. The result is a chart called a chromatogram: a line with a peak each time something comes out.

Reading the chart

• Retention time: when a peak appears. The right compound should come out at the same time as a known reference sample of it.
• Peak size: the area under each peak shows how much of that ingredient the detector saw.
• Purity: the main peak's share of all the peaks together, for example 99.4%.
• Small extra peaks: small amounts of other material, often slightly flawed copies of the peptide left over from manufacturing.

What HPLC can't show

Two different molecules can come out at the same moment and hide under one peak. Anything the detector can't see doesn't get counted. And a single clean peak doesn't prove it's the right molecule. That's the job of mass spectrometry.

Mass spectrometry: weighing the molecule

A mass spectrometer gives molecules a small electric charge and measures how they move, which tells it how heavy they are. A peptide can pick up more than one charge, so it may show up as a few related readings. Software combines them into one measured weight.

That weight is compared with the weight calculated from the peptide's known makeup. A match confirms identity. A different weight means a different molecule, or that something went wrong when it was made.

LC-MS: both at once

Many labs connect the two instruments, so each peak from HPLC goes straight into the mass spectrometer. That confirms the main peak is the right compound, and often identifies the small extra peaks too. When a report says LC-MS, identity and purity were checked in the same run.

Questions to ask of any report

• Which test gave the purity figure?
• Was identity confirmed by weight (mass spectrometry), and does the measured weight match the expected one?
• Is the chart included, or only a summary number?

For the rest of a report, see How to read a peptide lab report.

For research use only. Not for human or veterinary use.