Chromatogram
Definition
The detector trace a chromatographic run produces: signal against time, with each component appearing as a peak. The purity figure on a certificate is arithmetic performed on the areas of those peaks.
In more detail
The chromatogram is the primary record of a chromatographic run: detector signal on the vertical axis, time on the horizontal. Everything else on a purity line of a certificate is arithmetic performed on it.
Reading one is mostly about the baseline and the peak shape. A flat, quiet baseline means the method and the instrument were behaving. A peak that leans forward or drags a tail behind it suggests the column is overloaded or interacting with the sample in a way the method did not intend, and a shoulder on the side of a main peak is a second component that has not been fully separated.
A certificate that reports a number without the trace asks the reader to accept both the measurement and the integration. One that includes the trace lets a reader check where the baseline was drawn, which is the single judgement that moves the figure most.
Where this term comes up
Entries whose definition mentions Chromatogram.
What this means for research sourcing
Purity and identity verification are central to research reproducibility. Every Volta compound ships with >99% HPLC-verified purity and a certificate of analysis.
Related Terms in Quality
Retention Time
How long a component takes to travel through the column and reach the detector. It is characteristic of a compound under fixed conditions, which is why identity is often confirmed by a sample and a reference standard eluting at the same time.
Co-elution
Two components leaving the column together and arriving as one peak. It is the main way a purity figure can be honestly measured and still be too high, and it is why an orthogonal method is worth running.
Peak Integration
Deciding where a peak starts and stops so its area can be calculated. Where the baseline is drawn changes the number, which is why integration parameters belong in the method rather than in the analyst's judgement on the day.
Reversed-Phase HPLC (RP-HPLC)
The chromatographic mode almost all peptide purity work uses: a non-polar stationary phase with a polar moving phase, separating components by hydrophobicity. The gradient usually runs water and acetonitrile with an acidic modifier.
HPLC-UV
High-performance liquid chromatography with an ultraviolet detector, typically reading at 214 nm where the peptide bond absorbs. It reports how much of the absorbing material is the target peak, which is a purity measurement and not an identity one.
LC-MS
Liquid chromatography coupled to a mass spectrometer, so each separated component is also weighed. It answers identity and purity in one run, which HPLC-UV alone cannot: a UV detector cannot tell two compounds apart if they elute together.
Tandem Mass Spectrometry (MS/MS)
Selecting one ion, fragmenting it, and measuring the fragments. The fragment pattern is far more specific than mass alone, which is why certificates quote transitions rather than a single mass for confirmation.
Electrospray Ionisation (ESI)
The soft ionisation technique that gets peptides into a mass spectrometer intact, by spraying the solution through a charged needle. It tends to produce several charge states of one molecule rather than a single ion.