Two different questions
Identity asks: is the main component of this sample the substance named on the label? Purity asks: how much of what the method detects is that main component, as opposed to other detectable components? A sample can be the right substance at modest purity, or a very pure sample of the wrong substance. A complete report addresses both.
High-performance liquid chromatography (HPLC)
HPLC separates the components of a dissolved sample as they pass through a column, producing a chromatogram of peaks over time. Chromatographic purity is the area of the main peak divided by the total area of all detected peaks, expressed as a percentage. A result written as "99.59% (HPLC)" therefore means: under the stated conditions and detector, the main peak was 99.59% of everything the detector saw.
- It is a relative measure within one method. It is not a mass balance and does not account for water, counter-ions, or residual solvents unless those are reported separately.
- Components the detector cannot see, or that do not elute under those conditions, are not counted.
- The retention time of the main peak can support identity when compared with a reference standard, but the percentage alone does not identify anything.
Mass spectrometry (MS)
Mass spectrometry measures the mass-to-charge ratio of ions produced from the sample. For a research material the report typically states an observed mass (often as one or more charge states) and compares it with the theoretical mass calculated from the molecular formula. Agreement within the instrument's accuracy supports the identity of the main component. Reports may describe this as "identity confirmed", "consistent with", or list the observed and expected masses side by side.
- MS supports what the main component is. It is not a purity measurement, although some methods (LC-MS) combine the two.
- An observed mass that does not match the expected mass is a documentation question, whatever the purity line says.
- The theoretical mass on the report should follow from the molecular formula listed on the product page; both are published on Arctic Lab Supply product listings.
| Question | Method that addresses it | What the line looks like | What it does not prove |
|---|---|---|---|
| Is it the named substance? | Mass spectrometry (sometimes with HPLC retention time) | Observed vs. expected mass, "identity confirmed" | Purity, quantity per vial, absence of undetected substances |
| How much of the detectable material is the main component? | HPLC (UV or other detector) | "99.xx% (HPLC)" | Identity, water content, solvents, sterility, endotoxin |
| How much material is in the vial? | Net-content or quantitative assay, if performed | Mass or amount per vial | Anything not stated |
Reading them together
- Confirm the sample identity, strength, and lot on the report match the label.
- Check the MS line: does the observed mass agree with the expected mass for the named formula?
- Check the HPLC line: what is the main-peak percentage, and under what method?
- Note which attributes are absent from the report. Absence is information.
- Verify the certificate number with the issuing laboratory (how to verify).