HPLC vs LC-MS vs NMR: What Each Test Tells You
TL;DR · The short version
HPLC vs LC-MS vs NMR compares evidence for different sample questions. HPLC provides separation, LC-MS adds ion mass-to-charge information, and NMR examines chemical environments. Choose the measurement for the property you need to establish.
A longer test list can look more reassuring without answering more of your question. “Tested by HPLC” doesn’t tell you the property, method conditions or interpretation. Look for those details behind the label.
Begin with separation, identity, structure or quantity, then match the method and result to that task.
How the techniques fit together
TL;DR: HPLC and LC-MS overlap: liquid chromatography can provide the separation before mass spectrometry.
HPLC stands for high-performance liquid chromatography. Components travel through a column and reach a detector at different times under the chosen conditions.
LC-MS couples liquid chromatography to mass spectrometry. The detector provides information about ions and their mass-to-charge ratios. NMR (nuclear magnetic resonance) uses signals from nuclei to examine chemical environments. The CNRS LC-MS platform and EMBL-EBI’s NMR/MS comparison explain these complementary roles.
HPLC: examine the separation and reported percentage
TL;DR: A chromatogram must be interpreted with its detector, integration and calculation method.
Read an HPLC result with its assignments and recorded separation. For area percentage, identify which responses were included in the denominator. The percentage needs that definition.
Quantity is a separate question. Waters’ HPLC primer explains quantitation using detector response and reference standards. The largest peak alone does not establish how much peptide was in the original vial.
For a worked example, see how to read an HPLC chromatogram.
LC-MS: inspect the ion assignment
TL;DR: Mass-spectrometric evidence can support identity and impurity work, within the method’s demonstrated capabilities.
In a 2015 LC-HRMS study, researchers used salmon calcitonin, bivalirudin and exenatide as model systems. Their method characterized peptide-related impurities, including some that coeluted, and evaluated quantitative performance.
Mass-spectrometric data added useful evidence in this study. That doesn’t establish that every LC-MS run detects every impurity or resolves a complete sequence.
Find the laboratory’s assignment: intact mass, a specific ion or fragment evidence. Then see whether the report supports quantification or only an identity comparison.
NMR: inspect the experiment and usable signals
TL;DR: NMR can contribute structural or quantitative evidence, but those uses require an appropriate experiment.
NMR can address chemical environments and structure. Quantitative NMR needs an experiment designed for measurement; displaying a spectrum doesn’t independently make it quantitative.
In a 2014 study of valine and peptide T5, researchers addressed crowded peptide signals by removing unwanted exchangeable signals and using a suitable internal standard. Those choices were part of what made the measurement possible.
The EMBL-EBI comparison discusses differences in sensitivity and preparation between NMR and MS in metabolomics. Treat that as context, not as a fixed sample requirement for every peptide assay. The laboratory’s validated method determines what material and measurements it needs.
Match the evidence to the question
TL;DR: Compare results only after checking the property, units and reporting basis.
Use these questions when you request or review a report:
- Separation: What does the chromatogram show under the stated method?
- Identity: What reference, mass, fragment or structural evidence supports the assignment?
- Quantity: What was measured, against which reference and in which units?
- Comparability: Do the two results describe the same property on the same basis?
Why two percentages may differ
TL;DR: Different percentages may describe different quantities; their labels and denominators decide whether they can be compared.
A hypothetical area-purity result and a milligram-content result describe different quantities. One is a share of included detector response, the other a measured amount. Keep them separate.
Two percentages can still use different bases. Ask what each numerator and denominator represents before concluding that the results conflict.
Name the evidence and its limit. An assigned mass consistent with expectation is a specific finding. The word “tested” can’t replace separate evidence for identity, purity and quantity.