Overview
Biomolecules — carbohydrates, proteins, lipids, and nucleic acids — must be obtained in purified form before they can be studied. Chromatography and mass spectrometry are two of the most widely used physical methods for purifying, separating, and identifying these molecules.
Chromatography was first described in 1903 by Mikhail, a Russian botanist, who separated leaf pigments using solid adsorbents. The name comes from the Greek "chroma" (colour) and "graphein" (to write/detect). Mass spectrometry, meanwhile, measures the mass-to-charge ratio of ionized molecules, giving highly precise identification of compounds — the two techniques are frequently combined (e.g., LC-MS) in modern laboratories.
Learning Objectives
After this lesson you will be able to…- Define chromatography and mass spectrometry.
- Describe the principle and important types of chromatographic methods.
- Describe the principle and components of a mass spectrometer.
- Enlist the types of mass spectrometer, including ESI-TQ and MALDI-TOF systems.
- Describe the various uses of mass spectrometry in biochemical analysis.
Clinical Story
Why This MattersA newborn screening program flags a baby for suspected inborn error of metabolism. The confirmatory test uses tandem mass spectrometry (MS/MS) to measure amino acid and acylcarnitine profiles from a dried blood spot. The lab scientist relies on their understanding of chromatography and mass spectrometry to correctly prepare, separate, and interpret the sample — a decision that can change a child's life.
Core Concepts
Every chromatographic technique relies on two phases: the mobile phase (gas or liquid) which carries the sample and continuously moves through the instrument, and the stationary phase, a porous matrix packed inside a column that does not move and separates substances by adsorption. Components of a chromatograph include the mobile phase source, analyte, sample injection chamber, separating column, detector (which calculates retention time — the time between injection and detection), and recorder/analyser that plots the chromatogram.
Gas chromatography (GC) separates volatile compounds (fatty acids, essential oils) between a gaseous mobile phase and a stationary silica phase inside a heated column oven. Liquid chromatography (LC) uses a liquid mobile phase, with advanced forms HPLC (high performance liquid chromatography) and FPLC (fast protein liquid chromatography). Gel filtration chromatography (size exclusion) separates molecules by molecular weight/size using a gel matrix with defined pore size. Ion exchange chromatography separates molecules that form ions using charged bead matrices (cationic or anionic). Affinity chromatography separates proteins based on specific interaction with an immobilized ligand (enzyme, antibody, or metal ion).
A mass spectrometer measures the masses and relative concentrations of atoms and molecules using magnetic or electric fields exerted on charged particles. Just as a heavy cannonball is barely deflected by a jet of water while a light table-tennis ball deflects easily, the amount of deflection of an ion depends on its mass — the working principle is studying masses of ions/fragments separated by their mass-to-charge ratio (m/z). The three basic components are the Source (produces ions), Analyzer (separates ions by mass), and Detector (produces a signal from separated ions).
Laboratory Principle
In ESI-TQ mass spectrometry, proteins pass through the source and become ions via Electro Spray Ionization (ESI); the ions pass through a first analyzer where specific ions are selected, are broken up by collision-induced dissociation (CID), and a second analyzer catches the resulting fragment ions. In MALDI-TOF, a soft ionization technique (Matrix Assisted Laser Desorption/Ionisation) converts sample proteins into gas-phase ions using a laser, and a Time-of-Flight (TOF) analyzer measures the time each ion takes to reach the detector — ions of the same charge but different mass travel at different velocities, allowing mass determination.
Equipment Required
Reagents & Materials
| Reagent / Material | Concentration / Grade | Purpose | Storage |
|---|---|---|---|
| Mobile phase (gas/liquid) | Instrument-specific (e.g., helium, nitrogen, solvent gradients) | Carries sample through the column | Per manufacturer specification |
| MALDI matrix compound | Analytical grade | Co-crystallizes with sample for laser desorption/ionization | Dry, room temperature |
| Nebulizer gas (N2) | High purity nitrogen | Assists electrospray droplet formation in ESI source | Gas cylinder, ambient |
Step-by-Step Procedure
The extract solution is introduced at the start of the chromatography column.
The mobile phase (eluent) carries the sample through the stationary phase, creating separation as components move at different rates.
A detector identifies the change in composition of the eluate as compounds emerge, recording the retention time for each.
If coupled to mass spectrometry, separated compounds are ionized via ESI (Electro Spray Ionization) or MALDI, converting them into gas-phase ions.
Ions pass through a mass analyzer (Triple Quadrupole or Ion Trap for ESI; TOF for MALDI) and the detector produces a mass spectrum graph of intensity vs m/z.
Flow Diagram
Quality Control
Run known reference standards through the chromatography/MS system regularly to confirm retention times and m/z calibration remain within acceptable limits, and verify the detector baseline is stable before running patient samples.
Laboratories offering mass spectrometry-based diagnostic testing (e.g., newborn screening, toxicology) should enrol in external proficiency testing programs to validate accuracy against peer laboratories.
Reference Values
Typical Parameters⚠️ Reference ranges may vary between laboratories. Always apply your laboratory's established reference intervals.
Clinical Interpretation
| Finding | Possible Significance | Action / Follow-up |
|---|---|---|
| Unexpected m/z peak | Presence of an unknown or contaminant compound | Compare against reference spectral library; repeat run |
| Sharp resolved peaks | Good chromatographic separation, clean sample prep | Proceed with quantitation/identification |
| Broad, overlapping peaks | Column overload, poor resolution, or degraded stationary phase | Dilute sample, check column condition, re-run |
Common Errors & How to Avoid Them
Cause: Too much sample injected relative to the column's capacity.
Prevention: Dilute samples appropriately and follow manufacturer-recommended injection volumes.
Cause: Incorrect matrix selection for MALDI, or poor ESI spray stability.
Prevention: Select an appropriate matrix for the analyte class and verify nebulizer gas flow and voltage settings before the run.
Cause: Impure solvents or carryover from a previous run.
Prevention: Use HPLC/MS-grade solvents and run a blank between samples.
Laboratory Tips from the Bench
Always equilibrate the column with mobile phase before injecting the first sample of the day — this stabilizes baseline and retention time.
In MALDI, allow the sample-matrix spot to completely air-dry before firing the laser; residual moisture distorts ionization.
"TOF takes time" — Time-Of-Flight analyzers separate ions by how long they take to reach the detector, with lighter ions arriving faster.
Important Notes
Retention times vary with column condition, flow rate, and temperature — always confirm with a fresh standard rather than relying purely on historical values.
Gas chromatography requires the sample to be volatile and thermally stable, while liquid chromatography (including HPLC/FPLC) can handle a much broader range of biomolecules, including large proteins.
Interactive Quiz
Test Your KnowledgeFlashcards
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Clinical Case Study
Apply Your KnowledgeMarcus is enrolled in a routine newborn screening program. A dried blood spot sample is sent for tandem mass spectrometry to screen for inborn errors of amino acid, fatty acid, and organic acid metabolism.
Elevated phenylalanine with a raised Phe/Tyr ratio detected by MS/MS is consistent with phenylketonuria (PKU). Mass spectrometry separates and quantifies these amino acids by their unique mass-to-charge ratios after ionization.
- →Tandem MS can simultaneously screen for dozens of metabolic markers from a single dried blood spot.
- →Mass-to-charge ratio (m/z) is the key value used to identify and quantify each metabolite.
- →Early detection through MS-based newborn screening enables early dietary intervention.
Frequently Asked Questions
HPLC (high performance liquid chromatography) is a general-purpose technique used for a wide range of small and large molecules under high pressure, while FPLC (fast protein liquid chromatography) is optimized specifically for gentle, high-resolution purification of proteins and peptides.
A vacuum prevents ions from colliding with air molecules, which would scatter them and distort the mass measurement, and it also prevents unwanted chemical reactions during ionization and analysis.
Yes — combining the two (e.g., LC-MS or GC-MS) is extremely common. Chromatography first separates the components of a mixture, and mass spectrometry then identifies each separated component with high specificity.
Quick Revision
10-Minute ReviewKey Takeaways
- Chromatography and mass spectrometry are essential methods for separating and identifying large, complex biomolecules.
- Each method can be used individually or in combination to determine the composition of a sample.
- Different chromatographic types (gas, liquid, gel filtration, ion exchange, affinity) suit different molecule properties.
- Mass spectrometers use magnetic and electric fields to separate ions by mass-to-charge ratio.
- ESI and MALDI are complementary ionization techniques, each suited to different sample types.
Competency Checklist
Track Your MasteryReferences
- NIOS Biochemistry Module — Lesson 22: Chromatography and Mass Spectrometer.
- Skoog DA, Holler FJ, Crouch SR. Principles of Instrumental Analysis.
- Watson JT, Sparkman OD. Introduction to Mass Spectrometry.