How do LC-MS work?
In LC-MS, a high-pressure pump delivers a mobile phase through a column, typically C18, where analytes separate by their affinity for the stationary phase. The eluent, usually at 0.2 to 1 mL per minute, enters an atmospheric-pressure ion source. Electrospray ionization applies 3 to 5 kV to a nebulized stream so that charged droplets shrink and release gas-phase ions, while atmospheric-pressure chemical ionization uses a corona discharge for less polar compounds. Ions pass through a skimmer or capillary and ion guides into progressively lower-pressure regions, then into the mass analyzer. Quadrupole, ion trap, time-of-flight or hybrid analyzers then measure m/z. Mobile phases must be volatile, such as formic acid, acetic acid or ammonium formate, because non-volatile buffers foul the source.
Which LC-MS variants are available?
- Single Quadrupole LC-MS System — A single quadrupole LC-MS adds a compact mass detector to an HPLC or UHPLC, confirming molecular weight and supporting routine quantitation.
- LC-Triple Quadrupole MS/MS System — An LC-MS/MS triple quadrupole system uses multiple reaction monitoring to quantify known target compounds at picogram-per-milliliter levels in complex biological and environmental matrices.
- LC-Q-TOF High-Resolution MS System — An LC-Q-TOF combines a quadrupole precursor filter with a time-of-flight analyzer to deliver accurate-mass MS and MS/MS spectra.
- LC-Ion Trap MS System — An LC-ion trap MS stores ions in an electrodynamic trap and fragments them repeatedly, providing MSn spectra for structural elucidation.
- Mass-Directed Purification LC-MS System — A mass-directed purification LC-MS uses a preparative or semi-preparative LC, a flow splitter, a single quadrupole detector and a fraction collector triggered by target mass.
How do I choose the right variant?
The decisive choice is the mass analyzer. Single quadrupole LC-MS confirms molecular weight and performs simple quantitation at a modest cost. Triple quadrupole instruments deliver the best sensitivity for targeted quantitation in bioanalysis, residues and clinical assays. Q-TOF systems provide accurate mass and MS/MS of unknowns, suited to impurity profiling, metabolite identification and screening. Ion traps offer multi-stage fragmentation for structural work. Mass-directed purification systems add fraction collection. Then check the ion source options such as ESI, APCI and APPI, scan speed for UHPLC peaks below 3 seconds wide, polarity switching speed, and the robustness of the source with dirty matrices. Confirm compatibility with your LC pumps, available software for regulated work, and nitrogen consumption for sheath and drying gases.
Where are LC-MS used?
LC-MS are specified in drug impurity profiling and metabolite identification, bioanalysis of drugs in plasma and urine, pesticide and veterinary drug residue testing, PFAS analysis in water and food, clinical steroid and vitamin D assays and peptide and protein characterization.
Which standards and certifications apply?
Work with LC-MS is commonly governed by EPA Method 1633, EPA Method 537.1, EPA Method 533, USP <621> Chromatography, FDA Bioanalytical Method Validation Guidance, ICH M10 Bioanalytical Method Validation, EN 15662, CLSI C62-A, ISO/IEC 17025 and IEC 61010-1. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Provide a nitrogen supply of at least 99.5 percent purity, either from a generator delivering about 20 to 35 L per minute or from liquid supply, plus a fume extraction line for source exhaust. Use LC-MS grade solvents and additives, since impurities raise background and suppress ionization. Calibrate the mass scale regularly with the manufacturer's calibrant solution, and run system suitability injections before each batch. Clean the spray shield, capillary and ion transfer optics when sensitivity drops, and replace rotary pump oil on schedule. Monitor for ion suppression through post-column infusion during method development. Regulated laboratories need software with audit trails and electronic signatures compatible with 21 CFR Part 11, and instrument qualification to IQ, OQ and PQ protocols.
