Mass Spectrometer

Overview

The mass spectrometer identifies and quantifies chemical compounds by measuring the mass-to-charge ratio (m/z) of ions derived from a sample. This LC-MS instrument couples to a liquid chromatograph: the LC separates a mixture in time, and the mass spectrometer ionizes and weighs each eluting component, giving both the structure and the concentration of analytes down to trace levels. It is indispensable in pharmaceutical analysis, proteomics, toxicology, and environmental testing.

How it works

Liquid eluent enters the Electrospray Ion Source, where a heated electrospray needle held at several kilovolts disperses it into a charged aerosol. A curtain of heated desolvation nitrogen evaporates the solvent, and the bare ions pass through a sampling cone and skimmer into the first vacuum stage. The Ion Optics then use an RF-only multipole guide and electrostatic lenses to confine the diverging ion cloud and focus it into a tight beam.

The beam enters the Quadrupole Mass Analyzer, four hyperbolic rods driven by combined RF and DC voltages from the RF generator. Only ions within a narrow m/z window have stable trajectories and reach the far end; the rest collide with the rods. By ramping the voltages, the instrument scans across the mass range. Surviving ions strike the Electron Multiplier Detector, where a conversion dynode and electron multiplier turn each ion into a measurable current pulse that the preamplifier conditions for counting.

Construction

The entire ion path must be under high vacuum so ions travel without colliding with air. The Vacuum System system stages this: a rotary-vane backing pump roughs the chamber and two turbomolecular pumps pull the analyzer region down to roughly 10⁻⁵ mbar, with gauges and isolation valves dividing the pressure drop. The Gas Supply regulates nitrogen for the source and meters argon collision gas, while the Control Electronics provide programmable high-voltage and RF power and a fast data-acquisition board that synchronizes the quadrupole scan to detector counts. A recirculating chiller in the Cooling System system removes heat from the turbo pumps and RF stage, and the Control Interface interface links the instrument to the acquisition PC.