Quadrupole mass filter

Quadrupole Mass Filter

The Quadrupole Mass Filter (QMF) is a fundamental component used in mass spectrometry for filtering ions based on their mass-to-charge ratio (m/z). It operates on the principle of dynamic electric fields, allowing for the selective transmission of ions with specific m/z values, making it an essential tool in analytical chemistry for the identification and quantification of unknown substances.

Principle of Operation

The quadrupole mass filter consists of four parallel metal rods, each pair being connected to opposite poles of a radio frequency (RF) voltage with a direct current (DC) offset. This configuration creates a dynamic electric field in the space between the rods. Ions entering the quadrupole are subjected to this oscillating electric field, which affects their trajectory through the device.

The stability of an ion's trajectory through the quadrupole is determined by its m/z ratio and the parameters of the RF and DC fields. Only ions with specific m/z ratios will have stable trajectories and pass through the quadrupole to reach the detector, while others will collide with the rods and be filtered out. By adjusting the RF and DC voltages, the operator can select which m/z ratio is transmitted, thus allowing the quadrupole to act as a mass filter.

Applications

Quadrupole mass filters are widely used in various applications of mass spectrometry, including:

• Environmental Analysis: Detecting and quantifying pollutants in air, water, and soil.
• Clinical Diagnostics: Identifying biomarkers in biological samples for disease diagnosis.
• Pharmaceutical Analysis: Determining the composition and purity of pharmaceutical compounds.
• Proteomics: Analyzing protein mixtures by identifying and quantifying proteins in complex biological samples.

Advantages and Limitations

Advantages:

• High selectivity and sensitivity for targeted mass-to-charge ratios.
• Rapid scanning capability, allowing for quick analysis of multiple m/z values.
• Relatively simple and robust design, leading to widespread use in various analytical instruments.

Limitations:

• Limited mass range, as the performance can degrade for very high or very low m/z values.
• Resolution and sensitivity can be affected by the operational parameters and the design of the quadrupole.
• Requires careful calibration and maintenance to ensure accurate and reproducible results.

See Also

• Mass Spectrometry
• Ion Trap
• Time-of-Flight Mass Spectrometry (TOF-MS)
• Magnetic Sector Mass Spectrometer

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