Quadrupole mass analyzer

Quadrupole Mass Analyzer

The Quadrupole Mass Analyzer (QMA) is a key component in mass spectrometry, a technique widely used in analytical chemistry to identify substances within a sample by measuring the mass-to-charge ratio of its ions. The quadrupole mass analyzer utilizes a combination of electric and magnetic fields to filter ions based on their mass-to-charge ratio. This selective process allows only ions of a specific mass-to-charge ratio to reach the detector at any given time, enabling precise identification and quantification of compounds.

Principle of Operation

The quadrupole mass analyzer consists of four parallel metal rods, arranged in a square configuration. Each opposing rod pair is connected electrically. A combination of direct current (DC) and alternating current (AC) voltages is applied to the rods. The DC voltage remains constant, while the AC voltage oscillates. This creates a dynamic electric field within the quadrupole.

Ions introduced into the quadrupole are subjected to this electric field. The field's unique configuration allows only ions with a specific mass-to-charge ratio to remain stable and pass through the quadrupole to the detector. Ions of other mass-to-charge ratios are destabilized and collide with the rods, thus being filtered out. By varying the voltages applied to the rods, ions of different mass-to-charge ratios can be sequentially allowed to pass, enabling the mass spectrometer to scan across a range of masses and identify various components within the sample.

Applications

Quadrupole mass analyzers are utilized in a variety of applications, including:

• Environmental Monitoring: Detection and quantification of pollutants in air, water, and soil.
• Pharmaceuticals: Analysis of drug compounds and metabolites.
• Proteomics: Identification and quantification of proteins in biological samples.
• Food Safety: Detection of contaminants and adulterants in food products.

Advantages and Limitations

Advantages:

• High scan speed, allowing rapid analysis of samples.
• Good mass accuracy and resolution.
• Relatively low cost and maintenance requirements compared to other types of mass analyzers.

Limitations:

• Limited mass range, especially for high mass-to-charge ratio ions.
• Sensitivity can be lower than that of other mass analyzers, such as time-of-flight (TOF) or Fourier transform ion cyclotron resonance (FT-ICR) analyzers.

See Also

• Mass Spectrometry
• Time-of-Flight Mass Spectrometry (TOF-MS)
• Fourier Transform Ion Cyclotron Resonance (FT-ICR)
• Ion Trap Mass Spectrometry