JNTU B.Pharmacy IV ADVANCED INSTRUMENTATION TECHNIQUES Previous Question Paper (September - 2022 - R17)

Ionization is the process of converting neutral molecules into ions for detection in mass spectrometry. The choice of technique depends on the sample's volatility and thermal stability.

• Electron Ionization (EI): A high-energy electron beam (typically 70 eV) strikes gaseous molecules, causing them to lose an electron. It is a hard ionization technique that produces extensive fragmentation, providing structural information.
• Chemical Ionization (CI): A softer technique where a reagent gas (e.g., methane) is ionized by electrons, which then reacts with the analyte via proton transfer. It produces a strong molecular ion peak (M+H)+ with minimal fragmentation.
• Electrospray Ionization (ESI): A soft technique used for non-volatile, polar, and high-molecular-weight compounds. The sample is dissolved in a solvent and passed through a high-voltage capillary, creating charged droplets that evaporate to release gas-phase ions.
• Matrix-Assisted Laser Desorption/Ionization (MALDI): The analyte is embedded in a light-absorbing matrix and pulsed with a laser. This technique is ideal for large biomolecules like proteins and polymers, producing singly charged ions.
• Fast Atom Bombardment (FAB): The sample is dissolved in a viscous matrix and bombarded with a beam of high-energy neutral atoms (e.g., Xenon), suitable for thermally labile, polar compounds.

The mass spectrometer consists of several key components that work in a high-vacuum environment to ensure ions travel without colliding with air molecules.

• Sample Inlet System: Introduces the sample into the vacuum system, often coupled with GC or HPLC.
• Ion Source: Converts neutral sample molecules into ions using techniques like EI or ESI.
• Mass Analyzer: Separates ions based on their mass-to-charge (m/z) ratio. Common types include Quadrupole, Time-of-Flight (TOF), and Magnetic Sector analyzers.
• Detector: Records the abundance of ions at each m/z value, typically using an electron multiplier.
• Data System: Processes the electrical signals from the detector to produce a mass spectrum.

Applications include the identification of unknown compounds, determination of molecular weight, structural elucidation of organic molecules, quantification of drugs in biological matrices, and proteomics research.