Gas chromatography-mass spectrometer

Date：2025/7/7 18:16:49

I. Core Principle

It combines the high-efficiency separation capability of gas chromatography (GC) with the qualitative identification capability of mass spectrometry (MS). The components in the mixed sample are separated by GC and then sequentially introduced into MS for compound qualitative and quantitative analysis through mass-to-charge ratio (m/z) analysis. After vaporization, the sample is separated by the GC chromatographic column along with the carrier gas. Each component enters MS in the order of retention time, and characteristic fragment ions are generated through electron impact (EI) or chemical ionization (CI). These ions are screened by the mass analyzer and recorded by the detector, forming a mass spectrum and a total ion current chromatogram (TIC).

II. Key Structures and Functions

Components	Functions and Characteristics
Gas Chromatography Part	- Chromatographic column: Capillary column (such as DB-5MS, with 5% phenyl polysiloxane as the stationary phase), inner diameter 0.25mm, length 30m, with high separation efficiency;- Injection port: Split/splitless injection (split ratio 10:1-100:1), vaporizing samples at high temperature (such as 250℃);- Carrier gas: High-purity helium (He), flow rate 1-2mL/min, ensuring separation reproducibility.
Interface System	- Transfer line: Stainless steel/quartz material, maintaining a temperature of 280-300℃ to prevent sample condensation, connecting the GC column and the MS ion source;- Vacuum transition: Atmospheric pressure at the GC end, high vacuum (10??-10??Pa) at the MS end, maintained by a molecular turbopump.
Mass Spectrometry Part	- Ion source: Electron Ionization (EI) source: 70eV electrons bombard sample molecules to generate characteristic fragments (such as benzene generating m/z 78 and 51 ions), and the spectrum can be matched with standard spectral libraries (such as NIST library); Chemical Ionization (CI) source: Mild ionization, generating quasi-molecular ions (such as [M+H]?), suitable for compounds with high polarity and easy fragmentation;- Mass analyzer: Quadrupole (most commonly used, scanning range m/z 10-1050), time-of-flight (TOF, high resolution);- Detector: Electron multiplier, with a detection limit up to the pg level.
Data System	- Workstation software (such as Agilent MassHunter): Synchronously collects GC-MS data, automatically matches the NIST spectral library (containing > 300,000 standard spectra), and supports the development of quantitative methods (such as selected ion monitoring SIM).

III. Typical Analysis Process

Sample Pretreatment:

Liquid samples: Extraction (such as liquid-liquid extraction of VOCs in water), filtration (0.22μm membrane);

Solid samples: Headspace sampling (such as volatile flavor substances in food), derivatization (such as fatty acid methylation).

GC-MS Parameter Setting:

GC temperature program: Initial 50℃ for 2min, then rise to 280℃ at 10℃/min (for separating complex mixtures);

MS scanning mode:

Full scan (SCAN): m/z 35-500, for qualitative screening;

Selected ion monitoring (SIM): For target ions (such as m/z 235 and 237 of DDT) to improve quantitative sensitivity.

Separation and Detection: After being separated by GC, the sample enters the MS ion source through the interface. The EI source generates fragment ions, which are screened by the quadrupole and counted by the detector.

Result Analysis:

Qualitative analysis: Matching the NIST library according to retention time and mass spectrum (matching degree > 800/1000);

Quantitative analysis: Internal standard method (such as adding d5-benzene as internal standard) or external standard method, calculating content through peak area in SIM mode.

IV. Core Application Fields

Industry	Examples of Detection Objects
Environmental Monitoring	Volatile organic compounds (VOCs) in water (such as benzene series, chlorinated hydrocarbons), semi-volatile organic compounds (SVOCs) in soil (such as PAHs, pesticides).
Food and Flavors	Pesticide residues in food (such as organophosphorus, organochlorine), flavor substances in alcohol (such as esters, alcohols), allergens in flavors (such as benzaldehyde).
Medicine and Forensics	Drugs in blood (such as heroin, methamphetamine), drug metabolites (such as phenobarbital in urine), explosive residues (such as TNT).
Materials and Chemical Industry	Plasticizers in plastics (phthalates), VOCs emission from coatings, residual polymer monomers (such as styrene).
Archaeology and Cultural Relics	Analysis of organic components in ancient objects (such as oils in mural pigments), research on aging of cultural relic protection materials.

V. Comparison with Other Hyphenated Technologies

Comparison Item	GC-MS	LC-MS (Liquid Chromatography-Mass Spectrometry)	GC-FID (Gas Chromatography-Flame Ionization Detector)
Separation Objects	Volatile, thermally stable organic compounds	Polar, thermally unstable macromolecules (such as proteins, pesticides)	Carbon-containing organic compounds (general-purpose detection, weak qualitative ability)
Qualitative Ability	Strong (mass spectral library matching)	Strong (molecular ion peaks can be obtained)	Weak (only qualitative by retention time)
Detection Limit		0.1-1 pg (higher sensitivity)	10-100 ng (lower)
Sample Pretreatment	Derivatization required (for some polar substances)	Simple (direct injection or filtration)	Simple (suitable for conventional organic compounds)

High performance liquid chromatography mass spectrometer

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