2082f79a-6717-4019-828d-2d717623ffd5.pptx

PES Modern College of Pharmacy Nigdi. Gas chromatography.

Gas Chromatography Detector.

What Are GC Detectors?. Gas chromatography (GC) detectors convert analyte compounds into detectable signals, essential for accurate analysis; they vary in sensitivity and selectivity, influencing their applications significantly..

Mass Spectrometry Principle. Mass spectrometry (MS) is a powerful analytical technique used to determine the mass-to-charge ratio of ions, enabling the identification and quantification of various compounds in a sample Principle: MS detects compounds by ionizing, fragmenting, and then measuring ions based on their mass-to-charge ratio (m/z). It provides both qualitative (identification) and quantitative (amount) information..

MS Working Mechanism. This section outlines the workflow of Mass Spectrometry (MS), detailing how the GC effluent is transformed into measurable ions, leading to precise analysis. Working: Sample eluting from GC column enters the ion source through a transfer line. It undergoes electron-impact ionization, producing ions and fragments. Ions are sorted in a mass analyzer (commonly quadrupole ion trap). Ions are then detected by an electron multiplier, producing an electrical signal. A mass spectrum is generated → peaks represent fragments at different m/z values..

MS Features & Applications. Mass Spectrometry (MS) is known for its exceptional sensitivity and specificity, making it invaluable for identifying unknown compounds and analyzing complex mixtures in various scientific fields. Instrumentation Features: Ion source (electron impact) Quadrupole ion trap or other analyzer Electron multiplier detector Computer system for chromatogram + mass spectrum Advantages: Most powerful detector for GC. Provides exact molecular identification. Helps in resolving overlapping peaks. High sensitivity and specificity. Applications: Drugs, pesticides, environmental pollutants, impurity identification, forensic work..

Sensitivity of MS detectors. Mass spectrometry (MS) detectors offer unmatched sensitivity, allowing for the detection of trace amounts of compounds, making them invaluable in complex sample analysis and research applications..

Flame Ionization Detector. The Flame Ionization Detector (FID) is essential in gas chromatography, detecting organic compounds by measuring the electrical current produced when analytes are burned in a flame. FID detects organic compounds by burning them in a hydrogen–air flame. Combustion produces ions and electrons which generate a measurable current..

FID Working Mechanism. The Flame Ionization Detector (FID) operates by ionizing organic compounds in a flame, generating ions that create an electric current proportional to the amount of analyte present. GC effluent enters air–hydrogen flame. Organic compounds undergo pyrolysis → form ions & electrons. A potential difference collects ions → current measured by a picoammeter. Current is proportional to concentration of analyte..

FID Features & Limitations. The Flame Ionization Detector (FID) offers high sensitivity for hydrocarbons, but it is not suitable for inorganic gases and requires hydrogen as a fuel source. Key Features: Highly sensitive to hydrocarbons. Unaffected by non-combustible gases (N₂, CO₂, H₂O). Advantages: Very high sensitivity. Low noise, stable baseline. Wide linear range. Not affected by water or carrier gas impurities. Disadvantages: Requires hydrogen (flammable). Sample is destroyed. Not suitable for inorganic gases or CO₂, H₂O..

Thermal Conductivity Detector. The Thermal Conductivity Detector (TCD) operates on the principle of measuring the change in thermal conductivity of a gas mixture, providing universal detection capabilities for various analytes..

TCD Design & Evaluation. The Thermal Conductivity Detector (TCD) utilizes a dual-cell design, offering a universal detection method suitable for various analytes, though its sensitivity can be lower than other detectors. Design: Two cells: reference cell (carrier gas only) and sample cell (carrier + analyte). Works on Wheatstone bridge principle. Working: Uses electrically heated filament/wire (platinum/gold). Carrier gas (He/H₂) has high thermal conductivity → keeps filament cool. When analyte vapor enters, conductivity decreases → filament temperature rises → resistance changes. This change is detected and recorded..

Advantages: Universal detector – detects both organic and inorganic compounds. Non-destructive (sample can be collected). Simple and inexpensive. Disadvantages: Lower sensitivity than FID or ECD. Signal depends on flow rate and concentration. Not suitable for trace-level analysis. Applications: Permanent gases, light hydrocarbons, industrial gases, process monitoring..

Electron Capture Detector. The Electron Capture Detector (ECD) is a highly sensitive device that utilizes a radioactive source to measure the presence of electronegative compounds through electron capture. ECD detects compounds that capture electrons—especially those containing halogens, nitro groups, peroxides, quinones, etc..

Electron Capture Detector. The Electron Capture Detector (ECD) is known for its ultra-high sensitivity, making it ideal for detecting halogenated compounds and environmental pollutants despite challenges like oxygen sensitivity. Working: Uses a radioactive emitter (Ni-63 or tritium) to produce electrons. In pure carrier gas (usually N₂), a constant electron current is maintained. When an electronegative compound elutes, it captures electrons, reducing the current. Drop in current = analyte concentration. Key Characteristics: One of the most selective and sensitive detectors..

Advantages: Ultra-high sensitivity (detects femtograms). Best for halogenated pesticides, PCBs, chlorinated organic pollutants. Ideal for environmental analysis. Disadvantages: Limited range of detectable compounds (only electronegative ones). Radioactive source → safety concerns. Sensitive to O₂ contamination. Requires strict maintenance. Applications: Pesticides, herbicides, halogenated solvents, persistent organic pollutants (POPs)..

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