Gas Chromatography Flashcards
• Technique using analytical chemistry for separating and analyzing compounds in a complex mixtures
• it relies on the principle of differential partitioning of sample components between stationary phase and a mobile phase
• it has high sensitivity selectivity and efficiency making it an indispensable tool for qualitative and quantitative analysis of organic compounds
Gas chromatography (GC)
Gas chromatography relies on the principle of ___ ___ of sample components between a __ phase and a ___ phase
Differential partitioning
Stationary phase and mobile phase
2 phases of GC
Mobile phase
Stationary phase
• This is an inert gas typically helium or nitrogen that continuously flows through the system.
• it acts like moving platform carrying the vaporized sample components through the column.
Mobile phase (Carrier gas)
• This is a thin layer of high boiling liquid film coating the inner walls of a long, narrow column.
• it interacts with a sample components as they travel through the column
Stationary phase
Compounds have different affinities for the __ phase compared to the ___ phase
Stationary
Mobile
The sample is vaporized and carried by a gas through a ___.
Column
Inside the column the sample interacts differently with the ___ ___ causing some compounds to move ___ ( longer retention times) while others move ___
Stationary phase
Slower
Faster
The strength of this interaction in column is described by a value called the ?
distribution constant (Kc)
It represents the equilibrium between a compound in the stationary phase and the mobile phase
Distribution constant (Kc)
Compounds with ___ interactions with the stationary phase take longer to ___ (remove by washing with a solvent, especially in chromatography) from the column
Stronger
Elute
The equilibrium between the concentration of a compound in the stationary phase and the mobile phase is described by an equilibrium constant known as the ?
distribution constant or partition coefficient (Kc)
That distribution constant or partition coefficient (Kc) determines the ____ of compounds through the column and thus enables the chromatographic ____
Movement
Separation
_____ in the chemical nature of the stationary phase influences the distribution of ___
Temperature
Constant
___ phase interacts with the sample molecules differently causing separation based on ____ properties
Stationary
molecular
Mobile phase ___ the sample through the column. its flow rate affects separation efficiency.
Carries
They do not react with the sample components ensuring that the separation process is not affected by chemical interactions with the mobile phase.
Mobile phase
• it is where the sample is introduced into the system.
• It vaporizes the sample and injects it into the column.
Injector
located at the end of the column, it detects separated sample components.
Detector
The detector monitors the ___ leaving the column and provides a signal that corresponds to the concentration of the sample components
Eluent
The detector output is analyzed to determine the ___ and ___ of sample components
Identity
Concentration
It collects and analyzes detector output, providing information about sample components’ identities and concentrations.
Data system
The structure of the chromatographic column consists of a hollow tube pack with a stationary phase in gas ___ chromatography
Solid
The structure of the chromatographic column consists of coated with a thin layer of stationary phase in gas ___ chromatography
Liquid
• Filled with a solid support material providing a large surface area for interaction between the sample components and the stationary phase.
• they are suitable for separating less volatile compounds
Packed columns
They have thin coated layer on the inner walls providing high separation efficiency and resolving power
Capillary columns
Where sample components interact with the stationary phase as they pass through, leading to differential retention times and separation based on their physical and chemical properties
Chromatographic column
• transports the sample through the chromatographic system
• they must be inert, meaning they do not interact with the sample or stationary phase to ensure accurate analysis
• the choice of career gas affects resolution, efficiency, and analysis time in gas chromatography
Carrier gas system
Carrier gas system must be ___, meaning they do not interact with the sample or stationary phase to ensure accurate analysis
Inert
Types of carrier gases
Helium
hydrogen
nitrogen
• Most commonly used carrier gas due to its inertness, consistent flow rate, and road applicability
• suitable for a wide range of analytical applications and compatible with various detectors
Helium
• Provides higher efficiency and faster analysis compared to helium due to its lower viscosity
• offers improve separation of closely iluting compounds
• it is flammable and requires extra safety precautions
Hydrogen
• inexpensive and readily available carrier gas option
• less efficient than helium and hydrogen that suitable for routine analysis
• often use one high purity helium or hydrogen is not available or cost is concern
Nitrogen
Split injection divides the sample into two portions
- directed into the column for analysis
- vented out
• Suitable for samples with a wide range of concentrations preventing detector saturation
• enhances sensitivity for trace level analytes
Split injection
•Introduces the entire sample into the column without splitting initially
• ideal for trace level analysis by maximizing sample concentration on the column
• ensures higher sensitivity but requires careful optimization to prevent detector overload
Spitless injection
• Directly introduces the sample into the head of the chromatographic column
• suitable for thermally labile compounds or sample with a limited volume
• minimizes the sample degradation and provides short peak shapes
On-column injection
Techniques for injecting samples
Split injection
spitless injection
on column injection
• captures and processes chromatographic data facilitating data analysis and interpretation
• converts detector signals into digital information and generates chromatograms visual representation of analyte peaks
Recorder
Converts raw chromatographic data into actionable insights, aiding in quality control, research, and various analytical applications
Recorder
Analytical steps of GC
- injection of the sample into the injection port.
- Injected sample is vaporized by the injection ports heat and mixed with carrier gas before entering the chromatographic column
- Separation occurs within the chromatographic column based on differential interactions between sample components and the stationary phase
- Chromatograms generated by the detector are interpreted to identify sample components and assess their concentrations
Time taken for a compound to travel from injection to detection
Retention time
Involves identifying and quantifying sample components based on the retention times and peak areas
Peak analysis
Represent individual compounds, with peak height or area proportional to their concentration.
Peaks on the chromatogram
Provides additional information about compounds identity and purity
Retention times and peak shapes
