thermodynamic factors
The distance between the two peaks has nothing to do with it
Gas chromatography has nothing to do with it
kinetic factors
Liquid film thickness, diffusion speed, carrier particle size
Both involve: degree of separation
basic concept
Reserved parameters
The retention parameter that is independent of the mobile phase is: retention volume
Relative retention value α
Relevant to all stationary phases
When the column temperature is constant, the relative retention value can be improved by using a highly selective stationary phase.
Retention index Ix: the most common qualitative parameter between laboratories
number of theoretical plates
Increase the number of theoretical plates: lengthen the column
Reflects: the performance of the column
Improving chromatographic separation efficiency: changing the stationary solution
Improve column efficiency: appropriately increase column temperature
Reduce the chromatographic peak width and reduce the content of fixative
Distribution ratio k
Lower the column temperature to increase k
As the column temperature increases, k decreases
Distribution coefficient K
The separation principle of gas chromatography
Changing the stationary phase will cause it to change
Response time
The time required for the output signal of a component entering the detector to reach 63% of its true value
Detector “linearity”: The ratio of the maximum and minimum injection volumes at which the detector response is linear
Related to the carrier flow rate u: B, C
rate equation
Mass transfer resistance C
The main factors affecting column efficiency at high flow rates
Main controlling factors of tray height
molecular diffusion term
Van's equation can be ignored
Using nitrogen can improve column efficiency
Qualitative analysis
The qualitative method of using retained values is suitable for: tR can be accurately measured and there is a standard material
Qualitativeness using retention value two-column method
Quantitative analysis
Chromatographic peak
Chromatographic outflow curve, the distance between the two peaks is determined by the distribution coefficient
The width of a chromatographic peak depends on molecular diffusion and mass transfer rates in the column
Gaussian distribution
Multiply the peak height by the half-peak width
asymmetrical
Multiply the peak height by the average peak height
Homologues
Multiply the peak height by the retention value
all
Integration method using electronic integrator
Internal standard method: all components cannot peak or only a few components in the sample can be quantitatively determined
Normalization method: all peaks can be generated
liquid chromatography
Ways to improve column efficiency: reduce packing particle size
To improve separation efficiency and shorten analysis time, gradient elution should be used
Detection Systems
Ultraviolet visible detector (UVD)
Mobile phase: There is an absorption peak below the wavelength of 190nm.
Refractive Index Detector (RID)
Separation of mixtures of long chain saturated alkanes
Not suitable for gradient elution
Evaporative light scattering detector (ELSD)
Fluorescence Detector (FD)
Testing: Monitoring PAHs in Water Sources
steric exclusion
Separation principle: Osmotic balance
Separation mechanism: Separation due to different penetration or rejection by pores
Classification analysis of relative molecular weight of polystyrene
Any partition coefficient is less than 1
Analyze samples with relative molecular mass greater than 2000
ion
Separation principle: ion exchange balance
liquid liquid
Separation principle: distribution balance
normal phase liquid chromatography
Properties of Stationary Phases, Mobile Phases, and Separated Compounds: Polar, Nonpolar, and Polar
reversed-phase liquid chromatography
Properties of Stationary Phases, Mobile Phases, and Separated Compounds: Nonpolar, Polar, and Nonpolar
liquid solid
Separation principle: adsorption equilibrium
Research on plant pigment components
The final component that leaves the chromatographic column may be: p-hydroxyaniline
In order to obtain higher column energy, commonly used chromatography columns are: straight packed columns
Gas chromatography
Detector
Thermal Conductivity Detector (TCD)
Detection: ① Water in organic solvents; ② Can detect all organic and inorganic substances; ③ Determination of water content in wine
Carrier gas: hydrogen
Reason: The conductivity (thermal conductivity fraction) of hydrogen is large
Increasing the average flow rate of the carrier gas, the changes in the chromatographic outflow curve are as ti decreases and Ai decreases.
Electron Capture Detector (ECD)
Detection: ① Chlorine-containing pesticides; ② Detection of polyhalogen and organic gases containing electronegative groups
③ Determination of trace amounts of nitro compounds
Hydrogen Flame Ionization Detector (FID)
Detection: ① All trace amounts of carbon-containing organic gases
The factors related to the relative correction factor are: the selection of standards
Flame Photometric Detector (FPD)
Detection: Gases containing phosphorus and sulfur compounds
The upper limit temperature of the chromatographic column depends on: the maximum use temperature of the stationary solution
Samples containing aromatic isomers, fixative: organic bentonite or liquid crystal
The retention value reflects the interaction temperature of the component and stationary phase.
①Applicable to: separation and determination of non-corrosive gases and liquids that can be vaporized at vaporization temperature
②Programmed temperature rise is suitable for separating complex samples with a wide boiling point range
Stationary Phase
polarity
Separation of polar components, intermolecular forces: Coulomb force
Separation of non-polar components, intermolecular forces: induced forces
non-polar
Intermolecular forces: dispersion forces
For quantitative analysis, the resolution should be at least: 1.0
Related parameters: peak area
Qualitative analysis, relevant parameters: retained values
①The factors that have no effect on the retention volume are: changing the carrier gas flow rate
②The biggest impact on resolution: column temperature
③The factor that has nothing to do with the separation of the two solutes is: switch to a more sensitive detector
④Interaction between components and carriers will lead to: tailing peaks
Gas-solid chromatography analysis
Separation principle: adsorption equilibrium (separation of permanent gases and gaseous hydrocarbons)
The properties of the components flowing out of the chromatographic column first have small adsorption capacity.
Determine the nitrogen and oxygen content in the air
Stationary phase: solid adsorbent
gas liquid chromatography
The components that flow out of the column first: have low solubility
The purpose of aging treatment: to remove residual solvents and other volatile impurities
Column temperature affects thermodynamics and kinetics
Interactions between components and stationary phase: dissolution-volatilization
Solute type: available
in gradient elution
Gradient elution is suitable for samples with a wide range of distribution ratios
Often used to interpret chromatographic elution curves
What factors are related to the width of
Martin and Singer: Establishment of liquid-liquid partition chromatography,
For contributions to gas chromatography
Founder: Zwit (liquid-solid chromatography)
Features: Both separation and analysis
Concentration type: ①The peak height has nothing to do with the flow rate, and the peak area is inversely proportional to the flow rate.
②The response value is proportional to the concentration of the component in the carrier gas
The distance between the two peaks
Mass type: ① Relevant parameters: Relevant parameters of the recorder, area of chromatographic outflow curve, injection volume and carrier gas flow rate
②The peak height is proportional to the flow rate, and the peak area has nothing to do with the flow rate.
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