Lecture Notes on Supercritical Fluid Chromatography
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TOPIC 4
Course Learning Outcomes
Able to :
1. Explain the fundamental concepts & theories of separation techniques in SFC & SFE. 2. Sketch, label the schematic diagrams & discuss the function of each component in SFC & SFE. 3. Identify the strength & limitations of SFC & SFE technique. 4. Suggest and justify the most suitable & efficient separation technique to be employed for an analysis.
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What is supercritical fluid?
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Critical temperature (Tc) for any substance is a temperature above which it can no longer exist as a liquid, no matter how much pressure is applied. Critical pressure (Pc) is a pressure above which the substance can no longer exist as a gas no matter how high the temperature is raised.
A supercritical fluid is any substance that is above its Tc & Pc [critical point].
CRITICAL POINT
In other words, when a substance is above Tc & Pc, it exists in a single phase which is neither liquid nor gas; this is a supercritical fluid.
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Example :
CO2 usually behaves as a gas in air at STP or as a solid called dry ice when frozen. If the temperature & pressure are both increased from STP to be at or above the critical point for CO2, it can adopt properties midway between a gas & a liquid.
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More specifically, it behaves as a supercritical fluid above its Tc (31.1 °C) & Pc (72.9 atm/7.39 MPa), expanding to fill its container like a gas but with a density like that of a liquid. Above 304.2 K (31.2 oC) & 72.8 atm, CO2 behaves as a supercritical fluid & shows properties of both a liquid & a gas.
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Supercritical fluid has the unique ability : Diffuse through solids like a gas. Dissolve materials like a liquid. It can readily change in density upon minor changes in temperature or pressure.
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Characteristics of supercritical fluid : They have a combination of vapor & liquid properties. They have densities higher than gas & lower than liquid & viscosities less than liquids. Their diffusivities are gas-like. They
TOPIC 4
Course Learning Outcomes
Able to :
1. Explain the fundamental concepts & theories of separation techniques in SFC & SFE. 2. Sketch, label the schematic diagrams & discuss the function of each component in SFC & SFE. 3. Identify the strength & limitations of SFC & SFE technique. 4. Suggest and justify the most suitable & efficient separation technique to be employed for an analysis.
2
What is supercritical fluid?
3
Critical temperature (Tc) for any substance is a temperature above which it can no longer exist as a liquid, no matter how much pressure is applied. Critical pressure (Pc) is a pressure above which the substance can no longer exist as a gas no matter how high the temperature is raised.
A supercritical fluid is any substance that is above its Tc & Pc [critical point].
CRITICAL POINT
In other words, when a substance is above Tc & Pc, it exists in a single phase which is neither liquid nor gas; this is a supercritical fluid.
4
Example :
CO2 usually behaves as a gas in air at STP or as a solid called dry ice when frozen. If the temperature & pressure are both increased from STP to be at or above the critical point for CO2, it can adopt properties midway between a gas & a liquid.
5
More specifically, it behaves as a supercritical fluid above its Tc (31.1 °C) & Pc (72.9 atm/7.39 MPa), expanding to fill its container like a gas but with a density like that of a liquid. Above 304.2 K (31.2 oC) & 72.8 atm, CO2 behaves as a supercritical fluid & shows properties of both a liquid & a gas.
6
Supercritical fluid has the unique ability : Diffuse through solids like a gas. Dissolve materials like a liquid. It can readily change in density upon minor changes in temperature or pressure.
7
Characteristics of supercritical fluid : They have a combination of vapor & liquid properties. They have densities higher than gas & lower than liquid & viscosities less than liquids. Their diffusivities are gas-like. They