Gas Chromatography Flashcards

Flashcards covering the basics of Gas Chromatography, including its principles, instrumentation, columns, detectors, and applications, based on lecture notes.

How is Gas Chromatography different from Liquid Chromatography?

Sample is vaporized and injected onto the head of the column; Elution comes from a gas flowing through the column; the gas does not interact with the sample, only acts to make it flow along.

What are the two major types of Gas Chromatography?

Gas-solid chromatography (GSC) and Gas-liquid chromatography (GLC).

What is Gas-Solid Chromatography (GSC) based on?

GSC is based on the physical adsorption of solute molecules onto a solid, usually resulting in tailing due to a non-linear process. It is not widely used except for a few small molecules.

What is Gas-Liquid Chromatography (GLC)?

GLC is based on the adsorption of solute onto a liquid coating on a solid support and is widely used across scientific fields. It is commonly referred to as just GC.

What are the basic components of a GC instrument?

Carrier gas tank, flow regulators, sample injection chamber, column, oven, detector, data system

What type of gas is used in the Carrier Gas Supply, and what is used to remove trace elements?

Chemically inert gases such as He, N2, or H2. Molecular sieves are often used to remove trace O2 or H2O.

What is the goal when injecting a sample into the Sample Injection System?

To inject the sample in a small, discrete volume of gas or a ‘plug’ to avoid band spreading and poor resolution.

What are the two major types of column configurations in GC?

Packed columns and open tubular or capillary columns.

What are the Characteristics of an Ideal Detector?

Must be sensitive, stable, reproducible, have a linear response, operate over a range of temperatures, have a short response time, be reliable and easy to use, have a predictable response, and be non-destructive (though not always necessary).

Name three types of Detection Systems in GC

Flame Ionization Detectors (FID's), Thermal Conductivity Detectors (TCD) and Electron Capture Detector.

In Flame Ionization Detectors (FID), what is the relationship between the number of ions and the carbon compound?

The number of ions is proportional to the amount of reduced carbon in the compound.

What types of solutes is the Electron Capture Detector highly selective and sensitive towards?

The ECD is highly selective/sensitive toward solutes with electronegative functional groups, such as halogens,peroxides,quinones and nitro groups, and is relatively insensitive to amines, alcohols, and hydrocarbons.

What are the three major types of Open Tubular Columns?

Wall-coated open tubular (WCOT), Support-coated open tubular (SCOT), and Porous-layer open tubular (PLOT).

What are the characteristics of an Ideal Stationary Phase?

Low volatility, chemically inert, and solvent characteristics that allow all solutes to be resolved with appropriate k’ values.

Name some widely used stationary phases

Polydimethylsiloxanes with varying R groups (methyl, phenyl, cyanopropyl, trifluoropropyl) to modify properties, and polyethylene glycol.

Why are bonding and cross-linking used in stationary phases?

To form a chemical bond between the stationary phase and the Si support, enhancing stability and longevity and preventing bleeding.

What are the two major roles of Gas Chromatography?

Separations of volatile species (organic, metal-organic, biochem) and identification of unknowns.

For what purposes is GC used for Qualitative Analysis?

Purity checks of organics, identification of compounds via retention times (though limited), and quantification of contaminants.

What is the Retention Index (Kovats Index)?

Based on normal alkanes and is defined as 100 times the carbon number of the alkane. It is relatively independent of column variables and is a useful number for compound identification.

How are GC and spectroscopic methods interfaced?

Column effluent flows directly into a detector designed for gases, such as in GC/MS.

What Mass Spectrometry analyzers can be used with GC, and why are they compatible?

Quad, ion trap, and FTMS are all fast enough to scan a complete molecular spectrum in less than a second, allowing for MS of every component coming off the GC.