Organic Chemistry Ch. 18: Introduction to Gas Chromatography and Atomic Absorption

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CG is the method which is used to separate mixtures of substances into their individual components. All forms of chromatography work on the same principle.

They all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas). The mobile phase flows through the stationary phase and carries the components of the mixture with it. Different components travel at different rates. We'll look at the reasons for this further down the page.

Thin layer chromatography - using a thin, uniform layer of silica gel or alumina coated onto a piece of glass, metal or rigid plastic. The silica gel (or the alumina) is the stationary phase. The stationary phase for thin layer chromatography also often contains a substance which fluoresces in UV light - for reasons you will see later. The mobile phase is a suitable liquid solvent or mixture of solvents.

Equipment with which the class will become familiar with are but not exclusive to Gas Chromatographs, Atomic Absorption Spectrophotometers. For the purposes of the classroom when studying chromatography the class will use a gas-less chromatograph.

The Gas-less Educational GC system from Buck Scientific, will be ideal for our undergraduate chemistry classes where the principles of gas chromatography are demonstrated on the same equipment students will encounter in industry. The CCD detects combustible (hydrocarbon) molecules, and it operates on air carrier gas from the air compressor. This gas chromatograph will be perfectly suited for teaching experiments we will encounter where compressed gas cylinders cannot be used. Because it operates on its own infinite supply of room air, the Gas-less GC can be used to perform demonstrations in the classroom, instead of the lab.

The analytical procedure for the qualitative and quantitative determination of chemical elements employing the absorption of optical radiation by free atoms in the gaseous state is known as atomic absorption spectroscopy. Atomic absorption exploits different radiation wavelengths absorbed by different atoms. This technique is used for determining the concentration of a particular element in a sample to be analyzed, through AAS which can help determine over 70 different elements in solution.

Atomic absorption spectrophotometers will be employed to help better understand and research the amounts of a particular element which is present in our experiments. The instrument is most reliable when a simple line relates absorption-concentration. Relevant variables of AA include flame calibration and unique metal-based interactions. Flame spectrophotometers and flame calibration can become a difficult challenge in itself. The flame and atomizer are intended to break any molecular bonds they might have.

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Organic Chemistry Ch. 18: Introduction to Gas Chromatography and Atomic Absorption

This article was published on 2011/11/11