Sample Handling Analysis of Solids, Liquids, and Gases

2 Sample Handling Analysis of Solids, Liquids, and Gases 

In general, samples to be analyzed by infrared absorption spectroscopy require adequate support (infrared cells) in such a way as to enable the acquisition of the spectrum in the apparatus. There are different types of cells, and the choice among them depends on the sample characteristics and the objective of the analysis, such as surface characterization studies or chemical reaction monitoring. ConunerciaUy available cells are of the sealed, collapsible, and variable thickness kinds, for gas, flow, high-vacuum and -pressure and micro-cells. 

The high-vacuum cell is employed in studies of catalysts and absorbed molecules. The choice of window also depends on the range of interest, but care must be taken with the pressure applied, because CaF2, for example, can support pressures of up to 1200 atm. 

Liquid Analysis A sealed cell is used for volatile pure liquids or liquids in the solution. In case of dilution, the solvent must be as nonpolar as possible, in order to minimize solute-solvent interactions, and it cannot absorb strongly in the region of interest. 

Solid Analysis Finely divided and dispersed solids in alkali halides (KBr is the most widely used). The mixture in the proportion of 1 mg of sample 300 mg of KBr is pressed, forming a clear and transparent pellet. Material that may form films, such as polymers and resins, is directly analyzed and the film must be as thin as possible. For surface characterization the sample is prepared in a the form of a self-supported pellet, where a small quantity of solid ( 20 mg) is pressed in order to obtain a thickness of decimals of millimeters. 

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