Sample History

4.1 Sample History

original base polymers were, what other additives could As noted, we are seldom dealing with a true unknown,

be present, and what material, usually a solvent, was used and typical situations include the following:

for the extraction.

INTERPRETATION OF INFRARED SPECTRA, A PRACTICAL APPROACH

Looking at residues and residual products of a reaction compounds, and highly conjugated olefinic compounds, is similar to the concept of characterizing a contaminant.

such as carotenes, are similarly colored. This can be used Residues formed within products are often the result

as a guide to look for the specific functionality in the of a breakdown reaction or an unexpected interaction

spectrum.

between components. If derived from one or more of the Likewise, odor can be a useful guide. This author is components, then a knowledge of all of the ingredients

not advocating that a person should inhale the vapor is essential – again we would be looking for chemically

of a sample directly, for obvious reasons. However, if related species in the residue, and reference spectra of

under cautious sampling conditions a characteristic odor each of the ingredients would be important in attempting

is detected, then this can provide a valuable insight regard- to characterize the material. In the case of a reaction

ing the presence of particular functional groups. Common product, spectra for the reactants and any solvents or

examples are alcohols, esters, and ketones, which often substrates (catalysts, etc.) used would be helpful.

possess relatively pleasant fragrances, especially when Finally, the identification of an end product from its

associated with some degree of unsaturation. An almond- infrared spectrum is common practice. By definition,

like odor might indicate a nitro compound, benzaldehyde, unless the final product is a pure chemical, most

or a cyano compound (caution!), a fish-like odor is often manufactured products are mixtures, often featuring

associated with amino or amido compounds, and a putrid blended solid and/or liquid components from percentage

or ‘‘bad-cheese’’ odor is associated with certain carboxylic range concentrations to trace amounts. Often at issue is

acids. With time, one can build up a mental library of com- how much can be identified from the interpretation of

mon odors and fragrances, and these can be very valuable

a single spectrum. It is often necessary to perform some for initial material screening, by helping one look for the form of preconcentration on one or more ingredients,

presence of specific functional groups. or to perform a chemical modification to change the

Volatility and flammability can be useful guides. spectral response of one or more of the major ingredients.

Most volatile compounds tend to have a relatively low This latter operation may help to remove the spectral

molecular weight, and they usually are unassociated. This interferences from a major component for determining

latter point helps to rule out certain hydrogen-bonded the presence of minor components.

species, such as carboxylic acids, amines, and multiple hydroxy-substituted compounds (such as glycols). If a

4.2 Physical Characteristics of the Sample

sample is submitted for some form of combustion analysis, it is worthwhile monitoring how it burns. If it burns with

From considerations based on the discussions in the

a clean, bluish flame, that might indicate that the sample section above, a good working knowledge of the sample

is oxygenated (alcohol or ether). If it has a yellow and/or allows one to determine basic information about the

smoky flame, it indicates an excess of carbon, possible sample. This information can help in the determination of

unsaturation or an aromatic compound. The latter can the best method of sampling. It can also help to indicate if

produce a very smoky flame.

any special treatments to the sample are necessary before proceeding, such as the removal of residual solvents,