Chemical Systems under Indirect Observation: Latent Properties and Chemometrics

A fairly large set of chemical problems focus on the desire to know the value of some property of a substance that is very difficult or even impossible to measure in the laboratory. A well-known example is the evaluation of the octane number of a gasoline. Many of the properties of a gasoline mixture are relatively easily measured, but measuring octane number for a gasoline requires the running of the gasoline in a special octane engine, an expensive and tedious measurement. It would be helpful—not to mention simpler, faster, and (especially) cheaper—if we could measure something that is easy to measure like a spectrum and determine the octane number from it. The mathematical relation between our measurement—or measurements, because we might make several—and the property desired is all that is needed. We call the of properties like the octane number indirect because we measure other properties and infer the value of the property of interest through some mathematical relation. Our goal, then, is the indirect observation of a property, for good reasons such as speed and economy.