Fingerprints Can Now Be Dated To Within a Day of When They Were Made

Writing in Analytical Chemistry, Paige Hinners and Young Jin Lee of Iowa State University say they have figured out an accurate way to data to within 24 hours when a fingerprint under a week old was made -- and thus whether it is associated with a crime temporally, as well as spatially. The Economist reports: They knew from work conducted by other laboratories that the triglyceride oils contained in fingerprints change by oxidation over the course of time. That provides an obvious way to date prints. The problem is that the techniques which have been applied to analyze these oils are able to distinguish age only crudely. In practice, they can determine whether or not a print is over a week old, but nothing else. Dr Hinners and Dr Lee wondered if higher precision could be obtained by thinking a bit more about oxidation. Oxygen molecules in the air come in two varieties. Most have a pair of atoms but some, known as ozone, have three. Though far rarer than diatomic oxygen, ozone is more reactive and also reacts in ways different from those of its two-atomed cousin. The two researchers therefore decided to focus their attentions on ozonolysis, as triatomic oxidation is known.

Triglycerides, as their name suggests, are three-tailed molecules. Each tail is a chain of carbon atoms, with hydrogen atoms bonded to the carbons. The chains are held together by bonds between the carbon atoms. These are of two varieties, known as single and double bonds. Single bonds are, in chemistry-speak, saturated, and double bonds unsaturated. By extension, molecules with one or more double bonds in them are also referred to as unsaturated, while those with only single bonds are called saturated. Unsaturated bonds are more reactive, and it is here that ozonolysis does its work. Ozone breaks up triglycerides at their double bonds, with one or more of the ozone's oxygen atoms becoming attached to the carbon chain, to create new chemical species. In principle, this should result in a gradual loss of unsaturated triglycerides and a concomitant rise in the reaction products of ozonolysis. And that, in practice, is what Dr Hinners and Dr Lee found.