Since the first use of fingerprints to identify and convict a murderer, in 1892,
detectives the world over have come to rely heavily on print evidence to build their cases against suspects.
One limit on the value of fingerprints, though, is that it is hard to work out how old they are.
This is a particular problem when a crime is committed somewhere
that a suspect frequently and legitimately visits, such as a place of work.
In this case exactly when a print was made might be crucial to establishing guilt or innocence.
But it is information that science has, until now,been unable to provide with any accuracy.
As they write in Analytical Chemistry, Paige Hinners and Young Jin Lee of Iowa State University
正如他们在《As they write in Analytical Chemistry》所写的那样，爱荷华州立大学的
believe they can remedy this state of affairs. They knew from work conducted by other laboratories
Paige Hinners和Young Jin Lee认为他们可以改变这种状况。他们从其他实验的工作中了解到
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 analyse 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.