Extracting Elemental "Fingerprints" from Minute Physical Evidence

A microscopic shard of glass or a tiny wisp of adhesive tape may be the only evidence that links a suspect with a crime scene. In cases like this, forensics scientists need a way to analyze the microscopic specimen and reliably identify its origin.

Forensic investigators currently rely on various techniques to characterize physical evidence, including microscopy, refractive index, Fourier transform infrared, and X-ray fluorescence. These techniques have drawbacks for analyzing small samples and distinguishing between materials with physical, chemical and visual similarities. Some require extensive sample preparation, a time-consuming process that uses hazardous substances, increases the risk of contamination and destroys significant amounts of sample. Other techniques have difficulty discerning materials that are chemically inert or of the same brand, color, or matrix, or from different batches of the same manufacturing run.

Eliminating the drawbacks

A new method for analyzing forensic samples combines laser ablation with inductively coupled plasma-mass spectrometry (LA-ICP-MS) to overcome the limitations of traditional techniques. In LA-ICP-MS, a powerful pulsed laser vaporizes a small amount of a solid sample. A gas stream carries the sample vapor into a high-temperature plasma (the ICP) where the sample is ionized and extracted into a mass spectrometer for analysis.

LA-ICP-MS can characterize microscopic samples such as glass shards and clothing fibers at the parts per billion (ppb) level, providing an elemental "fingerprint" that can help investigators determine the origin of a material, sometimes down to the brand or manufacturer. Advantages of LA-ICP-MS in forensic analysis include:

• Accurate discrimination of similar samples by identifying trace elemental and isotopic characteristics
• Faster analysis enabled in part by simplified sample preparation
• Very low sample consumption (often less than one microgram), preserving the original sample and enabling further measurements for corroboration
• Clear and unambiguous data, which enables graphical presentations that are easy for jurors to understand

Applying proven instrumentation

Agilent has documented this approach in three application notes. One provides an introduction to LA-ICP-MS. The others describe an analysis of glass samples and an analysis of adhesive tape samples. All three notes feature a system that uses a New Wave Research Merchantek UP213 LA system coupled to an Agilent 7500 Series ICP-MS instrument.

The 7500 Series combines high performance with usability—it's equally capable of running the toughest sample matrices or the most demanding ultratrace applications. These instruments enhance lab productivity by providing high levels of automation and imposing low requirements for routine maintenance. And Agilent's powerful ChemStation software helps investigators control instruments, collect and manage data, process more evidence in less time, and ultimately connect the right suspect to the crime scene.

For more information

To learn more about related applications, please visit the Forensics section of our Web site. For information about other Agilent chemical analysis products and resources, please return to the Life Sciences/Chemical Analysis main page.