In 1994, a university student in China—Zhu Ling—started to experience disturbing symptoms characterized by severe abdominal pain, hair loss, and partial paralysis. Unfortunately, by the time physicians were able to give a diagnosis of thallium poisoning—Ling was in a coma. Although she survived, Ling suffered permanent neurological damage. Police confirmed that Ling was intentionally poisoned—but the case has remained unsolved.
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Now, two decades later science re-opens the cases thanks to mass spectrometry, a measuring technique detecting elements at the parts per billion level. Specifically, mass spectrometry was used to analyze trace elements using Ling’s hair samples in hopes to establish a timeline of her poisoning. Results of the analysis were published in the paper "Details of a thallium poisoning case revealed by single hair analysis using laser ablation inductively coupled plasma mass spectrometry" released in Forensic Science International.
"To my knowledge, this is the first use of mass spectrometry to reconstitute the timeline of a prolonged case of intentional heavy metal poisoning," explained Richard Ash, an associate research scientist in the University of Maryland's Department of Geology. "The analysis showed that the victim was poisoned in many doses that increased in frequency and concentration over time.”
Thallium was measured in the victim’s hair by the energy of an ultraviolet laser, which converted the outermost portion of the hair into tiny particles. The particles were then measured by a spectrometer of thallium analysis. The timeline of thallium ingestion was established using measurements from the growth rate of hair and scanning speed of the ultraviolet laser.
Hair samples from the victim are mounted on slides for analysis by mass spectrometry.
Credit: Faye Levine via University of Maryland
These findings suggested that a spike in thallium concentration in some of the old collected hair stands indicated that the victim has been poisoned via eye contact and later through oral ingestion. "I hope that the new information our work has provided may one day lead to the perpetrator being brought to justice and Zhu Ling's family gaining some solace from seeing that," Ash said.