Tag Archives: analytical chemistry

DNA Evidence – Not so airtight after all

March 2009. Police departments across Europe have been searching for a serial killer known as the Phantom of Heilbronn. Her DNA had been found at crime scenes all over the subcontinent. Other than the DNA, police had no other clues to her identity. Finally, a break, but not exactly what authorities were looking for. They had found an individual with matching DNA, only it was a man. Stumped as to how their profile was matching to a man – a genetic impossibility – investigators re-examined the evidence. They eventually determined that the Phantom of Heilbronn was just that, a phantom. The DNA belonged to a worker in the factory that manufactured the cotton swabs used by the forensic officers. The swabs had contained minor contamination from the worker, but had been used to collect samples at crime scenes. When analyzing the swabs, investigators found the DNA profile of the worker, instead of that of the culprit.

Every cell with a nucleus contains molecules of DNA, which function as the blueprint of life. Cells read the code in DNA and use it to construct and operate the body of the organism. Humans share 99.9% of their DNA sequence, but there is variation in the code. Modern technology can read an entire DNA sequence and isolate the parts in which there is known to be variation, known as loci. The variation at all loci produces a DNA profile that is as unique to an individual as a fingerprint. Forensic analysts working with police departments then use this to match a suspect’s DNA to that found as evidence at a crime scene.

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How DNA analysis works. Source: The National Forensic Science Technology Center (NFSTC)

Media and popular culture would have you believe that DNA fingerprinting technology is infallible. As the case of the Phantom demonstrates, it most certainly is not. Since with modern technology DNA can be extracted from only a few cells, post-crime contamination during crime scene handling is becoming increasingly problematic. Cells from anywhere or anyone can end up on pieces of vital evidence and be misidentified as the cells of the criminal. Sometimes, as in the case of the phantom, this wastes valuable time and resources. Other times, such as in the controversial Amanda Knox case, it can land the wrong person in jail.

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Crime scenes are at high risk of DNA contamination  Source: Wikimedia commons, By Tex Texin from Blogosphere, Cyberspace – “Crime Scene Do Not Cross” tape, CC BY 2.0

Crime scene contamination, along with other ways DNA evidence can be corrupted, cast doubt on the perceived faultless technique of DNA fingerprinting. Sometimes, even if with a DNA match cannot prove guilt beyond a reasonable doubt.

Megan Wolf

UBC Researcher Developing Marijuana Breathalyzer

Earlier this year at UBC Okanagan’s Advanced Thermo-Fluidic Laboratory, engineering professor Mina Hoorfar and PhD student Mohammad Paknahad developed a breathalyzer for tetrahydrocannabinol (THC), the active ingredient in marijuana. While attempting to make an affordable miniature gas chromatography-mass spectrometry (GC-MS) device, it occurred to them that, with marijuana becoming legalized in more parts of the world every year, there was a growing market they could to tap into. When testing out their device as a THC detector was a success, they started to develop their device specifically as a marijuana breathalyzer.

Unlike traditional breathalyzers, this device utilizes GC-MS and a computer, and is therefore highly adaptable – it can easily be used to search for concentrations of a variety of chemicals. Some other uses they’ve thought of for the device include analyzing the characteristics of wine, checking your own blood alcohol content, monitoring glucose levels in diabetic people, and finding gas leaks along pipelines.

Gas Chromatography-Mass Spectrometry schematic, courtesy of Wikimedia

Gas Chromatography-Mass Spectrometry schematic, courtesy of Wikimedia (https://upload.wikimedia.org/wikipedia/commons/b/b9/Gcms_schematic.gif) Gas is injected into the column, where it sorts itself into groups based on properties such as polarity and molecule size. The groups of molecules pass through the mass spectrometer, which analyzes how much of each chemical there is.

Mina Hoorfar specializes in microfluidics, the field of manipulating tiny amounts of gas and liquid using their chemical properties. In this device, the exhaled breath is channeled through a column that is only one micrometer thick, where the chemical components are separated by their properties and analyzed using the same processes as in regular GC-MS. The results are then sent via Bluetooth to a computer or smartphone, showing the user exactly what is in their breath. The device would cost about $15 to build – incredibly cheap for a GC-MS device, which often cost thousands of dollars – and Hoorfar says that she is working with a lab instrument company to bring the device to the market.

~ Nat Shipp

Rio’s Emerald Pools: A Scientific Whodunit

This summer, when I tuned in to the Rio de Janeiro Olympic games and saw cloudy green waters in the diving pools, I barely batted an eye. I thought this was merely a media stunt. The Brazilian authorities had harmlessly dyed the waters green because it fit with the country’s theme. They have a green flag, they have incredible natural greenery and so on. I soon learned that this was no dye. The waters had, seemingly spontaneously, turned green overnight.

The games’ organizers pointed the finger at an unnamed stadium worker who apparently poured copious amounts of hydrogen peroxide into the pool. Possibly this was an attempt to “super-sterilize” the pool, akin to using peroxide on a skinned knee? However, like most swimming pools, this one had already been treated with chlorine. More specifically, sodium hypochlorite (NaOCl). When NaOCl is combined with water it forms hypochlorous acid, a potent antimicrobial agent. Adding hydrogen peroxide to the mix would have reacted with the chlorine-containing NaOCl in the pool, producing NaCl, O2 and water. As NaOCl is added to kill microbes such as algae, its absence allowed them to proliferate and fill the pool.

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source: BBC sports

According to a recent article  in the C&En News, this response has been refuted by chemists and biologists alike. It seems impossible (or, in science terms: highly improbable) that the algae could reproduce so quickly to muddy the pool overnight. Some scientists believe it was a chemical reaction resulting from the addition of copper-containing antiseptic chemicals in improper quantities. In the presence of chlorine, copper forms a green complex. This theory even accounts for the smell reported by athletes: hydrogen sulfide, which is a by-product of this reaction.

Solutions

Which solution is THE solution?                                  Image Courtesy: Leiem, Wikimedia Commons

As the Newscripts article reports, we will never know the true solution to this chemistry mystery. All pool water, and potential analytic samples, has long gone down the drain. Nevertheless, chemists will always remember the time when their discipline had its moment in the hot Brazilian sun.

– Megan Wolf