Arsenic – The King of Poisons

Poison is perhaps a practical, if not cowardly, method of murdering people. The reason a person would choose to use poison is because they do not like confrontation. However, poison is often overlooked when considering the death of a person because even small doses can be fatal. This is why poisoners often get away with murder. Arsenic is known as the “King of Poisons” and its history started with Paracelsus, the father of modern toxicology. Arsenic is an ideal poison because it is colorless, odorless, and tasteless and is easily dissolvable in water.

Effects of Arsenic

A dose of 5 mg m-3 of arsenic is lethal when ingested. Pure arsenic is actually less dangerous than compounds of arsenic because the human body does not readily absorb the element. As2Oand AsH3 on the other hand are compounds that are absorbed easily. Symptoms that occur when exposed to toxic levels of arsenic include vomiting, abdominal pain, diarrhea, dehydration, vertigo, delirium, and shock.

Arsenic is disruptive to the processes in the body that produce ATP. This is because arsenate, which closely resembles phosphate, can mistakenly displace phosphate in enzymes. Phosphate is used as energy by cells so replacing arsenate limits the energy being transported to the cells in the human body. By upsetting the cellular pathways of ATP, the neurological and cardiovascular systems become messed up too. Also, arsenic likes to bind to sulfur that are needed in enzymes involved in metabolism, but when it does it ruins that enzyme’s ability to function normally.

Arsenic also varies in toxicity depending on the form of arsenic. Arsenic is commonly found as arsenic (+5) or arsenic (+3). When arsenic combines with other elements like sulfur, oxygen, and chlorine it forms inorganic compounds. If it binds with carbon, an organic compound is created. Generally, inorganic compounds of arsenic are considered more poisonous because they are more unstable.

Arsenic in Crimes

A newspaper journalist, Frank McKinney Hubbard, once said “when you consider what chance women have to poison their husbands, it’s a wonder there isn’t more of it done”. It is a common misconception that poisoners are mainly women but this is not the case. There are many infamous murders committed with arsenic: the Borgias family during the Italian Renaissance, Mary Ann Cotton, and Madame Giulia Toffana to name a few.

Detection of Arsenic

Poisoning was much more prevalent when there were no methods for detecting them in the human body. Often, a poisoner who was put on trial could not be convicted without factual evidence of the poison being in the victim’s body. It was mostly speculation and circumstantial evidence. However, there are now instrumental methods to determine unknown chemicals and substances found at crime scenes.

Gas Chromatography/Mass Spectrometer (GC/MS)


The picture above is the GC/MS machine that is located in our school. The Gas Chromatographer is responsible for separating chemical mixtures into pure chemicals while the Mass Spectrometer identifies and analyzes the amount of chemicals. In the GC there are the injection port, oven, and column. In the injection port (#1), the mixture is injected into the GC (#2). Because the inject port is heated to 300 degrees Celsius, the chemicals change into gases. The sample travels through the column (#3) which is located inside the oven. The oven is heated, in turn heating the column, and the sample is carried through it by helium. After traveling through the GC  the sample moves on to the Mass Spectrometer (#4). In the MS there is the ion source, filter, and detector. A picture of the interior of the MS could not be taken because the covering cannot be removed from it. In the ion source, the molecules are bombarded with electrons, thereby breaking the molecules into ions. The ions continue on to the filter where there is a magnetic field that sorts the ions based on mass. The detector counts the number of ions with the specific mass and the data is sent to a computer (#5) that creates a mass spectrum. An interactive diagram of the GC/MS can be found here.

Inductively Coupled Plasma – Mass Spectrometry (ICP- MS)

There are 5 main components in the ICP-MS: sample injection system, inductively coupled plasma (ICP), plasma sampling interface, mass spectrometer, and computer. Like the GC-MS machine explained above, the ICP-MS works in a similar fashion. One of the obvious difference is the use of argon plasma for the ICP-MS ion source.A more detailed explanation of ICP-MS is explained here.

The ICP-MS method is the current standard for testing for arsenic. This is because ICP-MS can detect arsenic in samples as small as 10 mg and also allows for the analysis of multiple elements at a time. The ICP-MS method is capable of analyzing elements with larger molar masses, such as arsenic. Another reason ICP-MS is preferred for the detection of arsenic is because the ions created by the ICP discharge tend to be positive. This is helpful for determining if a sample contains arsenic, because as mentioned previously, arsenic (+5) and arsenic (+3) are the most common forms of arsenic.

These instruments are helpful for identifying the presence of poisons in a substance. In a courtroom, a murderer can now be convicted of poisoning because there is evidence to back up any prior accusations. This could be a possible factor for the decrease in poisonings. Now it is harder to get away with poisoning someone. However, there are still instances where poisoning is overlooked.

“Poison is in everything and nothing is without poison. The dosage makes it either a poison or remedy” (Paracelsus). Would you believe it if I told you that arsenic could actually be used as medicine? Well, believe it or not, arsenic was used by Hippocrates to treat ulcers, and in 1786 arsenic was an ingredient in Fowler’s solution that was used to treat asthma to cancer. Arsenic can be a “poison or remedy” but it is infamous as a poison.

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