About Materials and Procedures Results and Conclusion References ©
ICP-MS
Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is an analytical method used to detect elements. Sample material in solution is introduced by pneumatic nebulization. This technique uses argon plasma as an ionization source, and a mass spectrometry, which separates the ions produced. The ions are separated on the basis of their mass-to-charge ratio by a quadrupole mass spectrometer. The ions transmitted are detected by an electron multiplier or Faraday detector. A data handling system then processes the information.

This method is used for quantitative, qualitative analysis and can compute isotopic ratios on water samples. Also, it can simultaneously measure elements in the periodic table and determine analyte concentrations.



Pros

1. ICP-MS is a better technique than other elemental analysis techniques such as ICP Atomic Emission Spectroscopy.
2. The ability to obtain isotopic information.
3. The ability of having minimum matrix interferences while handling simple and complex matrices due to high temperature of ICP source.

Cons

1. Samples with high total dissolved solids must be diluted before using ICP-MS. If not diluted, sensitivity and detection capability will decrease and require machine to be shut down for maintenance.
2. High resolution ICP-MS is expensive and there is limit of detection for analytes with low concentrations and not suitable for rapid, multi-elemental analyses.
3. Interferences with analysis: Direct nebulisation may cause high amounts of chloride to react with argon to form argon chloride which has the same mass as Arsenic (mass 75).



 Sunday, January 27, 2013 @ 9:32 PM

Introduction: The Story of Mary Ann Cotton
Britain's first serial killer, Mary Ann Cotton

Mary Ann Cotton was the first serial killer known to conformed to the psychological profile of the “Black Widow”, and was born in the late 1800s in England. She was thought to have killed up to 21 people, many of which were her own children to obtain insurance payouts. She was convicted and hanged in 1873.

 Mary Ann Cotton killed her victims using arsenic poisoning. Arsenic was common in Victorian England, easy to acquire and easy to handle as they can be dissolved in hot tea. It is a colourless and odourless substance that would be hard to detect. 
arsenic present in soap, an easily obtainable source

Furthermore, her victims showed similar symptoms,such as vomiting, diarrhoea and dehydration, as to diseases like gastroenteritis, Cholera and Typhoid fever. Primitive methods were used to detect arsenic and brief diagnosis were made. Thus, Mary Ann Cotton was able to escape suspicion. 

Detecting for Arsenic

arsenic acid
arsenic binding to cysteine residues

Arsenic is present in small amounts in our bodies but when there is excess arsenic, it can be lethal. Arsenic concentrates in hair, nails and lastly, bones. Therefore, excess arsenic can be tested for in these areas, even though after a long period of time. 

Arsenic in blood binds to protein of a complex of the amino acid, cysteine. Keratins are major structural protein in hair and nails, and they contain many cysteine residues, and thus, arsenic accumulates in these areas. Since keratin has high affinity for arsenic, concentration of arsenic in hair is much higher than other tissues.

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