Transcript Advantages
Jorge Pinho Alfredo Fuentes It is used to identify molecules based on their masses and how molecules fall apart into fragments The molecules are entered in a vacuum system in the vapor phase The molecule is shot with a beam of high-energy electrons to split the molecule into ions They pass a magnetic field used to deflect their straight path causing them to curve based on their mass The molecules will collide with the detector at certain positions based on their mass This method can be used to determine the chemical composition of an unknown found on the crime scene, making it relevant to forensics science and crime labs The mass spectrometer is usually very fast, convenient, reliable, and often readily available in forensic labs Evidence that it analyzes are drug related samples, powders and crystals, and toxicology samples Some pieces of evidence can be urine, blood, or powders like cocaine A internal standard solution is prepared with methanol or acetonitrile, based on the solubility of the solute: the blood, urine or powder; then the internal standard is mixed with the samples The solution is placed in a vacuum system, where it is converted into the vapor phase The molecules then collide with a beam of high-energy electrons which, stripping off an electron making the molecule a positive ion Electrical current is then applied to the ions to accelerate them along the tube It then passes a magnetic field which curves the path of the ions, lighter ions having a higher degree of deflection than heavier ones The ions then collide with the detector placed at the end of the tube, the mass is then determined by the position the ions land High Voltage The mass spectrometer generates low levels of radio frequency energy, which could interfere with devices such as pacemakers or a radio receivers. Wear gloves, goggles, and lab coats. The hazardous chemicals identified by the Mass spectrometer can detrimental to one’s health. Chemical leaks may present a hazardous safety concern. Must be used indoors in appropriate conditions according to the instructions. Avoid harmful chemicals from contact of the mass spectrometer that can potentially contaminate the instrument. Advantages The Mass Spectrometer is considered one of the most important tools in a crime laboratory. It can separate complex mixtures with great precision. Can distinguish small concentrations. High Sensitivity Disadvantages Usually is used together with a GC. Not well suited for pulsed ionization methods. Usually larger and higher cost than other methods of analysis. High dynamic range High sensitivity High resolution It can detect substances one-millionth of a gram. High Precision http://www.absciex.com/Documents/Downloads/Literature/tofsafety-guide-eng.pdf https://www.princeton.edu/chemistry/macmillan/groupmeetings/SL-mass%20spect.pdf http://www.chemguide.co.uk/analysis/masspec/howitworks.html Spencer, T. James, “An Introduction to Forensic Science: The Science of Criminalistics”, Ch 12.5 http://www.uab.edu/proteomics/pdf_files/2010/Class%2001-2910.pdf file:///C:/Users/Alfredo/Downloads/540dc3d00cf2f2b29a3a054a.p df Slides 2-6 done by Alfredo, Pictures and slides 7-10 done by Jorge