Mass Spectroscopy By Sandip, Amy & Jocelyn

Steps of Mass Spec The steps in the mass spec include: Ionisation: atoms are ionised by knocking one or more electrons off to create a positive ion. This happens to all atoms, even those that would normally form negative ions or ones that never form ions at all. This is because mass spectrometer always use positive ions. Acceleration: ions are accelerated to a finely focused beam so that they have the same kinetic energy. Deflection: In a mass spectrometer, the atoms are being deflected within it by a magnetic field. Each atom gives out a different electric or magnetic field that gives it different kinds of deflection. An easy way to picture it is being on the top of a tall building on a windy day and throwing different kinds of balls. A ball with a heavier mass would take a different path compared to a ball with a lighter mass. Imagine the balls are atoms and the different paths they take would be the equivalent of an atom having a stronger or weaker electric/magnetic field. The lighter the charged atoms are, the more they are deflected. Detection: the beam of ions passing through the machine is electrically detected. PTO →

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Typical Uses Mass spectrometry is mostly used for detecting drugs and toxins. It is capable in identifying drugs in a person and is often used to test athletes. It is also used for identifying the location in where a certain wine, rice or diamond originated. Mass spec can also be used for environment research as it can monitor and track air pollutants. Mass spec gives out quantitative data as the results processed by it are expressed through a line graph, also called the mass spectrum. There are different kinds of techniques for the use of a mass spectrometer but most of them detect various kinds of toxins and drugs in humans and the air around us.

Examples and Explanation The result graph of a mass spectrometer will often look like this (vertical bar graph, refer to next slide). On the y-axis there are numbers that go up to 100, this represents the intensity of the substance being measured. Each bar represents an ion and the length of the bar is its abundance. The ion with the highest abundance is considered to have an intensity of 100 and is referred to as the ‘base peak’. On the x-axis is the mass: charge ratios. Each ion formed in the mass spectrometer often only has a single charge and so the m/e ratio is equivalent to its mass. However, this is only works if the compound being tested is pure. The number of peaks on the graph indicate the number of isotopes present and the position of these peaks on the x- axis show the relative isotopic mass. Each peak also reveals the different fragments that ‘falls off’ the unknown substance. PTO →

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Safety Precautions One of the most dangerous chemicals involved in the use of a mass spec is hydrofluoric acid solutions. Extreme care should be taken while handling hydrofluoric acid due to its high toxicity and corrosiveness. Inhalation, ingestion and skin and eye contact should all be avoided by wearing gloves, safety glasses, lab coats and masks. It is best to handle the acid in a fume hood. Many GC/MS systems use hydrogen as a carrier gas. Hydrogen is extremely dangerous and the following precautions should be taken: make sure that all shipping clamps are closed tightly, but not too tight, as it may cause a gas leak if it is too tight; install an automatic shutoff valve as this will close hydrogen flow if a power failure occurs; after hydrogen is inside a mass spectrometer, removing it must be done with caution as an incorrect start up of a mass spec filled with hydrogen can cause an explosion. Avoid leaks in the carrier gas lines. Eliminate ignition sources. Use a hydrogen generator instead of bottled hydrogen.

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