When I was in college, I worked at an ice core vacuum lab interested in the history of trace gases obtained from ice cores (they also researched about oceanic trace gases responsible for atmospheric processes affecting climate change, but during my stay at the ice lab, I only handled ice cores). These trace gases were extracted and then quantified using gas chromatography mass spectroscopy. It was pretty labor intensive work, but I liked it. Not many people have had the experiences I had while working there.
The entire experimental process starts with the ice core. Now what is an ice core? And what makes them so special? Ice cores are samples of ice drilled from ice sheets. These samples offer direct information to past atmospheric and climate conditions. This is because the ice forms from layers of incremental buildup of annual snowfall, trapping atmospheric concentrations of gas bubbles, particles (like dust), and human pollutants.
Some of the trace gases of interest include: halocarbons (methyl chloride and methyl bromide → ozone depleters), carbonyl sulfide (COS → statospheric sulfate precursor), and hydrocarbons (ethane → biomass burning emission tracer).
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| What the Autospec mass spectrometer looked like |
A mass analyzer separates the ionized particles based on charge to mass ratios. In a magnetic sector mass analyzer, a magnetic field separates the charged particles by deflecting the charged ions to a circular motion perpendicular to the magnetic field... basically this means that moving charged ions will have a curved trajectory because of the magnetic field. Ions with distinct m/z values will have the same trajectory paths because their degree of deflection will be the same (degree of deflection proportional to the square root of m/z ratio), and only ions of mass to charge ratio with equal centrifugal and centripetal forces will go through to the detector. All this just means that magnetic sector mass analyzers focus angular dispersions.
A double focusing mass analyzer has a magnetic and an electrostatic sector. The electrostatic sector mass analyzer can be thought of as a kinetic energy selector (focus energies). The ions are separated while in flight by the electric field. The force on the ion (from electric field) is equal to the centripetal force. Passage to detection is only allowed for ions with specific energies. Having both sectors make the resolution loads better, producing some awesome data.
IMAGE SOURCE:Alamy... image taken from http://www.theguardian.com/science/2015/may/03/climate-change-scepticism-denial-lukewarmers, second image from http://www.ess.uci.edu/group/esaltzman/instrumentation
SOURCE: http://chemistry.clemson.edu/ChemDocs/marcusgroup/software/CONCEPT/DFA/DFA.HTM, Skoog et al, Principles of Instrumental Analysis, http://climatechange.umaine.edu/icecores/IceCore/Home.html
1 comments
Analyzing ice cores sound very complex. Thank you for your explanation.
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