waiting -> boredom -> GC-MS?

Well, I'm sitting here waiting for the GC-MS (an instrument used to analyze compounds) to finish off a single injection which will take 35 minutes. I was going to play games on the computer, but that ability has been disabled by the computer system people in the Chemistry building. So, I am going to do the next best thing: blog. So, considering I have nothing insightful to talk about and my mind is completely focused (yea right ;-) on GC-MS, I am going to talk about that.

For starters, GC stands for Gas Chromatography. Gas chromatography is a technique used to separate various molecules from each other based on some of their physical and chemical characteristics. For example, if you have a mixture of really big molecules and really small ones you can separate them based on size. If you have some molecules that are polar and others that are not, you can separate based on that. Etc. The solution containing the various molecules is injected onto a column, which is a really long, thin piece of tubing. In the column is some sort of stationary phase that remains there all the time. This stationary phase is what determines which molecules slow down when moving through the column, and which ones move really quickly through it. The mobile phase is generally some sort of gas, like Helium that is just pumped through the column.

Now, for a normal GC, there would be some sort of detector at the end of the column that records how much material is going through the column. This detector typically doesn't know what is coming off of the column, it just records the amount that is coming off. For this lab that we are doing, the detector is a Mass Spectrometer. A mass spectrometer first ionizes the molecules flowing through. Molecules are typically very stable and don't carry a charge, but when bombarded with electrons or other particles, something happens such like electrons being emitted and the molecules become charged. Now using the molecule's individual weight and charge, a mass spectrometer will analyze what sort of ionized molecules it has by using transducers and electric or magnetic fields. These characteristics are typically lumped together as one variable called the mass to charge ratio (m/z).

The mass spectrometer used in this experiment is an ion trap. For an ion trap, ionized molecules are ejected into the middle of a ring that has a radio frequency voltage moving through it. The ionized molecules react to this ring by circulating in a stable orbit. As the radio frequency across the ring is changed, certain ions have more stabilized orbits, and other ions' orbits destabilize. When an orbit becomes destabilized, the ion leaves the ring and hits a transducer, which detects how many times it gets hit. So, based on the times the transducer was hit at a certain moment (intensity) and the radio frequency across the ring that caused those ions to leave, a graph of these values is created, but with the radio frequency replaced with the mass to charge ratio associated with the appropriate radio frequencies. Using this graph, or spectrum, a user can identify the mass of the main group of molecules that came out of the column at that time.

So, by using a GC-MS, you are able to identify the molecules that are in your solution that you injected. Well, I hope this was understandable to any who read it.