Renee Renn: Week 7: Quadurpole Mass Spectrometer

This week I continued working in the lab, and learned how to use a different lab instrument called the quadrupole mass spectrometer.

Image from the internet

  The quadrupole mass spectrometer is one type of mass analyzer used in mass spectrometry.  It consists of four cylindrical rods, set parallel to each other.  In a quadrupole mass spectrometer the quadrupole is the component of the instrument responsible for filtering sample ions, based on their mass to charge ratio.  Ions are separated in a quadrupole based on the stability of their trajectories in the oscillating electric fields that are applied to the rods.

image from the internet

 Two opposite rods have an applied potential of (U+Vcos(wt)) and the other two rods have a potential of -(U+Vcos(wt)), where U is a dc voltage and Vcos(wt) is an ac voltage. The applied voltages affect the trajectory of ions traveling down the flight path centered between the four rods. For given dc and ac voltages, only ions of a certain mass-to-charge ratio pass through the quadrupole filter and all other ions are thrown out of their original path. A mass spectrum is obtained by monitoring the ions passing through the quadrupole filter as the voltages on the rods are varied.

Last week, I leached sediments samples from all four of the collection sites in the Pacific Ocean.  The four sites are at 200 m, 500 m, 1200 m and 3000 m.  I did an acetic acid leach, and a hydroxylamine leach.  All of this work resulted in a total of 72 samples that needed to be analyzed on the quadrupole.   Because of the sensitivity of the instrument, we did a dilution on the samples.  Another important thing that happens is preparing standards to run through the machine along with the samples.   The fundamental purpose of the rods is to translate the number of ions striking the rods into an electrical signal that can be measured and related to the number of atoms of that element in the sample via the use of the calibration standards.  Since this has been an ongoing project, there were standards available to use that also needed to be diluted that would be used to get usable data for Rare Earth Elements (REE).  The REE are the lanthanide row on the periodic table, and the primary focus of interest for testing. 

The machine ran for a little over four hours, and when it was finally done it left a rather large table of numbers.  I then took the data for the quadrupole program, and pasted it into an excel spread sheet.  I am coming up on my last week of my internship, and I will be spending the rest of the time moving the data around, finding out what the numbers mean, and creating graphs using excel. 

I am fascinated by the various lab instruments.  It is quite an amazing thing to spray a bit of sample through this machine, and come out on the other end with a chart of numbers that define exactly what was in each vial.  I feel lucky to have this opportunity to learn how to use this equipment, and also to know what each number represents.