ICP-MS

Today we ran our samples on the ICP-MS machine!
We took our samples off of the shakers first thing in the morning.  From there, we had to make our standard solutions and controls, measure our samples into ICP-MS tubes, acidify our samples, and put them in the correct order to be measured by the ICP-MS machine.

The general procedure with standard solutions is to first make a high standard, which contains each of the components to be measured at concentrations higher than the expected maximum concentration in any sample. The concentrations of each component in this high standard must be known very exactly, so prepared and certified standardized solutions are used. The high standard is then diluted a few times so that exact concentrations can be known and the ICP-MS machine can calibrate itself. For this, we needed to run around the labs trying to find the correct stock standards for all of the elements we were measuring (quite a few). We found all of them except barium, so we'll need to find a barium standard and run the samples again on the ICP-OES machine later.

Each ICP-MS tube requires about 6 mL of solution, so we had to label the tubes and measure in solution (the ICP-MS machine needs about 4.5 mL of solution to collect three data points for a particular sample). After filling all the tubes, I added a small amount of concentrated nitric acid to each tube in order to bring the solution to the optimal pH. I capped all the tubes, inverted them a few times to mix them, and then we had to make a spreadsheet indicating the measurement order of the tubes. After each group of samples, the machine needs to run a blank (in this case, just dilute nitric acid), and roughly every 10 samples a QC (quality control) sample is run made from the standard solution. That way, if the measurements are off, the machine can re-calibrate itself frequently. But because of this, it's super important that the standard solution's concentration be known extremely well!

Finally, we put our tubes in order and placed the rack of samples into the machine. The ICP-MS machine has a little robotic suction arm that dips into the samples one by one and sucks up some of the liquid. Everything is automated, and it was fun to watch. We'll get to see our data tomorrow and hopefully it'll be of good quality.