Always Buy in Bulk: The Batch TGA Process

By far, the best thing about being in lab everyday, all day is the sense of continuity. During the school year, I log about four hours a week and on rare occasions, a little extra. I’m finding out that’s not enough to get the true sense of continuity of the lab. Seeing projects and long procedures go from beginning to finish.

 

This week, one project I’ve been able to see go from beginning to end, to second incarnation is the Batch TGA. TGA stands for Thermogravimetric Analysis. For Dr. Kranbuehl’s lab, its a process that helps us measure mass loss of a sample and the plasticizer content of a sample. Of course, the ISC has a fancy machine that gives minute-by-minute data on the changes the sample is undergoing. The process is, however, slow and inefficient when you need to run…let’s say…fifty-six or so…samples. So the answer is the Batch TGA. Same thing, same idea, just doing it in bulk.

 

Our Batch TGA is a procedure that tests for two data points to be entered in our database for each sample. They are:

  • The % Change in Water

  • The % Change in Plasticizer

 

The process for running a Batch TGA, which I am about to become well acquainted with for a second time, is the following.

 

1) Make your spreadsheet. You can run 56 samples for each Batch TGA. Each Batch TGA pan has a number on the bottom, from 1 to 56. The first step in the spreadsheet is to match which sample is going into which pan. Print out your spreadsheet.

 

Now bask in the organization!

 

2) Now its time to mass all the pans, and the mass of the pan and the sample together. This is the part that consists of a mind numbingly tedious task. The challenge is to keep all the little pans in order, cut up enough sample, record all this data into a spreadsheet that you’ve been looking at long enough to make your head spin, and not drop any little tiny bits of sample. It almost seems impossible. Luckily, it’s not.

 

 

3) Now the tray of pans and samples goes into a 105 C oven for an hour. Wait.

 

4) Remove tray from the oven. Weigh all fifty-six pans again. They’ll weigh less this time – this data point is going to become key to calculating percent change in water.

 

5) The tray of pans and samples now move into a 240 C oven for a half hour. Wait, again.

 

6) Remove the tray from the oven. Weigh all fifty-six pans again, again. They’ll weigh even less this time – this last data point is the key to calculating the percent change in plasticizer. At this point, all the little sample bits will look a bit melted. Here’s a picture of a set of used pans:

 

 

Look at all those little bits of polymer!

 

7) Assuming you’ve recorded all the data, this is the time for CELEBRATION. Celebrate not losing any little pans, celebrate keeping all your pans and samples in order, celebrate the fact that nobody ran into you in the hallway causing you to drop all your samples in a tragic accident. Breathe easy.

 

8) Stop celebrating – there is work to do!

 

9) All the data is in a hand written spreadsheet right now. Transfer it to your electronic one which is programmed to give you all your missing columns. Bask in the glory of technology.

 

10) The Excel spreadsheet calculates the %Change Water and %Change Plasticizer. However, it doesn’t enter it into the database. The database is a complex MatLab program that I can only really think to describe as the “infrastructure of the lab”. This process is a pretty long one, but it is worth it.

 

11) Generate your tables as PDFs. Admire your data. Try to pretend you won’t have to do another Batch TGA for a while.

 

And that…is the process of doing a Batch TGA. It’s tedious but efficient. The other good  news is that the last run I worked on, we found some good things. As it turns out, increasing the sample size to 0.05 grams increases our accuracy. Our data looks good, consistent, and knowing it was efficient to run 56 samples at a time as opposed to constantly running one at a time is pretty good to know, too.

 

-Natalie