Resume/Work Experience

Here’s my basic resume condensed to one beautiful page!

Jessica’s resume (pdf)

Now,  to explain my current job further…

Gas Chromatography

I work in an analytical chemistry lab.  We test environmental samples for hazardous material with the purpose of advising our customers the proper waste disposal of their samples.  The specific contaminants (referred to as analytes) I test for are chlorinated pesticides, herbicides and PCBs (polychlorinated biphenyls).  I won’t go into detail about specific analytes, but the ones I test for are considered dangerous to people and the environment and have to be disposed of with special care.

What I really want to explain is the method by which I detect these analytes.  The lab I work for, as I’m assuming all labs of the type, follow EPA methods.  The specific series of methods I use fall under the 8000 series.  Here’s a link to the EPA’s website for the 8000 series test methods: EPA 8000 series test methods.

Basics

The 8000 series methods are called chromatographic methods.  This basically means they separate out a large group of compounds so they can be individually detected .  The instruments I specifically use to do this are called gas chromatography instruments. The following graphic shows the basics behind gas chromatography.

A – Samples are extracted into a solvent (like hexane) and collected into 2 mL vials

B – Then the instrument injects a small amount of that extract into the column via injection liner where it is heated to around 200 °C .  The extract enters the column (the circular bronze things) in the gas phase.  The column contains a liquid phase through which the extract will travel. The column is housed in an oven which ramps up its temperature based on a set oven program.  This change in temperature affects the interaction between the sample in gas form and the liquid phase of the column to separate out the individual analytes.

C – The samples travel through the column (being pushed by a carrier gas like helium) and then pass through a detector.  The detector connects with a PC which interprets the signals to give a graphical representation.  Without the column, a sample just passing through a detector would look like a big lump on the screen instead of the distinct peaks in the following picture.

Detectors

The specific detectors I work with are called electron capture detectors.  These detectors contain radioactive nickel-63 which emits electrons that collide with the make-up gas (nitrogen or argon/methane) to create an electron cloud.  A constant current is maintained though this cloud to create a baseline signal.  When analytes with electronegative molecules (like chlorine) pass through the electron cloud they “capture” electrons and the instrument detects the reduction of electrons in the cloud and converts this into the peaks you see above.  The baseline, or constant line at the bottom demonstrates when no analytes are passing through the detector.  In the above diagram, the bottom axis is time in minutes.  And that leads me into the analysis section…

Analysis

Different compounds pass through the detector at different times.  Remember that the purpose of the column is to separate them out.  There are two different ways I detect pesticides and the other analytes I test for.  One way is to compare the peak’s retention time (time when the peak appears on the graph) to a preset window of times for the analyte.  For example, if my retention window for TCMX (a pesticide analyte) is from 9.303 to 9.656 minutes,  I only report that analyte in the sample if there is a peak in that window.  If not, there is no TCMX in the sample.  The other way for me to recognize a given analyte in a sample is called pattern identification.  This is the method used specifically with PCBs.  This method has often been compared to fingerprint analysis.  It’s not as complicated as that, but I identify different PCBs because they consist of five or so peaks at specific places in specific ratios.  Take the above chromatogram.  The first and last peak are TCMX and DCB repsectively.  The group of peaks to the left of DCB are all one PCB compound called aroclor 1260.  From my training, I know that aroclor 1260 has five peaks to identify it and peaks 1,2, and 3 are right next to each other, each one bigger than the next.  Then peak 4 comes after a bunched set of random peaks and is smaller than peak 3.  Then peak 5 comes last and is also smaller than peak 3 but bigger than peak 4.  When I see that pattern of peaks, I know there is aroclor 1260 in the sample.

This is a basic explanation behind the qualitative analysis of the organic compounds I look at.  I don’t plan on going into the quantitative aspect of it, but basically we use the area under the peak (yes, an application of calculus!) to calculate the concentration of the analyte in the sample.  Our clients want to know the type and amount of hazardous compounds in their samples.