By Steven O’Connell (Student, Project 4)

Steven O’Connell sampling at the Portland Harbor Superfund Site

In the past few years, our Center has been conducting research to learn more about oxygenated polycyclic aromatic hydrocarbons (OPAHs). OPAHs are one of the degradation products of parent PAHs. OPAHs are studied because they are present in the environment and pose an unknown hazard to human health.

Although OPAHs have been measured in several samples all over the world, most analyses contained only a handful of OPAHs or used methods that may be inaccurate.  To address some of the analytical challenges measuring OPAHs, I was involved in a multi-year study: An Analytical Investigation of 24 Oxygenated-PAHs (OPAHs) using Liquid and Gas Chromatography-Mass Spectrometry.

Why is there a focus now on OPAHs?

Focus on this class of compounds has really increased in the last few years, although it’s interesting to note that there were reports of some of these compounds in the 1970’s and earlier.  There are several reasons researchers want to study these compounds.  OPAHs seem to be found in similar concentrations to the highly studied parent PAHs in a variety of samples ranging from diesel exhaust to urban air.  Additionally, not a lot is known about the toxicity of these compounds, although early evidence suggests that they may be on par with PAHs.  That’s why the OPAH research of students Andrea Knecht and Britton Goodale in Dr. Robert Tanguay’s Lab (Project 3) has been so important.

Why measure OPAHs at the Portland Harbor Superfund Site?

It makes a lot of sense to try and measure OPAHs at Portland Harbor Superfund. PAHs have been responsible for remediation at some sites for years now, and are the precursors of OPAHs.  In some cases, remediation approaches employ ultra violet (UV) light to try and degrade PAHs and thereby cleanup that site.  However, it is possible that PAHs could degrade to OPAHs during the process.  If no one is monitoring the products of this UV treatment, the site could remain hazardous.  That’s why Norman Forsberg’s upcoming paper and Marc Elie’s work with ultra violet light in the Anderson laboratory (Project 4) is so interesting.

What still needs to be understood?  

The formation and concentration of these compounds in the environment at contaminated sites are poorly understood. It is important to continue three areas of research that have been going on at OSU.

  1. Detection: If the compounds are not present, then there’s less to worry about.

    Good times with lab mates when Steven O’Connell (right) first started working in the Anderson lab.
  2. Toxicity:  Addresses concerns over compounds that are detected in environmental samples.
  3. Processes by which OPAHs are made or degraded.

With that knowledge, it will become easier to understand potential risks with this compound class.

Why is this paper important in advancing the science?

My paper is very analytical.  If you watch the television series Bones, I would be most like Hodgins, except there would be less talk of “particulates” and more talk of cleaning instrumentation.  But seriously, by providing two methods on very different instrumentation to measure over 20 OPAHs, I provided a helpful platform for other scientists to use and build upon to measure this compound class in a variety of applications.



A very powerful and sensitive instrument used to study trace amounts of chemicals is a gas chromatograph connected to a mass spectrometer, or GCMS. GCMS is especially useful for air samples, but it is also used to detect, quantify, and identify chemicals in water, soil, plant and animal tissue, and many other substances.

The GCMS can detect chemicals in amounts as small as a picogram. That is 0.000000000001 gram. One picogram is the equivalent of one drop of detergent in enough dishwater to fill a trainload of railroad tank cars ten miles long. Many of the pollutants found in air are present at concentrations lower than one picogram in a cubic meter of air. It is important for an the instrument to be able to detect these low concentrations.

The GCMS instrument is made up of two parts.

  1. The gas chromatography (GC) portion separates the chemical mixture into pulses of pure chemicals
  2. The mass spectrometer (MS) identifies and quantifies the chemicals.

The GC separates chemicals based on their volatility, or ease with which they evaporate into a gas. It is similar to a running race where a group of people begin at the starting line, but as the race proceeds, the runners separate based on their speed. The chemicals in the mixture separate based on their volatility. In general, small molecules travel more quickly than larger molecules.

The MS is used to identify chemicals based on their structure. Let’s say after completing a puzzle, you accidentally drop it on the floor. Some parts of the puzzle remain attached together and some individual pieces break off completely. By looking at these various pieces, you are still able to get an idea of what the original puzzle looked like. This is very similar to the way that the mass spectrometer works.

Gas chromatography (GC)

  • Injection port – One microliter (1 µl, or 0.000001 L) of solvent containing the mixture of molecules is injected into the GC and the sample is carried by inert (non-reactive) gas through the instrument, usually helium. The inject port is heated to 300° C to cause the chemicals to become gases.
  • Oven – The outer part of the GC is a very specialized oven. The column is heated to move the molecules through the column. Typical oven temperatures range from 40° C to 320° C.
  • Column – Inside the oven is the column which is a 30 meter thin tube with a special polymer coating on the inside. Chemical mixtures are separated based on their votality and are carried through the column by helium. Chemicals with high volatility travel through the column more quickly than chemicals with low volatility.

Mass Spectrometer (MS)

  • Ion Source – After passing through the GC, the chemical pulses continue to the MS. The molecules are blasted with electrons, which cause them to break into pieces and turn into positively charged particles called ions. This is important because the particles must be charged to pass through the filter.
  • Filter – As the ions continue through the MS, they travel through an electromagnetic field that filters the ions based on mass. The scientist using the instrument chooses what range of masses should be allowed through the filter. The filter continuously scans through the range of masses as the stream of ions come from the ion source.
  • Detector – A detector counts the number of ions with a specific mass. This information is sent to a computer and a mass spectrum is created. The mass spectrum is a graph of the number of ions with different masses that traveled through the filter.


The data from the mass spectrometer is sent to a computer and plotted on a graph called a mass spectrum.

Credit: Unsolved Mysteries of Human Health

The Unsolved Mysteries of Human Health web site was developed by the Environmental Health Sciences Center, another NIEHS-funded Center at OSU.  The GCMS section of the web site was developed in collaboration with Dr. Staci Simonich, Superfund Center Project 5 leader.  The interactive image above received about 37,000 pageviews this past year (up about 10,000 from the previous year). It is the most popular page coming out of our Centers.

Unfortunately, the interactive image does not currently work on an iPhone or iPad.