Please check out our Gas Chromatography section for more information or to find manufacturers that sell these products.
Though the term may evoke tree-huggers and spotted owl enthusiasts, environmental science is actually a surprisingly broad chemistry sub-discipline. It involves testing a diverse array of matrices—earth, air, and water—for highly divergent classes of compounds. Mercury in fish? Dioxins in the groundwater? Pesticides in the soil? All are aspects of environmental science, and many can be addressed with a single class of hardware: Gas chromatographs.
Gas chromatography (GC) is a technique in which heat-stable and volatile and semi-volatile samples (anything from napthalenes to benzenes) are separated in the gas phase as they pass through long, thin columns housed within a heated oven. Upon exiting the column, the separated compounds can be chemically characterized by an alphabet soup of detectors: FID (flame ionization detectors), ECD (electron capture detectors), NPD (nitrogen/phosphorous detectors), and MS (mass spectrometers), to name but a few.
Of these, environmental testing labs most frequently use MS, FID, and ECD detectors, with NPD and FPD (flame photometric detectors, for detecting phosphorous-containing compounds) being more of a specialty item, says William Goodman, chromatography applications manager at PerkinElmer.
At the Maine Health & Environmental Testing Laboratory in Augusta, team leader James Curlett has 12 GC systems online, including six GC/MS, three FIDs, and three ECDs. Each is dedicated to a specific task, he says: One FID system tackles diesel-range organics, for instance, while another has a purge-and-trap system attached to detect volatiles in liquid samples. Three of the GC/MS systems are dedicated to trihalomethanes, semi-volatiles, and cyanides, respectively.
It's not that the hardware can't multitask, says Curlett. Instead, by dedicating specific equipment to specific types of samples and analyses, things tend to operate more smoothly. In an operation as busy as his, productivity is key.
"What we tend to find in the environmental business is, if you jump matrices a lot or change target analytes, it takes a long time to re-equilibrate and stabilize the system," he says. For example, "the worst thing you could do would be to put an extract from a fish onto a GC you're using for soil," he says. "It will never perform correctly again."
Curlett's GC systems all come from a single source: Agilent Technologies. Yet, according to Phil Stremple, environmental industry manager at Agilent, operations like Curlett's might one day look very different.
"Far and away the trend in environmental testing is to go away from standard GC detectors like ECD or FID and move towards more mass spectrometry," he says. That's because, though classical detectors like ECD, FID, and NPD may offer greater sensitivity for particular classes of molecules—NPD for nitrogen- and phosphorous-containing pesticides, ECD for organo-chlorinated pesticides, and FID for hydrocarbons, for example—MS can handle a far wider range of molecules, and provide richer data to boot.
GC/MS, says Stremple, "is an excellent default choice. It's the way 90% of samples are being analyzed." Adds Goodman, "GC/MS is a universal detector."
For most applications, Stremple recommends Agilent's 7890 GC system coupled to the 5975C single-quadrupole MS. That base system may be expanded with a head-space analyzer or purge-and-trap system, depending on the application, or even coupled to an ECD or FID if desired. For those with more "challenging needs," he recommends the company's 7000A GC/MS/MS triple-quad system instead.
"The triple-quad allows them to see trace-level components in a very complex matrix," Stremple explains. This is because the tandem instrument's mass-filtering capabilities allow users to sift away irrelevant matrix ions and focus on the ones they want.
That's not to say there aren't cases for which non-MS detectors are preferred, Stremple notes. Some customers are responding to an ongoing scandal involving drywall contaminated with sulfur with a sulfur chemiluminescence detector (SCD), says Stremple; the detector is "extremely selective and sensitive for sulfur compounds."
Yet according to Eric Phillips, environmental and food safety market manager for GC and GC/MS products at Thermo Fisher Scientific, such cases are becoming rarer. The GC industry is in the midst of something of a "technology shift," he says, precipitated both by EPA regulatory requirements and technologic improvements that are providing MS with sensitivity comparable to more classical detectors. Those who relied on standard GC detectors are moving to single-quad and ion trap-based MS systems; those who used single-quad systems are moving to triple-quads .
"Everybody is taking one step forward," Phillips says.
Thermo offers a complete range of GC and GC/MS instrumentation, including single-quads, triple-quads, and ion traps, as well as isotope ratio MS systems and the high-resolution, magnetic sector-based DFS system. According to Phillips, isotope ratio MS uses extreme heat to degrade a sample to its elemental composition and then record each element's relative abundance. Such information can be useful, among other applications, for determining where the oil came from in an oil spill. "The ratio of the isotopes in oil and other materials are specific to the location they are grown, raised, or produced. They can be used to determine the source of the contamination," he says. Magnetic sector instruments, on the other hand, detect and differentiate such compounds as dioxins and steroids with mass accuracy up to four decimal places. Other GC manufacturers in the environmental science arena include PerkinElmer and
Shimadzu Scientific Instruments.
PerkinElmer builds its systems around its flagship Clara 600 GC, while Shimadzu founds its systems on the GC 2010. The Clara 600 can be coupled to up to two standard detectors plus one MS via a "Swafer microchannel switch device," which splits the gas output to each detector as desired. For instance, a user could send 50% of the effluent to the MS, and 25% each to an FID and ECD, says Goodman. Similarly, the 2010 can be coupled to up to four detectors (including a single-quad MS) and two injectors, says Rich Whitney, senior GC and GC/MS product specialist at Shimadzu Scientific Instruments.
Fortunately for would-be environmental chemists, GC and GC/MS industry is sufficiently mature, such that, in many ways, any system will serve your needs to some extent. Yet there are distinguishing features.
According to Whitney, before making a purchasing decision consider such factors as sensitivity, stability, reliability, and ease of maintenance. Manufacturers will typically report sensitivity values in product literature; by convention, that parameter is given as the signal-to-noise ratio observed when injecting 1 pg of octafluoronapthalene (OPN), he says. "The better the signal-to-noise, the better the sensitivity," he says.
Stability, reliability, and ease of maintenance, on the other hand, "are a little harder to quantify." His advice: Get feedback from other users, and try to demo the instrument yourself. Curlett suggests checking the literature to see what other researchers in the area are using.
Other factors to consider are automation and software. "The software is very important," says Goodman. As more and more environmental scientists come from outside the world of analytical chemistry, he says, it's more important than ever that the software be easy to use and develop new methods on.
Finally, says Curlett, plan for future expansion. "Go for as much flexibility as you possibly can," he says.
Please check out our Gas chromatography section for more information or to find manufacturers that sell these products.