To separate the components in a sample with gas chromatography (GC), proper sample preparation is important. The sample may be cleaned up in various ways to improve the selectivity of the separation, and it must be volatilized prior to injection into a GC platform. The preparation can be manual or automated, depending on the application, as well as the required throughput.
In some cases, automating the preparation of GC samples just doesn’t make sense in time or financial cost. “We do not have our GC preps automated,” says Rachel Behrens, lab manager at the polymer characterization facilities at the University of California, Santa Barbara. As she notes, GC is not used that often in her lab. “My researchers only prepare a few samples at a time, and it is often to help identify analytes that they might not be able to address via other means, such as nuclear magnetic resonance and other techniques.”
For labs that run more GC and at higher throughputs, taking the time to automate sample preparation can be crucial, and may be achieved with various methods.
The market offers several options for automating GC sample preparation. In many cases, a scientist can simply buy a device that does the sample prep. As an example, Germany-based GERSTEL offers its MultiPurpose Sampler MPS. This robot can automatically prepare samples for GC and GC-MS (gas chromatography-mass spectrometry).
That’s just one of many manufactured platforms to consider. California-based Agilent offers a collection of options, including several GC autosamplers that can run dilutions, derivatizations, and more.
Refined research methods
Some scientists started automating sample preparation for GC decades ago. In 1994, scientists working on MIT’s NASA-sponsored Advanced Global Atmospheric Gases Experiment (AGAGE) installed an automated GC-MS system in Ireland, as part of AGAGE’s mission to study changes in chemicals and climate around the world. This platform could capture a two-liter sample of air, concentrate desired samples with an adsorbent-filled trap kept at about -55°C, and analyze the chemical components, down to concentrations of 0.2 parts per trillion.
That system triggered even more advanced technology. For instance, at the University of California, San Diego/Scripps Institution of Oceanography, Jens Mühle notes that AGAGE uses “our most advanced GC-MS systems—the ‘Medusa’ automated gas chromatographic systems with mass spectrometric detection—for ultra-low-level, high-precision, long-term reproducible measurements of ozone depleting substances and synthetic greenhouse gases.” This system uses two traps, which are filled with polymer absorbents to automatically concentrate specific analytes. These traps are kept at a colder temperature, about -165°C, to allow the capture of a wider range of chemicals, especially more volatile ones. With dual traps, it uses fractional distillation to purify analytes of interfering compounds, refocusing from a large trap to a smaller one. Consequently, this automatic sample preparation produces reproducible injections for GC-MS.
From the comfort of a lab to some distant testing site, automating parts of GC sample preparation can come in handy in some cases and be indispensable in others. It all depends on the lab and the application.