GC was once commonly called “GLC,” where the “L” stands for liquid. Inside GC columns are particles of a ceramic or inert material coated with a viscous liquid stationary phase that interacts with the analyte. By contrast, HPLC stationary phases are bonded to the base material. New GCs are sold with software that integrates peaks, stores methods, assists in report writing, and controls instrument functions.
GC detectors have been evolving rapidly to provide greater sensitivity. Flame ionization detectors (FIDs) have been the most widely used, as they detect any molecule containing carbon. Numerous other detector types have been introduced over the years, but the most interesting is the mass detector, which is essentially a miniaturized mass spectrometer. Mass detectors provide unequivocal identification of peaks emerging from the chromatograph based on the molecules’ molecular weights and fragmentation patterns.
High-throughput analysis was once associated with commercial labs, but today even academic groups value productivity, says Jim Edwards, business development manager at Thermo Fisher Scientific (Austin, TX). Instruments that perform faster separations are available, but this has introduced a detection bottleneck. “Vendors who place a premium on accelerating chromatography should similarly speed up detection to acquire data at a speed appropriate to good precision and performance.” Less easily achieved is the design of instruments that do not suffer from “fatigue effects,” that is, show signs of slowing down or require maintenance after one or two thousand cycles. Maintenance downtime, Edwards observes, is a productivity killer that easily negates the benefits of more rapid analysis or cycling.
GC systems have become faster and more selective to the point where analysts now look to dead times during analytical runs to eliminate inefficiencies. Alessandro Baldi, business manager for chromatography software at PerkinElmer (Waltham, MA), says this is best achieved by avoiding changes that will disrupt workflows or force analysts to alter established methods.
Oven equilibration is one obvious bottleneck. PerkinElmer tackled equilibration by designing an oven with very low mass that cools down rapidly by fast-moving, non-recirculated air.
Next, the company went after autosampling by implementing lookahead functions. “It takes time to inject, clean the needle, and load and unload the sample,” Baldi says. In an optimal configuration, the autosampler engages not at the precise moment it is needed, but when the oven is almost at the right temperature.
A third approach is to integrate the GC with sample prep devices to provide greater flexibility and less of a hardwired configuration. PerkinElmer has recently collaborated with Tekmar (Mason, OH) on purge-and-trap sample concentration and with CTC (Zwingen, Switzerland) on solid-phase microextraction. Baldi says the goal is to minimize sample preparation.
Reductions in per-injection cycle times may be achieved through the use of flow-splitting techniques that divert eluent to multiple columns or post column to one of several detectors. Splitting allows analysts to switch columns or detectors on the fly without having to turn off the instrument, allow components to cool down, and swap them out. In essence, splitting creates “multiple” chromatographs from one instrument.
GC-2010 Plus Capillary
• Features third-generation Advanced Flow Controllers (AFC) for high-speed analysis at a maximum pressure of 970 kPa and 1,200 mL
• Enables a rapid cooling time of 450°C to 50°C in 3.4 minutes
• Flame ionization detector (FID) ensures a minimum detected quantity of 1.5 pgC/s
Shimadzu Scientific Instruments
I-Graph X Portable
• No external carrier gas supply required
• Integrated vacuum pump allows for measurement of non-pressurized samples
• Features active column cooling, allowing for a lower starting temperature
• Analysis time ranges from 30 seconds to 3 minutes
Clarus® 680 GC
• Features twin-walled oven design with concentric air exhaust for greater separation
• Features oven cool-down from 450°C to 50°C in less than 2 minutes
• Includes 108 vial liquid autosampler for flexibility and automation
• Includes programmable pneumatic control (PPC) for added automation
• Features a low-maintenance, consumable-free thermal modulator
• Offers a wide dynamic range (4 orders of magnitude)
• Includes a secondary oven for enhanced selectivity
• Cryo-focusing prior to release on secondary column provides up to a tenfold increase in analyte detectability