Advances in Gas Chromatography Instrumentation at Pittcon® 2013

The buzzwords for Pittcon® 2013 in gas chromatography instrumentation were “smaller,” “portable,” and “helium.” Despite the fact that some of the major vendors did not exhibit, others were on hand with new innovations, and they swept the medals awarded by the jury of editors (http://www.americanlaboratory.com/ 913-Technical-Articles/136811-Awarding-Innovation-The-Pittcon-2013-Editors-Awards/).

Micro-gas chromatographs

Several firms introduced or significantly expanded their micro-GC instruments. Micro-gas chromatographs have been around for at least 20 years. They usually entail some compromise compared to the large lab instruments.

The jury of editors awarded Analytical Pixels Technology SAS (APIX; www.apixtechnology.com) a bronze award for its innovative temperature- programmed chip-based GC. Two versions were on display: the GCAP™ for the lab, and the MAX-ONE for at-site assays such as a wellhead or refinery pipe.

In more detail, gas chromatography on a chip is a three-decades-old concept that has been difficult to reduce to practice. However, new manufacturing technology appears to have finally solved the problems. The 2-m capillary column is etched into a chip the size of a postage stamp. It needs only 1 mL/min for a typical 1-min separation. The stationary phase and detector are selected depending upon the application. Isothermal runs can be selected up to 50 °C or temperature programmed up to 200 °C Tmax.

The detector of the GCAP is an array of 400 microquartz resonators that change mass and hence frequency upon adsorption of the analyte. Each resonator has a surface area of 1 μm2. The array design improves the S/N by (400)0.5 = 20, giving detection limits lower than 10–18 g. Concentration detection limits are in the low ppm range without sample concentration and low ppb range with sample concentration. The detection resonator can be coated with polymers with different structure and hence adsorption selectivity. This could be exploited for modifying detection sensitivity. The capillary column and detector array are similar in size to a CPU chip, but the umbilicals, including sample concentrator, increase the size to about that of a shoebox.

The MAX-ONE is specifically designed for process environments such as measuring light hydrocarbons such as C1–C8 in various process streams. The instrument is an NeSSI-compatible enclosure and mounts directly on an EIF/ASTUTE interface. With a total weight of only 6 kg, it can be easily mounted onto most any pipe.

APIX was created in 2011 to manufacture and sell gas chromatography products based on joint research by CEA-Leti and the California Institute of Technology (Caltech). APIX-designed silicon devices are manufactured at Leti’s Grenoble, France site, one of the world’s leading complementary metal–oxide–semiconductor (CMOS) and microelectromechanical systems (MEMS) facilities. APIX is headquartered in Grenoble, and has engineering and business operations in the United States.

INFICON (www.inficon.com) introduced the Micro GC Fusion, which is designed as a field-portable instrument with thermal conductivity detection (TCD) with a 1-ppm detection limit. This is about 10 times more sensitive than a conventional large box GC’s TCD. Temperature programming facilitates separation of analytes up to C12. A modular design facilitates independent temperature control for the column injector and detector. The Fusion communicates with the world via wireless computer technology.

SRA Instruments (www.sra-instruments.com) also introduced a GC analyzer designed for the process floor. The SRA Micro-GC NeSSI Analyzer places a capillary GC with μTCD (micro-thermal conductivity detector) inside an NeSSI enclosure. The injector and electronic pressure controller are also inside. TCDs become more versatile as the size decreases. SRA’s TCD is linear over the range from ppm to 100%. Target applications include assay of light hydrocarbons in natural gas and petroleum refining.

Application-specific GCs

Carbon dioxide is a major article of commerce. Many grades are available at a corresponding range in prices. Also, there are many potential sources, each with unique impurity profiles. Baseline (www.Baseline-mocon.com) introduced the 9100, a rack-mounted GC for assay of impurities in CO2. The instrument is marketed as a CO2 analyzer so the user does not even know the technology behind the panel. Target analytes include acetaldehyde, benzene, toluene, ethylbenzene, xylene, and methanol. Each instrument is factory-optimized by Baseline for the particular application. Various outputs include 4–20 mA, 0–20 mA, and RS232.

Pesticide analysis

When a particular application gets large enough, most vendors will consider configuring an applications package. Since multiresidue pesticide analysis by LC/MS is a common application in food safety, Thermo Fisher Scientific (www.thermoscientific.com) built a GC/MS by combining the 1300 Trace GC with the TSQ 8000. Triple-stage quadrupoles are preferred for quantitative analysis. Add a column and the required consumables, including standards, and the lab is ready to go. The instrument comes loaded with a database of over 600 analytes that includes m/z peaks and multiple reaction monitoring (MRM) fragments.

Simulated distillation

Both Shimadzu Scientific Instruments (www.ssi.shimadzu.com) and Falcon Analytical (www.falconfast.net) introduced gas chromatographs for simulated distillation of petroleum. Shimadzu combines LabSolutions software with the GC-2010 Plus GC to provide accurate analysis of high-boiling components (up to C120). The injection unit is designed for low carryover. The software facilitates comprehensive postrun analysis including calculation of physical properties and integration of data from other assays. Shimadzu reports that its system meets all ASTM, ISO, EN, and JIS standards for simulated distillation.

Falcon Analytical announced that ASTM Method D-7798 for fast simulated distillation can be run on its CALIDUS GC with a run time of 84 sec, which is six times faster than prior methods. The maximum boiling point is 538 °C. The ASTM ballot announced in December of 2012 validates the applicability of micro-GCs to difficult assays.

Sulfur analysis in fuels and petroleum gases

Sulfur-containing compounds in petroleum and refinery streams must be monitored.

Consolidated Sciences (www.consci.com) introduced a gas chromatograph/inductively coupled plasma/mass spectrometer (GC/ICP/ MS) particularly tuned to monitor sulfur analytes such as H2S, COS, MeSH, EtSH, and 10 more targets with a method detection limit of 10 ppb. Since the analytical reference standards of several of the analytes do not exist, Consolidated Sciences uses the isotopic abundance and the ICP/MS for quantitation.

Conflicting currents on helium supply

It seems that each gas chromatographer at Pittcon had a different story on the helium shortage. Some said that they were not expecting any problems; others reported being put on insufficient allocations, and others seemed to be using the fear to justify switching to hydrogen as the carrier gas, which they knew that they should do anyway. After all, capillary GC is generally much better with hydrogen. The most significant downside is the Hindenburg risk, which has been seared into the minds of safety officers. Chromatographers point out that some calibration plots are not linear but quadratic. Fortunately, this is not a problem for most chromatography data systems.

Bruker (www.bruker.com) introduced SCION™ 436 and 456 Helium Free Gas Chromatographs, which are specifically configured to use hydrogen as the carrier gas. These GCs have internal leak detection, which activates internal and external shutdown protocols. Bruker also supplies filters for carrier gas and flame ionization detector (FID) fuel. After all, hydrogen can be supplied as needed by small, economical hydrogen generators. Indeed, these are used in the less-developed world since helium and hydrogen in high-pressure bottles are heavy, expensive, and too often contaminated. It seems that the time has come for the first world to learn from the third, and also benefit from improved separation efficiency, shorter run times, and lower operating costs.

In one of the sessions, Dr. James D. McCurry of Agilent (www.agilent.com) described steps that could help mitigate the helium supply problem. The most obvious is to switch to another inert gas such as nitrogen whenever the GC is not running assays. Helium is used only when preparing and running samples. Agilent software supports “sleep” and “wake” protocols. Or, if the assay has plenty of resolution with helium as the carrier gas, one can investigate the possibility of switching to nitrogen, even for the assays. The criterion should be, “Is the assay still providing results that are suitable for the purpose?” If so, save the money and hassle. 

One exception to avoid helium is the new Barrier Discharge Ionization Detector from Shimadzu….

Gas chromatography detectors

GC based on helium plasma detector

For decades, chromatographers have searched for a detection technology to replace the thermal conductivity detector. Shimadzu has found one and calls it the Barrier Discharge Ionization Detector. Helium is the required carrier gas. The detector was developed in collaboration with Dr. Katsuhisa Kitano of Osaka University (Japan). The detector uses a 17.7-eV helium plasma generated in a quartz dielectric chamber. Analytes from the column are mixed and ionized by the helium plasma. The ions travel to the collection electrode, where the current is detected. This is similar to flame ionization detection (FID), electroconductivity detection (ECD), pulsed discharge detection (PDD), and a host of thermionic detection techniques. Radar plots of detection limits for representative analytes including hydrogen, hydrocarbons, and halohydrocarbons show a 100× improvement compared to TCD and about 2× better for FID. Helium and neon are the only nondetects so far. The Tmax is 350 °C, which is about C44. The detector is incorporated in Shimadzu’s Tracera GC. Illustrative applications include gases from lithium ion batteries, photosynthesis, and light gases.

Detector for catalytic combustion ionization

Two years ago, DETector Engineering and Technology, Inc. (DET; www.det-gc.com) introduced a novel detector for GC based on the selective oxidation of –CH2– groups. With Catalytic Combustion Ionization Detection (CCID), analytes are catalytically oxidized to produce negative ion currents at the surface of ceramic materials. This is similar to the mechanism of the popular FID, except that the catalytic surface provides selectivity, where the FID burns nearly everything. This year, Dr. Paul Patterson, President and Founder of DET, explained that different hydrocarbon groups can be selectively detected by controlling the oxygen content of the CCID gases. At low oxygen, CCID is highly selective for linear alkanes. Increase the oxygen partial pressure and alkenes are also oxidized. Increase the O2 still more and peaks for the branched hydrocarbons pop up, too. Aromatics are not seen. CCID is now used to characterize the hydrocarbon content of petroleum, processed fuels, and lipids.

Gas generators for GC

Traditionally, resistance to change is a common human attribute. Witness the prevalence of gas cylinders still providing carrier gas and fuel to gas chromatographs in the developed world. In the developing world, with little tradition, the preference is for gas generators. This year, Parker Balston (www.parker.com) introduced the H2PEM PD Hydrogen Generator for labs with up to 20 GCs using H2 for carrier gas and FID. Purity is 99.9995. Other applications include hydrogenation reactors and collision gases. The H2PEM PD meets the requirements of CSA, IEC 1010, and CE for laboratory use. The footprint is less than 1 ft2, plus the unit is much shorter and lighter than the cylinders it replaces.

Many laboratories are now prohibited from placing hydrogen cylinders on their premises due to health and safety restrictions. A gas generator is a safe alternative to cylinders since it is designed to contain a minimal amount of hydrogen, typically <300 cc. Earlier this year, Peak Scientific (www.peakscientific.com) launched the new Precision Series, a modular system that can be tailored to any GC laboratory’s needs. The series offers both hydrogen trace and standard analysis solutions, providing up to 500 cc/min of 99.9999% pure hydrogen, using proven PEM Technology to generate hydrogen safely and reliably. For extra peace of mind, the company developed a hydrogen detector that can be connected to a GC to measure the hydrogen content within the GC oven and alert the user before there is a critical buildup.

Autosamplers for GC

Although not a recognized brand name in the laboratory segment, HTA (www.hta-it.com) is a leading Italian engineering and manufacturing company specializing in automation for laboratories and chemical processing. I was really impressed with the elegant industrial design of the HT3200A autosampler. It can store and process 209 × 2 mL samples in a bi-level drawer. A barcode reader is included. Syringes are individually keyed to monitor size and remaining service life, i.e., no volume mismatch. The 3200 is fast: Injection cycle is complete in less than 100 msec. Six extra 10-mL vials are available for wash solutions to reduce carryover. The syringe is located behind a glass screen. The backlight clearly shows the existence of bubbles, etc. The HTA spokesperson assured me that the 3200 fi ts on all GCs from major vendors.

Headspace sampling

Headspace sampling is unique to GC, and hence reported in the GC section. Reports on supplies that are useful in both GC and LC can be found in the sample prep report (http://www.americanlaboratory.com/913-Technical-Articles/136812-Sample-Prep-for-LC-GC-and-SFC-at-Pittcon-2013/).

In principle, headspace sampling for GC assays improves work flow by reducing labor compared to other sample preparation techniques. But the details are important. Shimadzu seems to have covered all the bases with the introduction of the HS-20 Series Headspace Samplers. One is for static headspace using a fixed-volume sample loop, and the other traps the analytes on a concentrator module, which is subsequently heated rapidly to flash off the analytes and improve detection sensitivity. Flow paths are short and chemically inert to ensure complete transfer and minimize carryover to the next sample. A barcode reader provides machine-readable sample identification. Control and reporting software is compliant with CFR 21 Part 11. Applications include assay of residual solvents in pharmaceuticals and blood alcohols, flavor/fragrance samples, and quantitation of volatile organic carbons (VOCs) in environmental matrices.

The TriPlus 300 Headspace Autosampler from Thermo Fisher Scientific features a 120-vial capacity plus a thermostated 18-vial incubation oven. The sample fl ow path is constructed of chemically inert materials and is heatable to 300 °C. Priority samples can be placed in any position in the rack. Once the priority samples have been run, the 300 resumes working on the queue.

Air sampling

For the last few years, Torion Technologies (www.torion.com) has focused on applications of the portable TRIDION™-9 GC-TMS, where the “T” stands for toroidal. The instrument seems mature and now the focus has shifted to sampling: Welcome the FUZION™-3 sampling products, which can accommodate up to three modules: 1) sample desorption, 2) heated headspace, and 3) purge-and-trap. A common internal standard (IS) module delivers a calibrated volume of vapor from a thermostated vial to one of the three modules above.

The conventional modules trap and deliver the analytes to Torion’s CUSTODIAN needle trap where they are concentrated still further. Then the CUSTODIAN is inserted into the TRIDION for analysis. Detection limits are in the range of 10–50 ppb.

Thermal desorption

Markes International (www.markes.com) introduced two thermal desorption sampling systems for GC. The pocket-sized ACTI-VOC™ sampling pump is designed for personal monitoring at remote locations. The pump delivers a constant fl ow rate of sample gas to the sorption tube regardless of the tube’s permeability.

However, the new Markes TT24-7™ Series 2 Thermal Desorption Trap attracted the most attention. Building on the success of its predecessor, the Series 2 uses two temperature-controlled traps to ensure 100% sampling coverage. Electronic cooling replaces cryogenic gases. Expected applications include trace contaminants in gas streams, air monitoring, detection of chemical/biological warfare (CBW) agents, and monitoring of odor profiles. The trap is compatible with all current GCs. Detection limits are in the low ppt.

Low-thermal-mass nanovalves

Usually valves for column switching as in comprehensive GC are mounted outside the oven. Until now, the thermal mass of the valve could not keep up with changing column temperature, which created cold spots that adversely affect the chromatography. Chromatographers resorted to complex valving schemes such as Deans switching for flow control via valves mounted external to the oven. Stan Stearns, President of Valco Instruments Co. (www.vici.com) introduced a line of four- and six-port nanovalves that have very low thermal mass, plus they can be electronically heated. Cool-down is less than 1 min, which is nearly as fast as the column. These valves will follow the temperature of the column oven at heating rates of 25 °C or slower. Port-to-port volume is only 10 nL, which is very small. Tmax is 380 °C, cycle time is faster than 250 msec, and fittings are 360 μm.

In the last of three lectures introducing the new valve, Stan used the valve to automatically recycle the analytes between two columns. As leading and tailing peaks fell out of the window, they were routed to waste. But the keepers, which were coeluting on one pass through the 2 × 30 m column set, were baseline-resolved after traveling the equivalent of 1500 m in 78 min. The plate count was about 5 million. Target assays include argon in oxygen and trace components in permanent gases. In the Valco booth, Stan showed a high-resolution separation of diesel fuel complete in 80 sec. The nickel-clad column was resistively heated.

GC columns

The world is getting smaller, as seen in the Polymicro Technologies™ (www.molex.com) booth, where a range of fused-silica capillaries compatible with 1/32-in. fittings (798 μm) were shown. Internal diameters range from 50 to 500 μm. The exterior of each capillary is coated with 24 μm of polyimide to increase durability. Tmax is 350 °C. The tubing is available in rolls or in precut lengths. Capillary columns are the target market, but with the narrow i.d., these may include HPLC capillaries also.

Thermo Fisher Scientific introduced TraceGold GC columns, which are based on capillaries with 150- or 180-μm i.d. for fast GC. It was pointed out that if the diameter, length, and phase ratio are reduced proportionately, the chromatograms look similar to those obtained with conventional columns, but 30% to 5 times faster. For temperature-programmed runs, Thermo provides simple equations to calculate the initial hold time. Plus the new columns are designed for hydrogen carrier gas.

Conclusion

It is clear that we have not heard the end of the helium story. As GC matures, we will certainly see more applications-driven designs and packages. In the near future, I expect that the ultrafast GCs with small-diameter capillary columns will evolve into mainline instruments. Please check back at Pittcon 2014.

Robert L. Stevenson, Ph.D., is a Consultant and Editor of Separation Science for American Laboratory/Labcompare; e-mail: rlsteven@comcast.net.

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