Product
Review
GC AT A STANDSTILL The analytical instrument market is dominated by chromatography. LC is the biggest and one of the fastest growing areas, with worldwide annual revenues estimated at $2.2 billion. Coming in second is GC at $1 billion. Unlike LC, however, the GC market has seen no growth over the past three years. GC is a mature technology that has been evolving for more than 30 years but has seen little innovation in the past decade. As a result, there hasn't been much incentive for users to replace older systems with newer ones. In addition, approximately one-third of the demand for GC came from the environmental-testing market, which fell into a lull in the mid-1990s. Although some sources predict that the environmental market is on the road to recoverv no one expects its growth rate to match that seen during the glory days from the late 1980s to the early 1990s Biotechnology is the fastest growing area today but proteins peptides and DNA fragments are not volatile and therefore are not amenable to GC
Britt Erickson
Has the market peaked out at $1 billion? GC/MS is also to blame for the lack of growth in conventional GC. "The number of people using GC/MS compared to GC continues to increase dramatically," one manufacturer told Analytical Chemistry. II is estimated that 60-70% of users still use GC rather than GC/MS, but the gap is getting smaller every year. (Benchtop GC/MS systems will be reviewed in the June 1 issue of Analytical Chemistry)
prehensive and does not include instruments dedicated for field or process applications. Portable GC and GC/MS systems were reviewed in a previous article {Anal. Chem. 1997,69,195 A). A glossary of abbreviations is available on page 276 A For the most part, the gas chromatographs in Table 1 are based on the same concept and have the same analytical capabilities. However, a close look at their features reveals some differences, primarily in the injectors and detectors. In addition, there are less obvious differences in software, autosampler capacity, and temperature-programming rates, which could be important, particularly for high-throughput applications.
Analytical Chemistry surveyed several representative GC manufacturers, and the specifications and features of selected benchtop, analytical-scale gas chromatographs are presented in Table 1. Several of the manufacturers listed in Table 1 offer more than one benchtop GC system. Readers are encouraged to contact the individual manufacturers for information on their complete product lines. This review is not intended to be com-
Front end "Injection is the most difficult part of capillary GC," says Konrad Grob of Kantonales LaboriumZurich (Switzerland). Unfortunately, buying the proper injector won't solve all injection problems, he says. In a review article on capillary GC injection, Grob wrote that the user must understand the background of injection techniques in order to
Analytical Chemistry News & Features, April 1, 1999 271 A
Product
Review
Table 1 . Summary of selected gas chromatographs Model
Series 8 1 6
HP 6 8 9 0 Plus
AutoSystem XL
GC-17Aver.3
Manufacturer
GOW-MAC Instrument Co. 277 Brodhead Rd. Bethlehem, PA 18017 610-954-9000
Hewlett-Packard 2850 Centerville Rd. Wilmington, DE 19808 800-227-9770
Perkin-Elmer 761 Main Ave. Norwalk, CT 06859 800-762-4000
Shimadzu 7102 Riverwood Dr. Columbia, MD 21046 800-477-1227
URL
www.gow-mac.com
www.hp.com/go/chem
www.perkin-elmer.com
www.shimadzu.com
Dimensions W x D x H (cm)
58 (or 68) x 54 x 50
58 x 54 x 50
66 x 64 x 48
51.5x52x43.7
Average weight (kg)
49
49
49
35
Autosampter capacity
8 or 100
8 or 100; 44 (headspace); 16 (purge and trap)
82, plus one priority
150(1.5mL)or96 (4mL); 40 (headspace)
Injectors Max. no.
2
2
2
3
S/SL, COC, PTV, packed, vola- S/SL, COC (autoinjection into tiles interface, and GSV (up to 7) 0.25-0.53 mm i.d. columns), PTV, packed, volatiles interface, GSV, and LSV
S/SL, COC, PTV, and packed
S/SL, COC, PTV, direct, PYR, packed, and GSV
31 x 1 6 x 2 8
31 x 1 6 x 2 8
10,600 cm 3
28 x 18.4 x 28
4 degrees above ambient to 450 (down to - 8 0 with liq. N 2 and - 5 5 with C 0 2 cryogenic units)
4 degrees above ambient to 450 (down to - 8 0 with liq. N 2 and - 5 5 with C 0 2 cryogenic units)
10 degrees above ambient to 450 (down to - 9 9 with subambient accessory)
- 8 0 to 450
Max. temperature ramp rate (°C/min)
120
120
45
Max. no. of temperature ramps
6
6
3
2
2
2
4
FID, TCD, DID, NPD, FPD, PID, TCD/FID, FID/DID, and TCD/ DID
FID, TCD, ECD, micro-ECD, NPD, FPD (single- or dualwavelength), AED, and MSD
FID, TCD, ECD, NPD, PID, ELCD, FPD, PID/ELCD, FID/FPD, FPD/FPD, and FPD/FPD/FID
FID, TCD, FTD, ECD, FPD, ELCD, PID, SID, PDD, and combinations thereof as long as only the last detector is destructive
Software
FrontRunner
ChemStation (includes HP Com- TurboChrom panion interface, LAN control)
Chromatopac C-R7Aplus Data Processor, Class VP (fully automated, Windows NT compatible)
Options
Helium purifier; oxygen trap; hydrogen separator
RT locking software; 150 psi S/SL, 240 V oven, and oven insert for fast GC; pesticide screening method and RT library; LAN communication
Built-in liquid autosampler; headspace sampler; thermal desorber
Purge and trap; headspace; thermal desorption; SPME; single- and multivalve custom separations; multidimensional GC
Special features
Complete applicated systems for turn-key analyses
EPC with real-time ambient pressure compensation; EPC provides 0.01 psi setpoint resolution; 0.001 min RT repeatability (average standard deviation); 100 ms auto-injection speed; EPC allows leak detection and automatic shutdown; ambient headspace
Optional prevent injector system for enhanced LVI
Air pressure and temperature compensation for carrier flow; %-in. packed columns to .05-mm i.d. microbore capillary columns; 14 channels of electronic gas control or APC for control of all detector gases for up to 5 detectors; automatic carrier gas minimization; up to 4 standard 7-in. capillary column cages at the same time; autostart timer lights FID at predetermined time of day; auto relight of FID; column protection for loss of carrier flow
Reader service number
401
402
403
404
Available types*
Column oven Dimensions W x D x H (cm) Operating temperature range (°C)
Detectors Max. no. Available types*
*See glossary on page 276 A.
272 A
Analytical Chemistry News & Features, April 1, 1999
120 5 (6 holds)
861OC
Flash-GC
TRACE GC 2 0 0 0
ProGC
CP3800
SRI Instruments 20720 Earl St. Torrance, CA 90503-2162 310-214-5092
Thermedics Detection 220 Mill Rd. Chelmsford, MA 01824 978-251-2213
ThermoQuest CE Instruments 2215 Grand Avenue Pkwy. Austin, TX 78728 800-867-6711
Unicam Chromatography P.O. Box 205 Cambridge CB1 2SS U.K. 44-1223-374446
Varian 2700 Mitchell Dr. Walnut Creek, CA 94598 800-926-3000
www.srigc.com
www.tdxinc.com
www.thermoquest.com
www.unicam.co.uk
www.varian.com/inst/csb/ products
49.5 x 36.8 x 31.8
8 1 . 3 x 5 5 . 9 x 55.9 1105.4 with autosampler)
55.8 x 64.8 x 44.4
58 x 50 x 50
66 x 53 x 53
18-32
36
60
35
43
42; 10 (purge and trap)
90 plus three priorities
90; 32 (headspace)
100
48; 50 (headspace)
4
2
2
2
3
COC, heated, S/SL, liquid autosampler, and GSV (up to 3)
S/SL and GSV
COC (manual or automated operation, LVI option), dual S/SL, S/SL, PTV, and packed
S/SL, PTV, COC, packed, GSV, and 0.53-mm capillary
Packed or universal capillary injector (S/SL, COC, LVI)
19.8 x 19 x 7.6
M/A
27x17x27
27x27x17
28 x 1 9 x 2 8
Ambient to 400
Ambient to 450 (-55 with C 0 2 option)
Few degrees above ambient to 450 (down to - 9 9 with N 2 cryogenic unit)
5 degrees above ambient to 450 (down to - 5 5 with subambient accessory)
4 degrees above ambient to 450 (down to - 9 9 with cryogen)
40
1800
120
49.9
100
unlimited
unlimited
7
3
7
4
4
3
2
3
TCD, FID, FID/DELCD, HID, NPD, NPD/ELCD, ECD, PID, FPD, FID/FPD, FPD/FPD, and FPD/FPD/FID
FID, CHEMI, and PDD (HID, ECD, or PID modes)
FID, TCD, ECD, NPD, FPD, PID, ECD/FID, ECD/NPD, ECD/FPD, PID/ECD/FID, PID/ECD/NPD, PID/ECD/ FPD, quadrupole and ion trap MS detectors
FID, ECD, TCD, NSD, FPD, PID, DID, and PDD (HID, ECD, or PID modes)
TCD, FID, TSD, ECD, PFPD, and micro-TCD
PeakSimple for Windows (16-bit and 32-bit versions)
TDX Flash Software plus analog output
ChromQuest (Windows NT), ChromCard (PC-based data integrator)
ProGC Data Station for Windows
Star Chromatography Workstation
Dual independently programmable column ovens; built-in purge and trap; built-in heated headspace; built-in "whisper quiet" air compressor
Autosampler; additional injec- Computer assisted LVI for tors; additional columns; up COC and PTV to 4 Cold Spots; up to 3 heated rotary valves; additional detectors
Multipoint sampling; at-line sampling; ProLink application specific software
EPC of all injector and detector gases
Portable (can travel as airline baggage); built-in data system that can run on laptop computer with serial interface; EPC of all gases (carrier gas is pressure programmable); low cost; two-year warranty; instant technical support (no voice mail)
High-temperature ramp rates; simultaneous independent temperature ramping of multiple columns; Cold Spots
Built-in automatic column characterization for guaranteed instrument-to-instrument repeatability
Full chromatography guarantee; application-engineered systems; pulsed DID for trace gas analysis
Multivalve configurations; built-in (optional) sample preconcentration trap; automated SPME (optional)
405
406
407
408
409
Analytical Chemistry News & Features, April 1, 1999 273 A
Product
Review
choose the appropriate experimental conditions. (Anal. Chem. 1994,66,1009 A). In concept, injection is straightforward— evaporate the sample and transfer it rapidly and quantitatively to the column. There simply aren't that many ways of accompllshing it. One look at the large number of commercially available injector combinations, however, might make you think otherwise. Split/splitless injection. Unlike packed columns, which typically accommodate sample volumes up to 10 uL (liquids), capillary columns require sample sizes on the order of 1 uL. As a result, ,he sample ii often split so that only a fraction actually reaches the column. One of the oldest inlet systems for capillary GC is the split/splitless (S/SL) injector. In the split mode, a liquid sample is injected into a hot chamber (200-350 °C), and the vapors are divided so that a large portion exits through a split vent and only a small portion enters the column. In the splitless mode the split vent is closed for 30-60 s and almost the entire vapor cloud enters the column. Splitless injection is commonly used for trace analysis, whereas split injection is used with relatively concentrated samples. Split injection is simple in practice, says Grob; however isis not very reliable quantitatively Splitless injection has numerous weaknesses because compromises were made so that it could be used with a splitinjector. Cold on-column injection. Because of numerous problems associated with S/SL injectors, alternative injection techniques have been developed. Historically, the first . . . . . . .' o
,
h
m i u u g i i a v*wiu iiuiuci \XJ ivtttj uiit oain^jiv;
l l l g L\J \ J l \ J c , V ^ W l o lllKJl k LJUClllLlKUlV\* 111(411
o / ox^ Uljci^uuil. n u w c v c i t S a m p l e s HlUbl u c
inlet, says urob. Despite alternativd techniques that oner Deriesaccuracy and reproQUCioiniy, analysts in tDe uniteu otates sun use the classical S/SL injector 90-95% of the time, estimates Grob. The primary reason is thet S/SL injectors are standard, low-cost parts ,f gas chromatographs. Other modes are lesS common, 274 A
sometimes not available, and much more expensive. In addition, most standardized methods require S/SL injection. "A lot of times people don't know what else to buy," one manufacturer told Analytical Chemistry. For quantitative results, however, most sources agree that COC is the best choice. Large-volume injection. Injection volumes are typically in the 1- to 2-uL (liquid) range for COC and S/SL injection. There have been several attempts, however, to increase the sample size, in order to increase sensitivity. With a few modifications, COC injection can accommodate up to 500 uL, says Grob. For large-volume injection (LVI), the injector is the same as conventional COC.
Buying the proper injector won't solve all injection problems. A T-piece, installed after a precolumn and branching to a solvent vapor exit, is added to create an outlet for releasing solvent vapors. In addition, special software is needed for automation of LVI, says Grob. Although the only dedicated instrument for LVI is the ThermoQuest UltraTRACE, almost any gas chromatograph can be modified to accommodate manual LVII ,ays Grob. Programmable temperature vaporizer. Yet another injector, the programmable temperature vaporizer (PTV), was originally designed for LVI, but it also permits S/SL injection. On paper, the PTV looks like a classical S/SL injector. But in reality, the chamber is usually smaller and can be rapidly cooled and heated. For injection, the vaporizing chamber is kept around the boiling point of the solvent (below 100 °C). For LVI by "solvent splitting", the solvent vapors are driven out of the chamber through the split outlet by the carrier-gas flow Meanwhile the solute remains trapped on an adsorbent material inside the chamber After the solvent is vented the chamber is ranidlv heated to vannrize the tranned analvtes which are
then transferred to the columw n gan chromatograpc can typicallv ac-
Analytical Chemistry News & Features, April 1, 1999
commodate two, and occasionally, three or four injectors; however, only one injector can be used at a time. The three most common injectors—-S/SL, COC, and PTV—can be purchased from nearly all manufacturers. However, from one manufacturer to the next, "[the injectors] do differ in the chamber dimensions, the plumbing of the gas supply, as well as in the split outlet," says Grob. In addition, he warns, there are quality differences that are important for quantitative analysis. Grob believes that the injector should be the number one consideration when purchasing a gas chromatograph Solid-phase microextraction. "People are working on all kinds of exotic ways to get more samples into the gas chromatograph," says Harold McNair of Virginia Tech. Today there is a demand to use more complex samples at lower concentrations. "A lot of emphasis has been placed on solidphase microextraction [SPME], which is a novel way to rapidly concentrate most organics from water," says McNair. A complete gas chromatograph equipped with a special injector for SPME which was developed by Janusz Pawliszyn of the University of Waterloo (Canada) is commercially available from SRI Instruments Varran's 8200 GC aatosampler also accommodates SPME Headspace. Headspace, which has been around for at least 30 years, is having a rebirth because of new accessories that make it more sensitive, says McNair. There are two types of headspace—static and dynamic. In static headspace, the sample reaches chemical and thermal equilibrium inside a closed system (usually by heating and sometimes by shaking), and only a small fraction of the material is desorbed onto the GC column, explains James Stuart of the University of Connecticut. On the other hand in dynamic headspace (also referred to as purge and trap) the sample is completely transferred onto the column Purge and trap is a specialized technique, developed by Tom Bellar at EPACincinnati, for the analysis of volatile organic compounds (VOCs) in water. Tekmar (Cincinnati, OH) was the first company to commercialize purge-and-trap devices, although today several manufacturers provide them. Headspace is typically a $10,000-$30,000 accessory.
Several companies add their own specialized detectors onto platforms, such as the HP 6890.01 Analyttcal (College Station, TX) offers a volatiles system with a PID/ELCD mounted onto an HP 6890. The system is used primarily in EPA methods for detecting aromatic and halogenated VOCs in drinking water and wastewater. OI also offers a pesticide system with a thermionic emission detector (XSD), designed to detect halogens in pesticides. The detector is similar to an NPD but is specific to halogens, primarily chlorine rather than nitrogen and phosphorus. Detectors According to the manufacturer an XSD Nearly all gas chromatograph manufacturers doesn't have interferences offer a range of detectors. Typically, systems can handle up to two or three detectors oper- ECD and offers good selectivity in comolex ating simultaneously. The most common matrixes such as agricultural products detectors include the thermal conductivity detector (TCD), the flame ionization detector (FID), the electron capture detector (ECD), the thermionic emission or nitrogen/phosphorus detector (NPD), and the flame photometric detector (FPD). FIDs are used primarily for detecting hydrocarbons, ECDs for halogenated compounds, NPDs for nitrogen/phosphorus compounds, and GOW-MAC also uses the HP 6890 sysFPDs for sulfur/phosphorus compounds. tem and customizes it with its own detecCommercially available ECDs (Anal Chem tors, including the TCD, FID, and DID. A 1995 67 439 A) and NPDs (Anal Chem DID is used for detecting part-per-billion 1998 70 599 A) were eeviewed in previous levels of impurities in gases. articles Other commonly used detectors include the helium ionization detector Carrier gases
ibility of doing five samples rather than one or two, precision and accuracy could increase dramatically by running more standards," he emphasizes. The lack of interest in fast GC stems from GC's notoriously slow sample preparation. "If it takes 30 min to work up a sample, you're not really concerned whether you can run the sample in 2 min or 10 min," he adds. Because retention time is directly proportional to length, shorter columns yield faster separations. Speed, however, comes at the expense of resolution. In order to gain back some of the resolution, columns typically have smaller inner diameters and special inner films. "At this point, you've now sacrificed the capacity of the column," says McNair. "You cannot do ultratrace and fast GC at the same time." Thermedics is the only manufacturer that provides a full-blown, high-speed GC system. Thermedics' Flash-GC is a complete gas chromatograph that wasfirstincorporated in the EGIS explosives detection system. Thermedics also offers the EZ Flash, an upgrade kit that retrofits any conventional gas chromatograph into a Flash-GC. Both the Flash-GC and the EZ Flash are compatible with standard capillary GC columns. It is not the column that is unique in this case, but rather the heating of the column. Instead of being heated in a large /TTTT~J\ ^ „ discharcre ionization Hptprtor oven inside the gas chromatograph, the The most common carrier gas used in GC column is inserted into a low-mass, thinis helium, but other inert gases (e.g., ar(DID) and the photoionization walled metal tube and resistively heated. gon, nitrogen, and hydrogen) are also (PID) HIDs are about 200 ttmes more (and used. The choice of carrier gas depends DIDs are about 103 times more') sensitive The Flash-GC offers a unique way to than TCDs but are similar in that they detect largely on the type of detector installed. introduce samples using what are called Nitrogen is commonly used with an FID, nearly everything. PIDs are about 10 times Cold Spots. The sample is vaporized in the helium or hydrogen with a TCD, and hemore sensitive than FIDs and offer mterestinjector and transferred to a Cold Spot, lium with MS because of its low mass. Car- which traps the compounds of interest but ing selectivity for aromatic compounds. allows the solvent to pass through. The Cold SRI Instruments offers a unique, dry elec- rier gases are usually moisture- and oxygen-free, to avoid oxidation of the staSpot is rapidly heated (up to 3000 °C/s)) trolytic conductivity detector (DELCD), tionary phase. However, SRI Instruments sending the analytes to the column in a tight which is specific to chlorine and bromine, has just introduced the Gas-less GC which band. Rapid temperature programming, one in combination with either an FID or an uses 3xv 3.s the carrier fifcis A catalytic of the key features of the Flash-GC and the NPD. The DELCD can operate after an cornEZ Flash, provides sharper, narrower peaks, FID, despite the fact that FIDs are usually bustion detector capable of running in air is improved sensitivity, and increased sample thought of as destructive detectors. Acincluded The claims that manv throughput. cording to the manufacturer, the DELCD columns can tolerate air as a carrier gas can detect chlorine atoms in the FID exAnother approach for high-speed GC haust, which is particularly useful for anaHigh-speed GC arose largely out of Richard Sacks' laboralyzing compounds, such as polychlorinated Despite the obvious advantages of faster tory at the University of Michigan (Anal. biphenyls (PCBs) in waste oil. The hydroChem. .998, 70,29 A). Their technology analyses, there seems to be little demand carbons from the oil combust in the FID uses an inlet system that produces a narrow for high-speed GC. "People have not so they do not interfere with the analysis of bought into fast GC as much as they sample plug, shorter column lengths, and the chlorine from the PCBs should," says McNair. "If you have the flex- faster carrier-gasflows.In 1991, ChromatoThermodesorption. For about the same price as a headspace unit, several manufacturers offer a thermodesorption sample introduction device. Thermodesorption allows volatile and semivolatile compounds in soil or other solid matrixes to be injected with minimal sample preparation. In addition, it is commonly used for the analysis of trace contaminants in air. McNair's group uses thermodesorption to detect traces of explosives around airports and in suitcases.
You cannot do ultratrace and fast GC at the same time.
Analytical Chemistry News & Features, April 1, 1999 275 A
Product Review fast (Ann Arbor, MI), a company dedicated to fast GC, was formed to commercialize this technology. According to CEO Robin Risser, the high-speed GC technology can increase the speed of analysis anywhere from 10 to 100 times. In addition, "it acts as a sample collection and preconcentration device," he says.
Glossary Injectors COC: cold on-column GSV: gas-sampling valves LSV: liquid-sampling valves LVI: large-volume injection PTV: programmable temperature vaporizer PYR: pyrolysis injection SPME: solid-phase microextraction S/SL: split/splitless Detectors AED: atomic emission detector CHEMI: chemiluminescence detector (sensitive to organic N) DELCD: dry electrolytic conductivity detector DID: discharge ionization detector ECD: electron capture detector ELCD: electrolytic conductivity detector FID: flame ionization detector FPD: flame photometric detector FTD: flame thermionic detector (same as NPD) HID: helium ionization detector MSD: mass-selective detector NPD: nitrogen/phosphorus or thermionic emission detector NSD: nitrogen selective detector PDD: pulsed discharged detector PFPD: pulsed flame photometric detector PID: photoionization detector SID: surface ionization detector TCD: thermal conductivity detector TOF: time of flight TSD: thermionic specific detector (same as NPD) XSD: thermionic emission detector (specific for halogens) Other APC: advanced pressure controller EPC: electronic pneumatics control LAN: local area network RT: retention time
276 A
Chromatofast plans to introduce a device to retrofit any gas chromatograph into a high-speed instrument in the second quarter of 1999. "It will allow an existing gas chromatograph to function as either a fast or a slow gas chromatograph," says Risser. Although the technology uses the same capillary columns as a conventional gas chromatograph, it typically uses less of it. "A very narrow plug of concentrated sample is injected in about 5 ms, as opposed to standard GC injectors that are 20 to 50 times slower " Risser explains By having a narrow plug the compounds of interest are closer together when they arrive at the column A shorter column higher carrier-gas flow and having the compounds closer together to begin with all contribute to the faster analysis time says Risser HP has become more competitive in the high-speed GC market through its acquisition of MTI and its ultrafast micro-gas chromatographs, including both a laboratory and a portable version. Because there is no vaporizing inlet, samples must be in the gas phase. HP claims that the micro-GC systems can perform simple gas analyses in
