Structural Identity for LC, GC Systems
Early in the evolution of chromatography- mass spectrometry, one could consider the two components as separate boxes requiring a good deal of engineering to link them together.
Today, providing the integration and interoperability demanded by GC-MS or LC-MS users is virtually impossible without designing both instruments with the other in mind—and in most cases together. “Customers today view GC-MS or LC-MS as a single solution,” says Dr. Steve Smith, senior director for mass spectrometry products at Waters (Milford, MA).
Integration is the main reason for the virtual disappearance of the specialist GC or MS supplier that produces chromatographs for someone else’s mass detector, and vice versa. The level of component and software interoperability demanded by end users practically invalidates this business model.
Although chromatographs and mass detectors physically occupy different boxes, their common boundary is blurring from the perspectives of hardware design and software control. “Today’s instrumentation features system-level diagnostics, so you don’t have to worry if one component is smart enough to tell you what’s wrong. And this makes workflows more efficient,” Dr. Smith adds.
Terry Sheehan, GC-MS marketing manager at Agilent, compares the purchasing experience to buying a car: “People want to pay for it and drive away.”
This is all great news for users. As the education and expertise levels of chromatographers wanes, their employers increasingly look for turnkey systems. That means developers must spend more time thinking of the user experience and workflows. What information is being brought into the analysis at the front end, and where will the data go after it’s acquired? How will the system software handle two types of output while controlling two different instruments? “It’s very tough to visualize complex workflows these days if you’re only making one of the boxes,” Dr. Smith says.
More options for LC
LC has considerably more options than GC in terms of mass detection. “Mass detectors for LC show a much wider diversity in capability than GC detectors in terms of raw sensitivity and mass resolution,” Dr. Smith observes.
The basic options for GC include single quadrupoles, ion traps, and tandem quadrupoles. LC employs these MS modalities as well, but for each option there is significant stratification. For example, Waters offers three tandem quad detectors for GC, each with different performance characteristics. LC enjoys other options as well, for example, time-of-flight (TOF) and quadrupole TOF (QTOF) detectors, which are rarely found on GC instruments.
Lab Manager Magazine has recently completed a user survey for MS detectors used with chromatography systems. Among the GC-MS respondents, 22% primarily used a single-quadrupole MS, 16% used electron ionization (suitable for gases), and 8% used a quadrupole ion trap. Among LC respondents, quadrupole and ion trap were the most prevalent (17% and 10%, respectively), but TOF also weighed in at 10%.
If you can touch it, you can break it
Both GC and MS have been around for a long time. “GC-MS is improving, but we’re not talking about quantum leaps in sensitivity or detection limits any more,” says Agilent’s Terry Sheehan. “We’ve realized that for many applications, products from all the major vendors can satisfactorily do the job. The question is how well can they do it, how reliably, and what is the cost of ownership?”
Agilent’s California and Delaware GC-MS development teams have been paying increasing attention to these issues, as well as how to increase productivity by enhancing workflow and reducing “cost per test.”
Buyers—and salespeople as well— too often reflect on the list or sales price of an instrument, which Mr. Sheehan describes as “myopic.” Purchasers, he says, should consider the larger picture that includes reliability and operating costs. “If you expand your viewpoint regarding an instrument purchase to include cost of ownership for ten years, the list price takes on a different position in the argument.”
He points first to Agilent’s ten-year “Value Promise” on GC-MS and LCMS instruments, which guarantees that the systems will remain in working order for ten years. If not, the company will credit the residual value against the price of a new instrument.
Design features promote value as well. MS detectors have become more compact and robust, but they are still complex, expensive instruments. “My philosophy is if you can touch it, you can break it,” Mr. Sheehan jokes. “Every time you have to open up an MS, you risk messing something up.”
For example, conventional GC maintenance requires that users periodically bake high-boiling, non-eluting materials off the column at a high temperature. When an MS detector is at the back end, all that junk winds up in the MS source. “You can’t simply disconnect because you can’t break the vacuum, and unlike an LC-MS, you can’t just turn a valve.” The answer is backflush, which reduces downtime and maintenance of the MS detector by routing non-eluting materials away from the MS. Agilent has created a backflush software tool that facilitates setting up and executing regular backflush “without the need to be a GC guru,” says Mr. Sheehan.
Price vs. operating costs
Lowering cost of ownership through higher throughput is another strategy for reducing the effective price of an instrument. A workflow study conducted by the U.S. Dept. of Agriculture compared the entire workflows, including sample prep, for GC-MS (single quad) vs. GC-MS/MS (triple quad) analysis of trace residues. The tandem MS instrument costs twice as much as the single-quadrupole detector, so on the basis of sales price many organizations would not even consider the upgrade.
But the triple-quad detector significantly reduced the time and cost of sample preparation. Researchers concluded that very busy laboratories could recoup the difference in cost in less than a year by purchasing the more expensive instrument.
Mr. Sheehan explains that “many laboratories have two budgets—one for capital equipment and one for supplies. As long as you keep them separate, you’ll never realize that you could select triple quad and thereby begin saving money on sample prep almost immediately.”
For additional resources on mass spec detectors, including useful articles and a list of manufacturers, visit www.labmanager.com/ms
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