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pressor helps reduce the background and extends the range of application for UV detection in cases where an eluent such as carbonate absorbs UV more strongly before suppression than it does afterwards. Indirect detection is useful in a number of cases where the analytes don't absorb UV light but the eluent ions do; this method doesn't require suppression. Again, as for LC, absorbance and fluorescence detection are often enhanced by the use of a postcolumn reactor between the suppressor, if used, and the detector. In addition, says Dasgupta, the pulsed amperometric detector, introduced commercially a decade ago, is now being made by several companies and is particularly useful, for example, in carbohydrate analysis. This detector works by switching rapidly between working and self-cleaning modes to avoid the inactivation from buildup on the working electrode that is typical of amperometric methods. Hyphenated techniques
In the past few years, hyphenated IC techniques have crossed the boundary from
"homebrew" setups in individual labs to commercially available instrumentation. For instance, Dionex and Thermo Jarrell Ash have collaborated to produce dedicated instrumentation for IC/ICP-AES, and "chelation chromatographs" that use IC are also commercially available. Because ICP-AES requires a different matrix from the IC eluent, the adapted IC hardware elutes analytes as a plug in a more compatible solvent (often a suppressed eluent that has very little electrolyte) , analogous to analyte concentration by SPE. ICPMS, on the other hand, is compatible with standard IC fluids, at least in principle. If the eluent has high background salt, however, it is still preferable to operate in suppressed mode. With the burgeoning popularity of ICPMS and the introduction of several commercial instruments in the past year, systems that perform IC/ICPMS may be a commercial possibility. IC/MS is still in the exploratory stages; three or four research groups are actively pursuing it, Dasgupta says. Two persis-
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Analytical Chemistry, Vol. 67, No. 5, March 1, 1995
tent problems are the composition of the eluent from the chromatograph, because MS doesn't tolerate high salt concentrations, and flow incompatibility between IC and MS. The split-flow interfaces developed for commercial LC/MS might solve the second problem, but so few researchers are working with IC/MS that, Dasgupta says, "At this point, it's not clear that a sufficient market exists for commercial development." ProcessIC
Dasgupta notes that there is a growing need for commercial instrumentation in process monitoring. Nuclear power plants, for instance, require continuous on-line monitoring of high-purity water in the system. There's no substitute for suppressed IC because any off-line handling would contaminate the samples past the extremely low tolerance threshold. Dow Chemical also uses IC for a variety of processes but, says Dasgupta, the company often assembles its process IC equipment in house. Commercially available process ion chromatographs are elaborate and fairly expensive; as such, they may be out of range for small industrial users' budgets, but less sophisticated versions could fill a niche. Dasgupta says affordable instruments could readily be developed for many process applications. "There are always tradeoffs, but in most applications, you don't need the ultimate in resolution or sensitivity. With a larger particle-size column, there's a smaller pressure drop in the system and less maintenance is required. You could produce reasonably lowcost moderate pressure process IC systems." Outlook In the next few years, Dasgupta says, IC instrumentation is likely to move in the direction of improved column durability, increased separation speed, and the introduction of on-line protective methods that might include removal of undesirable matrix species from samples before separation. He adds that vendors should look at the possibility of making field-portable instruments with low solvent consumption for environmental and other on-site applications. "IC is a mature technique and is not changing very much," Dasgupta says. "However, its reliability and its ability to handle complex matrices are very good and, for routine use, better than any competing technique available today." Deborah Noble
