 July 2000
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 Volume 9, No. 7, 15, 16, 19. French Scientists Hunt Oyster-Bed Toxins Coupling GC to ICP-MS enables speciation of organotin compounds Ongoing concerns about the accumulation of tributyltin (TBT) in shellfish recently prompted researchers at the University of Pau in Pau, France, to conduct studies on the organotin content of oysters and sediments from the Bay of Arachon—one of France’s most productive areas for oyster farming. TBT has long been suspected as a culprit in the weakening of oyster and mussel shells and in reducing reproduction in field populations of the aquatic snail Nucella lapillus. In the 1970s, TBT was added to paints used on the hulls of ships to prevent the growth of barnacles, tubeworms, and algae. The leaching of TBT-containing paints into marinas, estuaries, and bays triggered apprehension on the part of environmentalists, and in the mid- to late 1980s a number of countries, including the United States, Japan, France, and several North Sea states, issued stringent regulations restricting the use of TBT-containing paints. Although these regulatory measures have succeeded in greatly reducing both the use of TBT and its impact on the environment, bioaccumulation of the compound in sediment and oyster tissue remains an issue. Challenges with TBT Analysis For the most part, contamination comes from either glassware that has been improperly cleaned or reagents that contain low levels of the target analytes. According to the Organotin Environmental Programme (ORTEP) Association (www.ortepa.org), common sources of contamination include polyvinyl chloride-containing materials, laboratory water, commercially purchased Grignard reagents, used polycarbonate containers, and organic solvents such as tropolone and florisil. Interference is most frequently encountered with sediment samples containing sulfur compounds that coelute with the butyltins or internal standards. A GC-ICP-MS Interface “Capillary gas chromatography offers fast and high-resolution speciation, and is well-suited for organotin compounds. Measurement limits using currently available GC detectors such as FPD, MS, or atomic emission detection [AED] are good, but the need for determination of organotins at ever-lower levels of concentration has fueled the investigation of alternative detection systems,” notes Donard. “The exceptional resolution of the chromatographic separation allows an anticipation of the formation of metabolite products from organotin compounds (e.g., methylation of butyltin compounds), opening the way to new understanding of environmental and biometabolic pathways for these contaminants after further investigation,” he adds. ICP-MS provides ultratrace detection limits and high selectivity for most elements. Individual isotopes can be measured, enabling isotopic fingerprinting and therefore confirmation of results. Samples are introduced into a high-temperature argon plasma where they are decomposed, atomized, and ionized. The resultant ions are transported, through a sampling interface, into an MS for measurement. Because the high temperature of the ICP source decomposes all forms of an element into individual atoms, ICP-MS results represent total element levels. “The general principle of combining GC with ICP-MS is simple,” says Yamanaka. “The end of the capillary GC column is fastened to the base of the ICP torch so that separated species are carried directly into the plasma by a heated argon flow. Using a heated transfer line to connect the GC to the ICP-MS prevents material condensing within the interface and so enables the analysis of high boiling point compounds,” he explains. Figure 1 is a schematic that describes the interface used in the experiments. Xenon was added to the argon make-up gas as a means of optimizing the ICP-MS operating conditions. The xenon–argon gas mixture was preheated by passing it through a stainless steel coil mounted within the GC oven. Initial Results Figure 2 is comparable to a GC-ICP-MS chromatogram from one of the oyster extracts, illustrating the separation and peak shape characteristic of the technique. “There are substantial and measurable amounts of a variety of organotin compounds in the sample,” notes Donard. Oysters sampled from nine areas in and around Arachon Bay, as well as one sediment sample, revealed TBT as the single largest component in each case, although several other species were present at significant levels, most notably monobutyltin and dibutyltin, which are breakdown products of TBT. In one particular region, referred to in the study as Area 9, there was a direct correlation between the highest levels of TBT detected and the lowest levels of oyster production. Future Applications for GC-ICP-MS The experimental interface for the combined system is designed to provide efficient transfer of analytes from the GC to the plasma without loss of signal or chromatographic resolution. Therefore, the most critical parameters associated with the development of the interface were the ability to provide a uniformly heated transfer line, low dead volume to minimize peak broadening, and an inactive transfer line that would not affect the chromatographic resolution. A noteworthy aspect of the interface development project is that it involves more than simply hardware. Agilent is currently developing total speciation solutions using its Plasma Chromatography software for real-time data collection and evaluation, such as the recently introduced LC-ICP-MS for arsenic speciation. Virtually any area of chemistry can benefit from the use of these speciation techniques. There is increasing interest in the determination of not just the total concentration of an element but also the forms in which it exists. Nearly all elements exist in a variety of species that can alter an element’s toxicity or mobility in the environment or biological system. Knowledge regarding the chemical species in which something exists provides valuable clues as to its source, its fate, and the best methods for treatment or removal if required. Donard’s preliminary findings suggest that GC-ICP-MS offers a highly sensitive and selective method for the determination of organometallic compounds in environmental matrices. “The exceptional chromatographic separation capability of the GC coupled to the sensitivity, selectivity, and multielemental capability of the ICP-MS detector certainly makes this combination a very promising tool for environmental as well as biological studies,” explains Donard. “Future applications work is under way, evaluating the potential of this interface for the simultaneous determination of other organometals such as tin, lead, and mercury compounds.” Reference
Crispin Littlehales is a freelance writer living in Cavalo, CA. Comments and questions for the author can be addressed to the Editorial Office by e-mail at tcaw@acs.org, by fax at 202-776-8166 or by post at 1155 16th Street, NW; Washington, DC 20036.
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