3, p. 118, 1988
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Chemical analysis near the sediment-water interface NIELS PETER REVSBECH Institute for Genetics and Ecology, Aarhaus University DK-800, Aarhaus, GC, Denmark
ANALYTICAL methods used to determine concentrations of chemical species near the sediment-water interface should, preferably, have good spatial and temporal resolution. Examples of methods which have these desired characteristics are the microelectrode based measurements of oxygen and pH, which can be performed with a spatial resolution of a few micrometers, and in the case of oxygen, also with temporal resolution of a fraction of a second. Unfortunately, most ion- or gas-specific electrodes do not exhibit sufficient selectivity and sensitivity to be used in marine environments. Sulfide microelectrodes have been used for analysis in benthic microbial mats where the sulfide concentrations are very high, but it should be possible to develop microelectrodes which would be useful at more moderate sulfide concentrations. Microelectrodes with reasonable characteristics may be developed for nitrate, ammonia, and bicarbonate, but the present ion exchangers would limit such microelectrodes to use in environments with high concentrations and steep gradients. Electrodes for analysis of organic molecules, which are based on immobilized enzymes
or bacteria, generally do not exhibit sufficient sensitivity to be used in marine environments. The most promising, yet largely unexplored methods for analysis of chemical species on a microscale, are in situ fluorometric and microcolorometric analyses based on glass fiber optics. The recent development of suitable fibers, light detection systems, and computers justifies a considerable effort to develop such analytical methods for use in environmental research. The optical detection may be preceded by chemical modification using immobilized enzymes or by purely chemical reaction with added reagents. Sensors ( " o p t r o d e s ' ) to measure oxygen and pH by fluorometric methods based on glass fiber optics have already been developed, and methods for analysis of several other chemical species of interest for ocean sciences will probably be developed. The methodological problem presently limiting the number of chemical species to be detected is the lack of suitable (preferably reversible) chemical reactions which result in fluorescence or light absorbance and which can take place in a microchamber at the tip of a microfiber.