A direct-injection high-efficiency nebulizer (DIHEN) is used to couple a thin-layer electrochemical flow cell on-line with an ICP-mass spectrometer to perform anodic stripping voltammetry (ASV) at a thin mercury film followed by subsequent ICPMS measurements for the stripped metal analytes. The resultant hyphenated technique (ASV-DIHEN-ICPMS) is capable of analyzing select heavy metals present at ultratrace levels (down to low-ppt to sub-ppt levels) that are lower than the detection limits obtained by conventional ICPMS. In addition to its good analytical performance, the technique offers other attractive features such as the ability to eliminate detrimental matrix effects that can compromise ICPMS analyses and the possibility of probing electrode reactions involving trace amounts metal species with ICPMS. For conducting ASV on-line with ICPMS, the DIHEN was found to be more advantageous than the microconcentric nebulizer in terms of minimizing memory effects and potential artifacts caused by the erosion of the Hg film into the flowing solution stream. Compared to a direct injection nebulizer (DIN), the DIHEN was easier to operate. Moreover, its simpler design and the lack of back pressure from the DIHEN capillary made it more compatible with coupling to the thin-layer electrochemical cell than a DIN system.
The dehydrogenation of ethylene on Pt(111) was studied by scanning tunneling microscopy (STM) under ultra-high vacuum conditions. Previous experiments have shown that thermal dehydrogenation following saturation exposure of ethylene on Pt(111) resulted in the formation of well-defined carbon clusters. The aggregation to form the carbon clusters leaves open Pt areas that could be available for additional adsorption. It had not been previously determined whether the adsorption and dehydrogenation of additional ethylene would lead to the growth of the initial clusters or the nucleation of additional clusters of the same size. The present study confirms previous reports that the initial carbon clusters are 15 ( 2 Å in diameter, 2.5 ( 0.3 Å in height, and contain an average of 34 ( 9 carbon atoms per cluster. We show that exposing this surface to additional ethylene at room temperature and annealing leads to an increase in the number of particles of the same size, with no growth in size of the initial particles. Dosing and dehydrogenation/annealing cycles were repeated until the dehydrogenation activity of the Pt(111) surface was completely suppressed, which occurred after the fourth such cycle. Continued cycling leads to the beginning of the formation of a graphite adlayer on the platinum, presumably via agglomeration of the clusters at a high cluster density.
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