Beiträge zur Chemie des Selens und seiner Verbindungen

Determination of selenite, selenate and selenocyanate in waters by ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS)

“…The chromatographic gradient (depicted in Fig. 2 and listed in Table 1) consists of three parts: during the first 4 min, Se(IV) is separated from Se(VI) by isocratic elution at 17.5 mmol L 21 NaOH, then SeCN is pushed off the column with 100 mmol L 21 NaOH from 4 to 12 min, and finally the column is re-equilibrated for the next analysis with 17.5 mmol L 21 NaOH from 12 to 15 min. The two major novel features of this separation are the use of the AS-16 column (Dionex) with a hydroxide eluant, and an uncommonly large injection volume of 1 mL.…”

“…Based on the optimized HBr concentration for the Se(VI) prereduction, we then determined the borohydride addition required for quantitative hydride generation from Se(IV), while sustaining the AFS flame independently with an external H 2 -stream of 45 mL min 21 . A dilute solution of KBH 4 (1% w/w~0.185 mol L 21 ) in 0.1 mol L 21 NaOH was used for this optimization (range 0.5-4 mL min 21 ), because it is stable for several days when stored in glass containers. In any kind of tested plastic container, the autocatalytic decomposition of BH 4…”

“…In this experiment, sensitivity for a given Se(IV) concentration appeared to decrease slowly at borohydride flow rates v2 mL min 21 , so the flow was set to 2.5 mL min 21 to assure robustness. To eliminate the possibility that this result was affected by changes in detection sensitivity caused by varying H 2 -concentration in the AFS flame, we performed the control experiment, in which the borohydride flow rate was kept constant (2.5 mL min 21 ), and H 2 was added to the flame (0-100 mL min 21 ).…”

“…In this experiment, sensitivity for a given Se(IV) concentration appeared to decrease slowly at borohydride flow rates v2 mL min 21 , so the flow was set to 2.5 mL min 21 to assure robustness. To eliminate the possibility that this result was affected by changes in detection sensitivity caused by varying H 2 -concentration in the AFS flame, we performed the control experiment, in which the borohydride flow rate was kept constant (2.5 mL min 21 ), and H 2 was added to the flame (0-100 mL min 21 ). Since the HG reaction is essentially instantaneous, 18 the reaction loop was designed just long enough to allow cooling of the prereduction mixture below room temperature, which minimizes water vapor that needs to be removed by the dryer membrane.…”

“…Inductively-coupled plasma-mass spectrometry (ICP-MS) is the only common detector that can be coupled directly to LC separations for measuring Se speciation at environmental levels. IC-ICP-MS achieves detection limits around 0.5 mg L 21 for Se(IV) and Se(VI), 7 but problems arise with the compensation of isobaric interferences from argon, chlorine, bromine and sulfur species; these effects are discussed in detail elsewhere. 17 Other potential detectors, including atomic absorption spectrometry (AAS), 15,16 atomic fluorescence spectrometry (AFS) 8,10 and inductively-coupled plasma-optical emission spectrometry (ICP-OES), 15 need to be coupled to the LC separation via hydride generation (HG) in order to be matrix-compatible, but only HG-AFS yields competitive detection limits in comparison to ICP-MS. 8,10 Coupling LC to ICP-MS via HG 16 should remove most spectroscopic interferences and lower detection limits significantly, but eliminates the principal advantage of using ICP-MS as a universal detector for every imaginable Se species.…”