Interfaces for liquid sample introduction for inductively coupled plasma-mass spectrometry and applications of elemental speciation with ICP-MS detection including arsenic in apples and selenium in dietary food supplements.

摘要

Liquid sample introduction with inductively coupled plasma-mass spectrometry (ICP-MS) can be a key issue in the development of separation techniques used for elemental speciation. A two-tube oscillating capillary nebulizer (OCN) was developed and evaluated for interfacing both high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The chief theoretical advantage of the OCN is in its low flow operation which makes it well suited for the ICP. A number of commercial nebulizers and spray chambers were compared to the developed OCN equipped with a single pass spray chamber; all nebulizers were compared using ion-pair HPLC conditions. Observed detection limits for arsenic compounds separated were 160 to 360 ppb for the OCN versus 2.0 to 11 ppb for the conventional nebulizer combinations using a small bore (2 mm ID) column. Also, a microbore (1 mm ID) column using a commercial micronebulizer produced low detection limits for the arsenic compounds.; Capillary electrophoresis is a low flow separation technique and is well suited for low flow nebulizers. All pneumatic nebulizers, however, have a problem with interfacing with CE. The aspiration generated by the nebulizer can greatly affect the flow rate through the capillary and compromise the CE separation. Different designs of CE OCN interfaces were tried using UV detection as a scouting technique. The use of a permeable frit in the sample side of the capillary was used to evaluate the OCN for possible ICP-MS interface. The novel concept of the fritted capillary was ultimately conducted on a more conventional micronebulizer.; The application of elemental speciation to actual samples not previously studied was performed. Freeze-dried apple samples were studied for trace levels of various arsenic compounds using ion-exchange HPLC interfaced to the ICP-MS. Total arsenic levels of three apple samples were determined, as well as an evaluation of extraction techniques used for speciation.; Finally, reversed-phase HPLC was used to study six different brands of yeast-based selenium dietary food supplements using ICP-MS detection. Although selenomethionine was the expected main component from yeast inoculated with selenium, only two of the brands of supplements showed high levels of selenomethionine. Two brands were found to contain high levels of inorganic selenium, and two brands had poor extraction results.