<p>Reactions
carried out in the presence of rubber septa run the risk of additives being
leached out by the solvent. Normally, such species are present at low enough
levels that they do not interfere with the reaction significantly. However,
when studying reactions using sensitive methods such as mass spectrometry, the
appearance of even trace amounts of material can confuse dynamic analyses of
reactions. A wide variety of additives are present in rubber along with the
polymer: antioxidants, dyes, detergent, and vulcanization agents, and these are
all especially problematic in negative ion mode. A redesigned Schlenk flask for
pressurized sample infusion (PSI) is presented as a means of practically
eliminating the presence of contaminants during reaction analyses.</p>
Spectral results are presented illustrating the capability of electrospray mass spectrometry (ES-MS) for the determination of the composition of solution samples. The solution components that can be determined include the elemental and molecular forms of anions and cations. Three modes of positive-ion ES-MS are described: the ion cluster mode, the metal-ion mode, and an intermediate mode. The modes are established by operating the electrospray source at specific voltages and curtain gas flow rate values, and each mode provides a unique mass spectral picture of the solution components with primary focus on cationic species (i.e., metal ions). Results are also presented for operation of the electrospray source in negative-ion mode. In this mode both elemental anions (i.e., halides) and molecular anions (i.e., oxo-anions) can be determined.
Capillary zone electrophoresis (CZE) paired with mass spectrometry (MS) is a powerful analytical technique for examining mixtures of ionic analytes such as glycosaminoglycans. This study examines the mechanics of the electrospray process for a sheath flow CZE-MS interface under reverse polarity negative ionization conditions. Liquid flow in a sheath flow nano-electrospray CZE-MS interface is driven by two mechanisms, electroosmotic flow and electrospray nebulization. The contribution of these two processes to the overall flow of solution to the electrospray tip is influenced by the surface coatings of the sheath flow emitter tip and by the solvent composition. We have investigated the application of this interface to the reverse polarity separation of glycosaminoglycans and find that the role of electroosmotic flow is far less than has been reported previously, and the electrospray process itself is the largest contributor to the flow of the sheath liquid.
A comparative study of the fragmentation of neutral lactooligosaccharides in negative-ion mode by UV-MALDI-TOF and UV-MALDI ion-trap/TOF mass spectrometry