Evaluation of dicationic reagents for their use in detection of anions using positive ion mode ESI-MS via gas phase ion association

Abstract

Twenty-three different dications were investigated for their effectiveness in pairing with singly charged anions, thereby allowing the electrospray ionization mass spectrometry (ESI-MS) detection of anions as positively charged complexes. Nitrate, iodide, cyanate, monochloroacetate, benzenesulfonate, and perfluoro-octanoate were chosen as representative test anions as they differ in mass, size-to-charge ratio, chaotropic nature, and overall complexity. Detection limits were found using direct injection of the anion into a carrier liquid containing the dication. Detection limits are given for all six anions with each of the 23 dications. Each anion was easily detected at the ppb (g/L) and often the ppt (ng/L) levels using certain dicationic reagents. The ability of dicationic reagents to pair with anions and produce ESI-MS signals varied tremendously. Indeed, only a few dications can be considered broadly useful and able to produce sensitive results. Liquid chromatography (LC)-ESI-MS also was investigated and used to show how varying the dicationic reagent produced significantly different peak intensities. Also, the use of tandem mass spectrometry can lead to even greater sensitivity when using imidazolium based dications. (J

Novel Cyclic Sulfonium‐Based Ionic Liquids: Synthesis, Characterization, and Physicochemical Properties

“…Combining the ESI-MS results with the fact that these cyclic sulfonium [DCA] À and [NTf 2 ] À salts have lower viscosities and high conductivities (detailed discussions will be provided in the following sections), we think that they may be forming supramolecular clusters of lower nuclearity (in both positive and negative modes), as observed for the imidazolium salts in solution [39] or even in the gas phase.…”

“…[28,36] Undoubtedly, knowledge of the electrostatic interactions and supramolecular assembly behavior of ILs by atmosphericpressure chemical ionization mass spectrometry (APCI-MS) [37] atmospheric-pressure thermal desorption ion mass spectrometry (APTDI-MS), [38] and electrospray ionization mass spectrometry (ESI-MS), [39] will be of great value for understanding intrinsically the ionic nature of ILs, and is therefore fundamental to understanding their unique properties. Herein, experimental evidence resulting from ESI-MS studies is provided, giving important information about the structural organization of these cyclic sulfonium salts.…”

The evaluation and comparison of trigonal and linear tricationic ion-pairing reagents for the detection of anions in positive mode ESI-MS

“…The LOD for benzenedisulfonate both by SIM and SRM is the lowest for the five singly charged anions tested. In comparison to the SIM LOD for the dicationic reagents tested in a previous study [43], the LOD for benzenedisulfonate ranks second using LTC 1 as a pairing reagent. The LODs in this study for perfluorooctanate and mono- *Limit of detection determined where the amount of analyte used results in S/N ϭ 3.…”

“…chloroacetate are better than 7 to 8 (of 23) of the dicationic pairing reagents previously studied [43]. The ability of the tricationic reagents to pair with doubly and singly charged anions shows that the use of a single tricationic pairing reagent could be used to evaluate both monovalent and divalent anions simultaneously.…”

“…These trications have fairly rigid structures and provided detection sensitivity enhancement for many of the anions tested. Past results have indicated that rigid dicationic pairing agents did not work as well as more flexible dications [43], so a second class of tricationic reagents was developed. The second group of tricationic reagents is linear and more flexible [46].…”