Gas-phase ions of poly(dimethylsiloxane) oligomers were formed by electrospray ionization either by protonating them in solution with formic acid or by generating adducts of the oligomers with the metal ions Li + , Na + , K + , and Ag + as well as with the organic cations NH4 + , CH3CH2NH3 + , and protonated glycine, aspartic acid, and 1,2-diphenylethylamine. The collision-induced fragmentation of the oligomeric ions was strongly dependent on the nature of the charging species. Ag + adducts dissociated in a manner previously observed in secondary ion mass spectrometry experiments generating a series of linear and cyclic fragment ions, while Li + adducts fragmented to form two ions: an adduct of the metal ion with the oligomer end-group and one with the remaining oligomer. Na + and K + adducts simply dissociate to form the bare metal ion. The organic species, to varying extents, transfer the proton to the oligomer to form a protonated poly(siloxane) ion. These protonated oligomers then dissociate at very low laboratory-frame collision energy along the siloxane backbone by loss of a silanol. These backbone fragments can then lose a methyl group to form a second series of fragment ions. Suggestions for probable mechanistic pathways for these processes are presented.Résumé : On a observé la formation en phase gazeuse d'ions d'oligomères poly(diméthylsiloxane) lors de l'ionisation par électronébulisation d'oligomères protonés en solution avec de l'acide formique ou par la génération d'adduits des oligomè-res avec les ions métalliques Li + , Na + , K + et Ag + , les cations organiques NH 4 + , CH 3 CH 2 NH 2 + , ou les formes protonées de la glycine, de l'acide aspartique et de la 1,2-diphényléthylamine. La fragmentation induite par des collisions des ions oligomè-res dépend fortement de la nature des espèces utilisées pour les charger. Les adduits avec le Ag + se dissocient de la façon observée antérieurement lors d'expériences de spectrométrie de masse d'ions secondaires pour une série de fragments ioniques linéaires et cycliques alors que les adduits avec le Li + se fragmentent pour donner deux ions, un adduit de l'ion métal-lique avec la partie terminale de l'oligomère et un avec le reste de l'oligomère. Les adduits du Na + et du K + se dissocient simplement pour donner un ion métallique nu. Les espèces organiques transfèrent à des degrés variables le proton vers l'oligomère pour former un ion poly(siloxane) protoné. Sous l'influence d'énergie de collisions très faibles dans le cadre d'un laboratoire, les oligomères protonés se dissocient alors le long du squelette siloxane pour conduire à des pertes de silanol. Ces fragments de squelette peuvent alors perdre un groupe méthyle pour conduire à la formation d'une deuxième série de fragments ioniques. On présente des suggestions concernant les voies mécanistiques probables pour ces processus.Mots-clés : oligomères poly(diméthylsiloxane), acide aminé, bases, ions métalliques, spectrométrie de masse, dissociation induite par des collisions, voies de fragmentations.[Trad...

A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However, the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion. This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7-1.8 ϫ 10 Ϫ3 mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to demonstrate the propensity of this system to generate transition-metal anions, as well. (J Am Soc Mass Spectrom 2010, 21, 1944 -1946) © 2010 American Society for Mass Spectrometry T he chemical concept of metals producing positive ions (cations) and non-metals negative ions (anions) is a fundamental precept taught as early as in high school and reinforced throughout a person's university career. However, under certain conditions, metal anions can be created and, as such, their electron affinities are well characterized and calculated both experimentally and theoretically [1]. In solution, alkali metal anions (except lithium) in 'supra molecule complexes' have been prepared in THF and crown ethers. These characteristically blue solutions are now fabricated to control the amount of metal ions, including metal anions. Such solutions have been extensively studied for use in organic synthesis and elucidation of charge-transfer to solvent dynamics (CTTS) [2][3][4][5][6][7][8][9]. In the gas phase, a beam of positively charged alkali cations created from metal vapor can undergo double electron capture to generate a low density negative ion beam [10]. Other means of negative ion generation include discharge and sputter ion sources, namely Cs ϩ ions with a suitable metal cathode [11]. Studies in ion traps utilize dissociative electron attachment to create metal anions [12]. Thus, metal anions are created only via complex experimental procedures or specific experimental apparatus. This paper outlines a method for the production of metal anions requiring a simple oxalate salt solution and a commercially available triple quadrupole mass spectrometer.Oxalic acid is one of the oldest known acids, first isolated from wood sorrel (Oxalis acetosella). It is often found as salt oxalates in many biological systems; particular well known is calcium oxalate found in rhubarb root, known for both its medicinal properties and as a potential poison. Ammonium oxalate is found in guano and there is evidence for the sodium and potassium salts pres...