Ketalization of phosphonium ions by 1,4-dioxane: Selective detection of the chemical warfare agent simulant DMMP in mixtures using ion/molecule reactions

Abstract

Phosphonium ions CH3P(O)OCH3+ (93 Th) and CH3OP(O)OCH3+ (109 Th) react with 1,4-dioxane to form unique cyclic ketalization products, 1,3,2-dioxaphospholanium ions. By contrast, a variety of other types of ions having multiple bonds, including the acylium ions CH3CO+ (43 Th), CH3OCO+ (59 Th), (CH3)2NCO+ (72 Th), and PhCO+ (105 Th), the iminium ion H2C=NHC2H5+ (58 Th) and the carbosulfonium ion H2C=SC2H5+ (75 Th) do not react with 1,4-dioxane under the same conditions. The characteristic ketalization reaction can also be observed when CH3P(OH)(OCH3)2+, viz. protonated dimethyl methylphosphonate (DMMP), collides with 1,4-dioxane, as a result of fragmentation to yield the reactive phosphonium ion CH3P(O)OCH3+ (93 Th). This novel ion/molecule reaction is highly selective to phosphonium ions and can be applied to identify DMMP selectively in the presence of ketone, ester, and amide compounds using a neutral gain MS/MS scan. This method of DMMP analysis can be applied to aqueous solutions using electrospray ionization; it shows a detection limit in the low ppb range and a linear response over the range 10 to 500 ppb. © 2003 American Society for Mass Spectrometry.