Selected ion flow-drift tube, SIFDT, study of reactions of H3O and NO with primary alcohols in the presence of water vapour under variable collisional energies.

Abstrakt

Alcohols are often present in foods and other biological media including exhaled breath, urine and cell culture headspace. Their analysis by chemical ionisation techniques such as SIFT-MS, PTR-MS and SIFDT-MS relies on the ion chemistry initiated by the reactions of the reagent ions H3O+ and NO+ with alcohol molecules in the presence of water molecules.

Kinetics of such reactions needs to be understood and quantitatively described to facilitate reliable quantitative calculation of absolute concentrations of alcohols in humid air samples. The reactions of H3O+ and NO+ ions have been studied with the primary alcohol molecules in SIFDT analyses (2 mbar He; 0.08 mbar air sample; 300 K; reduced field strength E/N up to 28 Td) and over a range of sample gas humidity up to 5.5%.

The H3O+ reactions leads to the formation of protonated alcohol molecules MH+ and (MH+H2O) fragments. The NO+ reactions result in the (M-H)+ product ions.

These primary product ions hydrate to MH+(H2O)1,2,3 and (M-H)+(H2O)1,2,3. The variation of the percentages of the hydrated product ions with E/N and with the air sample humidity is studied.

The experimental results are compared with a reaction system kinetics model based on numerical solution of a complete set of differential equations describing the ion chemistry. The data resulting from this study including the secondary hydrated ion product distributions will facilitate analyses of alcohol vapours in various media