Proton transfer reaction mass spectrometry investigations on the effects of reduced electric field and reagent ion internal energy on product ion branching ratios for a series of saturated alcohols

In this paper we report an investigation of the effects of E/N over the range of 90-140Td on the product ions resulting from the reactions of H3O+ with 12 saturated alcohols using a proton transfer reaction mass spectrometer (PTR-MS). The alcohols included in this study are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 2-butanol, cyclopentanol, 1-pentanol, cyclohexanol, and 1-hexanol. Only in the cases of methanol and ethanol are any substantial amounts of the protonated parent observed at any E/N. For the other saturated alcohols predominantly fragment ions are observed. This implies that attempts to identify and hence monitor saturated alcohols in trace concentrations in a complex chemical environment using PTR-MS will be fraught with difficulties because a given m/z will not be unique to a particular chemical compound, i.e., multiple species could be present at a given m/z. In addition to changes in E/N we present preliminary results with regards to changing the conditions in the generation of the reagent ions via altering the operational conditions within the ion source (a hollow cathode). We present product ion branching ratios as a function of hollow cathode emission current for cyclohexanol, 1-propanol and 2-propanol at fixed E/N. Although not part of the reaction chamber, we have found that changing the hollow cathode emission current results in modifications to the product ion branching ratios. We presume that these observed changes are a result of altering the internal energies of the reagent ions and thereby modify the reaction kinetics and dynamics occurring within the drift tube of a PTR-MS. (C) 2010 Elsevier B.V. All rights reserved.