HPLC/APCI Mass Spectrometry of Saturated and Unsaturated Hydrocarbons by Using Hydrocarbon Solvents as the APCI Reagent and HPLC Mobile Phase

Abstract

Saturated and unsaturated, linear, branched, and cyclic hydrocarbons, as well as polyaromatic and heteroaromatic hydrocarbons, were successfully ionized by atmospheric pressure chemical ionization (APCI) using small hydrocarbons as reagents in a linear quadrupole ion trap (LQIT) mass spectrometer. Pentane was proved to be the best reagent among the hydrocarbon reagents studied. This ionization method generated different types of abundant ions (i.e., [M + H] , with little or no fragmentation. The radical cations can be differentiated from the even-electron ions by using dimethyl disulfide, thus facilitating molecular weight (MW) determination. While some steroids and lignin monomer model compounds, such as androsterone and 4-hydroxy-3-methoxybenzaldehyde, also formed abundant M +• and [M+H] + ions, this was not true for all of them. Analysis of two known mixtures as well as a base oil sample demonstrated that each component of the known mixtures could be observed and that a correct MW distribution was obtained for the base oil. The feasibility of using this ionization method on the chromatographic time scale was demonstrated by using high-performance liquid chromatography (HPLC) with hexane as the mobile phase (and APCI reagent) to separate an artificial mixture prior to mass spectrometric analysis.

The unexpected formation of [M − H]+species during MALDI and dopant-free APPI MS analysis of novel antineoplastic curcumin analogues

“…+ ions was significantly reported with alkanes during chemical ionization (CI) [14,15] and APCI-MS. [3] Subsequently, [M À H] + ion formation has been detected with a wide range of compounds with various ionization techniques, such as ESI, [16,17] MALDI, [18][19][20][21][22] APPI, [23] desorption APPI, [24] desorption ESI [24] and direct analysis in real time. [25] Several mechanisms have been proposed to explain the formation of [M À H] + during MS-analysis that could be summarized into three main mechanisms: (1) loss of hydrogen molecule from the protonated [M + H] + ion, (2) hydrogen transfer from the analyte radical cation or (3) hydride abstraction from the neutral analyte molecule [14][15][16][17][18][19][20][21][22][23][26][27][28] (Scheme 4).…”

The formation of [M–H]+ ions in N‐alkyl‐substituted thieno[3,4‐c]‐pyrrole‐4,6‐dione derivatives during atmospheric pressure photoionization mass spectrometry

“…As a general trend, TPD derivatives with the N ‐alkyl side chain C n H 2n+1 (n ≥4) favored the formation of [M–H] + ions under APPI conditions. This phenomenon is also common for alkanes …”

“…This phenomenon is also common for alkanes. [12][13][14][15] (Fig. 7) exhibited a completely different fragmentation pattern compared to the MS/MS fragmentation of [M + H] + ions generated from the same molecules as shown in Fig.…”

“…[8,9] Intriguingly, during the analysis of some N-alkyl-substituted thieno [3,4- ] + ions were first observed with alkylamines during chemical ionization (CI), due to the abstraction of hydride ions by reactant ions. [10,11] More recently, the formation of [M-H] + ions has been identified as a typical reaction when alkanes are observed during desorption atmospheric pressure photoionization (DAPPI), [12] atmospheric pressure chemical ionization (APCI), [13,14] and direct analysis in real time. [15] In addition, secondary and tertiary amines have been reported to form [M-H] + ions that correspond to dehydrogenation in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS).…”

Direct Detection of Inorganic Nitrate Salts by Ambient Pressure Helium-Plasma Ionization Mass Spectrometry

“…19 It is a simple adaptation that enables any conventional electrospray ionization mass spectrometer to be converted to a helium-plasma instrument by passing high-purity helium gas through the sample delivery metal tube. 18 When a high potential is applied to the capillary, a zone of plasma is observed at the tip of the tube.…”