Molecular Weight Distributions of Heavy Aromatic Petroleum Fractions by Ag⁺ Electrospray Ionization Mass Spectrometry

Abstract

The ability of electrospray ionization mass spectrometry (ESI MS) to analyze heavy aromatic petroleum fractions using silver nitrate as a reagent compound to form characteristic adduct ions has been examined. The complexation of aromatic compounds containing long alkyl substituents with the silver ion leads to the formation of abundant adduct ions such as [M + Ag]+ and [2M + Ag]+. The concentration of the [2M + Ag]+ ions can be reduced by increasing the sampling cone voltage. Molecular ions and other adduct ions may also be formed depending on the structure of the aromatic molecule. Results obtained from the analysis of representative heavy petroleum fractions and vacuum residues by the Ag+ ESI MS method and conventional ionization methods were in good agreement. The current method extends the applicability of electrospray ionization to the analysis of neutral hydrocarbons in heavy aromatic petroleum fractions. It is simple and compatible with widely available LC/MS instrumentation. The extreme complexity of the Ag

Anisole, a new dopant for atmospheric pressure photoionization mass spectrometry of low proton affinity, low ionization energy compounds

“…In some recent reports the ionization of non‐polar compounds was achieved by introducing a transition metal salt into the ESI source after HPLC separation, after which the analytes were usually detected as their metal ion adducts 12–16. The sensitivity for weakly polar and non‐polar analytes has been especially enhanced by the use of silver cations that attach to carbon–carbon double bonds.…”

Radical Cations in Electrospray Mass Spectrometry: Formation of Open‐Shell Species, Examination of the Fragmentation Behaviour in ESI‐MSn and Reaction Mechanism Studies by Detection of Transient Radical Cations

“…[16][17][18][19][20] Consequently, ESI of polar compounds is more a technique for efficient transfer of preformed solution-phase ions into the gas phase rather than a true ionization process in which neutral molecules are converted into ions. [4,9] An alternative ionization concept is demanded for ESI-MS of neutral, relatively apolar compounds, [21] such as hydrocarbon polyenes, [22][23][24] polycyclic aromatic hydrocarbons (PAHs), [25,26] porphyrins [27] and metalloporphyrins, [28] because these analytes lack basic or acidic sites amenable to solution-phase acid/base chemistry. [29] For the ionization of apolar but easily oxidizable compounds, electrochemical oxidation is relevant, since molecular radical cations of the corresponding analytes are frequently generated and observed in the positive-ion mode.…”

Quantitative aspects of and ionization mechanisms in positive-ion atmospheric pressure chemical ionization mass spectrometry

“…Gas chromatography (GC) and GC coupled with electron ionization (EI) mass spectrometry (GC/ MS) are normally employed for samples containing robust, thermally stable analytes [4,5]. Atmospheric pressure ionization methods [6]-electrospray ionization (ESI) [7], atmospheric pressure chemical ionization (APCI) [8], and atmospheric pressure photoionization (APPI) [9]-in conjunction with liquid chromatography (LC) have been used for samples of more problematic analytes.It is generally believed that ESI suffers more from nonlinear response and matrix effects than APCI. Linear response over a wide concentration range is an attractive feature of APCI and has been reported by several authors [10,11].…”

“…Gas chromatography (GC) and GC coupled with electron ionization (EI) mass spectrometry (GC/ MS) are normally employed for samples containing robust, thermally stable analytes [4,5]. Atmospheric pressure ionization methods [6]-electrospray ionization (ESI) [7], atmospheric pressure chemical ionization (APCI) [8], and atmospheric pressure photoionization (APPI) [9]-in conjunction with liquid chromatography (LC) have been used for samples of more problematic analytes.…”