Development of a Novel Mass Spectrometric ... - Jacobs University
Development of a Novel Mass Spectrometric ... - Jacobs University
Development of a Novel Mass Spectrometric ... - Jacobs University
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Introduction<br />
products). Other molecules reacted by loss <strong>of</strong> methyl radical and two hydrogen<br />
molecules like 5-α-cholestane. This group applied the same LIAD/CpCo •+ CI<br />
method in another study for polyethylene (PE) samples with low molecular weight<br />
(200-655). 94 Later on Kenttamaa co-workers selected a less aggressive chemical<br />
ionisation reagent, the water cluster <strong>of</strong> Manganese cation, [ClMn(H 2 O) + ],<br />
combined with LIAD for examining a variety <strong>of</strong> hydrocarbons. 95 This ion was<br />
useful to ionise all types <strong>of</strong> hydrocarbons forming only one product ion<br />
[ClMn+M] + via water loss and without fragmentation. This latter method was<br />
described to be an efficient mass spectrometric method for the analysis <strong>of</strong><br />
branched saturated hydrocarbons forming exclusively pseudomolecular ions<br />
(adduct-H 2 O). Such ionisation was found better characterising than atmospheric<br />
pressure chemical ionisation (APCI) and ESI <strong>of</strong> nonpolar lipids and steroids as<br />
according to their observations. 96<br />
Another LIAD/ClMn(H 2 O) + method was applied for the analysis <strong>of</strong> base oils<br />
(major components <strong>of</strong> Lubricants). 88 The product ion [ClMn+M] + was the only ion<br />
representing each components (M) within the complex mixture <strong>of</strong> the base oil as<br />
shown in Scheme 1. The molecular weight distribution for base oil samples was<br />
found in the range <strong>of</strong> 350-600 Da.<br />
ClMn(H 2 O) + + M H<br />
2<br />
<br />
O<br />
<br />
[ClMn+M] +<br />
Scheme 1. Generation <strong>of</strong> adduct ions using LIAD/ClMn(H 2 O) +<br />
Coupling LIAD to APCI by kenttamaa’s group enabled the evaporation and<br />
ionisation <strong>of</strong> polar and nonpolar analytes yielding predominantly molecular ions<br />
with minor fragmentation using carbon disulfide (CS 2 ) as a reagent. 97 Protonated<br />
molecules (M+H) + were observed to be found in higher branching ratios when<br />
benzene was used as APCI reagent. The investigated compounds were structurally<br />
similar to those present in petroleum. Petroleum cuts were as a result analysed<br />
upon LIAD/APCI using nitrogen gas as the reagent. Explanations were elaborated<br />
according to the results <strong>of</strong> model mixture <strong>of</strong> the hydrocarbons. Just recently, an<br />
APCI/CS 2 method utilized by the same group demonstrated the production <strong>of</strong><br />
abundant stable molecular ion (M +• ) for nonpolar aromatic, polar aromatic and<br />
16