Lorente E, Berrueco C, Herod AA, Millan M, Kandiyoti R. The detection of high-mass aliphatics in petroleum by matrix-assisted laser desorption/ionisation mass spectrometry.
RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2012;
26:1581-1590. [PMID:
22693113 DOI:
10.1002/rcm.6261]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
RATIONALE
The development of simplified procedures for isolating high-mass alkanes present in crude oils is described. The new procedures, which bypass the sample recovery step with hot toluene in the conventional alkane-isolation procedure, also provide an effective sample preparation route, prior to analysis by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS).
METHODS
Urea-alkane adducts are formed by mixing sample and urea solutions on chromatographic paper or silica-coated plates. Unreacted hydrocarbons are removed by developing the plates with chloroform. In a second development with water, adducts are broken up in situ and the liberated urea removed, leaving bands of isolated alkanes behind. For MALDI-MS, strips of paper/plates, carrying the isolated alkanes, are fixed on metal target plates. The samples are treated with matrix (AgNO(3)) and analysed by MALDI-MS.
RESULTS
The observed signal represents silver ion adducts of the isolated alkanes. Silver appears to work without much fragmentation and to generate whole silver adduct ions. Much improved MALDI-MS detection sensitivity and a wider range of masses was observed when samples were ablated from paper/plate surfaces, than by ablation from bulk samples spread over a smooth surface--the conventional method. Chromatographic paper gave better resolution and a broader range of masses than silica-coated plates.
CONCLUSIONS
The analytical sequences have been confirmed using standard alkanes (C(20)-C(60)) and Polywax. The proposed procedures enhanced the sensitivity and detection range of the MS analysis. The method was useful in detecting n-alkanes to m/z 1500 (C(100)) and required relatively small quantities of sample and reagents. It provides a promising qualitative analysis route for the rapid isolation and reliable determination of alkanes in crude oils.
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