Non-linear effects in the determination of paleotemperature U 37k′ alkenone ratios by chemical ionization mass spectrometry

R. Chaler, J. Villanueva, Joan O. Grimalt

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8 Citations (Scopus)

Abstract

The performance of gas chromatography coupled to mass spectrometry in the positive chemical ionization mode using ammonia as reagent gas (GC-PCI-MS) in the analysis of C37 alkenones for paleotemperature estimation has been re-evaluated. In some conditions, the discrepancies observed in the measurement of the U37k′ index with this technique as compared with GC equipped with flame ionization detection (GC-FID) cannot be explained by differences in sensitivity between the tri- and diunsaturated alkenones. Thus, at low (currently <0.3) or high (currently >0.4) U 37k′ values the GC-PCI-MS determinations may be observed to be lower or higher, respectively, than those measured with GC-FID. As shown by analysis of a series of synthetic C37 alkenone standards these discrepant results can be explained by non linear effects in the GC-PCI-MS response factors. Second-order polynomial functions provide equations that describe better the signal to amount of analyte ratios. Users of GC-PCI-MS should calibrate their instruments with standards of known C37 alkenone composition in order to minimize non-linear effects.

Original languageEnglish
Pages (from-to)87-93
Number of pages7
JournalJournal of Chromatography A
Volume1012
Issue number1
DOIs
Publication statusPublished - 12 Sept 2003

Keywords

  • Alkenones
  • Geochemistry
  • Ketones
  • Paleotemperature
  • U index

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