71 research outputs found
Towards a universal detector for small molecule application: Direct-EI in LC-MS.
This article describes the operating principles of the direct-electron
ionization (EI) interface, which is becoming more popular in many LC-MS
applications. Matrix effects and the role of direct-EI as a universal detector
for small molecule analysis are also discussed in detail. The advantages
and drawbacks of this approach are described and a comparison with
atmospheric pressure ionization (API) interfaces is made. The potential of
direct-EI is illustrated with a selection of practical applications
Profiling of non-esterified fatty acids in human plasma using liquid chromatography-electron ionization mass spectrometry
This paper focuses on the development of a
novel approach to analyze underivatized fatty acids in
human plasma. The method is based on liquid–liquid
extraction followed by reversed phase liquid chromatography
coupled to direct-electron ionization mass spectrometry
(LC-Direct-EI-MS). The assay is validated. Calibrations
show satisfactory linearity and precision in the investigated
range of linearity. Recoveries span from 75% to 104%. The
method limits of detection, varying from 0.53 to 5.35 μM,
are satisfactory for the quantitation of non-esterified fatty
acids (NEFAs) in plasma at physiological levels. The
method has been successfully applied to the NEFAs
profiling of plasma samples from healthy adult volunteers
and subjects affected by diabetes mellitus. Compared with
published protocols based on gas chromatography–mass
spectrometry and liquid chromatography coupled to electrospray
ionization mass spectrometry, this method does not
require derivatization and does not show matrix effects,
thus simplifying sample preparation procedure and reducing
the total time of analysis to approximately 90 min. In
addition, Direct-EI-MS allows the acquisition of highquality
NIST library-matchable EI spectra, allowing an
easy-to-obtain identification of the target NEFAs
AN OVERVIEW OF MATRIX EFFECTS IN LIQUID CHROMATOGRAPHY–MASS SPECTROMETRY
Matrix-dependent signal suppression or enhancement represents
a major drawback in quantitative analysis with liquid
chromatography coupled to atmospheric pressure ionization
mass spectrometry (LC–API-MS). Because matrix effects (ME)
might exert a detrimental impact on important method
parameters (limit of detection, limit of quantification, linearity,
accuracy, and precision), they have to be tested and evaluated
during validation procedure. This review gives a detailed
description on when these phenomena might be expected, and
how they can be evaluated. The major sources of ME are
discussed and illustrated with examples from bioanalytical,
pharmaceutical, environmental, and food analysis. Because
there is no universal solution for ME, the main strategies to
overcome these phenomena are described in detail. Special
emphasis is devoted to the sample-preparation procedures as
well as to the recent improvements on chromatographic and
mass spectrometric conditions. An overview of the main
calibration techniques to compensate for ME is also presented.
All these solutions can be used alone or in combination to
retrieve the performance of the LC–MS for a particular
matrix–analyte combination
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