22 research outputs found
Profiling of non-esterified fatty acids in human plasma using liquid chromatography-electron ionization mass spectrometry
No full textThis 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
No full textMatrix-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
Organochlorine Pesticides by LC-MS
No full textContamination of water resources by organochlorine pesticides (OCPs) continues to receive widespread attention because of the increasing concern regarding their high persistence and bioaccumulation. These organic pollutants are not amenable by liquid chromatography (LC) coupled to atmospheric pressure ionization-mass spectrometry, which represents the method of choice for the characterization of pesticide residues in water. Gas chromatography-mass spectrometry provides excellent response for OCPs, but it falls short when complex, multiresidue analyses are required. As recently demonstrated, an efficient EI-based LC-MS interface can generate very good spectra for an extremely wide range of small-medium molecular weight molecules of different polarity and can represent a valid tool in solving the analytical challenge of analyzing OCPs by LC-MS. Based on this assumption, we present a new approach for the determination of 12 OCPs in water samples. The method requires a solid-phase extraction preconcentration step followed by nanoscale liquid chromatography coupled to a direct-electron ionization direct interface (Direct-EI). Direct-EI is a miniaturized interface for efficiently coupling a liquid chromatograph with an EI mass spectrometer. The capability to acquire high-quality EI spectra in a wide range of concentrations, and to operate in selected ion monitoring mode during analyses, allowed a precise quantification of the OCPs. Without sample injection enrichment, limits of detection of the method span from 0.044 to 0.33 íg/L, corresponding to an instrumental detection limit of 120-850 pg. In addition, a careful evaluation of the matrix effect showed that the response of the Direct-EI interface was never affected by sample interferences. From our knowledge, the proposed method represents the first application of LC-MS in the analysis of organochlorine pesticides
Single-Step LC/MS Method for the Simultaneous Determination of GC-Amenable Organochlorine and LC-Amenable Phenoxy Acidic Pesticides.
No full textWater pollution by organochlorine pesticides (OCPs) is considered as an analytical challenge, since these persistent and nonbiodegradable pollutants are not amenable by liquid chromatography coupled to atmospheric pressure ionization mass spectrometry (LC/API-MS). This represents a significant constraint in multiresidue analysis of real samples, when high polar, poorly volatile compounds are present as well. This paper reports the development of an innovative single-step method for the simultaneous determination of OCPs and polar pesticides belonging to the class of phenoxy acids in water samples. The method is based on an off-line solid-phase extraction (SPE) procedure with Carbograph 4 followed by liquid chromatography coupled to a direct electron ionization mass spectrometer (LC/direct-EI-MS). The direct-EI capability of acquiring high-quality EI spectra and operation in selected ion monitoring mode allowed a precise quantification of OCPs and phenoxy acids in a single chromatographic run without derivatization. The instrumental response was characterized by excellent sensitivity, linearity, and precision. The SPE recovery rates in river water gave values equal or better than 80% for most of the compounds. The method limits of detection (LODs) span from 0.002 to 0.052 μg/L, allowing the detection of the selected pesticides at the limits required by the European Union (EU) legislation for drinking water
Advanced liquid chromatography-mass spectrometry interface based on electron ionization
No full textMajor progress in interfacing liquid chromatography and
electron ionization mass spectrometry is presented. The
minimalism of the first prototype, called the Direct-EI
interface, has been widely refined, improved, and applied
to modern instrumentation. The simple interfacing principle
is based on the straight connection between a
nanoHPLC system and a mass spectrometer equipped
with an EI source forming a solid and reliable unicum
resembling the immediacy and straightforwardness of GC/
MS. The interface shows a superior performance in the
analysis of small-medium molecular weight compounds,
especially when compared to its predecessors, and a
unique trait that excels particularly in the following
aspects: (1) It delivers high-quality, fully library matchable
mass spectra of most sub-1 kDa molecules amenable
by HPLC. (2) It is a chemical ionization free interface
(unless operated intentionally) with accurate reproduction
of the expected isotope ion abundances. (3) Response is
never influenced by matrix components in the sample or
in the mobile phase (nonvolatile salts are also well
accepted). A deep evaluation of these aspects is presented
and discussed in detail. Other characteristics of the
interface performance such as limits of detections, range
of linear response, and intra- and interday signal stability
were also considered. The usefulness of the interface has
been tested in a few real-world applications where matrix
components played a detrimental role with other LC/MS
techniques
Towards a universal detector for small molecule application: Direct-EI in LC-MS.
No full textThis 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
A new liquid chromatography–mass spectrometry approach for generic screening and quantitation of potential genotoxic alkylation compounds without derivatization
No full textOne of the crucial tasks of pharmaceutical industry is to quantify the potential genotoxic impurities (PGIs)
coming from the process of drug production. The European Medicines Agency (EMEA) imposes analytical
testing limits in the order of g/g, depending on drug dosage and exposure period, that means the need of
a sensitive and selective method of analysis. Liquid chromatography coupled to electrospray ionization
mass spectrometry (LC–ESI-MS) has been demonstrated as the most versatile approach to detect PGIs in
complex matrices. However, time consuming derivatization processes are needed to enhance sensitivity
and selectivity, and to overcome matrix effects (ME) that may arise from active pharmaceutical ingredients
(APIs) or excipients. We propose the use of the Direct-EI LC–MS as an alternative approach to detect
and quantify PGIs in drug formulations. The Direct-EI LC–MS interface is based on electron ionization (EI)
which is well suited for the detection of low molecular weight compounds of different polarity, without
derivatization and with no sign of ME. The method has been successfully applied to the detection of PGIs
belonging to the class of alkylation agents. Calibration experiments show satisfactory linearity and precision
data. Recoveries in low enriched samples spanned from 55 to 82%, and were not affected by ME. The
method limits of detection (LODs), varying from 0.13 to 1.5 g/g, were satisfactory for the quantitation
of the target PGIs at the level required by regulatory agencies
Determination of natural pyrethrins by liquid chromatography-electron ionisation-mass spectrometry.
No full textIntroduction – Pyrethrum extract is a mixture of six insecticidal compounds from the flower heads of Chrysanthemum cinerariaefolium
L.. Since they only have low to moderate mammalian toxicity they can be used as natural insecticides in agriculture
or to develop low cost and safe dermatological formulations. Because of the thermal instability of pyrethrins, analytical
methods based on liquid chromatography (LC) are preferred over those based on gas chromatography (GC). A few applications
using LC with mass spectrometry detection are presented in the literature. Current protocols for their characterisation
by LC rely on the use of less sophisticated detectors such as UV detection.
Objective – To develop the first liquid chromatography‐electron ionisation‐mass spectrometry (LC‐EI‐MS) method for pyrethrins
detection and quantitation in pyrethrum extracts.
Methodology – A commercial pyrethrum extract and various samples of flower heads from C. cinerariaefolium L. were investigated
using reversed‐phase nano‐liquid chromatography coupled to direct electron ionisation‐mass spectrometry (nanoLCdirect
EI‐MS). The eluted compounds were identified through searches of the US National Institute of Standards and
Technology (NIST) library, exploiting the direct EI capability to produce high quality EI mass spectra.
Results – The method demonstrated satisfactory sensitivity (limit of detection (LOD) range: 0.04–0.38 mg/g), linearity (R2
range: 0.9740–0.9983) and precision (RSD% range: 4–13%) for the quantitation of the natural pyrethrins in extracts from
C. cinerariaefolium L.
Conclusion – The nanoLC‐direct EI‐MS technique can be a useful tool for the detection of pyrethrins
DIRECT-EI IN LC-MS: TOWARDS A UNIVERSAL DETECTOR FOR SMALL-MOLECULE APPLICATIONS
No full textThis review article will give an up-to-date and exhaustive
overview on the efficient use of electron ionization (EI) to
couple liquid chromatography and mass spectrometry (LC–
MS) with an innovative interface called Direct-EI. EI is based
on the gas-phase ionization of the analytes, and it is suitable for
many applications in a wide range of LC-amenable compounds.
In addition, thanks to its operating principles, it prevents
unwelcome matrix effects (ME). In fact, although atmospheric
pressure ionization (API) methodologies have boosted the use of
LC–MS, the related analytical methods are sometime affected
by inaccurate quantitative results, due to unavoidable and
unpredictable ME. In addition, API’s soft ionization spectra
always demand for costly and complex tandem mass spectrometry
(MS/MS) instruments, which are essential to acquire an
‘‘information-rich’’ spectrum and to obtain accurate quantitative
information. In EI a one-stage analyzer is sufficient for a
qualitative investigation and MS/MS detection is only used to
improve sensitivity and to cut chemical noise. The technology
illustrated here provides a robust and straightforward access
to classical, well-characterized EI data for a variety of
LC applications, and readily interpretable spectra for a wide
range of areas of research. The Direct-EI interface can
represent the basis for a forthcoming universal LC–MS
detector for small molecules
