21 research outputs found
Solid-Phase Microextraction in Targeted and Nontargeted Analysis: Displacement and Desorption Effects
An aqueous multicomponent mixture
containing a wide range of volatility
and polarity compounds (log <i>K</i><sub>ow</sub> range
1.26â8.72) was used to clearly define the capabilities and
limitations of headspace solid-phase microextraction in quantification
of multicomponent complex samples. Commercially available fiber coatings
were evaluated by investigating the extraction efficiency and desorption
carryover. Comprehensive two-dimensional gas chromatography/time-of-flight
mass spectrometry was selected to map out the differences between
the coatings. The investigated components were chosen to represent
several homologous groups of metabolites most frequently present in
complex food and environmental samples, including straight-chain hydrocarbons,
primary alcohols, secondary alcohols, 2-ketones, aldehydes, ethyl
esters, and terpenes. Particular emphasis was placed on examination
of coating saturation and interanalyte displacements. These effects
were assessed by evaluating the linear dynamic range obtained for
spiked aqueous samples with divinylbenzene/Carboxen/polyÂ(dimethylsiloxane)
fiber. This coating was found to provide the optimum extraction coverage
and sensitivity for the widest range of analytes. Displacement investigations
were extended to apple homogenate characterized by high chemical diversity.
The results indicate that interanalyte displacements are infrequent
in the naturally occurring samples considered in this study. When
displacements take place, they tend to occur for analytes characterized
by small distribution constants, and they can be effectively detected
by adding such compounds to the sample and corrected by selecting
a shorter extraction time
Effect of Binding Components in Complex Sample Matrices on Recovery in Direct Immersion Solid-Phase Microextraction: Friends or Foe?
The
development of matrix compatible coatings for solid-phase microextraction
(SPME) has enabled direct extraction of analytes from complex sample
matrices. The direct immersion (DI) mode of SPME when utilized in
conjunction with such extraction phases facilitates extraction of
a wide range of analytes from complex matrices without the incurrence
of fouling or coating saturation. In this work, mathematical models
and computational simulations were employed to investigate the effect
of binding components present in complex samples on the recovery of
small molecules varying in logP for extractions carried out using
the direct immersion approach. The presented findings corroborate
that the studied approach indeed enables the extraction of both polar
and nonpolar analytes from complex matrices, provided a suitable sorbent
is employed. Further results indicated that, in certain cases, the
kinetics of extraction of a given analyte in its free form might be
dependent on the desorption kinetics of their bound form from matrix
components, which might lower total recoveries of analytes with high
affinity for the matrix. However, the binding of analytes to matrix
components also enables SPME to extract a balanced quantity of different
logP analytes, facilitated by multiphase equilibria, with a single
extraction device
Preparation of a Particle-Loaded Membrane for Trace Gas Sampling
A divinylbenzene (DVB) particle-loaded
membrane with high extraction
capacity was prepared using the bar coating method. The prepared membrane
was evaluated in terms of morphology, effect of particle ratio, and
membrane size on extraction efficiency, as well as linear calibration
curve and limit of detection. The SEM (scanning electron microscope)
images showed that the DVB particles were uniformly distributed in
the PDMS base, ensuring the repeatability of the membranes. The extraction
amount was quantified by gas chromatographyâmass spectrometry
coupled with a thermal desorption unit. Results showed that the extraction
efficiency of the prepared membrane increased about 2 orders of magnitude
for benzene sampling as the particle ratio increased from 0% to 30%,
and the extraction amount was linearly proportional to the size of
the membrane. A comparison with a pure PDMS membrane and DVB/PDMS
fiber for outdoor air sampling showed that the extraction efficiency
of the DVB/PDMS membrane was significantly enhanced, especially for
volatile and polar compounds. The limit of detection was about 0.03
ng/mL for benzene in air, and the linear dynamic range extended to
100 ng/mL. An equilibrium calibration method was proposed for low-level
air pollutant sampling using this high capacity membrane, and a displacement
effect was not observed. To demonstrate the power of the technique,
the developed approach was applied to monitor both spot and time weighted
average (TWA) concentrations of benzene in outdoor air. A high spot
concentration of benzene was observed in morning and afternoon rush
hours, with TWA concentrations of 10.7 ng/L measured over the 11-h
monitoring period
Reusable Solid-Phase Microextraction Coating for Direct Immersion Whole-Blood Analysis and Extracted Blood Spot Sampling Coupled with Liquid ChromatographyâTandem Mass Spectrometry and Direct Analysis in Real TimeâTandem Mass Spectrometry
Three different biocompatible polymers were tested and
evaluated
in order to improve the whole-blood biocompatibility of previously
developed C18âpolyacrylonitrile (C18âPAN) thin-film
solid-phase microextraction (SPME) coating. Among all methods of modification,
UV-dried thin PAN-over C18âPAN provided the best results. This
coating presented reusable properties and reproducible extraction
efficiency for at least 30 direct extractions of diazepam from whole
blood [relative standard deviation (RSD) = 12% using external calibration
and 4% using isotope dilution calibration]. The amount of absolute
recovery for direct immersion analysis and based on the free concentration
of diazepam in blood matrix was about 4.8% (desorption efficiency
= 98%). The limit of quantitation (LOQ) for the developed solid-phase
microextraction liquid chromatographyâtandem mass spectrometry
(SPME-LCâMS/MS) method for direct whole-blood analysis was
0.5 ng/mL. The optimized modification of the coating was then used
for an extracted blood spot (EBS) sampling approach, a new sampling
method which is introduced to address the limitations of dried blood
spot sampling. EBS was evaluated using LCâMS/MS and direct
analysis in real time (DART)âMS/MS, where, for a 5 ÎŒL
blood spot, LOQs of 0.2 and 1 ÎŒg/mL, respectively, were achieved
for extraction of diazepam
Sorbent Coated Glass Wool Fabric as a Thin Film Microextraction Device
A new approach for thin film microextraction (TFME) with
mixed-phase
sorptive coating is presented. Carboxen/polydimethylsiloxane (CAR/PDMS)
and polydimethylsiloxane/divinylbenzene (PDMS/DVB) TFME samplers were
prepared using spin coating and glass wool fabric mesh as substrate.
The samplers were easily tailored in size and shape by cutting tools.
Good durability and flat-shape stability were observed during extraction,
stirring in water, and thermal desorption. The latter characteristic
obviates the need for an extra framed holder for rapid TFME and makes
the samplers more robust and easier to deploy. The samplers combine
the advantages of adsorptive solid-phase microextraction (SPME) and
TFME, including one-step solvent-free extraction and preconcentration,
direct thermal desorption, and enhanced sensitivity without sacrificing
analysis time due to thin film geometry. The analytical performance
of these new devices was demonstrated using water samples spiked with
N-nitrosamines (NAs) as model compounds. Over an order of magnitude
enhancement of extraction efficiencies was obtained for the model
compounds compared with the SPME fibers of similar coatings and PDMS
thin film membrane. The results of this study indicate that these
novel thin film devices are promising for rapid and efficient microextraction
of polar analytes in water
Optimization of Fiber Coating Structure Enables Direct Immersion Solid Phase Microextraction and High-Throughput Determination of Complex Samples
This study presents a new approach for improving the
structure,
and hence the robustness, of the SPME fiber coating applied for gas
chromatography (GC) analysis. It involves application of an external
layer of polyÂ(dimethyl siloxane) (PDMS) over the commercial PDMS/divinyl
benzene (DVB) extraction phase. The fiber provided extraction capabilities
similar to that exhibited by the original PDMS/DVB fiber toward triazole
pesticides from water samples. Furthermore, the fiber could be utilized
for over 100 extractions in direct contact with a complex food matrix
such as whole grape pulp, with no sample pretreatment required. The
amount of extracted pesticides from whole grape pulp had RSD values
below 20% throughout 130 extraction/desorption/conditioning cycles,
which is a dramatic improvement when compared to commercial PDMS/DVB
fiber coating applied in food analysis facilitating high-throughput
automation
Direct Immersion Solid-Phase Microextraction with Matrix-Compatible Fiber Coating for Multiresidue Pesticide Analysis of Grapes by Gas ChromatographyâTime-of-Flight Mass Spectrometry (DI-SPME-GC-ToFMS)
A fast
and sensitive direct immersionâsolid-phase microextractionâgas
chromatographyâtime-of-flight mass spectrometry (DI-SPME-GC-ToFMS)
method for the determination of multiresidue pesticides in grapes
employing a PDMS-modified PDMS/DVB coating was developed utilizing
multivariate approaches for optimization of the most important factors
affecting SPME performance. A comprehensive investigation of appropriate
internal standards using a bottom-up approach led to the selection
of suitable compounds that adequately covered a range of 40 pesticides
pertaining to various classes. The validated method yielded good accuracy,
precision, and sensitivity and has been successfully applied to the
analysis of commercial samples. With regard to the limitations of
the proposed method, the DI-SPME method did not provide a satisfactory
performance toward more polar pesticides (e.g., acephate, omethoate,
dimethoate) and highly hydrophobic pesticides, such as pyrethroids.
Despite the challenges and limitations encountered by this method,
the practical aspects of the PDMS-modified coating demonstrated here
create new opportunities for SPME applied in food analysis
Development of a Carbon Mesh Supported Thin Film Microextraction Membrane As a Means to Lower the Detection Limits of Benchtop and Portable GC/MS Instrumentation
In
this work, a durable and easy to handle thin film microextraction
(TFME) device is reported. The membrane is comprised of polyÂ(divinylbenzene)
(DVB) resin particles suspended in a high-density polydimethylsiloxane
(PDMS) glue, which is spread onto a carbon fiber mesh. The currently
presented membrane was shown to exhibit a substantially lesser amount
of siloxane bleed during thermal desorption, while providing a statistically
similar extraction efficiency toward a broad spectrum of analytes
varying in polarity when compared to an unsupported DVB/PDMS membrane
of similar shape and size which was prepared with previously published
methods. With the use of hand-portable GC-TMS instrumentation, membranes
cut with dimensions 40 mm long by 4.85 mm wide and 40 ± 5 Όm
thick (per side) were shown to extract 21.2, 19.8, 18.5, 18,4, 26.8,
and 23.7 times the amount of 2,4 dichlorophenol, 2,4,6 trichlorophenol,
phorate D10, fonofos, chloropyrifos, and parathion, respectively,
within 15 min from a 10 ppb aqueous solution as compared to a 65 ÎŒm
DVB/PDMS solid phase microextraction (SPME) fiber. A portable high
volume desorption module prototype was also evaluated and shown to
be appropriate for the desorption of analytes with a volatility equal
to or lesser than benzene when employed in conjunction with TFME membranes.
Indeed, the coupling of these TFME devices to hand-portable gas chromatography
toroidial ion trap mass spectrometry (GC-TMS) instrumentation was
shown to push detection limits for these pesticides down to the hundreds
of ppt levels, nearing that which can be achieved with benchtop instrumentation.
Where these membranes can also be coupled to benchtop instrumentation
it is reasonable to assume that detection limits could be pushed down
even further. As a final proof of the concept, the first ever, entirely
on-site TFME-GC-TMS analysis was performed at a construction impacted
lake. Results had indicated the presence of contaminants such as toluene,
ethylbenzene, xylene, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate,
and trisÂ(1-chloro-2-propyl)Âphosphate, which stood out from other naturally
occurring compounds detected
Headspace versus Direct Immersion Solid Phase Microextraction in Complex Matrixes: Investigation of Analyte Behavior in Multicomponent Mixtures
This work aims to investigate the
behavior of analytes in complex
mixtures and matrixes with the use of solid-phase microextraction
(SPME). Various factors that influence analyte uptake such as coating
chemistry, extraction mode, the physicochemical properties of analytes,
and matrix complexity were considered. At first, an aqueous system
containing analytes bearing different hydrophobicities, molecular
weights, and chemical functionalities was investigated by using commercially
available liquid and solid porous coatings. The differences in the
mass transfer mechanisms resulted in a more pronounced occurrence
of coating saturation in headspace mode. Contrariwise, direct immersion
extraction minimizes the occurrence of artifacts related to coating
saturation and provides enhanced extraction of polar compounds. In
addition, matrix-compatible PDMS-modified solid coatings, characterized
by a new morphology that avoids coating fouling, were compared to
their nonmodified analogues. The obtained results indicate that PDMS-modified
coatings reduce artifacts associated with coating saturation, even
in headspace mode. This factor, coupled to their matrix compatibility,
make the use of direct SPME very practical as a quantification approach
and the best choice for metabolomics studies where wide coverage is
intended. To further understand the influence on analyte uptake on
a system where additional interactions occur due to matrix components, <i>ex vivo</i> and <i>in vivo</i> sampling conditions
were simulated using a starch matrix model, with the aim of mimicking
plant-derived materials. Our results corroborate the fact that matrix
handling can affect analyte/matrix equilibria, with consequent release
of high concentrations of previously bound hydrophobic compounds,
potentially leading to coating saturation. Direct immersion SPME limited
the occurrence of the artifacts, which confirms the suitability of
SPME for <i>in vivo</i> applications. These findings shed
light into the implementation of <i>in vivo</i> SPME strategies
in quantitative metabolomics studies of complex plant-based systems
Development of a Biocompatible In-Tube Solid-Phase Microextraction Device: A Sensitive Approach for Direct Analysis of Single Drops of Complex Matrixes
The
aim of the current study is to develop a sensitive solid-phase
microextraction (SPME) device for direct and rapid analysis of untreated
complex matrixes (i.e., single drop of the samples, <i>V</i> †2 ΌL). A thin layer of a biocompatible nanostructured
polypyrrole (PPy) was electrochemically deposited inside a medical
grade spinal needle, minimizing the matrix effect. Microsampling was
facilitated by loading the sample inside the in-tube SPME device (withdraw
of sample via plunger), where extraction was performed under static
conditions. Two strategies were used for analysis of the compounds
including offline desorption and running the extract to the liquid
chromatographâtandem mass spectrometer (LCâMS/MS) or
direct coupling of the in-tube SPME device to the MS. Given the high
surface-area-to-volume ratio of the coating, a short equilibrium time
(i.e., <i>t</i> †2 min) was obtained. The whole
analytical procedure (i.e., extraction, rinsing, desorption, and LCâMS/MS
analysis) was performed within 10 min by LCâMS/MS, and 3 min
by in-tubeâMS/MS. Possible matrix effects for the prepared device were evaluated in
whole blood samples at three levels of concentration, and encouraging
results were achieved in the range of 83â120%. The obtained
results, no matrix effect, are attributed to the smooth surface and
small pore size of the biocompatible PPy coating, which was prepared
in the presence of cetyltrimethylammonium bromide (CTAB) surfactant.
The in-tube SPME device was shown to be very sensitive, with high
total recoveries obtained for all compounds in phosphate-buffered
saline (PBS) and urine samples owing to the large volume and capacity
of the coating. Subnanogram per milliliter levels of detection were
achieved for urine samples, and low nanogram per milliliter levels
were found in whole blood samples for all studied compounds with a
high protein binding index. Rapid analysis of whole blood samples
was achieved without need of any pretreatment or manipulation of sample,
revealing the developed in-tube SPME device as an ideal probe for
forensic application, drug monitoring, and point-of care-diagnosis