Microextraction By Packed Sorbent Research Articles

Application of Fe3O4@TbBd nanobeads in microextraction by packed sorbent (MEPS) for determination of BTEXs biomarkers by HPLC–UV in urine samples

A relatively new adsorbent based on covalent organic frameworks (COFs) was employed for the first time to extract and determine Trans, trans-muconic acid (tt-MA), Mandelic acid (MA), Hippuric acid (HA), and 3-Methylhippuric acid (m-MHA) in urine. For this purpose, microextraction was performed using the packed sorbent (MEPS) method. Following the extraction process, the prepared samples were specified via the high-performance liquid chromatography-ultraviolet detector system. The precipitation polymerization was applied to synthesize the Fe3O4@TbBd nanobeads, and the morphological and dimensional structures of the products were specified with FE-SEM images. Some key variables affecting the extraction efficiency (i.e., sample volume, elution volume, condition and washing solvents, type and volume of elution solvent, extraction cycles, temperature, and pH of the sample solution) were investigated. In ideal conditions, the limit of detection (LOD) was obtained from 0.02 µg/ml for tt-MA to 0.5 µg/ml for MA. Calibration curves (at five-point) were plotted in the range 0.05–5 µg/ml for tt-MA to 1–300 µg/ml for MA (R2 > 0.98). Moreover, intra- and inter-day precision values were 3.1–5.5 and 4.6–9.8%, respectively. The developed method was successfully employed to determine four analytes in three concentrations (low, medium, and high QCs). The results showed a satisfactory recovery (70–87%). COF-MEPS technique is a rapid, easy, user-friendly, and environment-friendly method for separating the minimum values of all BTEXs chief biomarkers from urine samples without using complicated processes and only with one adsorbent. Also, it can be a good alternative for biomonitoring the workers exposed to BTEX compounds in occupational and environmental access.

Novel Applications of Microextraction Techniques Focused on Biological and Forensic Analyses

In recent years, major attention has been focused on microextraction procedures that allow high recovery of target analytes, regardless of the complexity of the sample matrices. The most used techniques included liquid-liquid extraction (LLE), solid-phase extraction (SPE), solid-phase microextraction (SPME), dispersive liquid-liquid microextraction (DLLME), microextraction by packed sorbent (MEPS), and fabric-phase sorptive extraction (FPSE). These techniques manifest a rapid development of sample preparation techniques in different fields, such as biological, environmental, food sciences, natural products, forensic medicine, and toxicology. In the biological and forensic fields, where a wide variety of drugs with different chemical properties are analyzed, the sample preparation is required to make the sample suitable for the instrumental analysis, which often includes gas chromatography (GC) and liquid chromatography (LC) coupled with mass detectors or tandem mass detectors (MS/MS). In this review, we have focused our attention on the biological and forensic application of these innovative procedures, highlighting the major advantages and results that have been accomplished in laboratory and clinical practice.

Solventless Microextration Techniques for Pharmaceutical Analysis: The Greener Solution.

Extensive efforts have been made in the last decades to simplify the holistic sample preparation process. The idea of maximizing the extraction efficiency along with the reduction of extraction time, minimization/elimination of hazardous solvents, and miniaturization of the extraction device, eliminating sample pre- and posttreatment steps and reducing the sample volume requirement is always the goal for an analyst as it ensures the method’s congruency with the green analytical chemistry (GAC) principles and steps toward sustainability. In this context, the microextraction techniques such as solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), microextraction by packed sorbent (MEPS), fabric phase sorptive extraction (FPSE), in-tube extraction dynamic headspace (ITEX-DHS), and PAL SPME Arrow are being very active areas of research. To help transition into wider applications, the new solventless microextraction techniques have to be commercialized, automated, and validated, and their operating principles to be anchored to theory. In this work, the benefits and drawbacks of the advanced microextraction techniques will be discussed and compared, together with their applicability to the analysis of pharmaceuticals in different matrices.

Determination of Benzophenones in Water and Cosmetics Samples: A Comparison of Solid-Phase Extraction and Microextraction by Packed Sorbent Methods.

Benzophenones (BPs) are extensively used in a wide variety of cosmetic products and other materials (e.g., textiles or plastics) to avoid damaging effects of UV radiation. In the present work, we compared two extraction methods for the determination of BPs, namely, 2,4-dihydroxybenzophenone (BP-1), 2-hydroxy-4-methoxybenzophenone (BP-3) and 2,2-dihydroxy-4-methoxybenzophenone (BP-8), in water and cosmetics samples. The following extraction methods were used for the research: solid-phase extraction (SPE) and microextraction by packed sorbent (MEPS), whereas analysis was performed by gas chromatography with mass spectrometric detection. A comparison between the methods indicates that the MEPS technique(s) can be reliably used for analysis of BPs (sunscreen residue) in water samples and cosmetic samples with satisfactory results. This microextraction technique is cheap, easy, quick to implement, and consumes small amounts of solvents. On the other hand, the main advantage of the SPE method are low detection limits for the determination of BPs in water samples, i.e., from 0.034 to 0.067 µg L−1, while, for the MEPS method, LODs were at the level of 1.8–3.2 µg L−1. For both methods, the recoveries of BPs were 96–107% and 44–70% for water and cosmetics samples, respectively. The presented methods are suitable for use in cosmetics quality control and environmental pollution assessment.

Montmorillonite grafted on a cellulosic paper as a novel layered sorbent for microextraction by packed sorbent in combination with HPLC for determination of carvedilol in biological samples

In the present research, a novel nano-structured sorbent based on grafted montmorillonite on a cellulosic paper (MMT/Cell) has been prepared by chemically bonding to the surface of a cellulosic paper by glutaraldehyde as a cross linker. The prepared thin film was applied as the layered sorbent packed into a syringe for microextraction by packed sorbent (MEPS) of carvedilol (CAR) from biological samples followed by high performance liquid chromatography-ultra-violet absorption (HPLC-UV) detection. The morphology and the surface characteristics of the prepared thin layers were studied applying scanning electron microscopy (SEM) and their elemental analysis was studied by energy dispersive X-ray spectroscopy (EDX). Attenuated total reflection-Furier transform infrared spectroscopy (ATR-FTIR) was employed to study the presence of various functional groups on the MMT/Cell surface. The essential parameters affecting the extraction efficiency such as pH, sorbent layers, extraction draw-discard cycles, desorption draw-eject cycles, elution solvent and its volume were optimized. The linear dynamic range of the developed method was in the range of 1.5 to 300 ng mL−1 and the limit of detection (LOD) was 0.5 ng mL−1. The precision of the MEPS-HPLC-UV method in terms of relative standard deviation percentage (RSD %) considering three replications of extraction from spiked deionized water (100 ng mL−1) was 6.8%. Standard addition method was applied to determine CAR in urine and plasma samples, and the relative recovery percentage was 90.2 % and 80.0 % for urine and plasma samples, respectively, indicating the capability of the developed MEPS-HPLC-UV method to extract and determine CAR in biological samples.

Direct coupling of MEPS to ESI-QqTOF-MS for the simultaneous analysis of tricyclic antidepressants and benzodiazepines in postmortem blood

The combination of chromatography and mass spectrometry is the golden standard in forensic sciences. Although this approach provides high sensitivity and selectivity levels, it is time-consuming. The circumvention of the chromatography can increase the sample throughput, but the selectivity must be compensated by using a selectivity enhanced instrumental technique, such as high-resolution mass spectrometry (HRMS), and designing an appropriate sample preparation step. Microextraction by packed sorbent (MEPS) has proven potential to treat complex biological samples in a fast and reproducible way. It allows processing low sample volumes, remaining a green procedure due to low solvent consumption. This article presents the direct coupling of a MEPS syringe to the electrospray ionization source (ESI) of a quadrupole time-of-flight mass spectrometer (QqTOF) using an infusion pump for sample introduction, as a proof of concept. The developed method was validated for the simultaneous analysis of benzodiazepines and tricyclic antidepressants in postmortem blood samples. Limits of quantification (LOQ) were between 25 and 50 ng mL−1 for all compounds. Accuracy and precision were evaluated at three concentration levels (50, 125 and 350 ng mL−1) and expressed in terms of relative error (%RE) and relative standard deviation (%RSD), respectively. Both parameters were better than 20% for the lower concentration evaluated and better than 15% for the other two concentration levels. The developed method was used to analyze authentic postmortem blood samples, to test the applicability in the forensic toxicological context. The results are in agreement with the data provided by the medico-legal services. Also, the application of HRMS has allowed the identification of unexpected targets in the samples.

Rapid detection of sulfur mustard hydrolysis products based on microextraction by packed sorbent combined with nano-electrospray ionization mass spectrometry.

Sulfur mustard is a blister agent prohibited by the Chemical Weapons Convention, and the detection of its hydrolysis product, thiodiglycol (TDG), is an important indicator of blister agent contamination. Due to the poor volatility and low extraction efficiency of TDG, derivatization gas chromatography or liquid chromatography is required for conventional methods, and the detection process is cumbersome and time-consuming. A microextraction by packed sorbent (MEPS) device and a nano-electrospray ionization (nano-ESI) device were used. The central composite design (CCD) model of Response Surface Methodology was used to optimize the elution procedure; the variance analysis under equal repeated trials with multiple factors was used to quantitatively analyze the significance of the impact of related factors on the nano-ESI efficiency. The MEPS-nano-ESI-MS experimental conditions were optimized. A new detection method of sulfur mustard hydrolysis products in water based on MEPS-nano-ESI-MS was established; the detection limit was 1ng/mL and was linear between 5ng/mL and 100 ng/mL (R2 = 0.9911) with a precision of ≤7.2%, and the recovery rate was 107.89% when the sample concentration was 40 ng/mL. The experimental results showed that the proposed method could quickly detect the contaminated water samples without chromatographic separation and derivatization, thereby verifying the contamination of sulfur mustard on site.

A sensitive microextraction by packed sorbent-gas chromatography-mass spectrometry method for the assessment of polycyclic aromatic hydrocarbons contamination in Antarctic surface snow

For the first time an eco-friendly method involving microextraction by packed sorbent (MEPS) coupled to gas chromatography-mass spectrometry (GC-MS) was developed for the determination of the 16 US-EPA priority pollutant polycyclic aromatic hydrocarbons (PAHs) as indicators of anthropogenic contamination in snow samples collected in polar regions. MEPS was carried out by using C8 sorbent material packed in a barrel insert and needle (BIN) and integrated in the eVol® semi-automatic device. For optimization purposes a Face Centred Design and the multicriteria method of the desirability functions were performed to investigate the effect of some parameters affecting the MEPS extraction efficiency, i.e. the number of loading cycles and the number of elution cycles. The developed MEPS-GC-MS method proved to be suitable for PAHs analysis at ultra-trace level by extracting small sample volumes achieving detection limits for 16 PAHs in the 0.3–5 ng L−1 range, repeatability and intermediate precision below 11% and 15%, respectively, and good recovery rates in the 77.6 (±0.1)–120.8 (±0.1)% range for spiked blank snow samples. Enrichment factors in the 64 (±7)–129 (±18) range were calculated. Finally, the proposed method was successfully applied to the determination of PAHs in surface snow samples collected in 2020–2021 from four locations of Northern Victoria Land, Antarctica. Local emission sources such as ships and research stations were found to influence PAHs concentrations in the surface snow.

Microextraction by packed sorbent of selected pesticides in coffee samples employing ionic liquids supported on graphene nanosheets as extraction phase.

This paper describes the synthesis, characterization, and use of ionic liquids supported on silica, functionalized with graphene oxide through covalent bonding (ILz/Si@GO), as sorbents for microextraction by packed sorbent (MEPS). Seven selected pesticides (diazinon, heptachlor, aldrin, endrin, dieldrin, endosulfan, and methoxychlor), used for the prevention of pests in coffee crops, and endosulfan sulfate-an endosulfan metabolite-were selected for this study as model compounds for evaluating the sorbent performance of the synthesized materials in the MEPS device. The cycles of each of the stages were previously optimized through univariate experiments to carry out the extraction. The ILz/Si@GO phase was compared to other sorbents used in MEPS (GO, DVB-MMA, C4/SiO2, C8/SiO2, ILz/SiO2, and bare silica) and also with graphene functionalized through other methodologies, where ILz/Si@GO showed the best results. The material was characterized using a range of techniques. The selectivity of the sorbent material and its adsorption capacity were evaluated by gas chromatography coupled with tandem mass spectrometry. The precision and accuracy of the method showed a relative standard deviation lower than 10% and recoveries from 35 to 97%. Finally, the proposed method was employed for the determination of pesticide residues in coffee samples.

Quantitative Measurement of Plasma Free Metanephrines by a Simple and Cost-Effective Microextraction Packed Sorbent with Porous Graphitic Carbon and Liquid Chromatography-Tandem Mass Spectrometry.

Plasma free metanephrines are widely used for the diagnosis of pheochromocytoma and paraganglioma (PPGL), yet quantifying metanephrines using a simple and cost-effective approach may be challenging due to preanalytical and analytical constraints. In this study, we established and validated a new method for quantitative measurement of plasma free metanephrines based on microextraction by packed sorbent (MEPS) with porous graphitic carbon (PGC) and liquid chromatography-tandem mass spectrometry (HILIC-MS/MS). The elution step was fully compatible with HILIC mode without evaporation and reconstitution. The analytes were well resolved, and potential interferences (54 substances) were investigated. This method was linear from 24.7–2717 pg/mL for metanephrine (MN) and 24.5–4010 pg/mL for normetanephrine (NMN) with a coefficient of determination (R2) higher than 0.994. The limit of MN and NMN detection were 12.4 pg/mL and 12.3 pg/mL, respectively. The intra- and interassay impressions were ≤12.8% for spiked quality controls and ≤13.6% for commercial quality controls; the method recoveries ranged within 88.0–109.0%, respectively. The area under the receiver operating characteristic (ROC) curve was 0.848 ± 0.047 for MN and 0.979 ± 0.021 for NMN. Validation that was performed by comparing clinical specimens with various biochemical results showed that plasma free metanephrines in a seated position had comparable sensitivity and lower specificity to urinary free metanephrines, which could be compensated by combining other biochemical tests. The newly developed MEPS method resulted as a time-saving, reliable, and cost-effective microextraction technique that can be applied for a successful screening of PPGL.

Determination and Pharmacokinetics of Omeprazole Enantiomers in Human Plasma and Oral Fluid Utilizing Microextraction by Packed Sorbent and Liquid Chromatography-Tandem Mass Spectrometry.

In the present work, the determination of omeprazole (OME) enantiomers in oral fluid and plasma samples was carried out utilizing microextraction by packed sorbent (MEPS) and liquid chromatography-tandem mass spectrometry. A chiral column with cellulose-SB phase was used for the first time for enantiomeric separation of OME with an isocratic elution system using 0.2% ammonium hydroxide in hexane-ethanol mixture (70 : 30, v/v) as the mobile phase. OME enantiomers were determined utilizing a triple quadrupole tandem mass spectrometer in positive ion mode (ESI+) monitoring mass transitions: m/z 346.3 ⟶ 198.0 for OME and m/z 369.98 ⟶ 252.0 for internal standard. The limits of detection and quantification of the present method for both enantiomers were 0.1 and 0.4 ng/mL, respectively. The method validation provided good accuracy and precision. The matrix effect factor was less than 5%, and no interfering peaks were observed. The interday precision values ranged from 2.2 to 7.5 (%RSD), and the accuracy of determinations varied from −9.9% to 8.3%. In addition, the pharmacokinetics (PK) of omeprazole enantiomers in healthy subjects after a single oral dose was investigated. (S)-Enantiomers showed higher levels than (R)-enantiomers throughout 24 h. It was found that the mean maximum concentrations of (R)- and (S)-omeprazole in plasma samples were about two times higher than in oral fluid.

Rapid detection of Sarin hydrolysis products based on microextraction by packed sorbent combined with Nano-ESI mass spectrometry

Sarin is a nerve agent the use of which prohibited by the Chemical Weapons Convention. Methylphosphonic acid (MPA) and isopropyl methylphosphonic acid (IMPA) are produced when it is hydrolyzed. The detection of MPA and IMPA was an important marker of nerve agent use and contamination. Due to the low volatility and strong polarity of the hydrolysis products, traditional detection methods such as derivatization gas chromatography or liquid chromatography-mass spectrometry were used to detect these compounds. The detection process was complex and time-consuming. Microextraction by Packed Sorbent (MEPS) and Nano Electrospray Ionization (Nano ESI) experimental setup were built. Various parameters, such as the choice of adsorption material, microextraction procedure, and nanoelectrospray ionization, which influence the detection sensitivity, have been optimized. The limit of detection of Sarin hydrolysis products by the MEPS-Nano ESI-MS techniques was 1 ng/mL, and this was equivalent to the sensitivity of GC or LC. The results reveal that the method could be used to rapidly extract and analyze the contaminated water samples without derivatization and chromatographic separation to confirm the pollution of chemical warfare agents in the field.

Microextraction by packed sorbent optimized by statistical design of experiment as an approach to increase the sensitivity and selectivity of HPLC-UV determination of parabens in cosmetics

A new approach to the quantitative analysis of parabens (PBs) in cosmetics, based on microextraction by packed sorbent (MEPS) followed by HPLC-UV detection is proposed. The development of optimal conditions for the sample preparation step was carried out in two stages. The potentially important factors that could influence the extraction were screened using the Plackett–Burman design approach, as a result of which, three statistically significant factors were selected from the nine studied. Thereafter, the selected variables were optimized by response surface methodology using a Central Composite Design. Under optimal conditions, the linear ranges for PBs analysis in cosmetic samples were 0.05–4 μg/mL with excellent precision. Limits of detection (LOD) of PBs in cosmetic samples were 2–5 ng/mL, and the extraction recovery ranged from 89 to 105 %. By comparing the chromatograms of the diluted shampoo sample before and after MEPS, the benefits of developed approach were shown. Then it was applied to the analysis of PBs in commercial hair cosmetic products: parabens were determined in all samples in which they were indicated on the package and in 1 of 12 samples labeled “paraben-free”. Finally, the proposed method was compared with other analytical HPLC-UV methods with various sample pretreatment techniques for PBs analysis in cosmetics described in recent articles. Its sensitivity turned out to be one of the highest, while it is express, automated, meets the principles of green chemistry.

Mesoporous molecularly imprinted polymer core@shell hybrid silica nanoparticles as adsorbent in microextraction by packed sorbent for multiresidue determination of pesticides in apple juice

In this work, we report the synthesis of a mesoporous molecularly imprinted polymer on the surface of silica nanoparticles (core@mMIP) to be applied as adsorbent in microextraction by packed sorbent (MEPS) for selective determination of pesticides in apple juice. The core@mMIP was properly characterized, showing good adhesion of the polymer to the silica core. The best extraction conditions were: 200 µL of ultrapure water as washing solvent,150 µL of acetonitrile as eluent, 100 µL of sample at pH 2.5, five draw-eject cycles and 8 mg of adsorbent. Thereby, recoveries of 96.12 ± 1.05%, 76.88 ± 6.18% and 76.18 ± 5.57% were obtained for pyriproxyfen (PPX), deltamethrin (DTM) and etofenprox (ETF), respectively. After validation, the method presented linearity in the range of 0.02–10 µg mL−1 (r > 0.99), limit of detection of 0.005 µg mL−1, satisfactory selectivity, and proper precision and accuracy. The method was successfully applied real samples of processed and fresh apple juice.

An analytical strategy for designer benzodiazepines and Z-hypnotics determination in plasma samples using ultra-high performance liquid chromatography/tandem mass spectrometry after microextraction by packed sorbent

The illicit market for new psychoactive substances (NPS) is continuously growing. Designer benzodiazepines (DBZD) and Z-hypnotics are increasingly being used for self-medication or recreational purposes. The limited regulation and little biological information available about NPS have raised the need for analytical methods capable of extracting and quantifying them in human biological fluids. In this work, a procedure based on microextraction by packed sorbent (MEPS) in combination with ultra-high performance liquid chromatography and tandem mass spectrometry (UHPLC–MS/MS) has been developed to determine the designer benzodiazepines (clonazolam, deschloroetizolam, nifoxipam, flubromazolam and meclonazepam), and the Z-hypnotics (zolpidem, zaleplon and zopiclone) in plasma. A 3342//16 asymmetric screening design was used to study extraction variables such as the type and volume of eluent, pH, number of extraction cycles, volume of washing solvent and type of sorbent. The ensuing analytical method was validated in terms of linearity by standard addition calibration curves at eight different analyte concentration levels from 0.5–500 ng mL–1. R2 values, limits of detection (LOD) and limits of quantification (LOQ) fell in the ranges 0.9900–0.9988, 0.5–5 ng mL–1 and 1–10 ng mL–1. Intra and interday precision expressed as relative standard deviations, were < 10.6 % and process efficiency ranged from 63 to 117 % for the quality control samples. The proposed method detected zolpidem and various other benzodiazepines in plasma samples from overdoses cases.

Microextraction by packed sorbent and high performance liquid chromatography for simultaneous determination of lumefantrine and desbutyl-lumefantrine in plasma samples

A bioanalytical method for the determination of lumefantrine and its metabolite desbutyl-lumefantrine in plasma samples using microextraction by packed sorbent (MEPS) and high-performance liquid chromatography was developed and validated. A complete factorial planning and surface response approach were employed to optimize the extraction parameters sample volume, dilution, aspirated sample volume and extraction cycles. The method employed C18 MEPS sorbent and diazepam as internal standard (IS). Separation was performed on a Luna C18 column (250 mm × 4.6 mm, 5 μm) at 35 °C, with mobile phase composed of acetonitrile and 0.05 % trifluoroacetic acid (68:32, v/v), detection at 305 nm and injection volume of 25 μL. The developed method showed to be selective, precise, accurate and linear in the range of 50–5000 ng/mL for lumefantrine and desbutyl-lumefantrine. Using the optimized MEPS procedure, high recovery rates were obtained for both analytes and IS (92.2 %–99.0 %). The method was successfully applied for the determination of lumefantrine and its metabolite in human plasma samples after oral administration of lumefantrine tablets in healthy volunteers.

Montmorillonite reinforced polystyrene nanocomposite supported on cellulose as a novel layered sorbent for microextraction by packed sorbent for determination of fluoxetine followed by spectrofluorimetry based on multivariate optimisation

ABSTRACT In this work, a novel nanocomposite (NC) by reinforcing montmorillonite into polystyrene (MMT/PS) was prepared and was coated onto cellulose filter paper. The prepared thin film was applied as a novel sorbent for microextraction by packed sorbent (MEPS) in layered configuration. The incorporation of MMT into PS host polymer has lead to higher extraction capability due to the increase of surface multi-functionality and the increase of specific surface area. The elemental analysis of prepared thin layers was conducted by energy dispersive X-ray spectroscopy (EDX) and the surface characteristic and morphology of prepared thin films was studied applying scanning electron microscopy (SEM). The prepared thin films were inserted into MEPS device and were used for extraction of fluoxetine in environmental water samples and wastewater samples continued by spectrofluorimetry (FL) determination. Multivariate optimisation based on central composite design (CCD) was used for evaluating and optimising the effective parameters influencing the MEPS method including MMT doping level, extraction draw-discard cycles, pH, cycles of draw-eject in desorption step and sorbent layers. Based on the method validation, the calibration curve is linear in the concentration range of 7–500 ng mL−1 and the limit of detection (LOD) was 2 ng mL−1. The precision of the developed method (RSD %) by performing three replication of extraction from deionised water (300 ng mL−1) was 6.7%. The developed method was successfully employed for measurement of fluoxetine in wastewater, river and dam water samples; leading to the relative recoveries (RR%) ranged from 76.4 to 107.2%.

Determination of Third-Generation Synthetic Cannabinoids in Oral Fluids

A procedure has been developed for the determination of third-generation synthetic cannabinoids in oral fluid samples by using a semi-automated microextraction by packed sorbent (MEPS) procedure and gas chromatography-mass spectrometry (GC-MS) determination. Five synthetic cannabinoids were employed as model compounds 5F-ADB, MMB-CHMICA, THJ-2201, CUMYL-4CN-BINACA and MDMB-CHMCZCA. The most adequate operative conditions for MEPS were evaluated giving quantitative recoveries, from 89 to 124%, in synthetic and field saliva samples spiked with 125 and 250μg/L of the studied cannabinoids, with the exception of MDMB-CHMCZCA in field saliva samples that provided slightly lower recoveries from 62 to 66%. A high sensitivity was obtained for the proposed MEPS-GC-MS procedure with limits of detection from 10 to 20μg/L. The obtained results demonstrate the high potential of MEPS-GC-MS combination for semi-automated, selective and sensitive determination of synthetic cannabinoids in oral fluid samples.

Determination of Tryptophan Metabolites in Serum and Cerebrospinal Fluid Samples Using Microextraction by Packed Sorbent, Silylation and GC-MS Detection.

Indole-containing acids—tryptophan metabolites—found in serum and cerebrospinal fluid (CSF) samples of patients with diseases of the central nervous system (CNS) were determined with the use of microextraction by packed sorbent (MEPS) followed by silylation and gas chromatography–mass spectrometry (GC–MS) analysis. MEPS with the following silylation led to the reproducible formation of derivatives with an unsubstituted hydrogen ion in the indole ring, the chromatographic peaks of which are symmetric and can be used for GC–MS analysis without additional derivatization. The recoveries of analytes at the limit of quantitation (LOQ) levels were 40–80% for pooled CSF and 40–60% for serum. The limit of detection (LOD) and LOQ values were 0.2–0.4 and 0.4–0.5 µM, respectively, for both CSF and serum. The precision (the reproducibility, RSD) value of less than 20% and the accuracy (the relative error, RE) value of less than ±20% at the LOQ concentrations meet the Food and Drug Administration (FDA) recommendations. Linear correlations for all analytes were determined over a potentially clinically significant range of concentrations (0.4–10 µM for serum, R2 ≥ 0.9942, and 0.4–7 µM for CSF, R2 ≥ 0.9949). Moreover, MEPS significantly reduced the matrix effect of serum compared to liquid–liquid extraction (LLE), which was revealed in the example of reducing the amount of cholesterol and its relative compounds.

A new approach for urinary vanillylmandelic acid determination using eVol microextraction by packed sorbent coupled to liquid chromatography-tandem mass spectrometry

Vanillylmandelic acid (VMA) is one of the most important catecholamine metabolites, and it is usually used to aid in diagnosis of pheochromocytoma and paraganglioma. A new digital control microextraction by packed sorbent (MEPS) procedure coupled to liquid chromatography-mass spectrometry (LC-MS/MS) method has been developed to determine VMA in human urine. We evaluated important parameters influencing MEPS efficiency, including stationary phase, extracting cycles, and sample dilution. In optimized MEPS conditions, Only 10 μL of sample volume and 3 min preparation time for one sample were needed. Chromatographic separation was achieved with a hydrophilic interaction liquid chromatography (HILIC) column using gradient elution. VMA was detected using multiple reaction monitoring (MRM) with an electrospray source operating in negative ion mode. The method was validated for linearity, limit of quantification, accuracy, imprecision, matrix effect, and interference. Linearity was 0.5–100 μg/mL for VMA. Intra-assay, inter-assay, and total imprecision were less than 9.6%. Interferences precluding quantitation of VMA in dilute-and-shoot approach were reduced significantly using a MEPS approach. Method comparison of LC-MS/MS and homogeneous enzyme immunoassay was performed, and the reference interval was established. The developed MEPS-LC-MS/MS method certainly contributes to method robustness and makes it suitable for measurement of urinary VMA in routine clinical biochemistry laboratories.