Solid-phase Microextraction Mode Research Articles

Theory and protocol of dual mode unity solid-phase microextraction

The solid-phase microextraction (SPME) bias problem limits comprehensive analysis of volatile compounds in real samples. The study introduces dual mode unity solid-phase microextraction (DMU-SPME) as a novel SPME mode to achieve balanced extraction of both volatile and low-volatile compounds. The DMU-SPME method exhibits excellent linearity (R2 ≥ 0.994), low quantitation limits (0.12–240 μg/L), and notable stability (relative standard deviations below 20 % for both intra-day and inter-day analyses). In practical application to soy sauce, the DMU-SPME method identified a total of 107 compounds, encompassing all those detected by both headspace solid-phase microextraction (HS-SPME) and direct immersion solid-phase microextraction (DI-SPME). Theoretical insights indicate that DMU-SPME is less influenced by Kfs0 and Kfs in comparison to HS/DI-SPME, rendering it suitable for complex matrices containing both volatile and low-volatile compounds. In conclusion, DMU-SPME emerges as a highly effective extraction mode for analyzing volatile and low-volatile compounds in food, medical, and environmental samples.

Headspace solid-phase microextraction: Fundamentals and recent advances

Solid-phase microextraction (SPME) has become a powerful sample preparation technique which allows to efficiently isolate and enrich analytes from complex matrixes. One of the most widespread SPME modes, consists of the extraction directly from the headspace (HS) which is equilibrated with the sample. In this sense, HS-SPME provides one of the best platforms for sample preparation, especially for the analysis of volatile and semi-volatile organic compounds. Furthermore, this technique has demonstrated to be versatile, sensitive, robust, and environmentally friendly when applied to samples coming from a diverse variety of fields such as bioanalysis, environmental sciences, food and cultural heritage. Moreover, during last years, the implementation of HS-SPME has dramatically grown along with the need to monitor complex systems over time using in situ and in vivo approaches, taking advantage of its noninvasive nature. In this review article, the authors present the fundamentals of this technique aiming to critically understand its advantages and limitations, highlighting the recent advances published in the last ten years. To this aim, special sections dealing with extractive phase development, technological advances and relevant applications in different fields have been carefully designed. Finally, some thoughts and perspectives about the future of the technique are also discussed. Graphical Abstract

In-site and solvent-free exfoliation of porous graphene oxide from pencil lead fiber for solid-phase microextraction of cadmium ion before GF-AAS determination.

Graphene oxide (GO)-functionalized pencil lead fiber was prepared for the first timeby in situ oxidation and exfoliation of graphite contained in pencil lead fiber to porous graphene oxide structure via a one-step solvent-free dielectric barrier discharge (DBD) microplasma treatment. This new fiber was demonstrated as a highly efficient and low-cost solid-phase microextraction (SPME) fiber for the determination of toxic metal ions. The fiber extraction performance was evaluated by using cadmium as a model analyte in a direct immersing SPME mode. Unlike mostcommercially available and other lab-built fibers, the preparation of the graphene oxidized pencil lead fiber is environmentally friendly, low cost, and non-toxic without using any organic solvents. The fiber is robust due to its coating-free configuration. Furthermore, high extraction efficiency and high sensitivity for cadmium can be obtained due to the abundant oxygen-containing functional groups on the surface of the novel fiber. After extraction, the cadmium adsorbed on the fiber was desorbed to 150-μL solution. Graphite furnace atomic absorption spectrometry (GF-AAS) with low sample consumption was used to determine cadmium. The calibration curve for cadmium ions was linear in a range 0.04-0.26μgL-1 with a detection limit of 0.005μgL-1. A relative standard deviation (RSD, n = 5) of 2.1% was obtained at 0.1μgL-1 of cadmium. The sensitivity enhancement factor (EF) value of the proposed SPME method was 25. The SPME fiber was successfully applied to determinecadmium in tap water, river water, and pond water with spike recoveries ranging from 94 to 105%. Pipe network water samples were also analyzed to evaluate the cadmium release to drinking water due to the corrosion of tubes.

A carbon dots-based coating for the determination of phthalate esters by solid-phase microextraction coupled gas chromatography in water samples

A rapid and facile route is followed to synthesize carbon dots (CDs) immobilized on the surface of steel wire from candle soot (CS) for the efficient and selective determination of phthalate esters (PAEs) as solid phase micro-extraction (SPME) coating. Five PAEs were selected as target analytes and detected through a head-space SPME mode coupling with gas chromatography-flame ionization detection (GC-FID) from aqueous samples. The effects of various factors on the extraction efficiency, such as extraction time, extraction temperature, salt content and stirring rate, were optimized through orthogonal experiment. Under the optimal conditions, the fiber showed a good linear in the concentration range of 1.0–500 μg·L−1 (R2 > 0.9909). The limit of detections (LODs) and quantifications (LOQs) ranged from 0.32 to 3.13 μg·L−1 and 1.07–10.43 for five PAEs, respectively. The relative standard deviation (RSD) of intra-day and inter-day for these PAEs at a concentration level of 10 μg·L−1 (n = 5) were 3.7–8.6% and 5.6–13.3%, respectively. The prepared fiber can be repeatedly used more than 50 times, showing a long lifetime and good stability. The proposed method had been successfully applied to the analysis of PAEs in real water samples with recoveries varied between 82 and 119%.

Simultaneous determination of trace levels of multiclass fungicides in natural waters by solid - phase microextraction - gas chromatography-tandem mass spectrometry

A solvent-free method based on solid-phase microextraction (SPME) followed by gas chromatography-tandem mass spectrometry (GC-MS/MS) has been developed for the simultaneous determination of eleven fungicides at trace levels in different types of waters. Several experimental SPME parameters such as temperature, fibre coating, and SPME mode, were optimized in order to obtain the highest extraction efficiency. Under the optimal conditions, 100 °C, polyacrilate fibre (PA) and direct-immersion mode, the method was validated showing good linearity, repeatability and reproducibility. Recovery studies were carried out in four different real water matrices and at three concentration levels (20, 200 and 2000 ng L−1), with overall recovery values between 92 and 104% and relative standard deviations (RSD) about 10%. Limits of detection (LODs) at the low ng L−1 were obtained. The method demonstrated its suitability for the determination of fungicides in real water samples using external calibration for quantification purposes as well as for photodegradation studies at low concentration levels.

Polyetherimide Nanofibres as Sorbents for Organochlorinated Pesticides Determination

Electrospun polyetherimide (PEI) nanofibres were fixed on a steel wire solid phase microextraction (SPME) assembly. The basic properties of the prepared nanofibres were determined by thermogravimetry, differential scanning calorimetry, adsorption, and SEM. The analytical performance of prepared PEI SPME fibres was compared with three commercially available SPME fibres, 7 μm PDMS, 100 μm PDMS, and DVB/Carboxene/PDMS. As model water pollutants, persistent organochlorinated pesticides hexachlorocyclohexanes (HCH) and chlorobenzene (ClB) were chosen as model water pollutants. The fibres were compared in the headspace- (HS-) SPME mode of GC-MS/MS instrumentation. The comparison omitted other method parameters and focused exclusively on the extraction time variability. Lab-made PEI SPME fibres showed significantly better response for the target compounds than the other tested fibres from industrial production. Based on the results, the extraction time could be shortened from 50 to 10 min, if PEI SPME fibres were used as a modification of existing analytical protocol.

Graphitic carbon nitrides modified hollow fiber solid phase microextraction for extraction and determination of uric acid in urine and serum coupled with gas chromatography-mass spectrometry.

An elevated uric acid (UA) in urine or serum can affect renal function and blood pressure, which is an indicator of gout, cardiovascular and renal diseases, hypertension, etc. In this work, a new type of mixed matrix membrane (MMM), based on graphitic carbon nitrides (g-CNs) and hollow fiber (HF), was prepared and combined with solid phase microextraction (SPME) mode to determine UA in urine and serum followed by gas chromatography-mass spectrometry (GC/MS). The porous g-CNs were dispersed in ammonia, and then the exfoliated g-CNs nanosheets were held in the pores of HF by capillary forces and sonification. The prepared g-CNs modified HF (g-CNs-HF) was immersed in biofluid directly to extract UA with SPME mode and the solvent-free mode is convenient for further derivatization and analysis. To achieve the highest extraction efficiency (EF), main extraction and derivatization parameters, such as g-CNs-HF immobilizing time, sonification power and time of extraction, derivatization and desorption time, were optimized. Under the optimum extraction conditions, a favorable linearity of UA was obtained in the range 0.1-200μgmL(-1) with correlation coefficients higher than 0.9990, and the average recoveries at three spiked levels of UA in urine and serum ranged from 80.7% to 121.6%, from 84.7% to 101.1%, respectively. The obtained results demonstrated the developed g-CNs-HF-SPME is a simple, rapid, cost-effective, solvent-free method for the analysis of UA in biofluid.

Application of a new fiber coating based on electrochemically reduced graphene oxide for the cold-fiber headspace solid-phase microextraction of tricyclic antidepressants

A new fiber based on the electrochemical reduction of graphene oxide was prepared on a copper wire for solid-phase microextraction (SPME) applications. The prepared fiber was used for the SPME and gas chromatographic analysis of tricyclic antidepressants (TCADs), including amitriptyline, trimipramine, and clomipramine. The feasibility of direct-immersion and headspace modes of SPME for the determination of TCADs was studied. The effects of four parameters including pH, salt content, extraction temperature with and without cooling the fiber, and extraction time were investigated. The comparison showed that headspace cold fiber SPME results in the best outcome for the extraction of TCADs. Under the optimized conditions of this mode, the calibration curves were linear between 2.0 and 500 ng/mL and the detection limits were between 0.30 and 0.53 ng/mL. The intraday and interday RSDs obtained at 20 ng/mL (n = 5), using a single fiber, were 5.5-9.0 and 7.5-9.8, respectively. The fiber to fiber repeatability (n = 4), expressed as the RSD, was between 12.8 and 13.2% at a 20 ng/mL concentration level. The method was successfully applied to the analysis of TCADs in plasma samples showing recoveries from 73 to 96%.

Graphenized pencil lead fiber: Facile preparation and application in solid-phase microextraction

Graphenized pencil lead fiber was facilely prepared by in situ chemical exfoliation of graphite in pencil lead fiber to few-layered graphene sheets via a one-pot, one-step pressurized oxidation reaction for the first time. This new fiber was characterized and demonstrated to be a highly efficient but low-cost solid-phase microextraction (SPME) fiber. The extraction performance of the fiber was evaluated with four bisphenol analogs [bisphenol A (BPA), bisphenol S (BPS), bisphenol AF (BPAF), and tetrabromobisphenol A (TBBPA)] as model analytes in direct SPME mode. Unlike commercially available fibers, the graphenized pencil lead fiber showed an excellent chemical stability in highly saline, acidic, alkaline and organic conditions due to its coating-free configuration. The fiber also showed a very long lifespan. Furthermore, high extraction efficiency and good selectivity for the analytes with a wide polarity range could be obtained due to the exceptional properties of graphene. The detection limits (LODs) for the analytes were in the range of 1.1–25ng/L. The fiber was successfully applied in the analysis of tap water and effluent samples from a waste water treatment plant with spike recoveries ranging from 68.5 to 105.1%. Therefore, the graphenized pencil lead fiber provides a high performance, cheap, robust, and reliable tool for SPME.

Applications of Solid-Phase Microextraction for the Analysis of Pesticide Residues in Fruits and Vegetables: A Review

This paper reviews the application of various modes of solid-phase microextraction (SPME) for the analysis of pesticide residues in fruits and vegetables. SPME is a simple extraction technique that eliminates the use of solvent, and it is applied for the analysis of both volatile and nonvolatile pesticides. SPME has been successfully coupled to both GC and LC. The coupling with GC has been straightforward and requires little modification of existing equipment, but interfacing with LC has proved challenging. The external standard calibration technique is widely used for quantification, while standard addition and internal or surrogate standards are mainly used to account for matrix effects. All parameters that affect the extraction of pesticide residues from fruits and vegetables, and therefore need to be optimized, are also reviewed. Details of the characteristics of analytical procedures and new trends in fiber production using sol-gel technology and molecularly imprinted polymers are discussed.

Headspace and direct immersion solid phase microextraction procedures for selenite determination in urine, saliva and milk by gas chromatography mass spectrometry

Two solid phase microextraction modes were investigated and compared for their performance on the determination of selenites in various biological liquids like human urine and saliva and various types of milk. Using sodium tetraethylborate (NaBEt 4) as ethylating reagent, selenites are converted in situ to volatile diethylselenides (DESe) in aqueous medium. The derivative is collected in situ by solid phase microextraction (SPME) using a silica fiber coated with poly(dimethylsiloxane) (PDMS) either from the headspace (HS-SPME) or directly from the liquid phase (LP-SPME) and finally determined by capillary GC/MS. Under optimum conditions of SPME, the GC separation was also optimized. Between the two examined microextraction techniques, direct immersion of the PDMS fiber in the liquid phase was proved less satisfactory. In contrast, the headspace procedure appears to be more efficient. The quantification of selenites was achieved in SIM mode with good analytical performance. A non-fat milk powder certified reference material was analyzed to evaluate the accuracy of the method. The overall precision of the method was ranged between 6.2% and 9.7%. Detection limits achieved were 0.05 μg L −1 for human urine, 0.08 μg L −1 for saliva and 0.03–0.06 μg L −1 in various milk matrices.

A Review on the Hyphenation of Solid Phase Microextraction with Capillary Electrophoresis and Mass Spectrometry

Hyphenation of analytical techniques is a promising trend due to their wide applicability. This article explains the hyphenation of solid phase micro-extraction to capillary electrophoresis. Different modes of solid phase microextraction (SPME) are reported to increase sensitivity of the methods. Various advantages and problems that occurred during the hyphenation are highlighted. Besides using this as a tool of separation, solid phase microextraction capillary electrophoresis (SPME-CE) is considered with special emphasis on applications utilizing its hyphenation to mass spectrometry. As SPME offers a high preconcentration factor, its hyphenation with capillary electrophoresis mass spectrometry (CE-MS) is very promising.

Sampling atmospheric pesticides with SPME: Laboratory developments and field study

To estimate the atmospheric exposure of the greenhouse workers to pesticides, solid phase microextraction (SPME) was used under non-equilibrium conditions. Using Fick's law of diffusion, the concentrations of pesticides in the greenhouse can be calculated using pre-determined sampling rates (SRs). Thus the sampling rates (SRs) of two modes of SPME in the lab and in the field were determined and compared. The SRs for six pesticides in the lab were 20.4–48.3 mL min −1 for the exposed fiber and 0.166–0.929 mL min −1 for the retracted fiber. In field sampling, two pesticides, dichlorvos and cyprodinil were detected with exposed SPME. SR with exposed SPME for dichlorvos in the field (32.4 mL min -1) was consistent with that in the lab (34.5 mL min -1). SR for dichlorvos in the field (32.4 mL min −1) was consistent with that in the lab (34.5 mL min −1). The trends of temporal concentration and the inhalation exposure were also obtained.

Ultrasonic assisted SPME Coupled with GC and GC--MS using Pencil Lead as a Fiber for Monitoring the Organic Volatile Impurities of Ceftazidime

A simple, rapid, non-destructive, and in-situ method for the isolation and sampling of organic volatile impurities in Ceftazidime is developed using solid-phase microextraction (SPME). For the monitoring of the extracted compounds, gas chromatography (GC) and GC-mass spectrometry analyses are used. The effective factors such as nature of the fiber, SPME mode, extraction temperature, and ultrasonic assistance have been investigated and detailed here. Qualification studies reveal the existence of pyridine (as a degradation product of ceftazidime) and the residual solvents; acetone, methylene-chloride, and diethylamine are the main impurities in the studied pharmaceutical. External standard method is used for quantitative analysis. The % relative standard deviation values are below 10%, and the limits of detection for the detected solvents are 1.06, 0.98, 0.83, and 0.51 ppm, respectively. The proposed method is both accurate and linear and could be used in quality control of ceftazidime and also its stability investigations.

In-Groove Carbon Nanotubes Device for SPME of Aromatic Hydrocarbons

A new solid phase microextraction (SPME) fibre using carbon nanotubes as fibre coating incorporated into a groove of a stainless steel rod is suggested. It is mechanically stable and exhibits relatively high thermal stability (up to 280 °C). The coating showed especially good extraction efficiency for aromatic hydrocarbons. The extraction properties of the fibre to benzene, toluene, ethylbenzene and o-xylene were examined using both direct and headspace SPME modes coupled to gas chromatography-flame ionization detection. The parameters affecting the extraction efficiency (extraction temperature and time, salt addition, desorption temperature and time) were investigated and quality parameters were measured under the optimized conditions. For both headspace and direct SPME the calibration graphs were linear up to 100 mg L−1 (R 2 > 0.996) and detection limits ranged from 0.09 to 0.39 μg L−1. The repeatabilities were 5.9–13.3%. The proposed coating was applied for aromatic hydrocarbons determination in petrol station waste waters.

Application of solid-phase microextraction in analytical toxicology

Solid-phase microextraction (SPME) is a miniaturized and solvent-free sample preparation technique for chromatographic-spectrometric analysis by which the analytes are extracted from a gaseous or liquid sample by absorption in, or adsorption on, a thin polymer coating fixed to the solid surface of a fiber, inside an injection needle or inside a capillary. In this paper, the present state of practical performance and of applications of SPME to the analysis of blood, urine, oral fluid and hair in clinical and forensic toxicology is reviewed. The commercial coatings for fibers or needles have not essentially changed for many years, but there are interesting laboratory developments, such as conductive polypyrrole coatings for electrochemically controlled SPME of anions or cations and coatings with restricted-access properties for direct extraction from whole blood or immunoaffinity SPME. In-tube SPME uses segments of commercial gas chromatography (GC) capillaries for highly efficient extraction by repeated aspiration-ejection cycles of the liquid sample. It can be easily automated in combination with liquid chromatography but, as it is very sensitive to capillary plugging, it requires completely homogeneous liquid samples. In contrast, fiber-based SPME has not yet been performed automatically in combination with high-performance liquid chromatography. The headspace extractions on fibers or needles (solid-phase dynamic extraction) combined with GC methods are the most advantageous versions of SPME because of very pure extracts and the availability of automatic samplers. Surprisingly, substances with quite high boiling points, such as tricyclic antidepressants or phenothiazines, can be measured by headspace SPME from aqueous samples. The applicability and sensitivity of SPME was essentially extended by in-sample or on-fiber derivatization. The different modes of SPME were applied to analysis of solvents and inhalation narcotics, amphetamines, cocaine and metabolites, cannabinoids, methadone and other opioids, fatty acid ethyl esters as alcohol markers, gamma-hydroxybutyric acid, benzodiazepines, various other therapeutic drugs, pesticides, chemical warfare agents, cyanide, sulfide and metal ions. In general, SPME is routinely used in optimized methods for specific analytes. However, it was shown that it also has some capacity for a general screening by direct immersion into urine samples and for pesticides and other semivolatile substance in the headspace mode.

Rapid headspace solid-phase microextraction–gas chromatographic–time-of-flight mass spectrometric method for qualitative profiling of ice wine volatile fraction: I. Method development and optimization

An analytical method for the determination of volatile and semi-volatile compounds representing various chemical groups in ice wines was developed and optimized in the presented study. A combination of the fully automated solid-phase microextraction (SPME) sample preparation technique and gas chromatographic–mass spectrometric (GC–MS) system to perform the final chromatographic separation and identification of the analytes of interest was utilized. A time-of-flight mass spectrometric (TOF-MS) analyzer provided very rapid analysis of this relatively complex matrix. Full spectral information in the range of m/ z 35–450 was collected across the short GC run (less than 5 min). Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) 50/30 μm fiber performed best during the optimization experiments and it was used in the headspace SPME mode to isolate compounds from ice wine samples, consisting of 3 mL wine with 1 g salt addition. After the sample incubation and extraction (both 5 min at 45 °C), analytes were thermally desorbed in the GC injector for 2 min (injector maintained at 260 °C) and transferred into the column. The MS data acquisition rate of 50 spectra/s was selected as optimal. The optimized analytical method did not exceed 20 min per sample, including both the isolation and pre-concentration of the analytes of interest, the final GC–TOF-MS analysis and the fiber bake-out. Both a linear temperature-programmed retention index (LTPRI) method using C 8–C 20 alkanes loaded onto the fiber and a mass spectral library search were employed to identify the target compounds. The repeatability of the developed and optimized HS-SPME-GC–TOF-MS method for ice wine analysis, expressed as relative standard deviation (RSD, %, n = 7), ranged from 3.2 to 9.0%.

Silicone glue coated stainless steel wire for solid phase microextraction

A new solid phase microextraction (SPME) fiber based on high-temperature silicone glue coated on a stainless steel wire is presented. The fiber coating can be prepared easily in a few minutes, it is mechanically stable and exhibits relatively high thermal stability (up to 260 °C). The extraction properties of the fiber to benzene, toluene, ethylbenzene, and xylenes (BTEX) were examined using both direct and headspace SPME modes coupled to gas chromatography-flame ionization detection. The effects of the extraction and desorption parameters including extraction and desorption time, sampling and desorption temperature, and ionic strength on the extraction/desorption efficiency have been studied. For both headspace and direct SPME the calibration graphs were linear in the concentration range from 0.5 μg L −1 to 10 mg L −1 ( R 2 > 0.996) and detection limits ranged from 0.07 to 0.24 μg L −1. Single fiber repeatability and fiber-to-fiber reproducibility were less than 6.8 and 21.5%, respectively. Finally, headspace SPME was applied to determine BTEX in petrol station waste waters with spiked recoveries in the range of 89.7–105.2%.

Application of polyphenylmethylsiloxane coated fiber for solid-phase microextraction combined with microwave-assisted extraction for the determination of organochlorine pesticides in Chinese teas

Polyphenylmethylsiloxane (PPMS) as a novel coating for solid-phase microextraction (SPME) combined with microwave-assisted extraction (MAE) has been applied to determine the concentrations of organochlorine pesticides (OCPs) in Chinese teas. The characteristics of PPMS fiber, the extraction modes of SPME, the extraction time, temperature, and salt effects were investigated. Microwave irradiation time and power were also studied. Compared with commercial polydimethylsiloxane (PDMS) fiber and homemade sol–gel polymethylsiloxane (PMS) fiber, the novel porous sol–gel PPMS fiber exhibited high sensitivity and selectivity for OCPs compounds, higher thermal stability (to 350 °C) and long service life (more than 150 times). The recoveries of MAE is compared with that of ultrasonic extraction (USE), MAE–SPME–gas chromatography (GC)/electron-capture detection (ECD) methods showed better results for Chinese teas. Linear ranges of OCPs in the blank green tea was 0.1–10 3 ng/l. Detection limits of this method are below 0.081 ng/l. Recoveries of this method are between 39.05 and 94.35%. The repeatability of the technique was less than 16% relative standard deviation (R.S.D.). The tested pesticides in three Chinese teas were at the ng/g level.