ZnO nanorod coating for solid phase microextraction and its applications for the analysis of aldehydes in instant noodle samples

In Vitro and In Vivo Human Body Odor Analysis Method Using GO:PANI/ZNRs/ZIF−8 Adsorbent Followed by GC/MS

Among various volatile organic compounds (VOCs) emitted from human skin, trans-2-nonenal, benzothiazole, hexyl salicylate, α-hexyl cinnamaldehyde, and isopropyl palmitate are key indicators associated with the degrees of aging. In our study, extraction and determination methods of human body odor are newly developed using headspace-in needle microextraction (HS-INME). The adsorbent was synthesized with graphene oxide:polyaniline/zinc nanorods/zeolitic imidazolate framework-8 (GO:PANI/ZNRs/ZIF−8). Then, a wire coated with the adsorbent was placed into the adsorption kit to be directly exposed to human skin as in vivo sampling and inserted into the needle so that it was able to be desorbed at the GC injector. The adsorption kit was made in-house with a 3D printer. For the in vitro method, the wire coated with the adsorbent was inserted into the needle and exposed to the headspace of the vial. When a cotton T-shirt containing body odor was transferred to a vial, the headspace of the vial was saturated with body odor VOCs. After volatile organic compounds were adsorbed in the dynamic mode, the needle was transferred to the injector for analysis of the volatile organic compounds by gas chromatography/mass spectrometry (GC/MS). The conditions of adsorbent fabrication and extraction for body odor compounds were optimized by response surface methodology (RSM). In conclusion, it was able to synthesize GO:PANI/ZNRs/ZIF−8 at the optimal condition and applicable to both in vivo and in vitro methods for body odor VOCs analysis.

Evaluation of New, Sputtered Carbon SPME Fibers with a Multi-Functional Group Test Mixture

We report the first fabrication of sputtered carbon, solid-phase microextraction (SPME) fibers. These fibers have competitive extraction capabilities compared with the commercial carbon wide range (CWR) SPME fiber. This report also includes a demonstration of a newly developed SPME test mix that includes 15 different compounds with a wide range of functional groups and chemical properties. The fiber fabrication process involves sputtering carbon onto fused silica fibers, and the effects of throw distance on the morphology of the carbon coatings were studied. Four different carbon coating thicknesses were evaluated, with PDMS added as a stationary phase. These fibers were characterized with multiple analytical techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) goniometry, as well as headspace (HS) and direct immersion (DI)–SPME–GC–MS. The best (11.5 µm) sputtered carbon SPME fibers, with and without PDMS, were evaluated using the new evaluation mix and compared with the commercial CWR fiber and a previously sputtered/developed silicon fiber. The new probe mix helped elucidate differences among the fibers, which would have been missed by current commercial test mixes. The sputtered carbon SPME fibers showed similar functional group selectivity as commercial CWR fibers. However, the sputtered carbon fibers showed higher responses per volume compared with the commercial CWR fiber, indicating the porous morphology of the sputtered carbon has the ability to overcome large phase thickness/volume discrepancies and increase the relative recovery for various compounds.

[Research progress in application of metal-organic framework-derived materials to sample pretreatment]

Sample pretreatment technology plays a vital role throughout the analysis of complex samples. Sample pretreatment can not only increase the concentration of trace targets in the sample, but also effectively eliminate interference from the sample matrix in instrumental analysis. Adsorbent materials are a key component of sample pretreatment technology. Therefore, the development of efficient and stable new adsorbent materials has acquired significance in research on pretreatment technology. Porous materials are advantageous for use in diverse applications, such as in adsorbents, when they possess controllable nanostructures, a tailored pore surface chemistry, and abundant porosity, and are inexpensive. Particularly in recent years, porous materials derived from metal-organic frameworks (MOFs) feature excellent properties, such as diverse morphology and structure, adjustable pore size, high specific surface area, good thermal stability, and chemical resistance. MOF-derived materials, when used as adsorbents for sample pretreatment, offer the following advantages: (1) The porous materials derived from MOFs typically possess a larger specific surface area than other porous materials. This characteristic is beneficial to improve the extraction capacity and extraction efficiency via an increase in the contact area between the materials and targets; (2) The microscopic porous structure of MOF-derived materials can be easily tuned (by controlling the temperature and time during pyrolysis, gas atmosphere, and heating rate), which is conducive to improve the selectivity of sample pretreatment methods; (3) The metal active sites can be evenly distributed. Owing to the ordered distribution of metal ions in the precursor MOFs and a good periodic framework structure, the metal active sites of the derivatives formed can still maintain a corresponding distance. These metal active sites will not form agglomerates and affect the extraction performance; conversely, other porous materials often require extremely complicated processes to achieve a uniform distribution; (4) Heteroatoms such as nitrogen and sulfur can be easily doped on the framework of MOF-derived porous materials. This doping enables the materials to induce additional interactions such as hydrogen bonding and π-π stacking for adsorbing target analytes. The excellent properties of MOF-derived materials make them promising for use in sample pretreatment. Novel sample pretreatment methods that use MOF-derived materials are constantly being developed. However, the use of MOF-derived materials is limited by the complex preparation process and high production cost of MOF precursors, along with difficulties in mass production. Further, the precise design or functionalization of MOF-derived materials according to the characteristics of targets is a new direction with immense challenges as well as application potential. This review summarizes the application of MOF-derived materials in sample pretreatment methods, including dispersive solid phase extraction (dSPE), magnetic solid phase extraction (MSPE), solid phase microextraction (SPME), stir bar sorptive extraction (SBSE), and dispersive micro solid phase extraction (DMSPE). The preparation methods, functional control, and enrichment efficiencies of various MOF-derived materials are also reviewed. Finally, the application prospects of MOF-derived materials in sample pretreatment are discussed to provide a clear outlook and reference for further related research.

6-Phenylhexyl silane derivatized, sputtered silicon solid phase microextraction fiber for the parts-per-trillion detection of polyaromatic hydrocarbons in water and baby formula

We report the fabrication of 6-phenylhexylsilane derivatized, sputtered silicon, solid phase microextraction fibers that show parts per trillion detection limits for polyaromatic hydrocarbons, and negligible carry over and phase bleed. Their fabrication involves sputtering silicon on silica fibers under various conditions. Six different fibers were evaluated by generating three different thicknesses of sputtered silicon at two different throw distances, which altered the morphologies of the silicon surfaces. All of the fibers were coated with similar thicknesses of 6-phenylhexylsilane (ca. 2 nm). These fibers were characterized with multiple analytical techniques. The optimum fiber configuration was then used to analyze polyaromatic hydrocarbons via direct immersion, gas chromatography mass spectrometry. Our best fiber for the extraction of low molecular weight polyaromatic hydrocarbons in water had similar performance to that of a commercial fiber. However, our fiber demonstrated ca. 3 times the extraction efficiency for higher molecular weight polyaromatic hydrocarbons. In addition, it outperformed the commercial fiber by showing better linearity, repeatability, and detection limits. A method for analyzing polyaromatic hydrocarbons in baby formula was developed, which showed very good linearity (0.5-125 ppb), repeatability (2-26%), detection limits (0.12-0.81 ppb), and recoveries (103-135%). In addition, our fiber showed much less (negligible) carry over and phase bleed than the commercially available fibers.

Selective and efficient solid-phase microextraction of polycyclic aromatic hydrocarbons in water by robust two-dimensional zinc oxide nanosheets grown on a superelastic nickel-titanium alloy fiber prior to determination by HPLC-UV

Oriented zinc oxide nanosheets (ZnONSs) were directly grown on pretreated nickel-titanium alloy (NiTi) fiber substrates without a traditional seeding layer of ZnO by electrochemical deposition for the first time. The fiber coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Direct growth of ZnONSs on the NiTi fiber substrate was dependent on the type of zinc salt. The adsorption performance of the ZnONSs coatings was evaluated using representative aromatic compounds as model analytes together with high performance liquid chromatography with ultraviolet detection. The as-prepared fiber shows higher extraction capability for the selected polycyclic aromatic hydrocarbons (PAHs) than for ultraviolet filters in water samples, and better extraction selectivity for PAHs. For this purpose, the important experimental parameters were optimized for the extraction of PAHs. Under the optimized conditions, the calibration curves are linear in the range of 0.03-200 μg L-1 with correlation coefficients greater than 0.999. Limits of detection ranged from 0.011 μg L-1 to 0.082 μg L-1. Intra-day and inter-day relative standard deviations (RSDs) of the developed method with a single fiber ranged from 2.69% to 4.18% and from 4.44% to 5.40%, respectively. RSDs for the fiber-to-fiber reproducibility varied between 5.57% and 7.66%. The developed method was successfully applied for selective preconcentration and determination of trace PAHs in five real water samples. Relative recoveries varied from 84.5% to 104% with RSDs between 1.65% and 8.30%. Furthermore, the as-prepared fiber is highly stable.

Combining microextraction methods with surface-enhanced Raman spectroscopy towards more selective and sensitive analyte detection by plasmonic metal nanoparticles

Raman signals of analytes can be enhanced on the surface of noble nanoparticles by generating SERS signals, which can be further enhanced using microextraction (ME) techniques.

SPME fiber coated by arrayed ZNRs for sampling and concentration of polar residual solvents for further analysis using GC FID

In this work, fused silica coated by arrayed ZNRs were successfully applied as a sorbent for analysis of polar residual solvents in pantoprazole feedstocks. ZnO nanoparticles were produced and deposited on a fused silica surface applying the dip coating technique and hydrothermal growth to synthesize the arrayed nanorods. The ZNRs array fiber coating was characterized by SEM, EDS, XRD, and TGA. The manufactured SPME fiber was coupled to a glass syringe of 10 μL and applied for the sampling of acetone, n-butanol, dichloromethane, ethyl acetate and methanol for further analysis using GC FID. Optimum operating conditions were determined for the incubation temperature (70 °C), incubation time (15 min), extraction time (120 s), and desorption time (0.6 min). Employing the optimum conditions, the proposed method resulted in a good linearity (> 0.997) and precision (< 7.1%) for the evaluated analytes. Recovery tests were also performed on three levels (below, equal to and above the ICH specification limit for residual solvents in pharmaceutical products). Recoveries ranging from 96% to 107% were obtained. Comparison between the reference method and developed method shows errors smaller than 4%.

Recent advances in microextraction procedures for determination of amphetamines in biological samples

Amphetamine and its related derivatives have stimulant and hallucinogenic properties. Illegal use of these drugs is an increasing global problem resulting in significant public health and legal problems. Deaths have been reported after intake of these drugs due to overdose. It is important to determine the type and concentration of illicit drugs in biological samples. These compounds are found in complex matrices at low concentration levels. The microextraction techniques are dominant sample preparation procedure and they are widely accepted as the most labor-intensive part of the bioanalytical process. For this purpose, a survey of recent published advances in microextraction procedures for quantification of amphetamines in biological samples found in the different databases from 2008 to date will be conducted.

A new strategy for electrochemical fabrication of manganese dioxide coatings based on silica nanoparticles deposited on titanium fibers for selective and highly efficient solid-phase microextraction

Electrochemical fabrication of a novel Ti@TiO₂@SiO₂NPs@MnO₂/PPyNPs fiber and its application in solid-phase microextraction coupled to HPLC-UV.

Oriented ZnO nanoflakes on nickel-titanium alloy fibers for solid-phase microextraction of polychlorinated biphenyls and polycyclic aromatic hydrocarbons

ZnO nanoflakes (ZnONFs) were electrochemically grown on a nickel-titanium alloy (NiTi) wire for use in solid-phase microextraction. Prior to the growth of ZnONFs, the NiTi wire was hydrothermally treated for in-situ growth of TiO₂/NiO nanoflakes as a seeding base. The applied potential was used to control the dimensions of vertically oriented hexagonal ZnONFs. After annealing at 600 °C, the resulting fiber display fairly selective affinity for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons. The fibers were applied to the preconcentration of PCBs which then were quantified by HPLC with UV detection. Compared to commercial polydimethylsiloxane coatings, the new coating displays high extraction capability, rapid extraction kinetics and superior cycling stability. This is assumed to be due to its high surface-to-volume ratio, double-sided open access structure, and enhanced structural stability. The assay excels by (a) a wide analytical range (0.10 to 200 μg L^-1 of PCBs), (b) low limits of detection (20-17 ng L^-1), and (c) low standard deviations for the single fiber repeatability (<9.8%) and for the fiber-to-fiber reproducibility (<7.5%). Satisfactory accuracy and precision were achieved when PCBs were determined by this method in spiked rain water, river water and wastewater samples. Graphical abstract ZnO nanoflakes were fabricated on a superelastic nickel-titanium alloy wire in desired orientation with enhanced extraction capability and good extraction selectivity. The fabricated fiber was suitable for the determination of PCBs in environmental water samples.

Polypyrrole coated ZnO nanorods on platinum wire for solid-phase microextraction of amitraz and teflubenzuron pesticides prior to quantitation by GC-MS

The authors describe a new sorbent for amitraz and teflubenzuron pesticides. It consists of a platinum wire coated with polypyrrole-coated ZnO nanorods. The nanocomposite was prepared by a two-step process. In the first step, oriented ZnO nanorods were hydrothermally grown in situ on a platinum wire. Subsequently, oxidative vapor phase polymerization of pyrrole was performed on FeCl₃-impregnated ZnO nanorods to give a porous polypyrrole film. The organic/inorganic nanocomposite synthesized through hydrothermal deposition and chemical vapor deposition polymerization yields material with attractive properties. The coated wire was applied to solid-phase microextraction of amitraz (in the form of 2,4-dimethylaniline resulting from the hydrolysis of amitraz) and teflubenzuron. The effects of extraction temperature, extraction time, sample pH value and salt concentration were optimized. The analytes 2,4-dimethylaniline and teflubenzuron were then quantified by GC-MS. Under optimum conditions, the LODs range between 0.1 and 0.15 ng.mL^-1. Relative standard deviations at two concentration are <8.3% for intraday precision and <10.3% for inter-day precision. In all cases, the fiber to fiber reproducibility is <12.2%. For both analytes the linear dynamic ranges are 0.5-300 ng.mL^-1. The procedure was successfully applied to the analysis of spiked agricultural water samples. Graphical abstract A novel inorganic/organic hybrid nanocomposite was synthesized through in situ hydrothermal deposition of ZnO nanorods and ten placing a thin layer of polypyrrole on them by chemical vapor deposition polymerization. This nanocomposite was applied to fabricate a solid-phase microextraction fiber for the extraction of amitraz and teflubenzuron pesticides residue from agricultural samples prior to their quantitation by GC-MS.

Electrochemical impedance spectroscopy measurements for determination of derivatized aldehydes in several matrices

A simple, selective and sensitive electrochemical method is described for the determination of different aldehydes at glassy carbon electrode using electrochemical impedance spectroscopy (EIS). The measurements were performed after their derivatization with 2,4-dinitrophenylhydrazine (DNPH) in acidic medium. The impedance measurements were investigated in the frequency range from 100 mHz to 100 kHz at a potential of 1.0 V versus Ag/AgCl. The Nyquist plots were modeled with a Randle's equivalent circuit. The charge transfer resistance was identified as the dependent parameter on relevant concentration of aldehydes (determined as their hydrazones). Under the optimized conditions, the linearity was established over the concentration range of 1000-0.05 μmol L^-1. The limits of detection (LODs) obtained were from 0.097 to 0.0109 μmol L^-1. Finally, the developed method has been applied to the determination of aldehydes in drinking water, orange juice and apple vinegar samples with relative standard deviations (RSDs) < 3.1% and acceptable recovery rate (around of 80%).

Phenyl carbamate functionalized zinc oxide nanorods for paper-based thin film microextraction

In this work, phenyl carbamate functionalized zinc oxide nanorods were fabricated on a cellulose filter paper and employed as a novel and low cost sorbent in a thin film microextraction (TFME) technique.

Solid-phase microextraction of ultra-trace amounts of tramadol from human urine by using a carbon nanotube/flower-shaped zinc oxide hollow fiber

A new method is successfully developed for the separation and determination of a very low amount of tramadol in urine using functionalized multiwalled carbon nanotubes/flower-shaped zinc oxide before solid-phase microextraction combined with gas chromatography. Under ultrasonic agitation, a sol of multiwalled carbon nanotubes and flower-shaped zinc oxide were forced into and trapped within the pore structure of the polypropylene and the sol solution immobilized into the hollow fiber. Flower-shaped zinc oxide was synthesized and characterized by Fourier transform infrared spectroscopy. The morphology of the fabricated solid-phase microextraction surface was investigated by scanning electron microscopy and X-ray diffraction. The parameters affecting the extraction efficiencies were investigated and optimized. Under the optimized conditions, the method shows linearity in a wide range of 0.12-7680 ng/mL, and a low detection limit (S/N = 3) of 0.03 ng/mL. The precision of the method was determined and a relative standard deviation of 3.87% was obtained. This method was successfully applied for the separation and determination of tramadol in urine samples. The relative recovery percentage obtained for the spiked urine sample at 1000 ng/mL was 94.2%.

Hydrothermally grown and self-assembled modified titanium and nickel oxide composite nanosheets on Nitinol-based fibers for efficient solid phase microextraction

A novel titanium and nickel oxide composite nanosheets (TiO₂/NiOCNSs) coating was in situ grown on a Nitinol (NiTi) wire by direct hydrothermal treatment and modified by self-assembly of trichlorophenylsilane for solid phase microextraction (SPME). TiO₂/NiOCNSs were radially oriented and chemically bonded to the NiTi substrate with double-faced open access sites. Moreover the phenyl modified TiO₂/NiOCNSs (TiO₂/NiOCNSs-Ph) coating exhibited original surface supporting framework favorable for effective SPME. The extraction performance of TiO₂/NiOCNSs-Ph coated NiTi (NiTi-TiO₂/NiOCNSs-Ph) fiber was investigated for the concentration and detection of ultraviolet (UV) filters, polycyclic aromatic hydrocarbons (PAHs), phthalate acid esters and polychlorinated biphenyls coupled to HPLC with UV detection. The novel fiber exhibited better selectivity for UV filters and PAHs and presented greater extraction capability compared to commercial polydimethylsiloxane and polyacrylate fibers. Under the optimized conditions for SPME of UV filters, the proposed method presented linear ranges from 0.1 to 300μg/L with correlation coefficients of higher than 0.999 and limits of detection from 0.030μg/L to 0.064μg/L. Relative standard deviations (RSDs) were below 7.16% and 8.42% for intra-day and inter-day measurements with the single fiber, respectively. Furthermore RSDs for fiber-to-fiber reproducibility from 6.57% to 8.93% were achieved. The NiTi-TiO₂/NiOCNSs-Ph fiber can be used up to 200 times. The proposed method was successfully applied to the preconcentration and determination of trace target UV filters in different environmental water samples. The relative recoveries from 87.3% to 104% were obtained with RSDs less than 8.7%.

Chlorophenol's ultra-trace analysis in environmental samples by chitosan-zinc oxide nanorod composite as a novel coating for solid phase micro-extraction combined with high performance liquid chromatography

In this study, a simple, novel, and efficient preconcentration method has been developed for the determination of some chlorophenols (4-chlorophenol, 2,5-dichlorophenol, 2,3-dichlorophenol, and 2,4,6-trichlorophenol) using a direct solid phase microextraction (D-SPME) based on chitosan-ZnO nanorod composite combined with high performance liquid chromatography (HPLC). A one step-novel hydrothermal method was demonstrated on the fabrication of ZnO nanorods arrayed on the fused silica fiber in the chitosan hydrogel solution (CZNC) as a new coating of SPME fiber. The coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) instruments. The CZNC coating has combined the merits of both ZnO nanorods and chitosan hydrogel; it has several improvements such as increased extraction efficiency of chlorophenols and longer life time (over 80 cycles of D-SPME-HPLC operation). Experimental design method was used for optimization of extraction conditions and determination of four chlorophenols in water samples by SPME-HPLC-UV method. The calibration curves were linear from 5 to 1000 µg L(-1) for analytes, and the limits of detection were between 0.1 and 2 µg L(-1). Single fiber repeatability and fiber-to-fiber reproducibility were in the range of 5.8-10.2% and 8.8-14.5%, respectively. The spiked recoveries at 50 µg L(-1) for environmental water sample were in the range of 93-102%.

Zinc oxide/polypyrrole nanocomposite as a novel solid phase microextraction coating for extraction of aliphatic hydrocarbons from water and soil samples

In this work, ZnO/PPy nanocomposite coating was fabricated on stainless steel and evaluated as a novel headspace solid phase microextraction (HS-SPME) fiber coating for extraction of ultra-trace amounts of environmental pollutants; namely, aliphatic hydrocarbons in water and soil samples. The ZnO/PPy nanocomposite were prepared by a two-step process including the electrochemical deposition of PPy on the surface of stainless steel in the first step, and the synthesis of ZnO nanorods by hydrothermal process in the pores of PPy matrix in the second step. Porous structure together with ZnO nanorods with the average diameter of 70 nm were observed on the surface by using scanning electron microscopy (SEM). The effective parameters on HS-SPME of hydrocarbons (i.e., extraction temperature, extraction time, desorption temperature, desorption time, salt concentration, and stirring rate) were investigated and optimized by one-variable-at-a-time method. Under optimized conditions (extraction temperature, 65±1°C; extraction time, 15 min; desorption temperature, 250°C; desorption time, 3 min; salt concentration, 10% w/v; and stirring rate, 1200 rpm), the limits of detection (LODs) were found in the range of 0.08-0.5 μg L(-1), whereas the repeatability and fiber-to-fiber reproducibility were in the range 5.4-7.6% and 8.6-10.4%, respectively. Also, the accuracies obtained for the spiked n-alkanes were in the range of 85-108%; indicating the absence of matrix effects in the proposed HS-SPME method. The results obtained in this work suggest that ZnO/PPy can be promising coating materials for future applications of SPME and related sample preparation techniques.

Fabrication and application of zinc-zinc oxide nanosheets coating on an etched stainless steel wire as a selective solid-phase microextraction fiber

A novel zinc-zinc oxide (Zn-ZnO) nanosheets coating was directly fabricated on an etched stainless steel wire substrate as solid-phase microextraction (SPME) fiber via previous electrodeposition of robust Zn coating. The scanning electron micrograph of the Zn-ZnO nanosheets coated fiber exhibits a flower-like nanostructure with high surface area. The SPME performance of as-fabricated fiber was investigated for the concentration and determination of polycyclic aromatic hydrocarbons, phthalates and ultraviolet (UV) filters coupled to high performance liquid chromatography with UV detection (HPLC-UV). It was found that the Zn-ZnO nanosheets coating exhibited high extraction capability, good selectivity and rapid mass transfer for some UV filters. The main parameters affecting extraction performance were investigated and optimized. Under the optimized conditions, the calibration graphs were linear over the range of 0.1-200μgL(-1). The limits of detection of the proposed method were 0.052-0.084μgL(-1) (S/N=3). The single fiber repeatability varied from 5.18% to 7.56% and the fiber-to-fiber reproducibility ranged from 6.74% to 8.83% for the extraction of spiked water with 50μgL(-1) UV filters (n=5). The established SPME-HPLC-UV method was successfully applied to the selective concentration and sensitive determination of target UV filters from real environmental water samples with recoveries from 85.8% to 105% at the spiking level of 10μgL(-1) and 30μgL(-1). The relative standard deviations were below 9.7%.