Determination of free formaldehyde in vaccines and biological samples using solid‐phase microextraction coupled to GC–MS

A headspace solid‐phase microextraction method coupled to GC–MS was successfully developed for the trace determination of formaldehyde in veterinary bacterial and human vaccines, and diphtheria–tetanus antigen. The formaldehyde was derivatized by means of the Hantzsch reaction prior to extraction and subsequent determination. Three different types of solid‐phase microextraction fibers, polar, and nonpolar poly(dimethylsiloxane) and polyethylene glycol were prepared by using a sol–gel technique. The effects of different parameters such as type of fiber coating, extraction time and temperature, desorption conditions, agitation rate, and salt effect were investigated. Under the optimized conditions, the detection limit of the method was 979 ng/L using the selected ion‐monitoring mode. The interday and intraday precisions of the developed method under the optimized conditions were below 13%, and the method shows linearity in the range of 1.75–800 μg/L with a correlation coefficient of 0.9963. The optimized method was applied to the determination of formaldehyde from some biological products. The results were satisfactory compared to the standard method.     

Ultra‐rapid non‐equilibrium solid‐phase microextraction at elevated temperatures and direct coupling to mass spectrometry for the analysis of lidocaine in urine

Solid‐phase microextraction (SPME) has been directly coupled to an ion‐trap mass spectrometer (MS) for the determination of the model compound lidocaine in urine, hereby applying MS/MS [fragmentation of [M + H]⁺ (m/z 235) to a fragment with m/z 86]. The throughput of samples has been increased using non‐equilibrium SPME with polydimethylsiloxane (PDMS) fibers. The effect of temperature on the sorption and the desorption was studied. Elevated temperatures during sorption (65°C) and desorption (55°C) had a considerable influence on the speed of the extraction. The desorption was carried out with a home‐made desorption chamber allowing thermostating. Only 1 min sorption and 1 min desorption were performed, after which MS detection took place, resulting in a total analysis time of 3 min. Detection limits below 1 ng/mL could be obtained despite yields of only 2.1 and 1.5% for a 100‐ and a 30‐μm PDMS‐coated fiber, respectively. Furthermore, the determination of lidocaine in urine had acceptable reproducibilities, i.e., relative standard deviations (RSDs) below 10%. A limit of quantitation (RSD < 15%) of about 1 ng/mL was obtained. No extra wash step of the extraction fiber was required after desorption if a 30‐μm coating was used, whereas not all the analyte was desorbed from the 100‐μm coating in a single desorption. Therefore, the SPME‐MS/MS system with a 30‐μm PDMS‐coated fiber for rapid non‐equilibrium SPME at elevated temperatures has interesting potential for high‐throughput analysis of biological samples.     

Application of solid‐phase microextraction in current biomedical research

Extraction of endogenous compounds and drugs and their corresponding metabolites from complex matrices, such as biofluids and solid tissues, requires adequate analytical approach facilitating qualitative and quantitative analysis. To this end, solid‐phase microextraction has been introduced as modern technology that is capable of efficient and high‐throughput extraction of compounds due to its ability to amalgamate sampling, extraction, and pre‐concentration steps, while requiring minimal use of organic solvents. The ability of solid‐phase microextraction to enable analyses on small‐volume biological samples and growing availability of biocompatible solid‐phase microextraction coatings make it a highly useful technology for variety of applications. For example, solid‐phase microextraction is particularly useful for identifying biomarkers in metabolomics studies, and it can be successfully applied in pharmaceutical and toxicological studies requiring the fast and sensitive determination of drug levels, especially those that are present at low levels in biological matrices such as plasma, urine, saliva, and hair. Moreover, solid‐phase microextraction can be directly applied in in vivo studies because this extraction technique is non‐exhaustive and its biocompatible probes offer minimal invasiveness to the analyzed system. In this article, we review recent progress in well‐established solid‐phase microextraction technique for in vitro and in vivo analyses of various metabolites and drugs in clinical, pharmaceutical, and toxicological applications.     

Paper‐based solid‐phase microextraction for analysis of 8‐hydroxy‐2’‐deoxyguanosine in urine sample by CE‐LIF

An easy‐to‐do paper‐based solid‐phase microextraction (p‐SPME) was developed for determination of 8‐hydroxy‐2’‐deoxyguanosine (8‐OHdG) in urine sample by CE‐LIF. Small piece of filter paper was used as a solid phase to extract 8‐OHdG from urine sample. Its primary mechanism is based on the hydrogen‐bonding interaction between 8‐OHdG and cellulose molecules. The effects of the pH of the sample solution, extraction time, and temperature on the peak area of the analyte were investigated in order to obtain the optimal p‐SPME conditions. Comparing with the untreated sample, the p‐SPME can significantly reduce the interference to the separation of 8‐OHdG by CE‐LIF. Meanwhile, the p‐SPEM can provide more than three times concentrated effect. The developed method was evaluated according to an FDA guideline for biological analysis. The precisions (RSD%, n = 5) of the peak area and migration time of the analyte at three different concentrations were within 3.02–5.82% and 0.92–1.58%, respectively. The limit of identification of the method is about 5 nM according to the significant difference between two sets of the samples with and without spiking the standard (Student's t ‐test, p < 0.05). Good linearity was obtained in the range of 10–1000 nM (R ²>0.99) based on the standard addition. The recoveries at three different concentrations were within 99.8–103.5%. The results of the real sample analysis are consistent with those reported in our previous paper (Electrophoresis 2014, 35, 1873–1879).     

Evaluation of matrix effects in the analysis of volatile organic compounds in whole blood with solid‐phase microextraction

The complexity and matrix variability of biological samples requires an accurate evaluation of matrix effects. The dilution of the biological sample is the simplest way to reduce or avoid the matrix effect. In the present study, a set of volatile organic compounds with different volatilities was used to assess the effect of the dilution of blood samples on the extraction efficiency by headspace solid‐phase microextraction. It was found that there was a significant matrix effect but that this effect differs significantly depending on the volatility of the compound. A 1:2 (blood/water) dilution was enough to allow quantitative recoveries of those compounds with boiling points <100°C. For compounds with boiling points between 100 and 150°C, the matrix effect was stronger and a 1:5 dilution was required. The dilution of blood samples proved to be inefficient for quantitative recovery of compounds with boiling points >150°C. A 1:5 dilution of the sample allowed detection limits in the range of nanogram per liter to be obtained. This was sufficient to detect the main volatile compounds present in blood and contamination after exposure.     

All‐in‐one solid‐phase microextraction: Development of a selective solid‐phase microextraction fiber assembly for the simultaneous and efficient extraction of analytes with different polarities

In the present work, for the first time, an all‐in‐one solid‐phase microextraction technique was developed for the simultaneous and efficient extraction of analytes within a vast polarity range. A novel fiber assembly composed of two different steel components each coated with different coatings (polydimethylsiloxane and polyethylene glycol) in terms of polarity by sol–gel technology was employed for the extraction of model compounds of different polarity in a single run followed by gas chromatography with mass spectrometry. Effective parameters in the extraction step and gas chromatography with mass spectrometry analysis were optimized for all model compounds. The detection limits of the developed method for model compounds were below 0.2 ng/L. The repeatability and reproducibility of the proposed method, explained by relative standard deviation, varied between 7.22 and 9.15% and between 7.95 and 14.90 (n = 5), respectively. Results showed that, under random conditions, compared to separate extractions performed by two other differently end‐coated components that had not been assembled as the final dual fiber, as two individual fibers; simultaneous, efficient and relatively selective extraction of all model compounds was obtained in a single run by the proposed all‐in‐one technique. Finally, the optimized procedure was applied to extraction and determination of the model compounds in spiked water samples.     

Palladium‐coated stainless‐steel wire as a solid‐phase microextraction fiber

A novel palladium solid‐phase microextraction coating was fabricated on a stainless‐steel wire by a simple in situ oxidation–reduction process. The palladium coating exhibited a rough microscaled surface and its thickness was about 2 μm. Preparation conditions (reaction time and concentration of palladium chloride and hydrochloric acid) were optimized in detail to achieve sufficient extraction efficiency. Extraction properties of the fiber were investigated by direct immersion solid‐phase microextraction of several polycyclic aromatic hydrocarbons and phthalate esters in aqueous samples. The extracted analytes were transferred into a gas chromatography system by thermal desorption. The effect of extraction and desorption conditions on extraction efficiency were investigated. Under the optimum conditions, good linearity was obtained and correlation coefficients between 0.9908 and 0.9990 were obtained. Limits of detection were 0.05–0.10 μg/L for polycyclic aromatic hydrocarbons and 0.3 μg/L for phthalate esters. Their recoveries for real aqueous samples were in the range from 97.1 to 121% and from 89.1 to 108%, respectively. The intra‐ and interday tests were also investigated with three different addition levels, and satisfactory results were also obtained.     

Graphene‐coated fiber for solid‐phase microextraction of triazine herbicides in water samples

Graphene is a novel and interesting carbon material that could be used for the separation and purification of some chemical compounds. In this investigation, graphene was used as a novel fiber‐coating material for the solid‐phase microextraction (SPME) of four triazine herbicides (atrazine, prometon, ametryn and prometryn) in water samples. The main parameters that affect the extraction and desorption efficiencies, such as the extraction time, stirring rate, salt addition, desorption solvent and desorption time, were investigated and optimized. The optimized SPME by graphene‐coated fiber coupled with high‐performance liquid chromatography‐diode array detection (HPLC‐DAD) was successfully applied for the determination of the four triazine herbicides in water samples. The linearity of the method was in the range from 0.5 to 200 ng/mL, with the correlation coefficients (r) ranging from 0.9989 to 0.9998. The limits of detection of the method were 0.05‐0.2 ng/mL. The relative standard deviations varied from 3.5 to 4.9% (n=5). The recoveries of the triazine herbicides from water samples at spiking levels of 20.0 and 50.0 ng/mL were in the range between 86.0 and 94.6%. Compared with two commercial fibers (CW/TPR, 50 μm; PDMS/DVB, 60 μm), the graphene‐coated fiber showed higher extraction efficiency.     

Fast analysis of glycosides based on HKUST‐1‐coated monolith solid‐phase microextraction and direct analysis in real‐time mass spectrometry

Glycosides are a kind of highly important natural aromatic precursors in tobacco leaves. In this study, a novel HKUST‐1‐coated monolith dip‐it sampler was designed for the fast and sensitive analysis of trace glycosides using direct analysis in real‐time mass spectrometry. This device was prepared in two steps: in situ polymerization of monolith in a glass capillary of dip‐it and layer‐by‐layer growth of HKUST‐1 on the surface of monolith. Sufficient extraction was realized by immersing the tip to solution and in situ desorption was carried out by plasma direct analysis in real time. Compared with traditional solid‐phase microextraction protocols, sample desorption was not needed anymore, and only extraction conditions were needed to be optimized in this method, including the gas temperature of direct analysis in real time, extraction time, and CH₃COONH₄ additive concentration. This method enabled the simultaneous detection of six kinds of glycosides with the limits of detection of 0.02–0.05 μg/mL and the linear ranges covering two orders of magnitude with the limits of quantitation of 0.05–0.1 μg/mL. Moreover, the developed method was applied for the glycosides analysis of three tobacco samples, which only took about 2 s for every sample.     

Thermoelectric‐based temperature‐controlling system for in‐tube solid‐phase microextraction

A temperature‐controlling device for in‐tube solid‐phase microextraction was developed based on thermoelectric cooling and heating. This device can control the temperature of the capillary column from 0 to 100°C by applying a voltage to a Peltier cooler or stainless steel tube. The extraction temperatures for angiotensin I, propranolol, and ranitidine were optimized. In all cases, setting the temperature to 10°C for extraction achieved the best extraction efficiency. Desorption showed minimum peak broadening at 70°C, contributing to better chromatographic performance. Propranolol was selected as a model compound to compare the performance of temperature‐controlled in‐tube solid‐phase microextraction at optimized conditions. Calibration curves exhibited good linearity (R² > 0.999) over the studied range, and the limit of detection and limit of quantification were about three times lower than those obtained at standard conditions (30°C extraction and desorption).     

Preparation of monolithic fibers for the solid‐phase microextraction of chlorophenols in water samples

Monolithic fibers were synthesized and applied for the solid‐phase microextraction and determination of chlorophenols in environmental water samples by coupling with HPLC. The fibers were prepared by copolymerization of vinylimidazole and ethylene dimethacrylate as functional monomer and cross‐linker, respectively. The effect of the preparation conditions of monolithic fibers on the extraction efficiencies was investigated in detail. Several characteristic techniques, such as elemental analysis, infrared spectroscopy, mercury‐intrusion porosimetry, and SEM were used to characterize the monolithic material. The effect of the extraction parameters, including desorption solvent, extraction and desorption time, pH values, and ionic strength in sample matrix on the extraction performance was investigated thoroughly. Under the improved extraction conditions, the linear ranges of 2‐chlorophenol, 2,4‐dichlorophenol and pentachlorophenol were 1.0–200 μg/L and 2.0–200 μg/L for 2,4,6‐trichlorophenol. The detection limits (S/N = 3) were in the range of 0.16–0.45 μg/L, the RSDs for intraday and interday precisions were <7.0%. Finally, the proposed method was successfully used to detect different environmental water samples. The recoveries of spiked water samples were ranged from 90.0 to 115%. At the same time, satisfactory repeatability was achieved with RSDs < 9.0%.     

Sampling free and particle‐bound chemicals using solid‐phase microextraction and needle trap device simultaneously

The possibility of sampling the free and particle‐bound concentrations of organic compounds was studied using two different sampling techniques at the same time: needle trap device (NTD) and solid‐phase microextraction (SPME). In this study, a mosquito coil was used to produce gaseous (free) and particle‐bound compounds. Allethrin, the active ingredient in mosquito coils, was chosen as the target analyte. Under the same sampling conditions, the amount of allethrin extracted from the mosquito‐coil smoke was higher for the NTD compared to the SPME fiber, while the extracted amounts were almost the same for both devices when sampling gaseous samples of allethrin. These results can be explained by the fact that the SPME fiber can only extract free molecules (based on diffusion), whereas the NTD, an exhaustive sampling device, collects both free and particle‐bound allethrin. Breakthrough for NTD and carryover for both NTD and SPME were negligible under the given sampling and desorption conditions.     

Nanostructured copper‐coated solid‐phase microextraction fiber for gas chromatographic analysis of dibutyl phthalate and diethylhexyl phthalate environmental estrogens

A novel nanostructured copper‐based solid‐phase microextraction fiber was developed and applied for determining the two most common types of phthalate environmental estrogens (dibutyl phthalate and diethylhexyl phthalate) in aqueous samples, coupled to gas chromatography with flame ionization detection. The copper film was coated onto a stainless‐steel wire via an electroless plating process, which involved a surface activation process to improve the surface properties of the fiber. Several parameters affecting extraction efficiency such as extraction time, extraction temperature, ionic strength, desorption temperature, and desorption time were optimized by a factor‐by‐factor procedure to obtain the highest extraction efficiency. The as‐established method showed wide linear ranges (0.05–250 μg/L). Precision of single fiber repeatability was <7.0%, and fiber‐to‐fiber repeatability was <10%. Limits of detection were 0.01 μg/L. The proposed method exhibited better or comparable extraction performance compared with commercial and other lab‐made fibers, and excellent thermal stability and durability. The proposed method was applied successfully for the determination of model analytes in plastic soaking water.     

Speciation of inorganic and tetramethyltin by headspace solid‐phase microextraction and gas chromatography–mass spectrometry

A headspace solid‐phase microextraction (HS‐SPME) method coupled to GC‐MS was developed in order to determine trace levels of tetramethyltin (TeMT) and inorganic tin (iSn) after ethylation to tetraethyltin (TeET) in various matrices. The derivatization of iSn and the extraction of both TeMT and iSn as TeET were performed in one step. Sodium tetraethylborate (NaBEt₄) was used as derivatization agent and the volatile derivatives were absorbed on a PDMS‐coated fused silica fiber. The conditions for the HS‐SPME procedure were optimized in order to gain in repeatability and sensitivity. Several critical parameters of GC‐MS were also studied. The detection of TeMT and iSn as TeET peaks was performed by the SIM mode. The precision of the proposed method is satisfactory providing RSD values below 10% for both tin species and good linearity up to 10 μg/L. The developed method was successfully applied to the determination of tin species in several samples like canned fish, fish tissues, aquatic plants, canned mineral water and sea water. The proposed HS‐SPME‐GC‐MS method was proved suitable to monitor the concentration levels of toxic tin compounds in environmental and biological samples.     

Polypyrrole–montmorillonite nanocomposite as sorbent for solid‐phase microextraction of phenolic compounds in water

A fiber‐coated polypyrrole–montmorillonite nanocomposite was prepared for solid‐phase microextraction. The fiber coating can be prepared easily; it is mechanically stable and exhibits relatively high thermal stability. The prepared fiber was evaluated for the extraction of some phenolic compounds from aqueous sample solutions by gas chromatography–mass spectrometry. The effects of the extraction and desorption parameters including extraction time, extraction temperature, stirring rate, ionic strength, pH and desorption temperature and time have been studied. At optimum conditions, the repeatability for one fiber (n = 5), expressed as % relative standard deviation was between 6.5 and 7.8% for the phenolic compounds. The detection limits for the studied phenolic compounds were between 0.05–1.3 ng/mL. The developed method offers the advantage of being simple to use, with shorter analysis time, lower cost, thermal stability of the fibers, and high relative recovery in comparison to conventional methods of analysis.     

Cadmium sulfide nanoparticles as a novel coating for solid‐phase microextraction

CdS nanoparticles coated on a stainless‐steel wire for solid‐phase microextraction was prepared. Scanning electron microscopy showed that the CdS nanoparticles clustered together to form a porous structure and X‐ray diffraction confirmed that the CdS nanoparticles were the wurtzite phase. Coupled to gas chromatography with flame ionization detection, the extraction abilities of the fiber for polycyclic aromatic hydrocarbons were examined by the headspace method. The parameters of adsorption time, adsorption temperature, salt concentration, desorption time, and desorption temperature were investigated and optimized. For the method, wide linearity and low limits of detection from 5 to 15 ng/L were obtained. The relative standard deviations for single‐fiber repeatability and fiber‐to‐fiber reproducibility were less than 10.2 and 12.6%, respectively. The enrichment factors were from 1155.6 to 3905.4, showing the fiber has good extraction capacity for polycyclic aromatic hydrocarbons. Moreover, the fiber can be used more than 50 times, exhibiting good stability. The established method was also used to analyze the polycyclic aromatic hydrocarbons in two real samples, and the recoveries from 82.7 to 114.2% further proved the reliability of the method.     

Determination of Aroclor 1260 in soil samples by gas chromatography with mass spectrometry and solid‐phase microextraction

A novel fast screening method was developed for the determination of polychlorinated biphenyls that are constituents of the commercial mixture, Aroclor 1260, in soil matrices by gas chromatography with mass spectrometry combined with solid‐phase microextraction. Nonequilibrium headspace solid‐phase microextraction with a 100 μm polydimethylsiloxane fiber was used to extract polychlorinated biphenyls from 0.5 g of soil matrix. The use of 2 mL of saturated potassium dichromate in 6 M sulfuric acid solution improved the reproducibility of the extractions and the mass transfer of the polychlorinated biphenyls from the soil matrix to the microextraction fiber via the headspace. The extraction time was 30 min at 100°C. The percent recoveries, which were evaluated using an Aroclor 1260 standard and liquid injection, were within the range of 54.9–65.7%. Two‐way extracted ion chromatogram data were used to construct calibration curves. The relative error was <±15% and the relative standard deviation was <15%, which are respective measures of the accuracy and precision. The method was validated with certified soil samples and the predicted concentrations for Aroclor 1260 agreed with the certified values. The method was demonstrated to be linear from 10 to 1000 ng/g for Aroclor 1260 in dry soil.     

Direct immersion solid‐phase microextraction with gas chromatography and mass spectrometry for the determination of specific biomarkers of human sweat in melted snow

To provide a reliable tool for investigating diffusion processes of the specific components of the human odor 3‐hydroxy‐3‐methylhexanoic acid and 3‐methyl‐3‐sulfanylhexan‐1‐ol through the snowpack, we developed and optimized an analytical method based on direct immersion solid‐phase microextraction followed by gas chromatography with mass spectrometry. Direct immersion solid‐phase microextraction was performed using polyacrylate fibers placed in aqueous solutions containing 3‐hydroxy‐3‐methylhexanoic acid and 3‐methyl‐3‐sulfanylhexan‐1‐ol. After optimization, absorption times of 120 min provided a good balance to shorten the analysis time and to obtain suitable amounts of extractable analytes. The extraction efficiency was improved by increasing the ionic strength of the solution. Although the absolute extraction efficiency ranged between 10 and 12% for 3‐hydroxy‐3‐methylhexanoic acid and 2–3% for 3‐methyl‐3‐sulfanylhexan‐1‐ol, this method was suitable for analyzing 3‐hydroxy‐3‐methylhexanoic acid and 3‐methyl‐3‐sulfanylhexan‐1‐ol concentrations of at least 0.04 and 0.20 ng/mL, respectively. The precision of the direct immersion solid‐phase microextraction method ranged between 8 and 16%. The variability within a batch of six fibers was 10–18%. The accuracy of the method provided values of 88–95 and 86–101% for 3‐hydroxy‐3‐methylhexanoic acid and 3‐methyl‐3‐sulfanylhexan‐1‐ol, respectively. The limit of detection (and quantification) was 0.01 ng/mL (0.04 ng/mL) for 3‐hydroxy‐3‐methylhexanoic acid and 0.06 ng/mL (0.20 ng/mL) for 3‐methyl‐3‐sulfanylhexan‐1‐ol. The signal versus concentration was linear for both compounds (r² = 0.973–0.979). The stability of these two compounds showed that 3‐hydroxy‐3‐methylhexanoic acid was more stable in water than 3‐methyl‐3‐sulfanylhexan‐1‐ol. We applied the method to environmental samples in correspondence with an olfactory target buried previously.     

Inorganic–organic hybrid coating material for the online in‐tube solid‐phase microextraction of monohydroxy polycyclic aromatic hydrocarbons in urine

An inorganic–organic hybrid nanocomposite (zinc oxide/polypyrrole) that represents a novel kind of coating for in‐tube solid‐phase microextraction is reported. The composite coating was prepared by a facile electrochemical polymerization strategy on the inner surface of a stainless‐steel tube. Based on the coated tube, a novel online in‐tube solid‐phase microextraction with liquid chromatography and mass spectrometry method was developed and applied for the extraction of three monohydroxy polycyclic aromatic hydrocarbons in human urine. The coating displayed good extraction ability toward monohydroxy polycyclic aromatic hydrocarbons. In addition, long lifespan, excellent stability, and good compression resistance were also obtained for the coating. The experimental conditions affecting the extraction were optimized systematically. Under the optimal conditions, the limits of detection and quantification were in the range of 0.039–0.050 and 0.130–0.167 ng/mL, respectively. Good linearity (0.2–100 ng/mL) was obtained with correlation coefficients larger than 0.9967. The repeatability, expressed as relative standard deviation, ranged between 2.5% and 9.4%. The method offered the advantage of process simplicity, rapidity, automation, and sensitivity in the analysis of human urinary monohydroxy polycyclic aromatic hydrocarbons in two different cities of Hubei province. An acceptable recovery of monohydroxy polycyclic aromatic hydrocarbons (64–122%) represented the additional attractive features of the method in real urine analysis.     

Heat‐shrink tubing as a solid‐phase microextraction coating for the enrichment and determination of phthalic acid esters

Heat‐shrink tubing, which shrinks in one plane only (its diameter) when heated, commonly used for sealing protection in electrical engineering, was found to be able to function as a solid‐phase microextraction coating. Its utility was demonstrated for the determination of phthalic acid esters in an aqueous solution combined with high‐performance liquid chromatography equipped with a UV absorbance detector. The preparation procedure was rather simple and only ～10 min was needed. The fiber cost is extremely low (～10 cent each). The parameters affecting the extraction were optimized. Heat‐shrink tubing fiber exhibited a significant enrichment effect for the three examined phthalic acid esters and up to 931‐fold enrichment factor was obtained. The limit of detection was <10 μg/L for all analytes. The operation repeatability and fiber‐to‐fiber reproducibility were 1.2–8.3 and 5.4–9.1%, respectively. It was successfully applied for the analysis of bottled drinking water with recoveries ranging from 90.1–100.5%.