Determination of polycyclic aromatic hydrocarbons in food samples by automated on-line in-tube solid-phase microextraction coupled with high-performance liquid chromatography-fluorescence detection

A simple and sensitive automated method, consisting of in-tube solid-phase microextraction (SPME) coupled with high-performance liquid chromatography-fluorescence detection (HPLC-FLD), was developed for the determination of 15 polycyclic aromatic hydrocarbons (PAHs) in food samples. PAHs were separated within 15 min by HPLC using a Zorbax Eclipse PAH column with a water/acetonitrile gradient elution program as the mobile phase. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 μL of sample using a CP-Sil 19CB capillary column as an extraction device. Low- and high-molecular weight PAHs were extracted effectively onto the capillary coating from 5% and 30% methanol solutions, respectively. The extracted PAHs were readily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME HPLC-FLD method, good linearity of the calibration curve (r > 0.9972) was obtained in the concentration range of 0.05–2.0 ng/mL, and the detection limits (S/N = 3) of PAHs were 0.32–4.63 pg/mL. The in-tube SPME method showed 18–47 fold higher sensitivity than the direct injection method. The intra-day and inter-day precision (relative standard deviations) for a 1 ng/mL PAH mixture were below 5.1% and 7.6% (n = 5), respectively. This method was applied successfully to the analysis of tea products and dried food samples without interference peaks, and the recoveries of PAHs spiked into the tea samples were >70%. Low-molecular weight PAHs such as naphthalene and pyrene were detected in many foods, and carcinogenic benzo[a]pyrene, at relatively high concentrations, was also detected in some black tea samples. This method was also utilized to assess the release of PAHs from tea leaves into the liquor.     

Determination of patulin in fruit juice and dried fruit samples by in-tube solid-phase microextraction coupled with liquid chromatography–mass spectrometry

A simple and sensitive method for the determination of patulin in fruit juice and dried fruit samples was developed using a fully automated method consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–mass spectrometry (LC–MS). Patulin was separated within 5 min by high-performance liquid chromatography using a Synergi MAX-RP 80A column and water/acetonitrile (80/20, v/v) as the mobile phase. Electrospray ionization conditions in the negative ion mode were optimized for MS detection of patulin. The pseudo-molecular ion [M−H]⁻ was used to detect patulin in selected ion monitoring (SIM) mode. The optimum in-tube SPME conditions were 25 draw/eject cycles of 40 μL of sample using a Carboxen 1006 PLOT capillary column as an extraction device. The extracted patulin was readily desorbed from the capillary by passage of the mobile phase, and no carry-over was observed. Using the in-tube SPME LC–MS with SIM method, good linearity of the calibration curve (r = 0.9996) was obtained in the concentration range of 0.5–20 ng/mL using ¹³C₃-patulin as an internal standard, and the detection limit (S/N = 3) of patulin was 23.5 pg/mL. The in-tube SPME method showed >83-fold higher sensitivity than the direct injection method (10 μL injection volume). The within-day and between-day precision (relative standard deviations) were below 0.8% and 5.0% (n = 6), respectively. This method was applied successfully for the analysis of fruit juice and dried fruit samples without interference peaks. The recoveries of patulin spiked into apple juice were >92%, and the relative standard deviations were <4.5%. Patulin was detected at ng/mL levels in various commercial apple juice samples.     

Determination of aflatoxins in food samples by automated on-line in-tube solid-phase microextraction coupled with liquid chromatography–mass spectrometry

A simple and sensitive automated method for determination of aflatoxins (B1, B2, G1, and G2) in nuts, cereals, dried fruits, and spices was developed consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–mass spectrometry (LC–MS). Aflatoxins were separated within 8 min by high-performance liquid chromatography using a Zorbax Eclipse XDB-C8 column with methanol/acetonitrile (60/40, v/v): 5 mM ammonium formate (45:55) as the mobile phase. Electrospray ionization conditions in the positive ion mode were optimized for MS detection of aflatoxins. The pseudo-molecular ions [M+H]⁺ were used to detect aflatoxins in selected ion monitoring (SIM) mode. The optimum in-tube SPME conditions were 25 draw/eject cycles of 40 μL of sample using a Supel-Q PLOT capillary column as an extraction device. The extracted aflatoxins were readily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC–MS with SIM method, good linearity of the calibration curve (r > 0.9994) was obtained in the concentration range of 0.05–2.0 ng/mL using aflatoxin M1 as an internal standard, and the detection limits (S/N = 3) of aflatoxins were 2.1–2.8 pg/mL. The in-tube SPME method showed >23-fold higher sensitivity than the direct injection method (10 μL injection volume). The within-day and between-day precision (relative standard deviations) at the concentration of 1 ng/mL aflatoxin mixture were below 3.3% and 7.7% (n = 5), respectively. This method was applied successfully to analysis of food samples without interference peaks. The recoveries of aflatoxins spiked into nuts and cereals were >80%, and the relative standard deviations were <11.2%. Aflatoxins were detected at <10 ng/g in several commercial food samples.     

Electrochemically controlled in-tube solid phase microextraction

We report a new in-tube solid phase microextraction approach named electrochemically controlled in-tube solid phase microextraction (EC in-tube SPME). This approach, which combined electrochemistry and in-tube SPME, led to decrease in total analysis time and increase in sensitivity. At first, pyrrole was elctropolymerized on the inner surface of a stainless steel tube. Then, the polypyrrole (PPy)-coated in-tube SPME was coupled on-line to liquid chromatography (HPLC) to achieve automated in-tube SPME–HPLC analysis. After the completion of EC-in-tube SPME–HPLC setup, the PPy-coated tube was used as working electrode for uptake of diclofenac as target analyte. Extraction ability of the tube in presence and in absence of applied electrical field was investigated. It was found that, under the same extraction conditions, the extraction efficiency could be greatly enhanced by using the constant potential. Important factors are also optimized. The detection limit (S/N = 3) and precision were 0.1 μg L⁻¹ and 4.4%, respectively.     

Analysis of heterocyclic amines in hair by on-line in-tube solid-phase microextraction coupled with liquid chromatography−tandem mass spectrometry

Mutagenic and carcinogenic heterocyclic amines (HCAs) are formed during heating of various proteinaceous foods, but human exposure to HCAs has not yet been elucidated in detail. To assess long-term exposure to HCAs, we developed a simple and sensitive method for measuring HCAs in hair by automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Using a Zorbax Eclipse XDB-C8 column, 16 HCAs were analyzed within 15 min. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 μL sample at a flow rate of 200 μL min⁻¹ using a Supel-Q PLOT capillary column as an extraction device. The extracted HCAs were easily desorbed from the column by passage of the mobile phase, with no carryover observed. This in-tube SPME LC–MS/MS method showed good linearity for HCAs in the range of 10–2000 pg mL⁻¹, with correlation coefficients above 0.9989 (n = 18), using stable isotope-labeled HCA internal standards. The detection limits (S/N = 3) of 14 HCAs except for MeAαC and Glu-P-1 were 0.10–0.79 pg mL⁻¹. This method was successfully utilized to analyze 14 HCAs in hair samples without any interference peaks, with quantitative limits (S/N = 10) of about 0.17–1.32 pg mg⁻¹ hair. Using this method, we evaluated the exposure to HCAs in cigarette smoke and the suitability of using hair HCAs as exposure biomarkers.     

Rapid determination of triclosan in personal care products using new in-tube based ultrasound-assisted salt-induced liquid–liquid microextraction coupled with high performance liquid chromatography-ultraviolet detection

This paper describes the development of a novel, simple and efficient in-tube based ultrasound-assisted salt-induced liquid–liquid microextraction (IT-USA-SI-LLME) technique for the rapid determination of triclosan (TCS) in personal care products by high performance liquid chromatography-ultraviolet (HPLC-UV) detection. IT-USA-SI-LLME method is based on the rapid phase separation of water-miscible organic solvent from the aqueous phase in the presence of high concentration of salt (salting-out phenomena) under ultrasonication. In the present work, an indigenously fabricated home-made glass extraction device (8-mL glass tube inbuilt with a self-scaled capillary tip) was utilized as the phase separation device for USA-SI-LLME. After the extraction, the upper extractant layer was narrowed into the self-scaled capillary tip by pushing the plunger plug; thus, the collection and measurement of the upper organic solvent layer was simple and convenient. The effects of various parameters on the extraction efficiency were thoroughly evaluated and optimized. Under optimal conditions, detection was linear in the concentration range of 0.4–100 ng mL⁻¹ with correlation coefficient of 0.9968. The limit of detection was 0.09 ng mL⁻¹ and the relative standard deviations ranged between 0.8 and 5.3% (n = 5). The applicability of the developed method was demonstrated for the analysis of TCS in different commercial personal care products and the relative recoveries ranged from 90.4 to 98.5%. The present method was proven to be a simple, sensitive, less organic solvent consuming, inexpensive and rapid procedure for analysis of TCS in a variety of commercially available personal care products or cosmetic preparations.     

Determination of fluoroquinolones in environmental waters by in-tube solid-phase microextraction coupled with liquid chromatography-tandem mass spectrometry

We developed a sensitive and useful method for the determination of five fluoroquinolones (FQs), enoxacin, ofloxacin, ciprofloxacin, norfloxacin, and lomefloxacin in environmental waters, using a fully automated method consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC/MS/MS). These compounds were analysed within 7 min by high-performance liquid chromatography (HPLC) using a CAPCELL PAK C8 column and aqueous ammonium formate (pH 3.0, 5 mM)/acetonitrile (85/15, v/v) at a flow rate of 0.2 mL/min. Electrospray ionization conditions in the positive ion mode were optimized for MS/MS detection. In order to optimize the extraction of FQs, several in-tube SPME parameters were examined. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 μL of sample at a flow-rate of 150 μL/min, using a Carboxen 1010 PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase. Using the in-tube SPME LC/MS/MS method, good linearity of the calibration curve (r ≥ 0.997) was obtained in the concentration range from 0.1 to 10 ng/mL for all compounds examined. The limits of detection (S/N = 3) of the five FQs ranged from 7 to 29 pg/mL. The in-tube SPME method showed 60-94-fold higher sensitivity than the direct injection method (5 μL injection). This method was applied successfully to the analysis of environmental water samples without any other pretreatment and interference peaks. Several surface waters and wastewaters were collected from the area around Asahi River, and ofloxacin was detected in wastewater samples of a sewage treatment plant and other two hospitals at 17.5-186.2 pg/mL. The recoveries of FQs spiked into river water were above 81% for a 0.1 or 0.2 ng/mL spiking concentration, and the relative standard deviations were below 1.9-8.6%.     

In-tube solid phase microextraction using a beta-cyclodextrin coated capillary coupled to high performance liquid chromatography for determination of non-steroidal anti-inflammatory drugs in urine samples

A configuration of in-tube solid-phase microextraction (SPME) coupled to HPLC was constructed by using a pump and a six-port valve combined with a PEEK tube as the pre-extraction segment. The extraction capillary was fixed directly on the HPLC six-port valve to substitute for the sample loop. The whole system could be handled easily to perform accurate on-line extraction, and the possible inaccurate quantification caused by sample/mobile phase mixing when using an autosampler could be eliminated.A β-cyclodextrin coated capillary, prepared by sol-gel method, was used as the extraction capillary for in-tube SPME. Three non-steroidal anti-inflammatory drugs, ketoprofen, fenbufen and ibuprofen, were employed to evaluate the extraction performance of the capillary. After optimizing the extraction conditions, satisfactory extraction efficiency was obtained and detection limits for ketoprofen, fenbufen and ibuprofen in diluted urine samples were 38, 18 and 28 ng/mL, respectively. The extraction reproducibility was evaluated with intra-day and inter-day precision, and the R.S.D.s obtained were lower than 4.9 and 6.9%, respectively. The capillary was proved to be reusable and the extraction efficiency did not decrease after 250 extractions.     

Poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary for in-tube solid phase microextraction coupled to high performance liquid chromatography and its application to determination of basic drugs in human serum

A poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column was prepared for in-tube solid-phase microextraction. Comparing with the commonly used open tubular extraction capillary, which cannot provide sufficient extraction efficiency since the ratio of its coating volume to that of the capillary void volume is relatively small, the monolithic column with greater phase ratio combined with convective mass transfer provides the possibility to improve the extraction efficiency with shorter capillary. As to poly (methacrylic acid-ethylene glycol dimethacrylate), its hydrophobic main chains and acidic pendant groups make it a superior material for extraction of basic analytes from aqueous matrix.An on-line monolithic capillary column solid phase microextraction (SPME) method was developed for determination of theobromine, theophylline and caffeine in serum samples. The high extraction efficiency was obtained for all the three analytes, yielding the detection limits of 12, 8 and 6.5 ng/mL by UV detection, respectively. Excellent method reproducibility (R.S.D. < 2.9%) was found over a linear dynamic range of 0.05-2 μg/mL in serum sample. The monolithic capillary column was proved to be reusable in coping with serum samples, which would facilitate practical determination of basic drugs.     

Ultra-high-stability,pH-resistant sol–gel titania poly(tetrahydrofuran) coating for capillary microextraction on-line coupled to high-performance liquid chromatography

A sol–gel titania poly(tetrahydrofuran) (poly-THF) coating was developed for capillary microextraction hyphenated on-line with high-performance liquid chromatography (HPLC). Poly-THF was covalently bonded to the sol–gel titania network which, in turn, became chemically anchored to the inner surface of a 0.25 mm I.D. fused silica capillary. For sample preconcentration, a 38-cm segment of the sol–gel titania poly-THF coated capillary was installed on an HPLC injection port as a sampling loop. Aqueous samples containing a variety of analytes were passed through the capillary and, during this process, the analytes were extracted by the sol–gel titania poly-THF coating on the inner surface of the capillary. Using isocratic and gradient elution with acetonitrile/water mobile phases, the extracted analytes were desorbed into the on-line coupled HPLC column for separation and UV detection. The sol–gel titania poly-THF coating was especially efficient in extracting polar analytes, such as underivatized phenols, alcohols, amines, and aromatic carboxylic acids. In addition, this coating was capable of extracting moderately polar and nonpolar analytes, such as ketones and polycyclic aromatic hydrocarbons. The sol–gel titania poly-THF coated capillary was also able to extract polypeptides at pH values near their respective isoelectric points. Extraction of these compounds can be important for environmental and biomedical applications. The observed extraction behavior can be attributed to the polar and nonpolar moieties in the poly-THF structure. This coating was found to be stable under extremely low and high pH conditions—even after 18 h of exposure to 1 M HCl (pH ≈0.0) and 1 M NaOH (pH ≈14.0).     

Preparation and evaluation of an immunoaffinity sorbent for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry

In this study, we explored a procedure for the preparation of an immunoaffinity (IA) sorbent for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry (IA-SPE-CE–MS). We followed a site-specific antibody immobilization approach based on the covalent attachment of the oxidized antibodies through their carbohydrate moieties to hydrazide silica particles, using a polyclonal antibody against Endomorphin 1 and 2 (End1 and End2). The main features of the IA sorbent were studied, such as the amount of hydrazide groups and antibodies attached onto oxidized diol silica particles. Once the procedure was optimized, standard solutions of End1 and End2 were used in order to establish the IA-SPE-CE–MS methodology. Acceptable repeatability, reproducibility and linearity range values were obtained for the proposed methodology. The limits of detection (LODs) of 1 ng mL⁻¹ were approximately 100-fold better than those obtained by CE–MS. Selectivity of the IA sorbent was good but some cross-reactivity against Dynorphin A (1–7) was observed when a mixture of several opioid peptides was analyzed. Human plasma samples spiked with End1 and End2 were also analyzed and both peptides could be detected down to 100 ng mL⁻¹.     

A novel fatty-acid-based in-tube dispersive liquid–liquid microextraction technique for the rapid determination of nonylphenol and 4-tert-octylphenol in aqueous samples using high-performance liquid chromatography–ultraviolet detection

In this study, a novel fatty-acid-based in-tube dispersive liquid–liquid microextraction (FA-IT-DLLME) technique is proposed for the first time and is developed as a simple, rapid and eco-friendly sample extraction method for the determination of alkylphenols in aqueous samples using high-performance liquid chromatography–ultraviolet detection (HPLC–UV). In this extraction method, medium-chain saturated fatty acids were investigated as a pH-dependent phase because they acted as either anionic surfactants or neutral extraction solvents based on the acid–base reaction caused solely by the adjustment of the pH of the solution. A specially designed home-made glass extraction tube with a built-in scaled capillary tube was utilized as the phase-separation device for the FA-IT-DLLME to collect and measure the separated extractant phase for analysis. Nonylphenol (NP) and 4-tert-octylphenol (4-tOP) were chosen as model analytes. The parameters influencing the FA-IT-DLLME were thoroughly investigated and optimized. Under the optimal conditions, the detector responses of NP and 4-tOP were linear in the concentration ranges of 5–4000 μg L⁻¹, with correlation coefficients of 0.9990 and 0.9996 for NP and 4-tOP, respectively. The limits of detection based on a signal-to-noise ratio of 3 were 0.7 and 0.5 μg L⁻¹, and the enrichment factors were 195 and 143 for NP and 4-tOP, respectively. The applicability of the developed method was demonstrated for the analysis of alkylphenols in environmental wastewater samples, and the recoveries ranged from 92.9 to 107.1%. The extraction process required less than 4 min and utilized only acids, alkalis, and fatty acids to achieve the extraction. The results demonstrated that the presented FA-IT-DLLME approach is highly cost-effective, simple, rapid and environmentally friendly in its sample preparation.     

Nano-electromembrane extraction

The present work has for the first time described nano-electromembrane extraction (nano-EME). In nano-EME, five basic drugs substances were extracted as model analytes from 200 μL acidified sample solution, through a supported liquid membrane (SLM) of 2-nitrophenyl octyl ether (NPOE), and into approximately 8 nL phosphate buffer (pH 2.7) as acceptor phase. The driving force for the extraction was an electrical potential sustained over the SLM. The acceptor phase was located inside a fused silica capillary, and this capillary was also used for the final analysis of the acceptor phase by capillary electrophoresis (CE). In that way the sample preparation performed by nano-EME was coupled directly with a CE separation. Separation performance of 42,000–193,000 theoretical plates could easily be obtained by this direct sample preparation and injection technique that both provided enrichment as well as extraction selectivity. Compared with conventional EME, the acceptor phase volume in nano-EME was down-scaled by a factor of more than 1000. This resulted in a very high enrichment capacity. With loperamide as an example, an enrichment factor exceeding 500 was obtained in only 5 min of extraction. This corresponded to 100-times enrichment per minute of nano-EME. Nano-EME was found to be a very soft extraction technique, and about 99.2–99.9% of the analytes remained in the sample volume of 200 μL. The SLM could be reused for more than 200 nano-EME extractions, and memory effects in the membrane were avoided by effective electro-assisted cleaning, where the electrical potential was actively used to clean the membrane.     

In-tube solid-phase microextraction coupled by in valve mode to capillary LC-DAD: Improving detectability to multiresidue organic pollutants analysis in several whole waters

A simple and fast capillary chromatographic method has been developed to identify and quantify organic pollutants at sub-ppb levels in real water samples. The major groups of pesticides (organic halogens, organic phosphorous, and organic nitrogen compounds), some hydrocarbons (polycyclic aromatic hydrocarbons), phthalates and some phenols such as phenol and bisphenol A (endocrine disruptors) were included in this study. The procedure was based on coupling, in-tube solid-phase microextraction (IT-SPME) by using a conventional GC capillary column (95% methyl–5% phenyl substituted backbone, 80 cm × 0.32 mm i.d., 3 μm film thickness) in the injection valve to capillary liquid chromatography with diode array detection. A comparative study between the IT-SPME manifold and a column-switching device using a C₁₈ column (35 mm × 0.5 mm i.d., 5 μm particle size) has been performed. The IT-SPME procedure was optimal, it allows reaching limits of detection (LODs) between 0.008 and 0.2 μg/L. No matrix effect was found and recoveries between 70 and 116% were obtained. The precision of the method was good, and the achieved intra- and inter-day variation coefficients were between 2 and 30%. This procedure has been applied to the screening analysis of 28 compounds in whole waters from several points of the Mediterranean coast (Valencia Community, Spain).     

Silica nanoparticle-templated methacrylic acid monoliths for in-line solid-phase extraction–capillary electrophoresis of basic analytes

Polymeric ion-exchange monoliths typically exhibit low capacities due to the limited surface area on the globules of the monoliths. The ion-exchange binding of protonated weakly basic analytes on deprotonated carboxylate sites on methacrylate polymer monoliths has been increased by templating the monoliths with silica nanoparticles. The templating method is achieved by adding the nanoparticles as a suspension to the polymerisation mixture. After polymerisation, the nanoparticles are removed by washing the monolith with strong base. Monolithic columns prepared using this procedure have exhibited a 33-fold increase in ion-exchange capacity when compared to untemplated monoliths prepared and treated under similar conditions. The templating procedure does not alter the macroporous properties of the polymer monolith, confirmed through scanning electron microscopy and BET surface area analysis, but provides increased capacity predominantly through the re-orientation of more carboxylic acid groups. The resulting increase in ion-exchange capacity has proven to be useful for the preconcentration and separation of neurotransmitters by in-line solid-phase extraction–capillary electrophoresis. The increased capacity of the templated monolith allowed the injection time to be increased 10 times over that of an untemplated monolith, allowing 10 times more sample to be injected with the efficiencies and recoveries remaining unaffected. The enhancement in sensitivity for the test mixture of neurotransmitter (dopamine, norepinephrine and metanephrine) ranged 1500–1900 compared to a normal hydrodynamic injection in capillary electrophoresis. Efficiencies obtained for the neurotransmitters were 100 000–260 000 plates, typical of those obtained in capillary zone electrophoresis. The applicability of the increased capacity silica nano-templated polymer monolith was demonstrated by analysing trace levels of caffeine in biological, food and environmental samples.     

Simultaneous residue monitoring of four tetracycline antibiotics in fish muscle by in-tube solid-phase microextraction coupled with high-performance liquid chromatography

An on-line simple and rapid method for the simultaneous determination of tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC) residues in fish muscle was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with a photodiode array detector. Biocompatible poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary was selected as the extraction medium, and no precipitating protein and removing fat steps were required prior to extraction. In order to optimize the extraction of these compounds, several in-tube SPME parameters were investigated. Simply performed by extracting with 0.01 M EDTA-MacIlvaine buffer solution (pH 4.0) and centrifugation, the sample then could be directly injected into the device for extraction. The limits of detection of tetracycline, oxytetracycline, chlortetracycline and doxycycline were calculated to be 22, 16, 30 and 21 ng/g, respectively. The calibration curves showed linearity in the range of 100-10,000 ng/g with a linear coefficient R² value above 0.9980. Excellent method reproducibility was found by intra- and inter-day precisions, yielding the R.S.D.s less than 4.22% and 5.71%, respectively.     

Molecularly imprinted coated graphene oxide solid-phase extraction monolithic capillary column for selective extraction and sensitive determination of phloxine B in coffee bean

A method was developed to sensitively determine phloxine B in coffee bean by molecularly imprinted polymers (MIPs) coated graphene oxide (GO) solid-phase extraction (GO-MISPE) coupled with high-performance liquid chromatography and laser-induced fluorescence detection (HPLC–LIF). The GO-MISPE capillary monolithic column was prepared by water-bath in situ polymerization, using GO as supporting material, phloxine B, methacrylic acid (MAA), and ethylene dimethacrylate (EDMA) as template, functional monomer, and cross-linker, respectively. The properties of the homemade GO-MISPE capillary monolithic column, including capacity and specificity, were investigated under optimized conditions. The GO-MIPs were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FT-IR). The mean recoveries of phloxine B in coffee bean ranged from 89.5% to 91.4% and the intra-day and inter-day relative standard deviation (RSD) values all ranged from 3.6% to 4.7%. Good linearity was obtained over 0.001–2.0 μg mL⁻¹ (r = 0.9995) with the detection limit (S/N = 3) of 0.075 ng mL⁻¹. Under the selected conditions, enrichment factors of over 90-fold were obtained and extraction on the monolithic column effectively cleaned up the coffee bean matrix. The results demonstrated that the proposed GO-MISPE HPLC–LIF method can be applied to sensitively determine phloxine B in coffee bean.     

Improving analysis of apolar organic compounds by the use of a capillary titania-based column: Application to the direct determination of faecal sterols cholesterol and coprostanol in wastewater samples

This article reports a new procedure for the direct determination of faecal sterols coprostanol and cholesterol in wastewater samples as tracers of human sewage contamination. The method combines in-tube solid-phase microextraction (IT-SPME) for analyte enrichment and capillary liquid chromatography (LC) for separation with diode array detection for identification and quantification. A titania-based polymeric capillary column and a conventional octadecyl silica (ODS) capillary column were evaluated and compared for their ability to separate the analytes. The titania-based column allowed the separation of the analytes in much shorter chromatographic times and with better chromatographic profiles, which in turn resulted in better detectability. In addition, IT-SPME allowed the direct injection into the chromatographic system of sample volumes as large as 200 μL, thus making unnecessary off-line clean-up and concentration steps. In such a way, the tested compounds could be directly analysed in less than 10 min, the limits of detection (LODs) being 10 and 1.2 μg/L for coprostanol and cholesterol, respectively. The reliability of the proposed method was tested by processing several wastewater samples.     

Hybrid organic–inorganic silica monolith with hydrophobic/strong cation-exchange functional groups as a sorbent for micro-solid phase extraction

A hybrid organic–inorganic silica monolith with hydrophobic and strong cation-exchange functional groups was prepared and used as a sorbent for micro-solid phase extraction (micro-SPE). The hybrid silica monolith functionalized with octyl and thiol groups was conveniently synthesized by hydrolysis and polycondensation of a mixture of tetraethoxysilane (TEOS), n-octyltriethoxysilane (C8-TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) via a two-step catalytic sol–gel process. Due to the favorable chemical reactivity of mercapto pendant moieties, the obtained hybrid monolith was oxidized using hydrogen peroxide (30%, w/w) to yield sulfonic acid groups, which provided strong cation-exchange sites. The obtained hybrid monolith was characterized by diffused infrared spectroscopy, elemental analysis, scanning electron microscopy and mercury intrusion porosimetry. The results show that the resulting monolith contains much higher carbon (31.6%) and sulfur (4.8%) contents than traditionally bonded silica materials. The extraction performance of the hybrid monolith was evaluated using sulfonamides as testing analytes by micro-SPE on-line coupled to HPLC. The results show that the hybrid monolith with hydrophobic and strong cation-exchange functional groups exhibits high extraction efficiency towards the testing analytes. The column-to-column RSD values were 1.3–9.8% for the extraction of SAs investigated. The extraction performance of the hybrid silica monolith remained practically unchanged after treated with acid (pH 1.0) and basic solutions (pH 10.5). Finally, the application of the hybrid monolith was demonstrated by micro-SPE of sulfonamide residues from milk followed by HPLC–UV analysis. The limits of detection (S/N = 3) for eight SAs were found to be 1.0–3.0 ng/mL in milk. The recoveries of eight SAs spiked in milk sample ranged from 80.2% to 115.6%, with relative standard deviations less than 11.8%.     

A new strategy for synthesis of an in-tube molecularly imprinted polymer-solid phase microextraction device: Selective off-line extraction of 4-nitrophenol as an example of priority pollutants from environmental water samples

In this study a novel preparation protocol has been developed for the construction of an in-tube molecularly imprinted polymer-solid phase microextraction (MIP-SPME) device. Open tubular capillaries have been molded from a polymer sorbent imprinted for 4-nitrophenol as target molecule. Different parameters like inner diameter and volume of the polymer, porogen volume, swelling and shrinking effects of the polymer tubes, polymerization time, pH of the sample, extraction time, ‘salting out’ effect and serial connection of the tubes were evaluated and optimized. Particularly, an optimized polymer preparation process and extraction condition enhanced the final extraction recovery of 4-nitrophenol substantially. Using this new MIP-SPME technique with high-performance liquid chromatography-ultraviolet (HPLC-UV) analysis of the extracts, the linear range and the limits of detection and quantification are 0.001–10 mg L⁻¹, 0.33 μg L⁻¹ and 1.1 μg L⁻¹ respectively. At optimized conditions, a mixture of nitrophenols, alkylated and chlorinated phenols spiked into municipal waste water were analyzed to evaluate the matrix effects and cross selectivity of the new MIP capillary tubes.