Solid-phase Microextraction High-performance Liquid Chromatography Research Articles

Porous boronate affinity monolith for on-line extraction coupled to high-performance liquid chromatography for sensitive analysis of heterocyclic aromatic amines in food samples

Abstract A novel on-line solid-phase microextraction–high-performance liquid chromatography (SPME–HPLC) system was developed for the determination of heterocyclic aromatic amines (HAAs) in food samples. A poly(vinylphenylboronic acid-co-ethylene glycol dimethacrylate) polymer monolith was prepared for on-line efficient extraction and large-volume injection was used to increase the sensitivity of detection. The polymermonolith, based on a ternary porogen, was prepared by in situ polymerization of vinylphenylboronic acid (VPBA) and ethylene glycol dimethacrylate (EGDMA) in a fused-silica capillary column. It showed good permeability, high extraction capacity, and high selectivity. The column-to-column reproducibility was satisfactory, and the enrichment factors for HAAs were 3746–7414. Conditions influencing the on-line extraction efficiency, including pH of sample solutions, flow rate of extraction and desorption, and desorption volume, were investigated. The proposed method had low limit of detection (0.10–0.15 ng/L) and good linearity. Trace HAAs in roast beef and lamb samples were determined, and the amounts of 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline, and 2-amino-3,4,7,8-tetramethyl-3 H -imidazo[4,5-f]quinoxaline in these samples were 0.235–2.08 ng/g. The recoveries for the five HAAs ranged from74.3% to 119%, and the relative standard deviation (RSDs) were less than 8.2%. The results showed that the proposed on-line method was highly sensitive for monitoring HAAs in different food samples.

Highly sensitive copper fiber-in-tube solid-phase microextraction for online selective analysis of polycyclic aromatic hydrocarbons coupled with high performance liquid chromatography

A fiber-in-tube solid-phase microextraction (SPME) device was developed with copper wire and copper tube, which was served as both the substrate and sorbent with high physical strength and good flexibility. Its morphology and surface properties were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. It was coupled with high performance liquid chromatography (HPLC) equipment by replacing the sample loop of six-port injection valve, building the online SPME-HPLC system conveniently. Using ten polycyclic aromatic hydrocarbons (PAHs) as model analytes, extraction conditions including sampling rate, extraction time, organic content and desorption time were investigated and optimized. The copper fiber-in-tube exhibits excellent extraction efficiency toward PAHs, with enrichment factors from 268 to 2497. The established online SPME–HPLC method provides good linearity (0.05–100μgL−1) and low detection limits (0.001–0.01μgL−1) for PAHs. It has been used to determine PAHs in water samples, with recoveries in the range of 86.2–115%. Repeatability on the same extraction tube is in the range of 0.6–3.6%, and repeatability among three tubes is in the range of 5.6–20.1%. Compared with phthalates, anilines and phenols, the copper fiber-in-tube possesses good extraction selectivity for PAHs. The extraction mechanism is probably related to hydrophobic interaction and π-electron–metal interaction.

Mussel inspired polydopamine functionalized poly(ether ether ketone) tube for online solid-phase microextraction–high performance liquid chromatography and its application in analysis of protoberberine alkaloids in rat plasma

A novel and simple poly(ether ether ketone) (PEEK) tube-based solid-phase microextraction (SPME)-HPLC method was developed in this work. A mussel inspired polydopamine method was used to functionalize the chemically resistant surface of PEEK tube and a poly(acrylamide–ethylene glycol dimethacrylate) monolith was synthesized inside the PEEK tube and chemically bonded with its surface. The stability of the polydopamine layer was investigated and found to be well enduring to most of commonly used organic solvents and strong acidic conditions. The PEEK tube-based monolith was coupled with HPLC system through a six-port valve, and the performance of the online SPME–HPLC system was demonstrated by analyzing three protoberberine alkaloids in aqueous samples, namely jatrorrhizine (Jat), palmatine (Pal) and berberine (Ber). These analytes were well extracted and separated within 10min, and enrichment factors of about 400 were obtained. The limit of detection of the proposed method was decreased to 0.01ng/mL by using UV detection. Finally, the online SPME–HPLC method was applied for determining Jat, Pal and Ber in rat plasma samples. Reproducibility was obtained by evaluating the intra- and inter-day precisions with RSDs less than 6.1% and 8.5%, respectively, and recoveries of the analytes in spiked plasma samples ranged from 89.8% to 96.7%. The proposed method was also applied to determine the concentration of Jat, Pal and Ber in rat plasma after oral administration of Cortex Phellodendri Chinensis.

Development of a new SPME–HPLC–UV method for the analysis of nitro explosives on reverse phase amide column and application to analysis of aqueous samples

A rapid, simple, sensitive and accurate quantitative method has been developed for the determination of eleven nitroaromatic components by solid phase microextraction (SPME) coupled to high performance liquid chromatography (HPLC) with UV detection from aqueous samples. PDMS/DVB resin fiber (60 μm) was used for concurrent extraction of all the analytes from aqueous matrix. Static desorption was carried out in the desorption chamber of SPME–HPLC interface containing mobile phase; methanol:water 43:57 (v/v) with subsequent liquid chromatographic analysis at isocratic flow rate of 1.3 mL/min and detection at 254 nm. A reverse phase amide column (5 μm) was used as a separation medium. The limit of detection (S/N = 3) for TNT and Tetryl was found to be 0.35 and 0.54 ng/mL, respectively. Developed method has been applied successfully to the analysis of aqueous samples obtained from environmental and industrial sources like river water, ground water, drinking water and industrial waste water.

Utilization of solid-phase microextraction–high-performance liquid chromatography in the determination of aromatic analyte partitioning to imidazolium-based ionic liquid micelles

A solid-phase microextraction (SPME)–high-performance liquid chromatography (HPLC) approach is used, for the first time, to study the partitioning behavior of eight aromatic analytes to three imidazolium-based ionic liquid micelles, namely, 1-hexadecyl-3-methylimidazolium bromide (HDMIm-Br), 1-hexadecyl-3-butylimidazolium bromide (HDBIm-Br), and 1,3-didodecylimidazolium bromide (DDDDIm-Br). The model used to calculate the partition coefficients is improved by determining the accurate critical micelle concentration (CMC) value of the studied IL-micelles, which considers the nature and amount of organic modifier used in the experiments. Proper CMC values in the model improve the quality of the results and decrease the differences between theoretical and experimental intercepts. Surface tensiometry has been utilized to determine the CMC values for the micelles at different acetonitrile contents (1% and 1.5%, v/v). The calculated partition coefficient values for polycyclic aromatic hydrocarbons (PAHs) oscillate between 631 and 5980, whereas aromatic analytes with a lower number of fused rings in their structures suffer non-partitioning to any of the IL-micelles. The obtained partition coefficients to IL-micelles were highest with the DDDDIm-Br IL and were always higher than those obtained with the traditional surfactant cetyltrimethyl ammonium bromide (CTAB).

Elimination of matrix effects in the determination of bisphenol A in milk by solid-phase microextraction–high-performance liquid chromatography

Solid-phase microextraction coupled to high-performance liquid chromatography (SPME–HPLC) with fluorescence detection was employed to determine bisphenol A (BPA) in milk samples. The potential influence of the milk matrix on the determination of BPA by SPME–HPLC were investigated. Optimal conditions to eliminate any matrix effects were as follows: milk samples were deproteinized with trichloroacetic acid, diluted 20-fold with BPA-free Ultrapure water, dissolved in methanol, the precipitated protein was filtered out, rinsed with methanol and evaporated to remove the methanol. Then, a 40.0-ml solution was used for SPME extraction and HPLC analysis. Satisfactory recoveries (milk: 93.1–101%; soybean milk: 93.9–102%) were achieved. The proposed method was successfully applied to real samples, BPA being detected within the range 1.6–2.6 ng ml−1 in four brands of commercial milk but not in soybean milk.

A new method for simultaneous determination of Co(II), Ni(II) and Pd(II) as morpholine-4-carbodithioate complex by SPME–HPLC–UV system

A new approach for the analysis of Co(II), Ni(II) and Pd(II) as morpholine-4-carbodithioate (MDTC) complexes in aqueous medium by using solid phase microextraction (SPME)–high performance liquid chromatography (HPLC)–UV has been developed. The method involves sorption of metal complexes on PDMS fiber from aqueous solution followed by desorption in the desorption chamber of SPME–HPLC interface using acetonitrile:water (60:40) as mobile phase. A good separation of metal complexes is achieved on C 18 column. The detection limits of Co(II), Ni(II) and Pd(II) are 0.17, 0.11 and 0.06 ng ml −1, respectively. These can be determined by the proposed method without interference from other common metal ions such as Mo(VI), V(V), Ag(I), Sn(IV), Cd(II), Pb(II), Zn(II), Ag(I), Sn(II), Cr(III) and Cr(VI). The method was applied to the determination of these metals in different alloy samples and drinking water sample.

Determination of diethylhexyl phtalate in water by solid phase microextraction coupled to high performance liquid chromatography

Difficulties detected in the determination of the diethylhexylphthalate (DEHP) at trace levels by gas chromatography–mass spectrometry (GC–MS) using SPME, due to its ubiquitous distribution in the environment has been overcome and a new method for the determination of DEHP in drinking water has been proposed. The method is based on solid phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC). Detection was carried out spectrophotometrically. Calibration graph was linear in the range 10–110 μg/L with a regression coefficient of r 2 = 0.998 and a detection limit of 0.6 μg/L. The relative standard deviation was 5 and 2% ( n = 4) for chromatographic areas and retention times, respectively. The usefulness of the SPME–HPLC technique was confirmed.

Development of an improved heated interface for coupling solid-phase microextraction to high-performance liquid chromatography

The aim of the study described in this report has been the development and the evaluation of a new improved interface to be operated under continuous heating, for on-line coupling solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC). Heating is desirable to increase desorption rate and decrease carryover. The results obtained have been compared with that obtained by off-line desorption and online desorption without heating. The SPME–HPLC interface described here has an inner volume of 60 μL, fixation for infinite points and a novel leak less sealing system. When the heating system was used, the area values were almost 10-fold higher than that obtained using the off-line mode. The obtained chromatograms showed an increasing of the area and height of chromatographic peaks and proved the excellent performance and reproducibility of the interface developed in this work.

A Review on Solid Phase Micro Extraction—High Performance Liquid Chromatography (SPME-HPLC) Analysis of Pesticides

Pesticides are an important and diverse environmental and agricultural species. Their determination in formulations, in feed and food, and in complex environmental matrices (e.g., water, soil, sludge, sediments, etc.) often requires separation methods capable of high efficiency, unique selectivity, and high sensitivity. Because pesticides (organophosporus, organochlorine, carbamate, dithiocarbamate, etc.) are carcinogenic, they are problematic for humans in the course of the food chain. Residual analyses have been performed to find out the concentration and type of pesticides and their metabolites left in food at the time of consumption. This ultimately helps in production of better and human-friendly pesticides. A new and effective sampling technique, Solid-Phase microextraction (SPME), was developed in 1990 using a fused silica fiber coated on the outside with appropriate stationary phase in which analyte in the sample is directly extracted to the fibber coating. Two types of fiber techniques can be used to extract analytes: Headspace (HS-SPME), where the fiber is exposed to the vapor phase above a gas, and direct immersion (DI-SPME), where the fiber is directly immersed in the samples. More advanced in-tube SPME recently has been developed, which uses open tubular fused-silica capillary column instead of SPME fiber. SPME in combination with HPLC, GC, GC-MS, LC-MS is getting a wide acceptability as an analytical technique. These have great advantages over the classical sampling techniques, which are time consuming and require larger samples and solvents. This review discusses the various advantages and disadvantages of the SPME for the extraction of the pesticides and their analysis by HPLC.

Method based on solid-phase microextraction–high-performance liquid chromatography with UV and electrochemical detection to determine estrogenic compounds in water samples

We determined a group of estrogenic compounds by solid-phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC) with both ultraviolet (UV) and electrochemical detection (ED). A modified liquid chromatograph was used. Polyacrylate fibers (85 μm) were used to extract the analytes from the aqueous samples. Dynamic and static modes of desorption were compared and the variables affecting both absorption and desorption processes in SPME–HPLC were optimized. Static desorption gave the best recoveries and peak shapes. The performance of the SPME–HPLC–UV–ED method was checked with river water and wastewater. The method enabled estrogenic compounds to be determined at low-μg l −1 levels in real water samples. Limits of detection were between 0.3 and 1.1 μg l −1 using UV detection and between 0.06 and 0.08 μg l −1 using ED. β-Estradiol was found in samples from a wastewater treatment plant at concentrations between 1.9 and 2.2 μg l −1.

Analysis of anatoxin-a in aqueous samples by solid-phase microextraction coupled to high-performance liquid chromatography with fluorescence detection and on-fiber derivatization

A simple method for analysis of anatoxin-a in aqueous samples was developed using solid-phase microextraction (SPME) and high-performance liquid chromatography (HPLC) with fluorescence detection. Anatoxin-a was derivatized to a fluorogenic agent on the surface of the SPME fiber. In the method an SPME fiber was immersed for 30 min in the aqueous sample. The fluorogenic derivatizing reagent (4-fluoro-7-nitro-2,1,3-benzoxadiazole, 1.0 mg/ml in methanol) was dropped or sprayed onto the fiber containing extracted analytes. The fiber was then heated for 10 min in an empty vial at 70 °C in a waterbath to promote derivatization. The derivatives formed on the fiber were desorbed in a SPME–HPLC interface. The interface was filled with methanol–1 m M hydrochloric acid (7:3, v/v) before inserting of the fiber into the interface. For desorption, the fiber was inserted in the interface for 5 min. For anatoxin-a in an aqueous sample, the calibration curve showed linearity in the range of 50–1500 ng/ml and the limit of detection of anatoxin-a was 20 ng/ml. No interferences were found, and the time for analysis was 55 min for one sample.

Determination of bisphenol-type contaminants from food packaging materials in aqueous foods by solid-phase microextraction–high-performance liquid chromatography

A fast screening method consisting of off-line solid-phase microextraction coupled to HPLC and fluorescence detection, suitable for the analysis of several bisphenol derivatives and their degradation products in aqueous solution, has been developed. Detection limits of 0.7 ng ml −1 for 2,2-bis[4-(glycidyloxy)phenyl]propane, 0.9 ng ml −1 for bisphenol A bis(3-chloro-2-hydroxypropyl)ether, 1.1 ng ml −1 for 2,2-bis(4-hydroxyphenyl)propane and 2.4 ng ml −1 for bisphenol F diglycidyl ether have been achieved working in the linear range 10–500 ng ml −1. The good analytical features achieved make the proposed method an interesting option for the direct determination of these compounds in aqueous canned food such as peas, tuna, olives, maize, artichokes or palm hearts. Both the optimization process and the results, including the analysis of real samples, are given and discussed.

Solid-phase microextraction coupled to high-performance liquid chromatography to determine phenolic compounds in water samples

Solid-phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC) with ultraviolet (UV) and electrochemical detection (ED) has been applied to determine 11 phenolic compounds considered priority pollutants by the US Environmental Protection Agency. 85 μm polyacrylate fibers were used to extract the analytes from the aqueous samples. Two different designs of the liquid chromatograph were compared in combination with SPME. Dynamic and static modes of desorption in both HPLC designs were compared and the variables affecting both absorption and desorption processes in SPME–HPLC were optimized. Static desorption in both HPLC systems showed better recoveries for the phenolic compounds. The performance of the SPME–HPLC–UV–ED method was evaluated with river water and wastewater samples. The method enabled the determination of phenolic compounds at low levels in these water samples.

Solid-phase microextraction-high performance liquid chromatography and diode array detection for the determination of mycophenolic acid in cheese

SPME, using a carbowax/templated resin fiber, interfaced with HPLC–UV/DAD has been optimized for the determination of the mycotoxin mycophenolic acid (MPA) in cheese samples. All the parameters influencing the efficiency of the analyte extraction and desorption have been carefully explored. The procedure has been applied to the analysis of blue-cheese samples such as Gorgonzola and Danablu. Samples were subjected to a preliminary short sonication in bicarbonate buffer (0.2 M, pH 9.7); the subsequent SPME was capable of a selective extraction of MPA, characterized by high recovery yields and detection limits of 50 and 100 ppb for Danablu and Gorgonzola, respectively. The present method is faster and simpler than any other existing method for the extraction of MPA from cheese and does not involve the use of toxic organic solvents.

Detection of the isoflavone aglycones genistein and daidzein in urine using solid-phase microextraction–high-performance liquid chromatography–electrospray ionization mass spectrometry

An improved method of detection of the isoflavone aglycones, genistein and daidzein, is reported using solid-phase microextraction–high-performance liquid chromatography–electrospray ionization mass spectrometry (SPME–HPLC–ESI-MS). Extraction of the isoflavonoids from urine using SPME with a Carbowax–templated resin fiber coating allows rapid preconcentration of the analytes without the usual sample preparation required by other methods. Detection of the analytes is accomplished by HPLC–ESI-MS. Analysis of spiked samples of urine resulted in a linear range of 0.25 to 250 ng/ml for daidzein and 0.27 to 27.0 ng/ml for genistein. Limits of detection of daidzein and genistein were measured at 25.4 pg/ml for daidzein and 2.70 pg/ml for genistein. Daidzein and genistein were detected in urine following consumption of a soy drink.

Automated in-tube solid-phase microextraction–high-performance liquid chromatography for carbamate pesticide analysis

In-tube solid-phase microextraction (SPME) is an automated version of SPME that can be easily coupled to a conventional HPLC autosampler for on-line sample preparation, separation and quantitation. It has been termed “in-tube” SPME because the extraction phase is coated inside a section of fused-silica tubing rather than coated on the surface of a fused-silica rod as in the conventional syringe-like SPME device. The new in-tube SPME technique has been demonstrated as a very efficient extraction method for the analysis of polar and thermally labile analytes. The in-tube SPME–HPLC method used with the FAMOS autosampler from LC Packings was developed for detecting polar carbamate pesticides in clean water samples. The main parameters relating to the extraction and desorption processes of in-tube SPME (selection of coatings, aspirate/dispense steps, selection of the desorption solvents, and the efficiency of desorption solvent, etc.) were investigated. The method was evaluated according to the reproducibility, linear range and limit of detection. This method is simple, effective, reproducible and sensitive. The relative standard deviation for all the carbamates investigated was between 1.7 and 5.3%. The method showed good linearity between 5 and 10 000 μg/l with correlation coefficients between 0.9824 and 0.9995. For the carbamates studied, the limits of detection observed are lower than or similar to that of US Environmental Protection Agency or National Pesticide Survey methods. Detection of carbaryl present in clean water samples at 1 μg/l is possible.

Solvent-free method for the determination of polynuclear aromatic hydrocarbons in waste water by solid-phase microextraction–high-performance liquid chromatography with photodiode-array detection

Solid-phase microextraction (SPME) has rapidly been established among the practical alternatives for sample preparation for gas chromatography. Nevertheless polynuclear aromatic hydrocarbons (PAHs) are more effectively monitored by high-performance liquid chromatography (HPLC), but initially, there was no simple way to introduce analytes extracted by SPME into an HPLC system. A SPME–HPLC interface was developed by Supelco, which enables one to take advantages of the time and solvent savings offered by SPME. In the present work six PAHs from the European Union directives: fluoranthene, benzo[ b]fluoranthene, benzo[ k]fluoranthene, benzo[ a]pyrene, benzo[ghi]perylene, indeno[1,2,3- c d]pyrene were evaluated after optimization of a sample preparation method with a 100-μm poly(dimethylsiloxane) fiber. Repeatability, reproducibility, correlation coefficients, linearity, recoveries and limits of detection where determined and are indicated.

Effect of Heating the Interface on Chromatographic Performance of Solid Phase Microextraction Coupled to High-performance Liquid Chromatography

The effect of heating the injector was investigated for solid phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC). Analytes extracted with an SPME fiber were introduced to a HPLC separation column using the specially designed SPME–HPLC interface, where the analytes were desorbed with HPLC solvent mobile phase. The SPME fiber was heated in this interface to enhance desorption with a heating wire coiled around the chamber using a dc power supply or a capacitive discharge quick heating system. A temperature increase reduces the fiber coating–solvent distribution constant, and increases diffusion rates, thereby enhancing the mass-transfer rate from the stationary phase of the fiber to the mobile phase. A higher desorption rate reduces injection band width, and reduces peak broadening, thus enhancing the chromatographic performance. Desorption temperature was found to have a pronounced effect on the efficiency of desorption and separation. Increasing the desorption temperature significantly reduced carryover on the fiber and enhanced the chromatographic resolution.

Analysis of pesticides in environmental water samples by solid-phase micro-extraction—high-performance liquid chromatography

Solid-phase micro-extraction (SPME) followed by high-performance liquid chromatography (LC) has been applied to analyze pesticides in water samples. A device interfaces SPME to the LC injection process by solvent extracting analytes from the fiber and then introducing the solvent into the LC injector. LC analysis with UV detection was performed first with a conventional column (4.6 mm I.D.). To enhance efficiency of SPME, three extraction conditions, stirring, temperature and salt concentration, were optimized. Subsequently, semi-microcolumn LC (1.5 mm I.D.) was evaluated for this method, giving lower detection limits and less solvent consumption. Detection limits were within Japanese regulatory limits for drinking water. The SPME-LC method was applied to real-world environmental water samples.