Optimization Of Solid-phase Extraction Research Articles

Preparation of dummy molecularly imprinted polymers for selective extraction of aromatic amine genotoxic impurities

To ensure drug safety, the quality monitoring of genotoxic impurities (GTIs) which have very trace content in medicine is important. Therefore, it should be established an efficient sample pretreatment method to extract GTIs to achieve specific enrichment. In this work, dummy template molecular imprinting technology (DMIT) was used as dummy template molecule (DTM) to substitute for the target molecule (TM) for established the pretreatment of the sample containing aromatic amine GTIs. A novel strategy for screening out DTM by calculation of computer simulation is established, where the binding energy between the template and functional monomer has the relatively lowest value (-9.60 kcal/mol). Then dummy template molecular imprinted polymer (DMIP) was prepared by bulk polymerization according to the molar ratio of template molecule-functional monomer-crosslinker = 1:4:8, the prepared DMIP exhibited the highest adsorption (Q = 8.6 mg/g) and good blotting effect (IF = 1.3) and can simultaneously adsorb three aromatic amine GTIs. The optimal adsorption conditions were obtained by conditional optimization of solid phase extraction (SPE). The solution of pH 7 was chosen as the loading condition, and methanol/acetic acid (90:10, v/v) was chosen as the elution condition. Finally, we determined 2, 6-dichloroaniline in diclofenac sodium at a 5 ppm level and p-toluidine as the TMs in torasemide sample at 10 ppm by using DMIT-based solid phase extraction and analysis by HPLC, it satisfied the quality control of GTIs in pharmaceutics. DMIT by this strategy has great potential in the sample preparation of GTIs.

Optimized Sample Preparation and Microscale Separation Methods for High-Sensitivity Analysis of Hydrophilic Peptides.

The optimization of solid-phase extraction (SPE) purification and chromatographic separation is usually neglected during proteomics studies. However, the effects on detection performance are not negligible, especially when working with highly glycosylated samples. We performed a comparative study of different SPE setups, including an in-house optimized method and reversed-phase chromatographic gradients for the analysis of highly glycosylated plasma fractions as a model sample for glycopeptide analysis. The in-house-developed SPE method outperformed the graphite-based and hydrophilic interaction liquid chromatography (HILIC) purification methods in detection performance, recovery, and repeatability. During optimization of the chromatography, peak distribution was maximized to increase the peptide detection rate. As a result, we present sample purification and chromatographic separation methods optimized for the analysis of hydrophilic samples, the most important of which is heavily N-glycosylated protein mixtures.

Ultra-High-Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry for High-Neuroanatomical Resolution Quantification of Brain Estradiol Concentrations

Ventromedial hypothalamic nucleus (VMN) control of glucostasis is estradiol (E-2)-dependent. E-2 regulation of VMN reactivity to hypoglycemia may involve changes in signal volume due to altered aromatase expression. Here, high-resolution micropunch dissection tools for isolation of segmental VMN tissue were used with Design of Experiments-refined uHPLC-electrospray ionization-mass spectrometry (LC-ESI-MS) methodology to investigate the premise that effects of acute and/or recurring hypoglycemia on VMN E-2 content are sex-dimorphic. Relationships among multiple independent mass spectrometric operational variables were assessed by Central Composite Design (CCD) to amplify E-2 chromatogram area. Combinations of spectrometric temperature and gas pressure variable combinations were screened by Akaike Information Criterion correction modeling. A Fibonacci Sequence design using CCD minimum and maximal variable limits produced a small-run model that replicated maximal response from CCD. E-2 chromatographic response was further enhanced by optimization of solid phase extraction and instrument source and collision-induced dissociation voltages. In male rats, acute and chronic hypoglycemia respectively elevated or diminished E-2 concentrations relative to baseline in both rostral and caudal VMN. However, females exhibited regional variability in tissue E-2 profiles during acute (increased, rostral VMN; no change, caudal VMN) and recurring (no change, rostral VMN; increased, caudal VMN) hypoglycemia. Outcomes demonstrate requisite LC-ESI-MS sensitivity for E-2 quantification in small-volume brain tissue samples acquired with high-neuroanatomical specificity. Current methodology will facilitate efforts to investigate physiological consequences of VMN rostro-caudal segment-specific acclimation of E-2 profiles to recurring hypoglycemia, including effects on gluco-regulatory function, in each sex.

Optimization of solid-phase extraction (SPE) in the preparation of [18F]D3FSP: A new PET imaging agent for mapping Aβ plaques

IntroductionAlzheimer's disease is a common neurodegenerative disease that is characterized by the presence of Aβ plaques in the brain. The FDA has approved the use of Amyvid (florbetapir f18, AV-45) as a PET imaging agent for detecting Aβ plaques in the living human brain. In an attempt to reduce N-demethylation in vivo by taking advantage of more stable C-D bonds, an analog of AV-45, [18F]D3FSP ([18F]7), was synthesized to improve image contrast for detecting and monitoring the Aβ plaques. A convenient and improved preparation of [18F]D3FSP ([18F]7) is needed for widespread clinical application. We report herein the optimization of the radiosynthesis and solid-phase extraction (SPE) procedure. MethodsRadiosyntheses of [18F]D3FSP ([18F]7) under different fluorination conditions were evaluated, and the intermediate, containing an N-Boc protecting group, was deprotected using different acids. One of the major objectives was to simplify the final purification step via SPE to avoid the commonly employed HPLC purification and maximize the radiochemical yields of [18F]D3FSP ([18F]7) while simultaneously removing several chemical impurities (pseudocarriers). Washing various solid-phase cartridges with different combinations of ethanol/water and acetonitrile/water was explored to optimize the purification step. To evaluate the potential interference in Aβ plaques imaging from the presence of pseudocarriers, each chemical was identified and quantified by LC/MS and HPLC. An in vitro binding assay was employed to evaluate the binding affinities of [18F]D3FSP ([18F]7) and the pseudocarriers to Aβ plaques using postmortem AD brain tissue. ResultsUsing the optimized radiosynthesis method and SPE purification, the final dose of [18F]D3FSP ([18F]7) was obtained in 50 min with a very low content of pseudocarriers (21.7 ± 5.5 μg). The radiochemical yield was 44.4 ± 5.7% (decay corrected), and the radiochemical purity was >95%. SPE-purified doses of [18F]D3FSP ([18F]7) displayed excellent binding affinity and specificity for Aβ plaques as measured in an in vitro binding assay using AD brain homogenates, and the OH-pseudocarrier, 8 (Ki = 19.5 ± 0.5 nM), and the Cl-pseudocarrier, 10 (Ki = 18.6 ± 3.9 nM), showed lower binding affinities for Aβ plaques than those of AV-45 (Ki = 8.6 ± 0.5 nM) and D3FSP, 7 (Ki = 9.8 ± 0.5 nM). ConclusionsAn optimized radiosynthesis and fast SPE purification method suitable for the preparation of clinical doses of [18F]D3FSP ([18F]7) was accomplished. The results of quality control tests and binding studies suggested that the SPE-purified doses of [18F]D3FSP ([18F]7) are appropriate for imaging Aβ plaques in the human brain.

Bifunctional monomer molecularly imprinted sol-gel polymers based on the surface of magnetic halloysite nanotubes as an effective extraction approach for norfloxacin

Abstract An effective magnetic surface imprinted polymer with high adsorption ability and selectivity has been designed. Three magnetic halloysite nanotubes combined with molecularly imprinted polymer (MMIP) composites were fabricated. Halloysite nanotubes (Hal nanotubes) were us as supporting matrix, norfloxacin (NOR) as template molecules, Aminopropyltriethoxysilane (3-APTES) and Methacryloxypropyltrimethoxysilane (MTEOS) used as monomers and tetramethyl orthosilicate (TEOS) as cross linker through a one-pot sol-gel polymerization. The resulting MMIP were characterized by various techniques. The adsorption isotherms, adsorption kinetics and selective recognition of MMIP were investigated in detail. The imprinted polymers with bifunctional monomer possess the highest adsorption capacity (312.08 μg·mg−1) and the best select factor (5.41). After optimization of solid phase extraction (SPE) condition, imprinted polymer with bifunctional monomer possess the best extraction ability and can be successfully applied into the extraction of norfloxacin in lake water. In addition, the SPE-ultraviolet method established possesses good accuracy and precision. Hydrochloric acid (9:1/v:v) could be used as the best elution and the magnetic imprinted polymer could be reused for at least seven times.

Simultaneous determination of binary solution of triphenylmethane dyes in complex matrices onto magnetic amino-rich SWCNT using second-order calibration method.

This study suggested a new method for simultaneous quantification of two dyes in complex matrices using second-order data by spectrophotometry. Second-order data was generated simply without any expensive instrument using two independent variables including wavelength and the monotonic addition of sodium dodecyl sulfate. Solid-phase extraction (SPE) based on amino-rich magnetic single-walled carbon nanotube as an adsorbent was employed prior to second-order data generation. SPE optimization was performed by Box-Behnken design, and parameters and their interaction which were dependent on the simultaneous extraction of dyes were examined. Competitive Langmuir and Freundlich isotherms for a binary system and individual dyes could all represent the equilibrium data well. The second-order data was processed by parallel factor analysis (PARAFAC and PARAFAC2) and multivariate curve resolution-alternating least squares (MCR-ALS). Figures of merit of the model including a limit of detection of 3.0 and 2.5ngmL-1 for crystal violet and malachite green, respectively, were estimated using the MCR-ALS method. The combination of the second-order calibration and SPE presents an easy and versatile method for determination of the mixture of two dyes in the presence of uncalibrated interferences in environmental water, synthetic, and fish samples with the recoveries of 94-104.

Simultaneous determination of 20 trace organic chemicals in waters by solid-phase extraction (SPE) with triple-quadrupole mass spectrometer (QqQ-MS) and hybrid quadrupole Orbitrap high resolution MS (Q-Orbitrap-HRMS)

A sensitive method for simultaneous determination of 20 trace organic chemicals (TOrCs, including preservatives, antioxidants, disinfectants, oestrogens, alkyl-phenols and bisphenol-A) in surface water and wastewater has been developed and validated based on the optimisation of solid-phase extraction (SPE) followed by liquid chromatography-mass spectrometry (LC-MS) analysis. 500 mL acidified (pH = 2.5) water samples were pre-concentrated by Supel-Select HLB cartridge (200 mg, 6 mL) and eluted with 12 mL mixture of acetonitrile and ethyl acetate (50:50, v/v). This optimised SPE procedure could provide >75% recoveries for the majority of TOrCs. The instrumental methods were developed using two different LC-MS systems: a triple-quadrupole MS (QqQ-MS) and a hybrid quadrupole Orbitrap high resolution MS (Q-Orbitrap-HRMS). Both showed good performance data, but the former system provided better linearity and method precision, with the latter system providing 2–33 times lower detection limits. Different matrix effects were observed for both systems: No remarkable matrix effects were observed for Q-Orbitrap-HRMS but significant matrix effects were found in influent and river water samples for the QqQ-MS. This analytical method was subsequently employed to analyse the TOrCs in river waters and wastewaters from China successfully, which confirmed its applicability to environmental samples.

Optimization of solid-phase extraction and liquid chromatography-tandem mass spectrometry for simultaneous determination of capilliposide B and its active metabolite in rat urine and feces: Overcoming nonspecific binding

Capilliposide B, a novel oleanane triterpenoid saponin isolated from Lysimachia capillipes Hemsl, showed significant anti-tumor activities in recent studies. To characterize the excretion of Capilliposide B, a reliable liquid chromatography-tandem mass spectrometry (LC–MS/MS) method was developed and validated for simultaneous determination of Capilliposide B and its active metabolite, Capilliposide A in rat urine and feces. Sample preparation using a solid-phase extraction procedure was optimized by acidification of samples at various degrees, providing extensive sample clean-up with a high extraction recovery. In addition, rat urinary samples were pretreated with CHAPS, an anti-adsorptive agent, for overcoming nonspecific analytes adsorption during sample storage and process. The method validation was conducted over the curve range of 10.0–5000ng/ml for both analytes. The intra- and inter-day precision and accuracy of the QC samples showed ≤11.0% RSD and −10.4–12.8% relative error. The method was successfully applied to an excretion study of Capilliposide B following intravenous administration.

Optimization of Solid-phase Extraction by Experimental Design Methodology for Determination of Lead Ions Using Graphene Modified Nano-sheets as a Novel Sorbent

A novel sorbent was synthesized by modification of graphene nano-sheets by pyridine group and characterized by transmission electron microscopy (TEM), thermal analysis (TG/DTA), elemental analysis (CHN) and infrared spectroscopy (IR). The application of this sorbent in determination of lead ions in environmental samples was investigated. Some parameters such as pH and time on adsorption process were optimized and introduced . The other parameters including eluent concentration, eluent volume and elution time which are important factors in desorption process were optimized by using a three-level three variables Box-Behnken experimental design. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 3.5 ng mL-1, 2.2% and 98%, respectively. Finally the method was validated using several standard reference materials. Keywords: Geraphene nano-sheets, experimental design methodology, Pb(II) determination, solid-phase extraction.

A separation of tyramine on a 2-(4-methoxyphenyl)ethylamine imprinted polymer: An answer from theoretical and experimental studies

A 2-(4-methoxyphenyl)ethylamine imprinted polymer (MIP) was successfully applied for the selective separation of tyramine. A computational analysis was used to predict the affinity of the polymer matrix towards tyramine and a preliminary experimental evaluation was made for the target analyte. Then the experimental analysis of polymer towards tyramine was continued. The binding sites were characterized with employment of the Langmuir and Freudlich models. After the optimization of solid phase extraction towards tyramine, the most appropriate systems for the extraction steps were chosen: methanol–water 85:15 v/v for the loading and the washing as well as 0.04M aq. ammonium acetate–methanol 30:70 v/v for the elution steps. The biogenic compounds as tryptamine, serotonin, octopamine, synephrine, and l-tyrosine were used for the selectivity study on the basis of binding capacities of the analytes on the imprinted and the non-imprinted polymers. The theoretical approach to obtained results allowed to explain the adsorption selectivity of the tested polymer. Finally, the complex matrix of bovine serum albumin was used to show the usefulness of imprinted material for bioanalysis. The obtained recoveries showed the superiority of MIP over the commercial sorbent C18. Total recoveries of tyramine from spiked bovine serum albumin sample were determined as: 95±2%, 14±3%, and 1.9±0.4% for the imprinted, non-imprinted, and commercial C18 sorbents, respectively.

Evaluation of Two Statistical Tools (Least Squares Regression and Artificial Neural Network) in the Multivariate Optimization of Solid-Phase Extraction for Cadmium Determination in Leachate Samples

Este trabalho propoe a otimizacao multivariada de um procedimento para determinacao de cadmio em amostras de chorume usando-se espectrometria de absorcao atomica com chama apos a extracao em fase solida usando-se uma minicoluna empacotada com Amberlite XAD-4 modificada com acido 3,4-diidroxibenzoico. As variaveis relacionadas a pre-concentracao (pH, razao de amostragem e concentracao do tampao) foram otimizadas usando-se planejamento Doehlert. Duas ferramentas para modelagem estatistica (regressao por minimos quadrados e redes neurais artificiais) foram aplicadas aos dados e seus desempenhos foram comparados. Procedimentos de digestao do chorume por aquecimento em meio acido e por radiacao ultravioleta foram avaliados sendo este ultimo mais adequado para evitar a perda de Cd por volatilizacao. O procedimento desenvolvido apresentou um fator de enriquecimento de 9 vezes com limites de deteccao e de quantificacao (3s b ) de 0,72 e 2,4 µg L -1 , respectivamente, e precisao - expressa como porcentagem do desvio padrao relativo - de 4,0 e 6,4% (RSD%, n = 4 para 5,0 e 20,0 µg L -1 , respectivamente). Testes de adicao/recuperacao de Cd foram realizados obtendo-se valores entre 97 e 112%. O procedimento foi aplicado na determinacao de cadmio em amostras de chorume coletadas no aterro sanitario do municipio de Jaguaquara-BA, Brasil. This work proposes the use of multivariate optimization as a procedure for cadmium determination in leachate samples via flame atomic absorption spectrometry after solid phase extraction using a minicolumn packed with Amberlite XAD-4 modified with 3,4-dihydroxybenzoic acid. The variables related with the preconcentration (pH, sampling flow rate and buffer concentration) were optimized using Doehlert design. Two statistical modeling tools (least squares regression and artificial neural networks) have been applied to the data and their performances were compared. Digestion procedures of the leachate by heating in acid medium and ultraviolet radiation were evaluated being the latter more appropriate to prevent loss of Cd by volatilization. The developed procedure has promoted an enrichment factor of 9, with detection and quantification limits (3sb) of 0.72 and 2.4 µg L -1 , respectively, and precision - expressed as relative standard deviation percentage - of 4.0 and 6.4% (RSD%, n = 4 for 5.0 and 20.0 µg L -1 , respectively). Addition/recovery tests for Cd were carried out and values between 97 and 112% were obtained. The procedure was applied for cadmium determination in leachate samples collected at the sanitary landfill of Jaguaquara-BA, Brazil.

Optimization of solid-phase extraction based on a new sol-gel material using a response surface methodology for the determination of copper in water samples by flame atomic absorption spectrometry

A simple method for solid-phase extraction and pre-concentration of trace amounts of copper prior to determination by flame atomic absorption spectrometry (FAAS) has been developed. The method is based on the adsorption of Cu(II) ions on a micro-column packed with a sol-gel material doped with 1-hexylpyridinium hexafluorophosphate [C6py+] [] ionic liquid and 8-hydroxyquinoline (oxine) as a novel solid-phase extractor. Different variables affecting the separation/pre-concentration conditions of analyte, including pH of the sample solution, buffer concentration, sample loading flow rate and elution conditions were investigated and optimized utilizing the central composite design (CCD). In the optimum conditions, the limit of detection (LOD), limit of quantification (LOQ) and enrichment factor were 0.5 µg L−1, 1.7 µg L−1 and 50, respectively. The relative standard deviation (RSD) for nine replicate determinations of 25 and 50 µg L−1 Cu were 1.8 and 1.3%, respectively. The calibration graph using the pre-concentration system was linear in the range of 2−120 µg L−1 with a correlation coefficient of 0.9989. A standard reference material (NIST SRM 1566b), was used for validation of the presented method. The optimized method was successfully applied to the determination of copper in several water samples.

The automation and optimization of solid phase extraction inductively coupled plasma mass spectrometry analysis for the high throughput determination of aqueous levels of U, Th, Np, Pu, and Am

The development of an automated chemical and mechanical sequence is presented for actinide analysis by inductively coupled plasma mass spectrometry (ICP-MS) using a column-based chromatographic system with TRU resin for matrix separation. The approach yields a robust method that allows for simple handling with high sample throughput for use in rapid response scenarios. Nanogram-level studies were carried out using ICP-MS with mono-isotopic spiked samples. Sample throughput was extrapolated to successfully handle over 2000 samples a day. This process includes a manual valency adjustment allowing for direct optimal loading while simultaneously minimizing sample dilution, an automated solid phase extraction platform, and a unique transfer system for flow through from the extraction to the ICP-MS detection platform. Bed volumes, reagent compositions, resin environments as well as volume and flow rates were optimized to increase recovery. Under optimal conditions the average recoveries over the range from 0.1 to 1.0 μg L−1 were 238U 106.3 ± 5.4%, 237Np 100.5 ± 2.3%, 242Pu 94.3 ± 5.2% and 232Th 109.2 ± 4.8%. Using synthetic urine as a complex matrix the recoveries were 238U 96.2 ± 1.6%, 237Np 95.4 ± 1.7%, 242Pu 81 ± 2.4%, 232Th 98.8 ± 1.7% and 241Am 53 ± 3.6% for samples at the 1 μg L−1 level co-eluted with a 0.5 M HCl/0.3 M oxalic acid solution. These high recoveries were obtained while successfully removing 99.999% of monitored matrix ion constituents and minimizing reagent volumes, culminating in the development of a method that allows for rapid onsite handling of a large number of samples while maintaining high recovery and consistency inherent to automation.

Optimization of solid-phase extraction using artificial neural networks and response surface methodology in combination with experimental design for determination of gold by atomic absorption spectrometry in industrial wastewater samples

Solid-phase extraction (SPE) is often used for preconcentration and determination of metal ions from industrial and natural samples. A traditional single variable approach (SVA) is still often carried out for optimization in analytical chemistry. Since there is always a risk of not finding the real optimum by single variation method, more advanced optimization approaches such as multivariable approach (MVA) should be applied. Applying MVA optimization can save both time and chemical materials, and consequently decrease analytical costs. Nowadays, using artificial neural network (ANN) and response surface methodology (RSM) in combination with experimental design (MVA) are rapidly developing. After prediction of model equation in RSM and training of artificial neurons in ANNs, the products were used for estimation of the response of the 27 experimental runs. In the present work, the optimization of SPE using single variation method and optimization by ANN and RSM in combination with central composite design (CCD) are compared and the latter approach is practically illustrated.

Optimization of solid-phase extraction and liquid chromatography–tandem mass spectrometry for the determination of domoic acid in seawater, phytoplankton, and mammalian fluids and tissues

We previously reported a solid-phase extraction (SPE) method for determination of the neurotoxin domoic acid (DA) in both seawater and phytoplankton by liquid chromatography–tandem mass spectrometry (LC–MS/MS) with the purpose of sample desalting without DA pre-concentration. In the present study, we optimized the SPE procedure with seawater and phytoplankton samples directly acidified with aqueous formic acid without addition of organic solvents, which allowed sample desalting and also 20-fold pre-concentration of DA in seawater and phytoplankton samples. In order to reduce MS contamination, a diverter valve was installed between LC and MS to send the LC eluant to waste, except for the 6-min elution window bracketing the DA retention time, which was sent to the MS. Reduction of the MS turbo gas temperature also helped to maintain the long-term stability of MS signal. Recoveries exceeded 90% for the DA-negative seawater and the DA-positive cultured phytoplankton samples spiked with DA. The SPE method for DA extraction and sample clean-up in seawater was extended to mammalian fluids and tissues with modification in order to accommodate the fluid samples with limited available volumes and the tissue extracts in aqueous methanol. Recoveries of DA from DA-exposed laboratory mammalian samples (amniotic fluid, cerebrospinal fluid, plasma, placenta, and brain) were above 85%. Recoveries of DA from samples (urine, feces, intestinal contents, and gastric contents) collected from field stranded marine mammals showed large variations and were affected by the sample status. The optimized SPE–LC–MS method allows determination of DA at trace levels (low pg mL −1) in seawater with/without the presence of phytoplankton. The application of SPE clean-up to mammalian fluids and tissue extracts greatly reduced the LC column degradation and MS contamination, which allowed routine screening of marine mammalian samples for confirmation of DA exposure and determination of fluid and tissue DA concentrations in experimental laboratory animals.

Optimization of solid-phase extraction using developed modern sorbent for trace determination of ametryn in environmental matrices

In recent years, there has been a significant increase in molecularly imprinted solid-phase extraction (MISPE) technique for the purification and clean-up of environmental samples. In this study, solid-phase extraction using the imprinted polymer has been optimized with the experimental design approach for a triazine herbicide, named ametryn with regard to the critical factors such as sample pH, sample concentration, sample flow-rate, sample volume, elution solvent, washing solvent and sorbent mass. These factors were evaluated statistically and also validated with spiked drinking water samples and showed a good reproducibility over six consecutive days as well as six within-day experiments. Also, in order to the evaluate efficiency of the optimized MISPE protocols, enrichment capacity, reusability and cross-reactivity of cartridges have been studied. Finally, a selective MISPE was successfully demonstrated for ametryn with a recovery of above 90% for spiked drinking water samples. It was concluded that the central composite design could prove beneficial for aiding the MIP and MISPE development.

Application of experimental design in optimization of solid phase extraction of mycophenolic acid and mycophenolic acid glucuronide from human urine and plasma and SPE-RP-HPLC method validation

The aim of this study was to develop and optimize a solid phase extraction (SPE) procedure for purification of mycophenolic acid (MPA) and its metabolite mycophenolic acid glucuronide (MPAG) in biological samples. During optimization process chemometric approach was applied. First, in screening experiments fractional factorial design (FFD) was used for selecting the variables which affected the extraction procedure. The ionic strength of the phosphate buffer in the washing step and the percentage of acetonitrile in the elution step were statistically significant for the recovery of MPAG while the percentage of acetonitrile and pH of the washing solution were statistically significant for that of MPA. Afterwards, the significant variables were optimized using central composite design (CCD). The developed SPE method included phosphate buffer (pH 2.4; 0.056 M) in the washing step, and the mixture of acetonitrile and phosphate buffer of which pH was adjusted to 2.4 (70:30, v/v) in the elution step. The investigation was applied to both urine and plasma and the nature of biological matrix appeared to be of no importance. The extraction from both matrixes showed good repeatability with relative standard deviations up to 6% for MPAG and 8% for MPA, and recovery around 100% for both substances. Furthermore, new SPE-RP-HPLC method for determination of MPA and MPAG in both humane urine and plasma has been validated. The great advantage of this method is the chromatographic run of only 3 min.

Analysis of phenols in wastewater using capillary electrophoresis and solid phase extraction

A solid phase extraction (SPE) method was developed for phenol, 4-nitrophenol, 4-chlorophenol and 4-cyanophenol from the wastewater. The recoveries were 95%, 93%, 92% and 90% for phenol, 4-nitrophenol, 4-chlorophenol and 4-cyanophenol, respectively. The elution was carried out by methanol (1 mL) at 0.25 mL/min. flow rate. The optimisation of SPE was achieved by using different eluting solvents, pH of wastewater, flow rates and other factors. Validation of the developed methodology was carried out using Microsoft Excel program. Possible mechanisms were presented for SPE of phenols.

Optimization of solid-phase extraction using artificial neural networks in combination with experimental design for determination of resveratrol by capillary zone electrophoresis in wines

Solid-phase extraction (SPE) is often used for preconcentration of analytes from biological samples. Such an analytical step requires optimization for obtaining reliable results. Optimization in analytical chemistry is traditionally still often done with relaxation method, when an optimal value of a single variable is searched for (single variable approach (SVA)). However, if the optimized procedure is complex, there is a danger not to find the real optimum by SVA. Therefore, more advanced optimization approaches should be applied—multivariable approach (MVA). Applying MVA optimization and finding the real optimum, better experimental conditions are obtained and thus, time, chemicals and analytical procedure cost can be served. Nowadays, using artificial neural networks (ANN's) in combination with MVA is rapidly expanding. In this work, the optimization of SPE using relaxation method (SVA) and optimization by ANN's in combination with experimental design (MVA) are compared and latter approach is practically illustrated. Advantages of MVA over SVA for optimization are discussed. The prediction of the optimal SPE conditions for determination cis- and trans-resveratrol in Australian wines by capillary zone electrophoresis is described and the improvement of efficiency of SPE using MVA is confirmed.

Simple strategy for the optimization of solid-phase extraction procedures through the use of solid-liquid distribution coefficients application to the determination of aliphatic lactones in wine.

A practical strategy for the optimization of solid-phase extraction (SPE) systems is presented. Critical SPE volumes (sample loaded, rinsing and elution solvent) are calculated from solid-liquid extraction coefficients and from basic bed parameters determined in simple experiments, using the Lövkist Jonsson model and other expressions derived from the general theory of chromatography. The agreement between calculated and measured volumes is satisfactory, which makes it possible to consider different sorbents and rinsing and elution solvents in the SPE optimization with a relatively low experimental effort. The strategy has been successfully applied to the optimization of a SPE method directed to the selective extraction of aliphatic lactones from wine. Six different reversed-phase sorbents were studied and the one showing maximum extraction selectivity was selected. Wine (50 ml) is extracted in a 200 mg cartridge filled with Bond Elut-ENV resins. Interferences are removed with 20 ml of methanol-water (40:60) with 1% NaHCO3. Elution is carried out with 1.8 ml of dichloromethane. The extract is concentrated to 0.15 ml and analyzed by GC-ion trap MS. Eight odor-active aliphatic gamma and delta lactones (with 8-12 C atoms) from wine are recovered (R > 75%) in an extract free from wine major volatiles. Detection limits are in the 40-300 ng/l range, well below the odor detection threshold of these compounds. Linearity (r2 > 0.996) and precision (average R.S.D. 3.5%) are satisfactory in all cases. The levels in wine of some of these lactones (gamma-octa, undeca and dodecalactones) are reported by first time and results demonstrate that can be present at concentrations above or close to their corresponding odor thresholds.