Evaluation of an on-line coupled continuous flow liquid membrane extraction and precolumn system as trace enrichment technique by liquid chromatographic determination of bisphenol A

An on-line coupled continuous flow liquid membrane extraction (CFLME) and C₁₈ precolumn system was developed for sample preconcentration in liquid chromatography determination. After preconcentration by CFLME, which is based on the combination of continuous flow liquid–liquid extraction and supported liquid membrane, bisphenol A (BPA) was enriched in 960 μl of 1 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto a C₁₈ analytical column for separation and detected at 220 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor, and enrichment time were optimized. The proposed method presents a detection limit of 0.03 μg l⁻¹ (S/N=3) when 60 ml samples was enriched with an enrichment time of 30 min. Compared with C₁₈ based column-switching procedure, this proposed procedure presents similar sample throughput and lower detection limits. The proposed method was successfully applied to determine BPA in tap water, river water, and municipal sewage effluent samples.     

Determination of total flavonoids in Scutellaria barbata D. Don by dynamic ultrasonic extraction coupled with on-line spectrophotometry

A dynamic ultrasonic extraction (DUE) coupled with on-line detection by spectrophotometry is proposed for the determination of total flavonoids (calculated against scutellarin) in Scutellaria barbata D. Don. The extraction was performed in a common self-made extraction vessel put in an ultrasonic bath and a peristaltic pump was used to deliver the extraction solvent. Several experimental parameters of DUE, including flow rate and concentration of extraction solvent, ultrasonic power and sample amount, were optimized. In this work an on-line method was provided with the advantages of minimum sample amount (5 mg), on-line monitoring the extraction process and time saving (12.5 min). Compared with off-line method, the proposed method would be more convenient for obtaining continuous measurements and rapid optimization of the extraction process.     

High performance liquid chromatography determination of chlorophenols in water samples after preconcentration by continuous flow liquid membrane extraction on-line coupled with a precolumn

A continuous flow liquid membrane extraction (CFLME)-C₁₈ precolumn-liquid chromatography system was developed for preconcentration and determination of chlorinated phenols (CPs). After preconcentration by CFLME, which is based on the combination of continuous flow liquid-liquid extraction and supported liquid membrane, CPs were enriched in 960 μl of 0.5 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto the C₁₈ analytical column for separation and detected at 215 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor concentration were optimized. The proposed method presents detection limits of 0.02-0.09 μg l⁻¹ (S/N=3) when 100 ml samples were enriched. The proposed method was successfully applied to determine CPs in tap water and river water samples with spiked recoveries in the range of 70-121%.     

On-line solid-phase extraction and high performance liquid chromatography determination of polycyclic aromatic hydrocarbons in water using polytetrafluoroethylene capillary

Naphthalene, biphenyl, acenaphtene, anthracene and pyrene were extracted from water samples using inner walls of polytetrafluoroethylene capillary. Optimum conditions for sorption, desorption and heart-cutting of the analyte zone were found. Combined on-line solid-phase extraction and HPLC method for determination of these compounds was proposed. Limits of detection were: (μg L⁻¹): 0.4 (naphthalene), 0.3 (biphenyl), 0.6 (acenaphtene), 0.2 (anthracene) and 0.1 (pyrene).     

The determination of organochlorine pesticides based on dynamic microwave-assisted extraction coupled with on-line solid-phase extraction of high-performance liquid chromatography

A rapid technique based on dynamic microwave-assisted extraction coupled with on-line solid-phase extraction of high-performance liquid chromatography (DMAE-SPE-HPLC) has been developed. A TM₀₁₀ microwave resonance cavity built in the laboratory was applied to concentrate the microwave energy. The sample placed in the zone of microwave irradiation was extracted with 95% acetonitrile (ACN) aqueous solution which was driven by a peristaltic pump at a flow rate of 1.0 mL min⁻¹. The extraction can be completed in a recirculating system in 10 min. When a number of extraction cycles were completed, the extract (1 mL) was diluted on-line with water. Then the extract was loaded into an SPE column where the analytes were retained while the unretained matrix components were washed away. Subsequently, the analytes were automatically transferred from the SPE column to the analytical column and determined by UV detector at 238 nm. The technique was used for determination of organochlorine pesticides (OCPs) in grains, including wheat, rice, corn and bean. The limits of detection of OCPs are in the range of 19-37 ng g⁻¹. The recoveries obtained by analyzing the four spiked grain samples are in the range of 86-105%, whereas the relative standard deviation (R.S.D.) values are <8.7% ranging from 1.2 to 8.7%. Our method was demonstrated to be fast, accurate, and precise. In addition, only small quantities of solvent and sample were required.     

Dynamic microwave-assisted extraction coupled with on-line spectrophotometric determination of safflower yellow in Flos Carthami

A rapid dynamic microwave-assisted extraction and on-line detection by spectrophotometry is proposed for the determination of safflower yellow in Flos Carthami. A high pressure and a peristaltic pump were used to deliver the solvent. A TM₀₁₀ microwave resonance cavity was applied to concentrate the microwave energy and the forward power about 60 W was enough for the extraction. Other extraction conditions also were examined and optimized. In this work, the extraction process can be monitored by measuring the absorption of safflower yellow in the extract, which would be convenient for rapid optimization of the extraction process. The detection and quantification limits are 8 and 27 μg mL⁻¹, respectively. The within-day and between-day precision (R.S.D.) are 1.6-3.2% and 2.8-4.2%, respectively. Compared with off-line detection, the proposed method may provide more rapid measurement and is more convenient for obtaining continuous measurements.     

On-line solid-phase extraction coupled to hydrophilic interaction chromatography-mass spectrometry for the determination of polar drugs

The present study describes the first fully automated method based on on-line solid-phase extraction (SPE) coupled to hydrophilic interaction chromatography-electrospray-mass spectrometry (HILIC-(ESI)MS) to determine a group of polar drugs that includes illicit drugs (such as cocaine, morphine, codeine and metabolites) and pharmaceuticals in environmental water samples. The SPE was performed using a highly retentive polymeric sorbent. The HILIC separation was optimised and the initial high organic content of the chromatographic mobile phase, was also suitable for the proper on-line elution of the analytes retained in the SPE column and for enhancing the ESI ionisation efficiency. This method allows the loading of samples of up to 250ml of ultrapure water or 10ml of environmental water samples spiked at low ngl(-1) levels of the analytes. The method yields near 100% recoveries for all the analytes. The method was also validated with environmental water samples with linear ranges from 5 to 1000ngl(-1) and limits of detection ≤2ngl(-1) for most of the compounds.     

On-line coupling of solid-phase extraction to high-performance liquid chromatography for determination of estrogens in environment

A method based on on-line solid-phase extraction (SPE) coupling to high-performance liquid chromatography (HPLC) for the determination of estrogens has been developed. This method can continuously perform extraction of estrone, estradiol, estriol and diethylstilbestrol from aqueous samples without any other pretreatment, which can then be analyzed by HPLC with a UV detector at 230 nm. A pre-concentration column was adapted with methanol/water for chromatographic separation and two kinds of sorbents were involved, which are octadecyl-bonded silica and cigarette filter. The condition of pH of samples, sample loading flow rate and desorption time were all optimized, and the performances of both two sorbents were satisfactory. The on-line SPE system requires very low maintenance and just involved a switching-valve-filter system and a flow-inject pump, and the operation of the whole SPE-HPLC instrumentation is quite simple. The detection limits for pre-concentrating 50 mL of standard solution using cigarette filter as sorbent ranged from 0.98 to 78.1 ng L⁻¹. The enhancement factors were in the range of 197-326. The recoveries of estrogens spiked in real water samples ranged from 85 to 112%. The precisions for nine replicate measurements of a standard mixture (5.0 μg L⁻¹) were in the range of 1.0-3.4%.     

Solvent (ionic liquid) impregnated resin-based extraction coupled with dynamic ultrasonic desorption for separation and concentration of four herbicides in environmental water

A new method was developed for the determination of monolinuron, propazine, linuron, and prebane in environmental water samples. The solvent (ionic liquid) impregnated resin (IL-SIR)-based extraction coupled with dynamic ultrasonic desorption (DUSD) was applied to the separation and concentration of the analytes. The high performance liquid chromatography (HPLC) was applied to the determination of the analytes. The ionic liquid [C₆MIM][PF₆] was immobilized on Diaion HP20 resin by immersing the resin in ethanol solution containing [C₆MIM][PF₆]. The effect of extraction parameters, including pH value of sample solution, salt concentration in sample and extraction time, and elution conditions, including the concentration of ethanol in elution solvent, the flow rate of elution solvent and the ultrasonic power, were examined and optimized. The limits of detection and quantification for the analytes were in the range of 0.15-0.29 μg L⁻¹ and 0.51-0.98 μg L⁻¹, respectively. Some environmental water samples were analyzed and the analytical results were satisfactory.     

On-line trace enrichment of phenolic compounds from water using a pyrrole-based polymer as the solid-phase extraction sorbent coupled with high-performance liquid chromatography

A pyrrole-based conductive polymer was prepared and applied as new sorbent for on-line solid-phase extraction (SPE) of phenol and chlorophenols from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in non-aqueous solution. The efficiency of this polymer for extraction of phenol and chlorophenols was evaluated using 35 mg of PPy as the sorbent in an on-line SPE system coupled to reversed-phase liquid chromatography with UV detection. The mobile phase were mixture of phosphate buffer-acetonitrile and compounds were eluted by the mobile phase using a six-port switching valve. High volumes of water, up to 160 ml, could be preconcentrated without the loss of phenols, except for the more polar ones. The R.S.D. for a river water sample spiked with phenol and chlorophenols at sub-ppb level was lower than 7% (n=5) and detection limits of 15-100 and 35-150 ng l⁻¹ for tap and river water were obtained, respectively.     

Continuous determination of total flavonoids in Platycladus orientalis (L.) Franco by dynamic microwave-assisted extraction coupled with on-line derivatization and ultraviolet-visible detection

This paper describes a new method for the determination of total flavonoids in Platycladus orientalis (L.) Franco. The method was based on dynamic microwave-assisted extraction (DMAE) coupled with on-line derivatization and ultraviolet-visible (UV-vis) detection. The influence of the experimental conditions was tested. Maximum extraction yield was achieved using 80% aqueous methanol of extraction solvent; 80 W of microwave output power; 5 min of extraction time; 1.0 mL min⁻¹ of extraction solvent flow rate. The derivatization reaction between aluminium chloride and flavonoid is one of the most sensitive and selective reactions for total flavonoids determination. The optimized derivatization conditions are as follows: derivatization reagent 1.5% aluminium chloride methanol solution; reaction coil length 100 cm; derivatization reagent flow rate 1.5 mL min⁻¹. The detection and quantification limits obtained are 0.28 and 0.92 mg g⁻¹, respectively. The intra-day and inter-day precisions (R.S.D.) obtained are 1.5% and 4.6%, respectively. Mean recovery is 98.5%. This method was successfully applied to the determination of total flavonoids in P. orientalis (L.) Franco and compared with heat reflux extraction. The results showed that the higher extraction yield of total flavonoids was obtained by DMAE with shorter extraction time (5 min) and small quantity of extraction solvent (5 mL).     

On-Line coupling of supercritical fluid extraction with high performance liquid chromatography

Supercritical fluid extraction was coupled directly with high performance liquid chromatograph. The system was evaluated for direct injection of supercritical CO₂ and modified supercritical CO₂ at high pressure and temperature onto a HPLC system with varying mobile phase compositions and flow rates. Injection of 9 μL supercritical CO₂ onto the HPLC using methanol/water mobile phases from 100% methanol to 80% with a flow of 1.0 mL/min did not adversely affect the baseline of UV detector. However at higher percentages of water, CO₂ solubility in the mobile phase decreased and caused baseline interferences on the UV detector. At higher HPLC mobile phase flow rates, supercritical CO₂ was injected to higher percentages of water without any effect on the UV baseline. Also, increasing the extraction pressure or modifier concentration did not change the results. Separations of polynuclear aromatic hydrocarbons and linear alkenebenzene sulfonate test mixtures were obtained using on-line SFE/HPLC interfaced system.     

分子印迹固相萃取-高效液相色谱法测定饲料中莱克多巴胺

以莱克多巴胺为模板分子,丙烯酰胺为功能单体,乙二醇二甲基丙烯酸酯为交联剂,合成了对莱克多巴胺具有高选择性的分子印迹聚合物。考察了甲醇、乙腈、丙酮和氯仿-甲醇与三乙胺构成致孔剂合成的聚合物性能及其形貌特征。通过正交试验优化的聚合反应配方为: 1.0 mmol莱克多巴胺,4.0 mmol丙烯酰胺,20.0 mmol乙二醇二甲基丙烯酸酯,6.0 mL乙腈-三乙胺(30:1, v/v), 50.0 mg偶氮二异丁腈。建立的基于分子印迹固相萃取-高效液相色谱测定饲料试样中莱克多巴胺的方法,在0.50～100 mg/L质量浓度范围内有良好的线性关系(r=0.9994);饲料试样中1.0、10及100 mg/kg 3个添加水平的莱克多巴胺平均回收率大于80%;批内、批间测定的相对标准偏差小于10%;检出限(信噪比为3)达到0.1 mg/kg。该方法灵敏、可靠,用于饲料等复杂基质中莱克多巴胺检测的效果优于相关标准分析方法。     

Molecularly imprinted polymer for selective extraction of domoic acid from seafood coupled with high-performance liquid chromatographic determination

In this work, a highly selective sample cleanup procedure that combining molecular imprinting technique (MIT) and solid phase extraction (SPE) was developed for the isolation of domoic acid (a fascinating marine toxin) from seafood samples. The molecular imprinting polymer (MIP) for domoic acid was prepared using 1,3,5-pentanetricarboxylic acid as the template molecule instead of domoic acid. 4-Vinyl pyridine was used as the functional monomer and ethylene glycol dimethacrylate was used as the cross-linking monomer. The obtained imprinted polymer showed high affinity to domoic acid and was used as selective sorbent for the SPE of domoic acid from seafood samples. An off-line molecularly imprinted solid phase extraction (MISPE) method followed by high-performance liquid chromatography (HPLC) with diode-array detection for the detection of domoic acid was also established. Good linearity was obtained from 0.5 mg L⁻¹ to 25 mg L⁻¹ (R² > 0.99) with a quantitation limit of 0.1 mg L⁻¹, which was sufficient to determine domoic acid at the maximum level permitted by several authorities. The mean recoveries of domoic acid from mussel extracts were 93.4-96.7%. It was demonstrated that the proposed MISPE-HPLC method could be applied to direct determination of domoic acid from seafood samples.     

Improved high performance liquid chromatographic determination of amanitins with electrochemical detection

Summary The determination of amanitins, the main toxins of the poisonous fungus Amanita Phalloides, through an improved HPLC method with electrochemical detection is presented. It uses an improved reverse phase separation on a wide pore butyl column and amperometric detection in oxidizing mode at + 0.6 V. Compared to the previously reported methods employing narrow pore C18 packings and UV detectors, the described method gives a much lower detection limit (40, 80 and 70 pg ca. for alpha-, beta- and gamma-amanitin, respectively), and a better chromatographic efficiency. Coupled with a sample preparation procedure using disposable cartridges packed with C18 and underivatized silica (recovery of alpha-amanitin =65 %, RSD 4.1 at 20 ng/ml), the method permits the quantitative determination of alphaamanitin in serum at low concentrations (10–20 ng/ml). A tentative immuno-extraction of urine samples, by means of a solid phase antiserum, bound to nylon nets, allowing the detection of few nanograms of toxin per milliliter is also briefly described.     

A novel molecularly imprinted polymer for simultaneous extraction and determination of sudan dyes by on-line solid phase extraction and high performance liquid chromatography

A novel molecularly imprinted polymer was synthesized with attapulgite employed as matrix, which is simple and time-saving. In this method, sudan I was chosen as template molecule, 2-vinylpyridine as functional monomer and ethylene glycol dimethacrylate as cross-linking agent, respectively. The imprinted polymer was characterized by the infrared spectroscopy and transmission electron microscopy. Then the selectivity experiments were performed on sudan dyes and the recognition coefficients for sudan I, sudan II, sudan III and sudan IV were 2.9, 1.9, 1.9 and 2.3, respectively. As the packing material of solid-phase extraction, the imprinted polymer has been applied to on-line concentration of the four sudan dyes in samples from Yellow River water, tomato sauce and sausage. The corresponding analytical methods to determine these sudan dyes have been developed. The limits of detection for these sudan dyes were in the range of 0.01–0.05 ng mL⁻¹ for Yellow River water, 1.0–3.0 ng g⁻¹ for tomato sauce and 0.8–3.0 ng g⁻¹ for sausage.     

On-line renewable solid-phase extraction hyphenated to liquid chromatography for the determination of UV filters using bead injection and multisyringe-lab-on-valve approach

For the first time, an automatic sample pre-treatment/detection method is proposed for the multiclass determination of UV filters (namely, benzophenone-3, ethylhexylmetoxycinnamate, butylmethoxydibenzoylmethane and homosalate) in environmental samples. The new methodology comprises in-line solid-phase extraction (SPE) of the target analytes by exploiting the bead injection (BI) concept in a mesofluidic lab-on-valve (LOV) format, with subsequent determination by liquid chromatography (LC). The proposed microanalytical system, using a multisyringe burette as propulsion unit, automatically performed the overall SPE steps, including the renewal of the sorbent in each analytical cycle to prevent sample cross-contamination and the post-extraction adjustment of the eluate composition to prevent chromatographic band broadening effects. In order to expedite the LC separation, a C₁₈ monolithic column was applied and an accelerated isocratic elution was carried out by using a cationic surfactant as mobile phase additive. The LOV-BI-LC method was proven reliable for handling and analysis of complex matrices, e.g., spiked swimming pool water and seawater, with limits of detection ranging between 0.45 and 3.2 μg L⁻¹ for 9 mL sample volume. Linear calibration was attained up to 160 μg L⁻¹ for homosalate and up to 35 μg L⁻¹ for the other target analytes, with good reproducibility (RSD < 13%, for 5 different SPE columns). The hyphenated scheme is able to process a given sample simultaneously and within the same time frame than the chromatographic separation/determination of the formerly pre-treated sample, providing concentration values every 9 min. Hence, the sample throughput was enhanced up to 33 times when compared with previously reported off-line SPE methods. A drastic reduction in reagent consumption and effluent production was also attained, contributing to the development of an environment-friendly analyzer.     

Study on an on-line molecularly imprinted solid-phase extraction coupled to high-performance liquid chromatography for separation and determination of trace estrone in environment

Estrone is one of the important potential endocrine-disrupting compounds, and the sensitive and reliable analytical methods for the determination of estrone are required for the assurance of human health. In this paper, using estrone as template molecule, 3-aminopropyltriethoxysilane as function monomer, and tetraethoxysilicane as cross-linker, a highly selective molecularly imprinted microsphere was synthesized by surface molecular imprinting technique combined with a sol–gel process. The imprinted material was characterized by the Fourier transform infrared and static adsorption experiments, and the results showed that it exhibited good recognition and selective ability for estrone. A novel method for separation and determination of trace estrone in environmental sample was developed using on-line molecularly imprinted solid-phase extraction coupled to high-performance liquid chromatography. With a sample loading flow rate of 2.6 mL min⁻¹ for a 9.6-min extraction, the enrichment factor obtained by the slopes of the linear portion in comparison with the direct injection of 10 μL standard sample solution was 1,045. The detection limit (S/N = 3) was 5.7 ng L⁻¹, and the relative standard deviations for nine replicate extractions of 5.0 μg L⁻¹ estrone was less than 10.0%. This method was evaluated for quantitative determination of estrone in well and lake water samples spiked at two levels (0.5 and 1.0 μg L⁻¹) with recoveries ranging from 86% to 95%.      

Investigation of flavonoid profile of Scutellaria bacalensis Georgi by high performance liquid chromatography with diode array detection and electrospray ion trap mass spectrometry

Scutellaria baicalensis Georgi is a well-known medicinal plant widely used in China and other East Asian countries. High performance liquid chromatography combined with diode array detection and electrospray ion trap mass spectrometry was used to determine the flavonoid profile of S. baicalensis. Under the optimized experiment conditions, 32 flavonoids were clearly detected. Eighteen main ones were doubtless identified by comparing their retention time, UV and MS (MSⁿ) data with isolated or commercial standards. The UV characteristics of these 18 known standards were studied in detail. The rules summarized provided valuable indications for the subsequent on-line identification processes. By interpreting both the MS and the UV data in detail, other 13 minor flavonoids in S. baicalensis were on-line identified successfully.