Determination of lower sub ppt levels of environmental analytes using high-powered concentration system and high-performance liquid chromatography with fluorescence detection

The proposed method was successful in the determination and separation of lower sub ppt levels of polycyclic aromatic hydrocarbons (PAHs). In this study, a new phase separation phenomenon (i.e., homogeneous liquid-liquid extraction) was developed that rapidly and simply separated an immiscible liquid phase from water-miscible organic solvents. One liter of sample solution was preconcentrated by a solid phase extraction method, then the obtained eluate (5 mL) was further preconcentrated to just 20 microL by this homogeneous liquid-liquid extraction. The 20 [micro sign]L sedimented phase was directly injected into the high-performance liquid chromatography with fluorescence detection (FL-HPLC). The entire preconcentration factor was 50,000-fold. Six kinds of PAHs were determined in the range of 3.0 x 10(-18) approximately 4.5 x 10(-11) mol L(-1). These chemicals were also satisfactorily separated.     

Homogeneous liquid-liquid extraction method for the selective spectrofluorimetric determination of trace amounts of tryptophan

Twenty-one amino acids were derivatized with fluorescamine (FLA) under basic conditions (pH 9) and the extraction of the amino acid-FLA derivatives was investigated using a homogeneous liquid-liquid extraction with perfluorooctanoic acid (HPFOA) based on phase separation under strongly acidic conditions. Under the optimum concentration conditions for the reagents ([PFOA]T = 3 x 10(-3) mol dm-3, [acetone]T = 3 vol.%, [HCl]T = 1.8 mol dm-3), the concentration factor was approximately 1000-fold (i.e., 30 microliters of the sedimented liquid phase was produced from 33 ml of the homogeneous aqueous solution). The percentage extraction (E) was determined for the 21 amino acid-FLA derivatives; the value for the tryptophan (Trp)-FLA derivative was 80.9%, whereas the other derivatives were not almost extracted (E < 0.4%). The Trp-FLA derivative was selective for the extraction using the homogeneous liquid-liquid extraction method with HPFOA. After the sedimented liquid phase containing Trp-FLA has been placed on a polytetrafluoroethylene filter-paper, the fluorescence intensity was determined using a spectrofluorimeter with filter-paper as the solid-sample holder. The calibration graph of Trp was linear over the range 1.0 x 10(-8)-1.5 x 10(-6) mol dm-3. The relative standard deviation for the central value of the calibration graph was 4.5% (five determinations) and the detection limit (S/N = 3) was 8.9 x 10(-9) mol dm-3. When the proposed method was applied to the highly sensitive spectrofluorimetric determination of Trp in animalin-L syrup, the results were satisfactory.     

Homogeneous liquid-liquid extraction and micellar electrokinetic chromatography using sweeping effect concentration system for determination of trace amounts of several polycyclic aromatic hydrocarbons

A powerful capillary electrophoresis (CE) method, with preconcentration in excess of 100,000-fold, has been developed by using a specific characteristic of perfluoro surfactants. Highly sensitive determination and separation of polycyclic aromatic hydrocarbons (PAH) were achieved by following a combination of two kinds of efficient preconcentration method using perfluoro surfactants. The two preconcentration methods combined were homogeneous liquid-liquid extraction for off-line concentration and a sweeping method as on-line concentration. Five PAH (1,2,3,4-dibenzanthracene, 1,2,5,6-dibenzanthracene, benzo( a)pyrene, benzo( e)pyrene, and pyrene) were investigated, and were completely separated. When the concentration-factor (volume ratio) was 8335-fold, the determination limits were in the range 10(-10) to 10(-9) mol L(-1). The maximum concentration-factor (volume ratio) obtained was 125,000-fold. Addition and recovery experiments were performed for three kinds of natural water (rain water, river water, and spring water).     

Analysis of amphetamines in urine with liquid-liquid extraction by capillary electrophoresis with simultaneous electrochemical and electrochemiluminescence detection

Amphetamines including methamphetamine, 3,4-methylenedioxyamphetamine and 3,4-methylenedioxymethamphetamine were separated and detected by CE using simultaneous electrochemical (EC) and electrochemiluminescence (ECL) detection (CE-EC/ECL). Factors that influenced the separation and detection performance, such as the detection potential, the pH value and concentration of the running buffer, the separation voltage and the pH of the detection buffer, were investigated. LODs of 3.3x10(-8) mol/L (0.16 fmol), 1.6x10(-7) mol/L (0.78 fmol) and 3.3x10(-8) mol/L (0.16 fmol) were obtained for methamphetamine, 3,4-methylenedioxyamphetamine and 3,4-methylenedioxymethamphetamine, respectively. For practical application, a liquid-liquid extraction with ethyl acetate procedure was developed for urine sample pretreatment and extraction efficiencies higher than 90% were obtained. The established simultaneous CE-EC/ECL was successfully applied for urine sample analysis.     

微流控液液萃取-液液波导集成化分析系统

利用溴化1-丁基-3-甲基咪唑离子液体/碳酸钠溶液双水相体系,实现了多相层流液液萃取.以具有较高折射率的离子液体为液芯,较低折射率的盐溶液为包层,实现了液液波导吸光度检测.据此建立了一种液液萃取与液液波导检测集成化的微流控分析系统.该系统对甲酚红试样的萃取率在93%以上,对甲酚红试样检测的线性范围为0.01~0.40 mg/m L,相对标准偏差为3.4%(n=11),检出限为3.8μg/m L(3σ).该系统将萃取分离与液液波导长光程吸光度检测集成在一起,为拓展吸光度检测在微流控系统中的应用提供了新思路.     

UV-detection capillary electrophoresis for benzo[a]pyrene and pyrene following a two-step concentration system using homogeneous liquid-liquid extraction and a sweeping method

10(-9) mol l-1 levels of polycyclic aromatic hydrocarbons (PAHs) suspected for certain noxious materials can be determined and separated by UV-detection capillary electrophoresis following a two-step concentration system. When the conditions of the homogeneous liquid-liquid extraction were [THF]T = 5 vol%, [HCl]T = 0.66 mol l-1, and [PFOA]T = 2 x 10(-3) mol l-1 (i.e., the volume of sample solution; 50 ml-->sedimented phase; 30 microliters), the extraction percentages of benzo[a]pyrene (Bap) and pyrene (Py) at 10(-6) mol l-1 were 102 and 97.5%, respectively. Also, when the total concentration factor(volume ratio), which includes that of the sweeping method, was 8335-fold, the determination range of Bap was 6.4 x 10(-9)-8.0 x 10(-7) mol l-1 and for Py, 8.0 x 10(-9)-7.0 x 10(-7) mol l-1. The detection limits (3 sigma) of Bap and Py were 1.6 x 10(-9) and 4.8 x 10(-9) mol l-1, respectively.     

High performance liquid chromatographic analysis of time-dependent changes in urinary excretion of indoleamines following tryptophan administration

Analytical conditions of prepurification extraction and HPLC separation were optimized for determination of urinary serotonin and tryptamine. Under optimal conditions, serotonin, tryptamine and an internal standard were extracted with 15% v/v n-propanol in diethyl ether from urine samples alkalized with a phosphate buffer (0.75 mol/L, pH 10.0), and then they were re-extracted into an HCl solution (0.1 mol/L). Purified indoleamines were simultaneously separated by reversed-phase ion-pair HPLC with native fluorescence detection. Urinary serotonin and tryptamine were selectively determined within about 45 min per sample for the whole procedure. Analytical recovery, reproducibility and detection sensitivity were satisfactory for pursuing time-dependent changes in indoleamine levels. Urinary excretion profiles of serotonin and tryptamine in subjects dosed with L-tryptophan were successfully analyzed by our method.     

复杂基体中痕量多环芳烃分析测定方法的研究进展

介绍了环境样品（水和土壤）以及植物油中痕量多环芳烃的分析检测方法。对样品的预处理过程和分析方法做了评价。采用一些新的预处理方法（包括液相色谱法、固相萃取法、超临界二氧化碳萃取法）,并结合色谱-质谱在线联用分析检测方法能够获得比较理想的分析结果。引用文献52篇。     

Characterization and application of a DNA aptamer binding to L-tryptophan

DNA aptamers for specific recognition of L-tryptophan have been evolved by a SELEX (systematic evolution of ligands by exponential enrichment) technique. Truncation-mutation experiments suggest that a 34-mer sequence, Trp3a-1, possesses the strongest binding ability to L-tryptophan. Trp3a-1 is predicted to adopt a loop-stem secondary structure, in which the loop may further fold into a binding pocket for L-tryptophan with the help of the stem. The specificity investigation shows that Trp3a-1 strongly binds to L-tryptophan, has almost no binding to other amino acids, and weakly binds to some tryptophan analogs and peptides containing the L-tryptophan residue. The binding of Trp3a-1 to L-tryptophan is mainly contributed to by hydrogen bonds and precise stacking formed between the binding pocket of Trp3a-1 and all groups on L-tryptophan. This aptamer has also been proved to be an effective ligand for the chiral separation of D/L-tryptophan. L-tryptophan and its derivatives are known to play important biological roles; this aptamer ligand could be used as a tool for the analysis of tryptophan and other related studies.     

A rapid CE-potential gradient detection method for determination of quinolones

A rapid CE coupled with potential gradient detection (PGD) for the separation and detection of four quinolones, namely, enoxacin, ofloxacin (OFL), fleroxacin, and pazufloxacin, was described. Separation was performed in a fused-silica capillary (75 microm x 8.5 cm) using a buffer of 30 mM Tris and 4 mM phosphoric acid at pH 8.9. Under the separation voltage of 3 kV, the quinolones were separated within 2.8 min with good linearity (r(2) >or= 0.985). The method was successfully applied in determining OFL in a pharmaceutical formulation. Also, a liquid-liquid extraction (LLE) method was developed and coupled to CE-PGD in determining quinolones that spiked in milk samples. With dichloromethane and hexane for enrichment and purification, the LLE recoveries of the four quinolones were in the range of 77-106%. The detection limits of the quinolones with LLE-CE-PGD were from 23 to 65 ng/mL. The proposed CE-PGD method was validated with an HPLC method, and the results indicated consistency between the two methods.     

Determination of pesticide residues in red wines with microporous membrane liquid–liquid extraction and gas chromatography

A sample pretreatment method based on microporous membrane liquid-liquid extraction (MMLLE) was developed for the subsequent gas chromatographic determination of pesticides in wine. MMLLE provided efficient and selective extraction with enrichment factors in the range 3-13. The gas chromatographic separation was carried out using on-column injection and flame ionization detection. The method was linear, repeatable and sensitive. The limits of quantification were better than 0.006 mg/L for all the analytes except for iprodione (0.37 mg/L). The method was applied to the determination of pesticides in several red wines of different origin.     

Ionic liquid-based homogeneous liquid-liquid microextraction for the determination of antibiotics in milk by high-performance liquid chromatography

Ionic liquid-based homogeneous liquid-liquid microextraction (IL-based HLLME) high-performance liquid chromatography was developed and applied to the extraction, separation and determination of some antibiotics in milk. The proteins and lipids were removed by adding salt and adjusting the pH value. The homogeneous extraction was applied to the improvement of recoveries for IL phase and analytes. The experimental parameters of the IL-based HLLME, including salt concentration in sample solution, pH value of sample solution, volume of [C(6)MIM][BF(4)], amount of ion-pairing agent (NH(4)PF(6)), and extraction time, were evaluated. The limits of detection for enoxacin, pefloxacin, norfloxacin, enrofloxacin, sulfamethoxazole and sulfadimethoxine were 15.8, 7.07, 5.13, 4.00, 7.79 and 8.33 μg L(-1), respectively. When the proposed method was applied to the analysis of milk samples the recoveries of the analytes ranged from 92.5 to 118.6% and relative standard deviations were lower than 7.00%.     

全二维气相色谱-飞行时间质谱测定地下水中低环多环芳烃及其衍生物

建立了地下水中低环多环芳烃及其衍生物的全二维气相色谱-飞行时间质谱(GC×GC-TOF MS)检测方法。对比研究了液液萃取(LLE)和固相萃取(SPE)对地下水中低环多环芳烃及其衍生物的提取效率,优选液液萃取为前处理方法。在优化条件下,除1,2,3,4-四氢萘(r=0.987 2)和联苯(r=0.989 9)外,其它目标物在0.1~1 000μg/L范围内具有良好的线性关系,相关系数(r)均大于0.99。地下水的平均加标回收率为63.3%~111%,除喹啉的相对标准偏差(RSD,n=6)为24.9%外,其余目标物的RSD均小于9.5%,方法检出限在1.63~14.7 ng/L之间。该方法用于河北地区6个地下水样中低环多环芳烃及其衍生物的检测,4个样品有检出,最高浓度达353 ng/L。     

Determination of amoxapine and nortriptyline in blood plasma and serum by salt-assisted liquid-liquid microextraction and high-performance liquid chromatography

A new, selective and sensitive method has been developed for the determination of tricyclic antidepressant drugs, amoxapine and nortriptyline, in human blood plasma and serum, involving their reaction with allyl isothiocyanate and extraction of thiourea derivatives with water-miscible organic solvent acetonitrile. The phase separation was effected by addition of ammonium sulphate, a process called salt-assisted liquid-liquid microextraction. The extract was analyzed by HPLC with UV detection at 254?nm. The method has been optimized for derivatization reaction time and temperature, solvent for extraction, and salt for solvent phase separation. Under the optimal conditions, a linear calibration graph was obtained between the amount of drug and the peak area of thiourea derivatives in the range of 0.002-20?mg/L drugs. The correlation coefficient and limit of detection values for amoxapine and nortriptyline in serum/plasma samples were in the range of 0.9953-0.9999 and 0.46-0.58?μg/L, respectively. The recovery in spiking experiments ranged, respectively, 75-88% (RSD 3.4-7.2%) and 79-97% (RSD 3.7-7.9%) for the two drugs.     

Liquid chromatographic determination of microcystins in water samples following pre-column excimer fluorescence derivatization with 4-(1-pyrene)butanoic acid hydrazide

A method to measure the concentrations of microcystins (MCs) in water samples has been developed by incorporating pre-column fluorescence derivatization and liquid chromatography (LC). A solid-phase extraction for pretreatment was used to extract the MCs in water samples. The MCs were derivatized with excimer-forming 4-(1-pyrene)butanoic acid hydrazide (PBH). The MCs could then be detected by fluorescence after separation with a pentafluorophenyl (PFP)-modified superficially porous (core shell) particle LC column. The derivatization reactions of MCs with PBH proceeded easily in the presence of 4,6-dimethoxy-1,3,5-triazin-2-yl-4-methylmorpholinium (DMT-MM) as a condensation reagent, and the resulting derivatives could be easily separated on the PFP column. The derivatives were selectively detected at excimer fluorescence wavelengths (440–540 nm). The instrument detection limit and the instrument quantification limit of the MCs standards were 0.4–1.2 μg L⁻¹ and 1.4–3.9 μg L⁻¹, respectively. The method was validated at 0.1 and 1.0 μg L⁻¹ levels in tap and pond water samples, and the recovery of MCs was between 67 and 101% with a relative standard deviation of 11%. The proposed method can be used to quantify trace amounts of MCs in water samples.     

基于轻质萃取剂的溶剂去乳化分散液-液微萃取-气相色谱法测定水样中多环芳烃

以密度小于水的轻质溶剂为萃取剂,建立了无需离心步骤的溶剂去乳化分散液-液微萃取-气相色谱(SD-DLLME-GC)测定水样中多环芳烃的新方法。传统分散液-液微萃取技术一般采用密度大于水的有机溶剂为萃取剂,并需要通过离心步骤促进分相。而本方法以密度比水小的轻质溶剂甲苯为萃取剂,将其与丙酮(分散剂)混合并快速注入水样,获得雾化体系;然后注入乙腈作为去乳化剂,破坏该雾化体系,无需离心,溶液立即澄清、分相;取上层有机相(甲苯)进行GC分析。考察了萃取剂、分散剂、去乳化剂的种类及其体积等因素对萃取率的影响。以40 μL甲苯为萃取剂,500 μL丙酮为分散剂,800 μL乙腈为去乳化剂,方法在20～500 μg/L范围内呈现出良好的线性(r2=0.9942～0.9999),多环芳烃的检出限(S/N=3)为0.52～5.11 μg/L。用所建立的方法平行测定5份质量浓度为40 μg/L的多环芳烃标准水样,其含量的相对标准偏差为2.2%～13.6%。本法已成功用于实际水样中多环芳烃的分析,并测得其加标回收率为80.2%～115.1%。     

Separation and determination of L-tryptophan and its metabolites by capillary micellar electrokinetic chromatography with amperometric detection

A high-performance method of capillary micellar electrokinetic chromatography (CMEKC) with amperometric detection (AD), using a newly designed pre-aligned electrochemical cell, has been developed for the separation and determination of L-tryptophan (Trp) and its eight metabolites including 3-hydroxy-L-kynurenine (3-HK), 5-hydroxy-L-tryptophan (5-HTP), L-kynurenine (KN), 5-hydroxyindole-3-acetic acid (5-HIAA), xanthurenic acid (XA), indole-3-pyruvic acid (IPA), 5-hydroxytryptamine (5-HT), and tryptamine (Tryp). A carbon disk electrode was used as the working electrode and the optimal detection potential was 0.85 V (versus Ag/AgCl). At 24 kV of applied voltage, the nine compounds were completely separated, within 23 min, in a 10 mol/L Na(2)HPO(4)-NaOH buffer (pH 11.0) containing 40 mmol/L sodium dodecyl sulfate (SDS) and 3% methanol (v/v). A good linear relationship was obtained for all analytes in this paper and the detection limits of 3-HK, 5-HTP, KN, Trp, 5-HIAA, XA, IPA, 5-HT, and Tryp were 7.42, 5.18, 34.6, 3.99, 15.1, 12.7, 260, 6.72, and 8.01 nmol/L, respectively. This method has been applied to analyze the metabolism of Trp in rabbit urine.     

Determination of silver(I) by electrothermal-AAS in a microdroplet formed from a homogeneous liquid-liquid extraction system using tetraspirocyclohexylcalix[4]pyrroles.

A simple and efficient method for the selective separation and preconcentration of Ag+ using homogeneous liquid-liquid extraction was developed. Tetraspirocyclohexylcalix[4]pyrrole (TSCC4P) was synthesized and investigated as a suitable selective complexing ligand for Ag+. Zonyl FSA (FSA) was applied as a phase-separator agent under mild pH conditions. Under the optimal conditions ([TSCC4P] = 3.4 x 10(-4) M, [THF] = 25.0% v/v, [FSA] = 1.25% w/v, and pH = 4.5), 5 microg of Ag+ in 6.0 ml aqueous phase could be extracted quantitatively into 20 microl of the sedimented phase. The maximum concentration factor was 300-fold. The limit of detection of the proposed method was 0.005 ng/ml. The reproducibility of the proposed method was at most 3.5%. The influence of the pH, type and volume of the water-miscible organic solvent, concentration of FSA, concentration of the complexing ligand and the effect of different diverse ions on the extraction and determination of Ag+ were investigated. The proposed method was applied to the extraction and determination of Ag+ in different water samples.     

Magnetic separation as a new method for the extraction of small molecules from biological fluids of humans

A new version of extraction is proposed for the extraction of doping substances from urine. It is based on magnetic separation using ferromagnetic microparticles with the surface modified with C₁₈ groups. A procedure is developed on its basis for the quantification of selective modulators of androgen receptors and peroxisome proliferator-activated delta-receptor agonists using high-performance liquid chromatography coupled with tandem mass spectrometry. Using the proposed approach, the recovery of doping substances from human biological fluids approximates 100%, while the negative effect of the matrix components on the ionization of target compounds is reduced to a minimum. In contrast to solid phase extraction and liquid-liquid extraction, the method of magnetic separation appears to be more rapid and simple. The time of pretreatment for a sample intended for HPLC coupled to tandem mass spectrometry makes 5 min; the detection limit makes 0.25–5 ng/mL.     

Dispersive micro‐solid‐phase extraction combined with online preconcentration by capillary electrophoresis for the determination of glycopyrrolate stereoisomers in rat plasma

A simple and sensitive analytical method for four isomers of glycopyrrolate in rat plasma was developed using cation‐selective exhaustive injection‐sweeping cyclodextrin‐modified electrokinetic chromatography (CSEI‐Sweeping‐CDEKC) for online enrichment combined with dispersive micro‐solid‐phase extraction pretreatment. The CSEI‐Sweeping‐CDEKC was conducted on an uncoated fused silica capillary (40.2 cm × 75 μm) with an applied voltage of –20 kV. The electrophoretic analysis was carried out in 30 mM phosphate solution at pH 2.0 containing 20 mg/mL sulfated‐β‐cyclodextrin and 5% acetonitrile. Under these optimized conditions, the detection limit for racemic glycopyrrolate was found to be 2.0 ng/mL and this method could increase 495‐fold detection sensitivity compared with the traditional injection method. Additionally, the parameters that affected the extraction efficiency of dispersive micro‐solid‐phase extraction were also examined systematically. The glycopyrrolate isomers in rat plasma samples as low as 0.0625 μg/mL were able to be separated and detected by capillary electrophoresis with the aid of CSEI‐sweeping. The findings of this study show that the dispersive micro‐solid‐phase extraction pretreatment coupled with CSEI‐Sweeping‐CDEKC is a rapid and convenient method for analyzing glycopyrrolate isomers in rat plasma.