Optimizing separation conditions for polycyclic aromatic hydrocarbons in micellar electrokinetic chromatography

We report the separation of polycyclic aromatic hydrocarbons (PAHs) using 0.1% poly(ethylene oxide) (PEO) in micellar electrokinetic chromatography (MEKC). In the presence of PEO, adsorption of PAHs on the capillary wall was reduced, leading to better resolution and reproducibility. Effects of tetrapentylammonium iodide (TPAI), dextran sulfate (DS), methanol, and sodium lauryl sulfate (SDS) on the separation of PAHs were elucidated. In terms of resolution and speed, DS, compared to TPAI, is a better additive for separation of PAHs. When using 0.1% PEO solution containing 45% methanol, 50 mM SDS, and 0.02% DS, separation of 10 PAHs containing 2 to 5 benzene rings was accomplished in less than 12 min at 15 kV in a commercial CE system. The method has also been tested for separating seven PAHs with high quantum yields when excited at 325 nm using a He-Cd laser. Unfortunately, separation of the seven PAHs was not achieved and sensitivity diminished under the same conditions. To optimize sensitivity, resolution and speed, a stepwise technique in MEKC has been proposed. The seven PAHs were resolved in 35 min at 15 kV when separation was performed in 0.1% PEO solution containing 35 mM SDS, 40% methanol and 0.02% DS for 2 min, and subsequently in 0.1% PEO solution containing 20 mM SDS, 50% methanol, and 0.02% DS.     

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.     

Separation of polycyclic aromatic hydrocarbons by micellar electrokinetic chromatography with aqueous short-chain alcohol solvent

Micellar electrokinetic capillary chromatography (MEKC) with aqueous organic solvent has been developed to separate polycyclic aromatic hydrocarbons (PAHs). Methanol, ethanol or propanol as an organic modifier was added to sodium dodecyl sulfate (SDS) micellar solution in order to increase the solubility of very hydrophobic solutes in mobile phase. Both methanol and ethanol can be used as co-solvents for the separation of PAHs. Use of ethanol resulted in a shorter analysis time than use of methanol. The separations of some PAHs were unsatisfactory using propanol although the analysis time was much shorter than with ethanol. The influence of ethanol content, SDS concentration and temperature on the separations was studied. Benzene and nine polycyclic aromatic hydrocarbons were successfully separated using 50 mM SDS-20 mM phosphate-5 mM borate, containing 40% (v/v) ethanol at 35 degrees C. The relative standard deviation (R.S.D.) of t(R) ranged from 0.5 to 1.5% for six repeat injections.     

Hydrophobic interaction electrokinetic chromatography for the separation of polycyclic aromatic hydrocarbons using non-aqueous matrices

Capillary electrophoresis methodology is developed to provide a rapid, inexpensive and robust technique for screening polycyclic aromatic hydrocarbons (PAHs) in water using additive complexation. A series of conventional RPLC ion-pairing agents are investigated in three different totally non-aqueous separation solvents, and the relative role of hydrophobic interaction versus electrostatic association is evaluated. Methanol is found to provide optimal selectivity when coupled with the tetrahexylammonium cation providing total analysis times of approximately 15 min for the analysis of thirteen 2-7-ring PAH pollutants. Solid-phase microextraction is demonstrated to be an effective sample preparation technique for extraction/preconcentration of PAHs from water into methanol run buffer prior to injection.     

Determination of trace amounts of polycyclic aromatic hydrocarbons in soil

A method for monitoring the contamination of soil with polycyclic aromatic hydrocarbons (PAHs) is introduced. Drying at elevated temperature is omitted to avoid losses of the more volatile constituents (primarily naphthalene). The soil sample, including its natural water content, is extracted with 2-methoxyethanol and cleaned up using a disposable C₈ cartridge and the PAHs are eluted with pentane, concentrated and measured by capillary gas chromatography with flame ionization detection. Determination limits between 15 and 35μg kg^?1 are obtained and the recovery is 80–90% measured at the 125 μg kg^?1 spike level, except for naphthalene (66%). Special attention is given to the design of the spiking technique, which simulates natural incorporation as far as possible, takes account of evaporation losses and therefore allows “real” recovery rates to be determined.     

场放大进样-胶束扫集毛细管电脉法测定痕量泼尼松

建立了胶束毛细管电动色谱在线富集技术测定药品中痕量的泼尼松的方法。在胶束扫集的基础上联用场放大进样,使泼尼松的富集倍数提高了136倍;检出限由原来的2.7mg/L降至20μg/L。胶束扫集毛细管电泳缓冲体系为120mmol/LSDS、10mmol/LNaH2PO4(pH2.5)10%乙腈(V/V)。分离电压-20kV,进样电压-20kV,进样时间70s,进水时间180s,检测波长250nm。同时讨论了SDS浓度、样品基质pH、进样电压、进水时间和进样时间对分离效果的影响。实验结果显示:在优化实验条件下,样品的检测仅需8min,泼尼松在0.05～10mg/L的范围内线性关系良好(r=0.998)。回收率在89.4%～106%之间,相对标准偏差在2.1%～2.6%之间,可用于各种中药制剂中泼尼松的含量测定。     

Analysis of ephedra-alkaloids using sweeping and cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography methods

Two stacking methods of capillary electrophoresis (CE) were developed for the separation of very dilute solutions of ephedra-alkaloids, namely ephedrine, pseudoephedrine, methylephedrine, methylpseudoephedrine, norephedrine, and norpseudoephedrine. A sweeping method which uses a carrier comprised of phosphoric acid, sodium dodecyl sulfate (SDS), diethylamine and acetonitrile permits the detection of the alkaloids down to the 10(-1) microg/mL level, and the cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) method using phosphoric acid, SDS, and acetronitrile as electrolytes can detect down to the 10(-3) microg/mL level. The former requires the conductance of the sample solution to be adjusted beforehand, and only five peaks were observed, two of which were overlapped. The latter is capable of separating the six alkaloids but has a somewhat poorer reproducibility. Using an optimized injection time, it was found that the more diluted a solution is, the greater the sweeping effect will be. The CSEI-Sweep-MEKC method with a 600 s injection time and a 10(-1) microg/mL solution concentration provides an amplification effect of approximately 10(4). The method is suitable for analyses of dilute herb drug extracts and mouse sera. The effect of buffers on the separation and validation of the methods in this study are also discussed.     

Ultrasonic micellar extraction of polycyclic aromatic hydrocarbons from marine sediments

In this present study the extraction of polycyclic aromatic hydrocarbons (PAHs) from marine sediments with a micellar medium of Polyoxyethylene 10 lauryl ether by an ultrasound-assisted method has been studied. Factorial design experiments were used in order to optimize the extraction parameters: extraction time, surfactant concentration and surfactant volume:amount of sediment relationship. The results suggest that surfactant concentration is statistically the most significant factor. The analysis of extracts has been carried out by HPLC with UV detection. Fortified sediments gave an average recovery between 86.7 and 106.6%, with relative standard deviation of 2.02-6.83% for PAHs with a ring number higher than three.     

Homogeneous liquid-liquid extraction of trace amounts of mononitrotoluenes from waste water samples

Homogeneous liquid-liquid extraction method was studied based on a phase separation phenomenon in a ternary solvent system. According to this procedure, mononitrotoloenes were extracted by single-phase extraction in a water/methanol/chloroform, homogeneous ternary solvent system. Methanol and chloroform were used as consolute and extraction solvents, respectively. The homogeneous solution was broken by the addition of salt and a cloudy solution was formed. After centrifugation, the fine droplets of the extraction solvent were sedimented in the bottom of the conical test tube. Analysis of the extracts was carried out by gas chromatography. The optimization procedure was performed using Box-Behnken design. The variables involved were: sample and extraction solvent volumes, consolute solvent volume and phase separator reagent concentration. Optimum results were obtained under the following conditions: sample volume of 5 mL, extraction solvent volume of 55 μL, consolute solvent volume of 1 mL and phase separator reagent concentration; 5% (w/v). Under these conditions, the enrichment factors of 354, 311 and 300, dynamic linear ranges of 0.5-500, 1-500 and 1-500 μg L⁻¹, and limit of detections (LODs) of 0.09, 0.09 and 0.1 μg L⁻¹ were obtained for o-nitrotoluene, m-nitrotoluene and p-nitrotoluene, respectively. Finally, the method was successfully applied to the extraction and determination of MNTs in the waste water samples in the range of micrograms per liter with R.S.Ds. < 13.2%.     

胶束扫集毛细管电动色谱法测定药物中3种邻苯二甲酸酯

采用胶束扫集毛细管电动色谱技术,建立了测定药物中邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙酯(DZP)和邻苯二甲酸二丁酯(DBP)的方法。电泳缓冲体系含80 mmol/L SDS,20 mmol/L NaH2PO4(pH 2.20),5%甲醇(V/V),分离电压-18 kV,重力进样80s×15.0cm,检测波长225 nm,使用Φ50μm×62.0 cm石英毛细管,有效长度50.0 cm。讨论了磷酸盐浓度、有机改善剂、SDS浓度、分离电压、进样时间等因素的影响,并考察了胶束扫集法对DMP、DEP和DBP的富集能力。在优化条件下,线性关系良好,相关系数大于0.9986,DMP、DEP和DBP的线性范围分别为1.25～240,1.04～200和1.56～200 mg/L,检出限分别为0.26,0.26和0.39 mg/L。方法应用于肠溶片中DMP、DEP和DBP的测定,回收率在93.3%～108%之间,RSD≤5.2%。每次样品测定可在10 min内完成。     

Analysis of estrogens in water by magnetic octadecylsilane particles extraction and sweeping micellar electrokinetic chromatography

A method based on magnetic separation was developed for the extraction of several estrogens (including diethylstilbestrol, estrone and estriol) in water followed by sweeping micellar electrokinetic chromatography (MEKC) analysis with UV detection. Novel magnetic octadecylsilane (ODS) particles were prepared using a silanization method with octadecyl trimethoxysilane as the surface modification reagent of magnetic Fe₃O₄ particles. Octadecyl trimethoxysilane was covalently immobilized on the magnetic iron oxide particles. The particles were used as the sorbents in the magnetic separation for the extraction of trace amounts of estrogens from water. The extraction condition and efficiency of the particles for the estrogens were investigated. Combining the magnetic ODS particles extraction and sweeping MEKC with UV detection, the estrogens at concentrations as low as ng/mL in water can be detected without interference from other substances in the sample matrix.     

Homogeneous liquid–liquid extraction combined with high performance liquid chromatography–fluorescence detection for determination of polycyclic aromatic hydrocarbons in vegetables

In this article, homogeneous liquid–liquid extraction (HOLLE), combined with HPLC-fluorescence detector (HPLC-FLD), has been developed for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in vegetables. ACN was used as extraction solvent for the extraction of target analytes from vegetables. When the previous extraction process was over, the ACN extract was transferred to the water-immiscible organic phase, tetrachloroethane, used as extraction solvent in HOLLE procedures. Under the optimum conditions, repeatability was carried out by spiking PAHs at concentration level of 12.5 μg/kg, the RSDs varied between 1.1 and 8.5% (n = 3). The LODs, based on S/N of 3, ranged from 0.025 to 0.25 μg/kg. Relative recoveries of PAHs from cucumber and long crooked squash samples were in the range of 72.4–104.9% and 65.5–119.3%, respectively. Compared with the conventional extraction method, the proposed method has the advantage of being quick, easy to operate, and having low consumption of organic solvent.     

Dispersive liquid-liquid microextraction and solid-phase extraction of polar pesticides from natural water and their determination by micellar electrokinetic chromatography

Procedures for the determination of polar pesticides in surface and ground water after their preconcentration by dispersive liquid-liquid microextraction and solid-phase extraction on Oasis® HLB (3 cc/60 mg) extraction cartridges are proposed. Conditions for the separation and determination of pesticides from the following classes by micellar electrokinetic chromatography were chosen: arylhydroxycarboxylic acids, sym-triazines, triazinones, urea derivatives, neonicotinoids, carbamates, triazoles, imidazoles, benzimidazoles, and organophosphorus compounds. The determination limits of pesticides in water were 0.5–20 μg/L with consideration for preconcentration. The relative standard deviation of the results of analysis was no higher than 10%.     

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).     

Accelerated extraction for determination of polycyclic aromatic hydrocarbons in marine biota

A rapid and simple method is proposed for determination of polycyclic aromatic hydrocarbons (PAH) in complex matrices such as marine biota. The method uses sonication, by means of an ultrasonic probe, as a new tool for assisted extraction, coupled with reversed-phase liquid chromatography (RP-LC) with fluorescence detection (FL) for determination of 16 US EPA priority PAH. Separation and detection of the 16 PAH were complete in 45 min by RP-LC with a C₁₈ column and acetonitrile–water gradient elution. Multivariate optimisation of the variables affecting extraction (ultrasound radiation amplitude, sonication time, and temperature of the water-bath in which the extraction cell was placed) was conducted. The accuracy of the method was determined by analysis of a certified reference material and comparison of the results obtained with those from another method (microwave-assisted extraction and GC–MS). The new technique avoids the main problems encountered in the determination of PAH in complex matrices such as marine biota, and no clean-up step is necessary. The method was applied to determination of PAH in estuarine biota samples from the Urdaibai estuary (Biscay, Spain).     

Screening and determination of polycyclic aromatic hydrocarbons in seafoods using QuEChERS-based extraction and high-performance liquid chromatography with fluorescence detection

A rapid, sensitive, and accurate method for the screening and determination of polycyclic aromatic hydrocarbons (PAHs) in edible seafood is described. The method uses quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based extraction and HPLC with fluorescence detection (FLD). The method was developed and validated in response to the massive Deepwater Horizon oil spill in the Gulf of Mexico. Rapid and highly sensitive PAH screening methods are critical tools needed for oil spill response; they help to assess when seafood is safe for harvesting and consumption. Sample preparation involves SPE of edible seafood portions with acetonitrile, followed by the addition of salts to induce water partitioning. After centrifugation, a portion of the acetonitrile layer is filtered prior to analysis via HPLC-FLD. The chromatographic method uses a polymeric C18 stationary phase designed for PAH analysis with gradient elution, and it resolves 15 U.S. Environmental Protection Agency priority parent PAHs in fewer than 20 min. The procedure was validated in three laboratories for the parent PAHs using spike recovery experiments at PAH fortification levels ranging from 25 to 10 000 microg/kg in oysters, shrimp, crab, and finfish, with recoveries ranging from 78 to 99%. Additional validation was conducted for a series of alkylated homologs of naphthalene, dibenzothiophene, and phenanthrene, with recoveries ranging from 87 to 128%. Method accuracy was further assessed based on analysis of National Institute of Standards and Technology Standard Reference Material 1974b. The method provides method detection limits in the sub to low ppb (microg/kg) range, and practical LOQs in the low ppb (microg/kg) range for most of the PAH compounds studied.     

Concentration and determination of cotinine in serum by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC), combined with on-line concentration techniques, cation-selective exhaustive injection (CSEI) and sweeping, was developed for the analysis of cotinine, the primary biomarker for exposure to secondhand smoke. Experimental parameters including sample matrix, surfactant concentration, injection length and concentration of high-conductivity buffer, and sample electrokinetic injection time were optimized for electrophoretic enrichment and separation processes. Under the optimal conditions, the detection sensitivity of cotinine was enhanced by about 5000-fold using CSEI-sweeping MEKC compared to normal MEKC. The limit of detection for cotinine was found to be 0.2 ng/mL using ultraviolet absorbance detection. Furthermore, the developed method was successfully applied to the detection of cotinine in mouse serum samples.     

Derivatizing assay for the determination of aldehydes using micellar electrokinetic chromatography

In this work, the use of a novel derivatization agent for the determination of aldehydes (in this particular case: formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) using micellar electrokinetic chromatography is reported. The derivatization reaction is based on the reaction of aldehydes with benzhydrazide to form the corresponding derivates with maximum absorbance at 250 nm. The experimental conditions of the derivatization reaction as well of the separation were optimized. The adducts were separated with a +22 kV voltage at a temperature of 29°C. The adducts’ separation was performed in less than 14 min using as the running buffer a mixture containing 110 mmol/L of sodium dodecyl sulfate and 27 mmol/L of sodium tetraborate at pH 9.45. Samples were injected using hydrodynamic mode (50 mbar × 5 s). The calibration curves were linear up to 15.0 mg/L with r ² above 0.99. Intra and inter‐day precisions were in average 3 and 4%, respectively, and recoveries were in average of 95%. Limits of detection and quantification were around 0.5 and 1.5 mg/L, respectively. The developed method was successfully applied in the analysis of low molar weight aldehydes in yogurt and vinegar samples.     

Rapid determination of trace polycyclic aromatic hydrocarbons in particulate matter using accelerated solvent extraction followed by ultra high performance liquid chromatography with fluorescence detection

A method has been developed for the trace analysis of polycyclic aromatic hydrocarbons, which are known as persistent organic pollutants and ubiquitous constituents of fine particulate matter that causes growing airborne pollution. The method, which was especially for samples of airborne particulate matter less than 2.5 μm in diameter, utilized accelerated solvent extraction and ultra high performance liquid chromatography with fluorescence detector. Four principal parameters of accelerated solvent extraction were optimized to obtain maximum extraction efficiency. Using the established synergetic programs of gradient elution and fluorescence wavelength switching, a rapid separation was achieved in 6.56 min with good linearity for 15 polycyclic aromatic hydrocarbons (coefficient of determination above 0.999). The limits of detection ranged from 0.833 to 10.0 pg/m³. The precision of the method expressed as inter‐day relative standard deviation ranged from 0.2 to 1%, which was calculated from nine repetitive measurements of 8.00 μg/L analytes. Average spiked recoveries ranged from 71.6 to 97.7%, with the exception of naphthalene. The rapid, sensitive, and accurate method can meet the pressing needs of health risk assessment and increasingly heavy daily tasks of air quality monitoring.