Organic Solvent Drop Research Articles

Determination of Vanadium(IV) and Vanadium(V) in Beverages by Two-Step Direct Immersion Single-Drop Microextraction with Graphite Furnace Atomic Absorption Spectrometry (GFAAS)

A novel two-step direct immersion single-drop microextraction (TS-DI-SDME) was reported for the sequential separation and enrichment of V(V) and V(IV) followed by graphite furnace atomic absorption spectrometry detection. Theonyltrifluoroacetone (HTTA) and chloroform were used as the chelating reagent and extraction solvent for TS-DI-SDME. In the first step, V(V)-HTTA complexes were separated and enriched in one organic solvent drop at pH 2.5, while V(IV) remained in the solution. Next, another organic solvent drop containing HTTA was immersed in the original solution after the extraction of V(V) for the enrichment of V(IV) at pH 4.5. This procedure avoids tedious and complicated pre-oxidation/pre-reduction operations, which may cause contamination and error. Under the optimized conditions, the limits of detection were equal to 3.1 and 2.6 ng L−1 for V(IV) and V(V) with relative standard deviation values of 4.9 and 5.8%, respectively. An enrichment factor of 300-fold was achieved for V(IV) and V(V). This method was successfully utilized for the determination of V(IV) and V(V) in beverages. To validate this approach, a water-certified reference material was analyzed with satisfactory results.

Vacuum-assisted headspace single-drop microextraction: Eliminating interfacial gas-phase limitations

Gas-phase limitations have been neglected in headspace single-drop microextraction (HS-SDME) and rate control has been assumed to primarily reside in the liquid water and/or organic phases, but not in the headspace. Herein we demonstrate the presence of interfacial gas constraints and propose using reduced headspace pressures to remove them. To describe the pressure dependence of HS-SDME, the system was decoupled into two interfacial steps: (i) the evaporation step (water-headspace interface) formulated using the two-film theory and (ii) the analyte uptake by the microdrop (headspace-microdrop interface) formulated using the resistance model. Naphthalene, acenaphthene, and pyrene were chosen as model analytes for their large Henry’s law solubility constants in n-octanol (HOA > 103 M atm−1), and their low to moderate Henry’s law volatility constants in water as a solvent (KH). We have found that extraction times were significantly shortened for all analytes by sampling at pressures well below the 1 atm used in the standard HS-SDME procedure. The acceleration of naphthalene extraction, whose facile evaporation into the headspace had been assumed to be practically pressure independent, highlighted the role of mass transfer through the interfacial gas layer on the organic solvent drop. The larger accelerations observed for acenaphthene and (especially) pyrene upon reducing the sampling pressure, suggested that gas-sided constraints were important during both the evaporation and uptake steps. Model calculations incorporating mass transfers at the headspace-microdrop interface confirmed that gas-phase resistance is largely eliminated (>96%) when reducing the sampling pressure from 1 to 0.04 atm, an effect that is nearly independent of analyte molecular mass. The relative importance of the two interfacial steps and their gas- and liquid-phase limitations are discussed, next to the use of KH and HOA to predict the positive effect of vacuum on HS-SDME.

Two-phase micro-electromembrane extraction with a floating drop free liquid membrane for the determination of basic drugs in complex samples

A two-phase micro-electromembrane extraction (μ-EME) using a floating drop of an organic solvent was presented for rapid and efficient pretreatment of complex biological samples. The μ-EME system consisted of a glass vial containing aqueous sample (donor solution) and a small drop of a water-immiscible organic solvent (4-nitrocumene), which was floating on the surface of the aqueous solution in form of a free liquid membrane (FLM). The vial geometry and the optimized volume ratios of the donor and the FLM ensured a stable position of the FLM in the center of the vial during μ-EME, and one electrode of a d.c. power supply was inserted directly into the FLM while the other electrode was placed into the aqueous sample. The active surface area of the floating drop FLM contacting the sample was considerably larger in comparison to formerly reported μ-EME formats employing FLMs and resulted in a faster and a more efficient transfer of target analytes from the sample to the FLM. Four basic drugs (nortriptyline, papaverine, loperamide, and haloperidol) were selected as model analytes and were extracted from physiological solution, human urine, and dried blood spot samples. At the optimized μ-EME conditions (250 V, 15 min, 300 rpm, acidic donor) and the optimized ratio of the sample to the FLM volume (500:14 μL), extraction recoveries between 49 and 100% and enrichment factors up to 35.7 were achieved. Quantitative analyses of the basic drugs in the resulting FLMs (diluted with methanol) were performed by capillary electrophoresis with ultraviolet detection and demonstrated excellent repeatability (RSD ≤ 4.9%) and linearity (r2 ≥ 0.9997), and low limits of detection (5–28 ng/mL) of the method.

Efficient determination of amphetamine and methylamphetamine in human urine using electro-enhanced single-drop microextraction with in-drop derivatization and gas chromatography

An efficient method for the determination of amphetamine (AM) and methylamphetamine (MA) using electro-enhanced single-drop microextraction (EE-SDME) and gas chromatography has been developed. One advantage of this method is that the extraction efficiency is greatly enhanced by the electric field acceleration of the mass transfer of target analytes from the sample solution to the organic solvent drop. In addition, the extracted analytes were in situ derivatized with isobutyl chloroformate (IBCF) in the droplet, which further improved the sensitivity of this method. Under the optimum conditions, the enrichment factors (EFs) for AM and MA were 247 and 782, respectively. The proposed method exhibited low limits of detection (0.27 μg/L for AM and 0.14 μg/L for MA) and good linearity over the concentration range between 1 and 2000 μg/L with regression coefficients (r2) of more than 0.99. The intra- and interday recoveries were from 89.6 to 96.2% and 82.7–90.5%, respectively, and the intra- and interday precisions (RSDs) were from 5.2 to 8.3% and 8.9–12.8%. The proposed method was applied to the determination of amphetamines in a urine sample.

Rapid Analysis of the Bisphenol a in Slips of Store Receipts and ATM Machine with Head-Space Liquid-Phase Micro-Extraction Coupled to Gas Chromatography and Mass Spectrometry

A novel method has been developed for the determination of bisphenolA in slips of store receipts and ATM machine by head-space liquid-phase micro-extraction (HS-LPME) coupled with gas chromatography-mass spectrometry (GC-MS). The variable experimental conditions for the HS-LPME extraction process were optimized. The optimal conditions were using 2ul of toluene as organic solvent drop, 0.5g of the amount of sample and 1.0cm of the depth of micro-drop from the surface of the sample. After extracting for 10 min and detection limit of 1-100mg·L-1. Detection limit (3 S/N) of the method was found to be 0.3mg·L-1, precision and recovery of these methods were tested giving values of RSDs (n=6) less than 4.49%; and of recovery in th range of 98.80%-99.47%. The method shows advantages of simplicity, high sensitivity and high performance extraction to be in line with the analytical standard of the international organic pollutant.

Use of a capillary tube for collecting an extraction solvent lighter than water after dispersive liquid–liquid microextraction and its application in the determination of parabens in different samples by gas chromatography—Flame ionization detection

In this study a new dispersive liquid-liquid microextraction (DLLME) method is presented on the basis of a safe organic solvent, octanol, which is lighter than water. The proposed method is used for the extraction and pre-concentration of some preservatives including methyl paraben (Mep), ethyl paraben (Etp) and propyl paraben (Prp) from different matrices. The extracted compounds are monitored by gas chromatography-flame ionization detector (GC-FID). A mixture of suitable extraction and dispersive solvents including 20microL octanol and 0.5mL acetone is quickly injected into the aqueous sample. The mixture is centrifuged for 10min at 6000rpm, so a small drop of extraction solvent collects on the water surface. A portion of the collected solvent is removed by a capillary tube through simple dipping the tube into organic solvent drop. 0.4microL of extract into the tube is removed by a microsyringe and injected into GC. Some effective parameters such as kinds and volumes of extraction and dispersive solvents as well as extraction time have to be investigated. Under optimum conditions, enrichment factors and recoveries of the studied compounds were obtained in the range of 100-276 and 25-72%, respectively. Linear ranges of the calibration curves were between 0.05 and 30 for methyl- and 0.02 and 30microgmL(-1) for ethyl- and propyl parabens, respectively. Limit of detection for methyl paraben was 0.015microgmL(-1) and those of ethyl- and propyl parabens were 0.005microgmL(-1). Relative standard deviations (RSDs %) for six repeated measurements (C=2microgmL(-1)) were 2% for methyl-, and ethyl parabens and 3% for propyl parabens, respectively.

Behavior of an organic solvent drop during the supercritical extraction of emulsions

AbstractThe behavior of a drop of dichloromethane in water in contact with CO2 at high pressure has been investigated with the purpose of analyzing the phenomena that takes place during the supercritical fluid extraction of emulsions process. Experiments have been performed with and without a solute (β‐carotene) and a surfactant (n‐octenylsuccinic anhydride‐modified starch) dissolved in the drop, and the evolution of the drop volume as well as of the interfacial tension between the drop and the aqueous phase has been measured. Additionally, a mathematical model has been developed that allows describing the mass transfer. Results show that the drop undergoes swelling and shrinking processes due to diffusion of CO2 into the drop and dichloromethane out of the drop. CO2 concentration in the drop can be as high as 0.9 (molar fraction). Emulsion drops behave as miniature gas antisolvent precipitators and many particles are formed inside the drop. The interfacial tension between the drop and the aqueous phase increases during the process, therefore destabilizing the emulsion. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Immersed single-drop microextraction interfaced with sequential injection analysis for determination of Cr(VI) in natural waters by electrothermal-atomic absorption spectrometry

Single-drop microextraction (SDME) and sequential injection analysis have been hyphenated for ultratrace metal determination by Electrothermal-Atomic Absorption Spectrometry (ETAAS). The novel method was targeted on extraction of the Cr(VI)-APDC chelate and encompasses the potential of SDME as a miniaturized and virtually solvent-free preconcentration technique, the ability of sequential injection analysis to handle samples and the versatility of furnace autosamplers for introducing microliter samples in ETAAS. The variables influencing the microextraction of Cr(VI) onto an organic solvent drop, i.e., type of organic solvent, microextraction time, stirring rate of the sample solution, drop volume, immersion depth of the drop, salting-out effect, temperature of the sample, concentration of the complexing agent and pH of the sample solution were fully investigated. For a 5 and 20 min microextraction time, the preconcentration factors were 20 and 70, respectively. The detection limit was 0.02 µg/L of Cr(VI) and the repeatability expressed as relative standard deviation was 7%. The SDME-SIA-ETAAS technique was validated against BCR CRM 544 (lyophilized solution) and applied to ultrasensitive determination of Cr(VI) in natural waters.

Turbo-Mixing in Microplates

How to effectively mix small volumes of liquids within microplate wells is a still underestimated and often neglected challenge. The method the authors introduce here relies on violent turbulent motion within a liquid caused by spotting an organic solvent drop onto its surface. The amount needed, less than 1 to 3 microL, is generally small enough not to alter bioactive molecules. Moreover, a solvent may be selected for its compatibility with assay components. The method was tested with layers of aqueous liquids that differ in pH and concentration of a pH-dependent dye, allowing mixing to be monitored optically. Rapid mixing was caused by spotting drops of alcohols, acetone, acetonitrile, and aqueous solutions of these, as long as the difference of surface tension between the drop and the uppermost layer of the bulk liquid surpassed 30 dynes/cm. Along with this difference, position and velocity of spotting, as well as viscosity and geometry of the bulk liquid volume, may influence the turbulence evoked. No significant difference was found for the activity of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase when measured after mixing by shaking and after mixing by spotting 1 microL of methanol onto assays within 96-well microplates.

Determination of valproic acid in human serum and pharmaceutical preparations by headspace liquid-phase microextraction gas chromatography-flame ionization detection without prior derivatization

An efficient and fast extraction technique for the enrichment of valproic acid from human blood serum samples using the headspace liquid phase microextraction (HS-LPME) combined with gas chromatography (GC) analysis has been developed. The extraction was conducted by suspending a 2 μL drop of organic solvent in a 1 mL serum sample; following 20 min of extraction, withdrawing organic solvent into a syringe and injection into a GC with a flame ionization detector (FID), without any further pre-treatment. Four organic solvents, 1-decanole, benzyl alcohol, 1-octanol and n-dodecane, were studied as extractants, and n-dodecane was found to be the most sensitive solvent for valproic acid. The results revealed that HS-LPME is suitable for the successful extraction of valproic acid from human blood serum samples. Parameters like extraction time, ionic strength, pH, organic solvent volume, and temperature of the sample were studied and optimized to obtain the best extraction results. An enrichment factor of 27-fold was achieved in 20 min. The procedure resulted in a relative standard deviation of <13.2% ( n = 7) and a linear calibration range from 2 to 20 μg mL −1 ( r > 0.98), and the limit of detection was 0.8 μg mL −1 in serum blank samples. Overall, LPME proved to be a fast, sensitive and simple tool for the preconcentration of valproic acid from real samples. The proposed method was also applied to the analysis of valproate in pharmaceutical preparations.

Continuous flow microextraction combined with high-performance liquid chromatography for the analysis of pesticides in natural waters

Continuous flow microextraction (CFME) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection has been applied to the analysis of five widely used pesticides, simazine, fensulfothion, etridiazole, mepronil and bensulide, present at trace levels in water samples. CFME employs a single organic solvent drop positioned at the tip of a polyether ether ketone (PEEK) tubing, which is immersed in a continuous flowing aqueous sample solution in a 0.5-ml glass chamber. The PEEK tubing acts as the organic drop holder and fluid delivery duct. Analytes are partitioned between the organic drop and the bulk sample solution. Important extraction factors including type of solvent, its volume, sample solution flow rate, extraction time, its pH and addition of salt were investigated. All pesticides exhibit good linearity in the investigated concentration range of 25–250 ng ml −1 with coefficients of determination ( R 2) ranging from 0.9879 to 0.9999 under the optimized conditions. Detection limits lower than 4 ng ml −1 were obtained for all analytes. The method was evaluated by analyzing natural water sample collected from a reservoir in Singapore. This study for the first time demonstrated the compatibility of CFME procedure and HPLC separation.

Headspace Hanging Drop Liquid Phase Microextraction and Gas Chromatography-Mass Spectrometry for the Analysis of Flavors from Clove Buds

A novel sample pretreatment technique, headspace hanging drop liquid phase microextraction (HS-LPME) was studied and applied to the determination of flavors from solid clove buds by gas chromatography-mass spectrometry (GC-MS). Several parameters affecting on HS-LPME such as organic solvent drop volume, extraction time, extraction temperature and phase ratio were investigated. 1-Octanol was selected as the extracting solvent, drop size was fixed to 0.6 <TEX>$\mu$</TEX>L. 60 min extraction time at 25 <TEX>${^{\circ}C}$</TEX> was chosen. HS-LPME has the good efficiency demonstrated by the higher partition equilibrium constant (<TEX>$K_{lh}$</TEX>) values and concentration factor (CF) values. The limits of detection (LOD) were 1.5-3.2 ng. The amounts of eugenol, <TEX>$\beta$</TEX>-caryophyllene and eugenol acetate from the clove bud sample were 1.90 mg/g, 1.47 mg/g and 7.0 mg/g, respectively. This hanging drop based method is a simple, fast and easy sample enrichment technique using minimal solvent. HSLPME is an alternative sample preparation method for the analysis of volatile aroma compounds by GC-MS.

Headspace single-drop microextraction for the analysis of chlorobenzenes in water samples

Exposing a microlitre organic solvent drop to the headspace of an aqueous sample contaminated with ten chlorobenzene compounds proved to be an excellent preconcentration method for headspace analysis by gas chromatography–mass spectrometry (GC–MS). The proposed headspace single-drop microextraction (SDME) method was initially optimised and the optimum experimental conditions found were: 2.5 μl toluene microdrop exposed for 5 min to the headspace of a 10 ml aqueous sample containing 30% (w/v) NaCl placed in 15 ml vial and stirred at 1000 rpm. The calculated calibration curves gave a high level of linearity for all target analytes with correlation coefficients ranging between 0.9901 and 0.9971, except for hexachlorobenzene where the correlation coefficient was found to be 0.9886. The repeatability of the proposed method, expressed as relative standard deviation varied between 2.1 and 13.2% ( n = 5). The limits of detection ranged between 0.003 and 0.031 μg/l using GC–MS with selective ion monitoring. Analysis of spiked tap and well water samples revealed that matrix had little effect on extraction. A comparative study was performed between the proposed method, headspace solid-phase microextraction (SPME), solid-phase extraction (SPE) and EPA method 8121. Overall, headspace SDME proved to be a rapid, simple and sensitive technique for the analysis of chlorobenzenes in water samples, representing an excellent alternative to traditional and other, recently introduced, methods.

Application of single-drop microextraction to the determination of dialkyl phthalate esters in food simulants

A fast and simple method, using static single-drop microextraction (SDME), has been developed to facilitate the identification and quantification of seven dialkyl phthalate esters in the three aqueous food simulants. The simulants were: A, distilled water; B, 3% (w/v) acetic acid/water; and C, 15% (v/v) ethanol/water. The extraction is performed by simply suspending a drop of organic solvent in the aqueous sample using a conventional gas chromatography (GC) microsyringe. Following extraction, the organic phase is withdrawn into the syringe and analyzed by gas chromatography and flame ionization detection (FID). The optimized method yields a linear calibration curve over three orders of magnitude for all the simulants, and method detection limits (MDLs) allowing detection of all the studied compounds at concentrations below migration limits established by the European Union. The accuracy of the SDME method was tested and compared to that of solid-phase microextraction (SPME) by recovery experiments using spiked samples, with results ranging from 85 to 115% in most cases.

Polymer Patterns in Evaporating Droplets on Dissolving Substrates

Self-organized polymer patterns resulting from the evaporation of an organic solvent drop on a soluble layer of polymer are investigated. The patterns can be modulated by changing the rate of evaporation and also the rate of substrate dissolution controlled by its solubility. Both of these affect the contact zone motion and its instabilities, leading to spatially variable rates of substrate etching and redeposition that result from a complex interplay of several factors such as Rayleigh-Benard cells, thermocapillary flow, solutal Marangoni flow, flow due to differential evaporation, osmotic-pressure-induced flow, and contact-line pinning-depinning events. The most complex novel pattern, observed at relatively low rates of evaporation, medium solubility, and without macroscopic contact-line stick-slip, consists of a regularly undulating ring made up of a bundle of parallel spaghetti-like threads or striations and radially oriented fingerlike ridges. Increased rate of evaporation obliterates the polymer threads, producing more densely packed fingers and widely separated multiple rings due to a frequent macroscopic pinning-depinning of the contact line. Near-equilibrium conditions such as slow evaporation or increased solubility of the substrate engender a wider and less undulating single ring.

Solvent microextraction of chlorinated pesticides

This paper is a preliminary report on a fast method for the extraction of organochlorine pesticides from river water which is inexpensive, fast and has little to no waste that has been developed. Pesticide extraction was achieved using the relatively new technique of solvent microextraction. In this technique a 2 μL drop of organic solvent is suspended on the tip of a microsyringe in a stirred aqueous sample solution. After the prescribed extraction time the drop is drawn back into the syringe. The syringe is then removed and the contents are injected into a gas chromatograph for analysis. Extraction of eleven organochlorinated pesticides from aqueous solutions with concentrations down to 1 ng mL−1 was achieved. The developed procedure was tested as a screening method for pesticides with spiked river water samples and was found to be linear over the concentration range of interest.

Liquid-Phase Microextraction in a Single Drop of Organic Solvent by Using a Conventional Microsyringe

Two modes of liquid-phase microextraction (LPME) were developed for capillary gas chromatography. Both methodologies, i.e., static LPME and dynamic LPME, involve the use of very small amounts of organic solvent (<2 μL) in a conventional microsyringe. The performance of the two techniques is demonstrated in the determination of two chlorobenzenes extracted into a single drop of toluene by the use of a 10-μL syringe. Static LPME provided some enrichment (∼12-fold), good reproducibility (9.7%), and simplicity but suffered relatively long extraction time (15 min). Dynamic LPME provided higher (∼27-fold) enrichment within much shorter extraction time (∼3 min), and relatively poorer precision (12.8%), primarily due to repeated manual manipulation. Both methods allow the direct transfer of extracted analytes into a gas chromatograph.