Using dispersive liquid-liquid microextraction and liquid chromatography for determination of guaifenesin enantiomers in human urine

A simple, rapid, and efficient method, dispersive liquid–liquid microextraction (DLLME) coupled with high‐performance liquid chromatography‐fluorescence detector, has been developed for the determination of guaifenesin (GUA) enantiomers in human urine samples after an oral dose administration of its syrup formulation. Urine samples were collected during the time intervals 0–2, 2–4, and 4–6 h and concentration and ratio of two enantiomers was determined. The ratio of R‐(?) to S‐(+) enantiomer concentrations in urine showed an increase with time, with R/S ratios of 0.66 at 2 h and 2.23 at 6 h. For microextraction process, a mixture of extraction solvent (dichloromethane, 100 μL) and dispersive solvent (THF, 1 mL) was rapidly injected into 5.0 mL diluted urine sample for the formation of cloudy solution and extraction of enantiomers into the fine droplets of CH₂Cl₂. After optimization of HPLC enantioselective conditions, some important parameters, such as the kind and volume of extraction and dispersive solvents, extraction time, temperature, pH, and salt effect were optimized for dispersive liquid–liquid microextraction process. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 10 to 2000 ng/mL for target analytes. LOD was 3.00 ng/mL for both of the enantiomers.     

Optimization of alcohol‐assisted dispersive liquid–liquid microextraction by experimental design for the rapid determination of fluoxetine in biological samples

A sensitive and rapid method based on alcohol‐assisted dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography for the determination of fluoxetine in human plasma and urine samples was developed. The effects of six parameters on the extraction recovery were investigated and optimized utilizing Plackett–Burman design and Box–Benken design, respectively. According to the Plackett–Burman design results, the volume of disperser solvent, extraction time, and stirring speed had no effect on the recovery of fluoxetine. The optimized conditions included a mixture of 172 μL of 1‐octanol as extraction solvent and 400 μL of methanol as disperser solvent, pH of 11.3 and 0% w/v of salt in the sample solution. Replicating the experiment in optimized condition for five times, gave the average extraction recoveries equal to 90.15%. The detection limit of fluoxetine in human plasma was obtained 3 ng/mL, and the linearity was in the range of 10–1200 ng/mL. The corresponding values for human urine were 4.2 ng/mL with the linearity range from 10 to 2000 ng/mL. Relative standard deviations for intra and inter day extraction of fluoxetine were less than 7% in five measurements. The developed method was successfully applied for the determination of fluoxetine in human plasma and urine samples.     

Ultrasound‐assisted dispersive liquid–liquid microextraction combined with gas chromatography‐mass spectrometry in negative chemical ionization mode for the determination of polybrominated diphenyl ethers in water

A simple and economical method for the determination of eight polybrominated diphenyl ethers (BDE‐28, 47, 99, 100,153,154,183, and 209) in water was developed. This method involves the use of ultrasound‐assisted dispersive liquid–liquid microextraction combined with GC‐MS in negative chemical ionization mode. Various parameters affecting the extraction efficiency, including the type and volume of extraction and dispersive solvents, salt concentration, extraction time, and ultrasonic time, were investigated. A volume of 1.0 mL of acetone (dispersive solvent) containing 10 μL tetrachloroethylene (extraction solvent) was injected into 5.0 mL of water samples and then emulsified by ultrasound for 2.0 min to produce the cloudy solution. Under the optimal condition, the enrichment factors for the eight PBDEs were varied from 845‐ to 1050‐folds. Good linearity was observed in the range of 1.0–200 ng L^?1 for BDE‐28, 47, 99, and 100; 5.0–200 ng L^?1 for BDE‐153, 154, and 183; and 5.0–500 ng L^?1 for BDE‐209. The RSD values were in the range of 2.5–8.4% (n = 5) and the LODs ranged from 0.40 to 2.15 ng L^?1 (S/N = 3). The developed method was applied for the determination of eight BPDEs in the river and lake water samples, and the mean recoveries at spiking levels of 5.0 and 50.0 ng L^?1 were in the range of 70.6–105.1%.     

Solid‐phase extraction assisted dispersive liquid–liquid microextraction based on solidification of floating organic droplet to determine sildenafil and its analogues in dietary supplements

A novel analytical method for the simultaneous determination of the concentration of sildenafil and its five analogues in dietary supplements using solid‐phase extraction assisted reversed‐phase dispersive liquid–liquid microextraction based on solidification of floating organic droplet combined with ion‐pairing liquid chromatography with an ultraviolet detector was developed. Parameters that affect extraction efficiency were systematically investigated, including the type of solid‐phase extraction cartridge, pH of the extraction environment, and the type and volume of extraction and dispersive solvent. The method linearity was in the range of 5.0–100 ng/mL for sildenafil, homosildenafil, udenafil, benzylsildenafil, and thiosildenafil and 10–100 ng/mL for acetildenafil. The coefficients of determination were ≥0.996 for all regression curves. The sensitivity values expressed as limit of detection were between 2.5 and 7.5 ng/mL. Furthermore, intraday and interday precisions expressed as relative standard deviations were less than 5.7 and 9.9%, respectively. The proposed method was successfully applied to the analysis of sildenafil and its five analogues in complex dietary supplements.     

Cyclodextrin‐assisted dispersive liquid–liquid microextraction for the preconcentration of carbamazepine and clobazam with subsequent sweeping micellar electrokinetic chromatography

A new version of dispersive liquid–liquid microextraction, namely, cyclodextrin‐assisted dispersive liquid–liquid microextraction, with subsequent sweeping micellar electrokinetic chromatography has been developed for the preconcentration and sensitive detection of carbamazepine and clobazam. α‐Cyclodextrin and chloroform were used as the dispersive agent and extraction solvent, respectively. After the extraction, carbamazepine and clobazam were analyzed using micellar electrokinetic chromatography with ultraviolet detection. The detection sensitivity was further enhanced using the sweeping technique. Under optimal extraction and stacking conditions, the calibration curves of carbamazepine and clobazam were linear over a concentration range of 2.0–200.0 ng/mL. The method detection limits at a signal‐to‐noise ratio of 3 were 0.6 and 0.5 ng/mL with sensitivity enhancement factors of 3575 and 4675 for carbamazepine and clobazam, respectively. This developed method demonstrated high sensitivity enhancement factors and was successfully applied to the determination of carbamazepine and clobazam in human urine samples. The precision and accuracy for urine samples were less than 4.2 and 6.9%, respectively.     

Application of liquid–liquid microextraction for the effective separation and simultaneous determination of 11 pharmaceuticals in wastewater samples using high‐performance liquid chromatography with tandem mass spectrometry

A dispersive liquid–liquid microextraction method for the simultaneous determination of 11 pharmaceuticals has been developed. The method is based on a microextraction procedure applied to wastewater samples from different regions of Hungary followed by high‐performance liquid chromatography with mass spectrometry. The effect of the nature of the extractant, dispersive solvent, different additives, and extraction time were examined on the extraction efficiently of the dispersive liquid–liquid microextraction method. Under optimal conditions, the linearity for determining the pharmaceuticals was in the range of 1–500 ng/mL, with the correlation coefficients ranging from 0.9922 to 0.9995. The limits of detection and limits of quantification were in the range of 0.31–6.65 and 0.93–22.18 ng/mL, respectively.     

Dispersive liquid–liquid microextraction as an effective preanalytical step for the determination of estradiol in human urine

In this work, a fast and effective dispersive liquid–liquid microextraction was developed for the isolation and preconcentration of free 17 β‐estradiol, the main human estrogen, from real human urine samples. To optimize the extraction technique, few important parameters such as type and volume of extraction and dispersive solvents, centrifugation conditions, effect of salt addition, and extraction time were studied. Optimal conditions were obtained when injecting 600 μL mixture of tetrachloromethane as extraction solvent and ethanol as dispersive solvent (1:5, v/v) into 2 mL of urine containing 8% NaCl and following centrifugation at 10 000 rpm, thus reaching enrichment factor 28 and extraction recovery 98% for estradiol. Procedure was evaluated by means of high‐performance liquid chromatography with UV detection (λ = 280 nm) using a C‐18 column and methanol/water (60:40, v/v) as the mobile phase. The method was linear within the concentration range 1.0–250.0 mg/L (r  = 0.9997) and provided a limit of detection of 0.25 mg/L. The proposed method was applied to the determination of free estradiol in real human pregnancy urine.     

Ionic liquid‐based microwave‐assisted surfactant‐improved dispersive liquid–liquid microextraction and derivatization of aminoglycosides in milk samples

A green and simple method, ionic liquid‐based microwave‐assisted surfactant‐improved dispersive liquid–liquid microextraction and derivatization was developed for the determination of aminoglycosides in milk samples. Nonionic surfactant Triton X‐100 and ionic liquid 1‐hexyl‐3‐methylimidazolium hexafluorophosphate were used as the disperser and extraction solvent, respectively. Extraction, preconcentration, and derivatization of aminoglycosides were carried out in a single step. Several experimental parameters, including type and volume of extraction solvent, type and concentration of surfactant, microwave power and irradiation time, concentration of derivatization reagent, and pH value and volume of buffer were investigated and optimized. Under the optimum experimental conditions, the linearities for determining the analytes were in the range 0.4–10.0 ng/mL for tobramycin, 1.0–25.0 ng/mL for neomycin, and 2.0–50.0 ng/mL for gentamicin, with the correlation coefficients ranging from 0.9991 to 0.9998. The LODs for the analytes were between 0.11 and 0.50 ng/mL. The present method was applied to the analysis of different milk samples, and the recoveries of aminoglycosides obtained were in the range 96.4–105.4% with the RSDs lower than 5.5%. The results showed that the present method was a rapid, convenient, and environmentally friendly method for the determination of aminoglycosides in milk samples.     

Ionic liquid‐based dispersive liquid–liquid microextraction followed by RP‐HPLC determination of saquinavir in rat serum: application to pharmacokinetics

An ionic liquid‐based dispersive liquid–liquid microextraction followed by RP‐HPLC determination of the most commonly prescribed protease inhibitor, saquinavir, in rat plasma was developed and validated. The effects of different ionic liquids, dispersive solvents, extractant/disperser ratio and salt concentration on sample recovery and enrichment were studied. Among the ionic liquids investigated, 1‐butyl‐3‐methylimidazolium hexafluorophosphate was found to be most effective for extraction of saquinavir from rat serum. The recovery was found to be 95% at an extractant/disperser ratio of 0.43 using 1‐butyl‐3‐methylimidazolium hexafluorophosphate and methanol as extraction and dispersive solvents. The recovery was further enhanced to 99.5% by addition of 5.0% NaCl. A threefold enhancement in detection and quantification limits was achieved, at 0.01 and 0.03 µg/mL, compared with the conventional protein precipitation method. A linear relationship was observed in the range of 0.035–10.0 µg/mL with a correlation coefficient (r²) of 0.9996. The method was validated and applied to study pharmacokinetics of saquinavir in rat serum. Copyright © 2014 John Wiley & Sons, Ltd.     

New application of chitosan‐grafted polyaniline in dispersive solid‐phase extraction for the separation and determination of phthalate esters in milk using high‐performance liquid chromatography

Chitosan‐grafted polyaniline was synthesized and applied as a sorbent for the preconcentration of phthalate esters in dispersive solid‐phase extraction. By coupling dispersive solid‐phase extraction with high‐performance liquid chromatography and response surface methodology (central composite design), a reliable, sensitive, and cost‐effective method for simultaneous determination of phthalate esters including dimethyl phthalate, di‐n‐butyl phthalate, and di(2‐ethylhexyl)phthalate was developed. The morphology of sorbent had been studied by scanning electron microscopy and its chemical structure confirmed by Fourier transform infrared spectroscopy. Under optimum condition, good linearity was observed in the range of 5.0–5000.0 ng/mL. The limits of detection (S/N = 3) and limits of quantification (S/N = 10) were 0.1–0.3 and 0.3–1 ng/mL, respectively. The relative standard deviations were less than 8.8%. Finally, this procedure was employed for extraction of trace amounts of phthalic acid esters in milk samples, the relative recoveries ranged from 82 to 103%.     

Suitability of dispersive liquid–liquid microextraction for the in situ silylation of chlorophenols in water samples before gas chromatography with mass spectrometry

Trace analysis of chlorophenols in water was performed by simultaneous silylation and dispersive liquid–liquid microextraction followed by gas chromatography with mass spectrometry. Dispersive liquid–liquid microextraction was carried out using an organic solvent lighter than water (n‐hexane). The effect of different silylating reagents on the method efficiency was investigated. The influence of derivatization reagent volume, presence of catalyst and derivatization/extraction time on the yield of the derivatization reaction was studied. Different parameters affecting extraction efficiency such as kind and volume of extraction and disperser solvents, pH of the sample and addition of salt were also investigated and optimized. Under the optimum conditions, the calibration graphs were linear in the range of 0.05–100 ng/mL and the limit of detection was 0.01 ng/mL. The enrichment factors were 242, 351, and 363 for 4‐chlorophenol, 2,4‐dichlorophenol, and 2,4,6‐trichlorophenol, respectively. The values of intra‐ and inter‐day relative standard deviations were in the range of 3.0–6.4 and 6.1–9.9%, respectively. The applicability of the method was investigated by analyzing water and wastewater samples.     

Determination of four sulfonylurea herbicides in tea by matrix solid‐phase dispersion cleanup followed by dispersive liquid–liquid microextraction

Matrix solid‐phase dispersion combined with dispersive liquid–liquid microextraction has been developed as a new sample pretreatment method for the determination of four sulfonylurea herbicides (chlorsulfuron, bensulfuron‐methyl, chlorimuron‐ethyl, and pyrazosulfuron) in tea by high‐performance liquid chromatography with diode array detection. The extraction and cleanup by matrix solid‐phase dispersion was carried out by using CN‐silica as dispersant and carbon nanotubes as cleanup sorbent eluted with acidified dichloromethane. The eluent of matrix solid‐phase dispersion was evaporated and redissolved in 0.5 mL methanol, and used as the dispersive solvent of the following dispersive liquid–liquid microextraction procedure for further purification and enrichment of the target analytes before high‐performance liquid chromatography analysis. Under the optimum conditions, the method yielded a linear calibration curve in the concentration range from 5.0 to 10 000 ng/g for target analytes with a correlation coefficients (r²) ranging from 0.9959 to 0.9998. The limits of detection for the analytes were in the range of 1.31–2.81 ng/g. Recoveries of the four sulfonylurea herbicides at two fortification levels were between 72.8 and 110.6% with relative standard deviations lower than 6.95%. The method was successfully applied to the analysis of four sulfonylurea herbicides in several tea samples.     

Application of dispersive liquid–liquid microextraction with alcoholic solvents followed by HPLC–UV as a sensitive and efficient method for the extraction and determination of citalopram in biological samples using an experimental design

A sensitive and rapid method based on alcoholic-assisted dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for determination of citalopram in human plasma and urine samples was developed. The effects of six parameters (extraction time, stirring speed, pH, volume of extraction and disperser solvents, and ionic strength) on the extraction recovery were investigated and optimized utilizing Plackett–Burman design and Box–Behnken design, respectively. According to Plackett–Burman design results, the volume of disperser solvent, stirring speed, and extraction time had no effect on the recovery of citalopram. The optimized condition was a mixture of 172 µL of 1-octanol as extraction solvent and 400 µL of methanol as disperser solvent, pH of 10.3 and 1% w/v of salt in the sample solution. Replicating the experiment in optimized condition for five times, gave the average extraction recoveries equal to 89.42%. The detection limit of citalopram in human plasma was obtained 4 ng/mL, and the linearity was in the range of 10–1200 ng/mL. The corresponding values for human urine were 5.4 ng/mL with the linearity in the range of 10–2000 ng/mL. Relative standard deviations for inter- and intraday extraction of citalopram were less than 7% for five measurements. The proposed method was successfully implemented for the determination of citalopram in human plasma and urine samples.     

Quantitative determination of trace phenazopyridine in human urine samples by hyphenation of dispersive solid‐phase extraction and liquid‐phase microextraction followed by gas chromatography/mass spectrometry analysis

Magnetic dispersive solid‐phase extraction followed by dispersive liquid?liquid microextraction coupled with gas chromatography/mass spectrometry was applied for the quantitative analysis of phenazopyridine in urinary samples. Magnetic dispersive solid‐phase extraction was carried out using magnetic graphene oxide nanoparticles modified by poly(thiophene‐pyrrole) copolymer. The eluting solvent of this step was used as the disperser solvent for the dispersive liquid?liquid microextraction procedure. To reach the maximum efficiency of the method, effective parameters including sorbent amount, adsorption time, type and volume of disperser and extraction solvents, pH of the sample solution, and ionic strength as well as desorption time, and approach were optimized, separately. Characterization of the synthesized sorbent was studied by utilizing infrared spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray analysis. Calibration curve was linear in the range of 0.5?250 ng/mL (R² = 0.9988) with limits of detection and quantification of 0.1 and 0.5 ng/mL, respectively. Intra‐ and interday precisions (RSD%, n = 3) of the method were in the range of 4.6?5.4% and 4.0?5.5%, respectively, at three different concentration levels. Under the optimal condition, this method was successfully applied for the determination of phenazopyridine in human urine samples. The relative recoveries were obtained in the range of 85.0?89.0%.     

Simple determination of some antidementia drugs in wastewater and human plasma samples by tandem dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography

In this work, a simple method, namely, tandem dispersive liquid–liquid microextraction, with a high sample clean‐up is applied for the rapid determination of the antidementia drugs rivastigmine and donepezil in wastewater and human plasma samples. This method, which is based on two consecutive dispersive microextractions, is performed in 7 min. In the method, using a fast back‐extraction step, the applicability of the dispersive microextraction methods in complicated matrixes is conveniently improved. This step can be performed in less than 2 min, and very simple tools are required for this purpose. To achieve the best extraction efficiency, optimization of the variables affecting the method was carried out. Under the optimized experimental conditions, the relative standard deviations for the method were in the range of 6.9–8.7%. The calibration curves were obtained in the range of 2–1100 ng/mL with good correlation coefficients, higher than 0.995, and the limits of detection ranged between 0.5 and 1.0 ng/mL.     

Salting‐out assisted liquid–liquid extraction coupled to dispersive liquid–liquid microextraction for the determination of chlorophenols in wine by high‐performance liquid chromatography

A novel procedure of sample preparation combined with high‐performance liquid chromatography with diode array detection is introduced for the analysis of highly chlorinated phenols (trichlorophenols, tetrachlorophenols, and pentachlorophenol) in wine. The main features of the proposed method are (i) low‐toxicity diethyl carbonate as extraction solvent to selectively extract the analytes without matrix effect, (ii) the combination of salting‐out assisted liquid–liquid extraction and dispersive liquid–liquid microextraction to achieve an enrichment factor of 334–361, and (iii) the extract is analyzed by high‐performance liquid chromatography to avoid derivatization. Under the optimum conditions, correlation coefficients (r) were >0.997 for calibration curves in the range 1–80 ng/mL, detection limits and quantification limits ranged from 0.19 to 0.67 and 0.63 to 2.23 ng/mL, respectively, and relative standard deviation was <8%. The method was applied for the determination of chlorophenols in real wines, with recovery rates in the range 82–104%.     

Sensitive determination of three aconitum alkaloids and their metabolites in human plasma by matrix solid‐phase dispersion with vortex‐assisted dispersive liquid–liquid microextraction and HPLC with diode array detection

A simple and sensitive method for determination of three aconitum alkaloids and their metabolites in human plasma was developed using matrix solid‐phase dispersion combined with vortex‐assisted dispersive liquid–liquid microextraction and high‐performance liquid chromatography with diode array detection. The plasma sample was directly purified by matrix solid‐phase dispersion and the eluate obtained was concentrated and further clarified by vortex‐assisted dispersive liquid–liquid microextraction. Some important parameters affecting the extraction efficiency, such as type and amount of dispersing sorbent, type and volume of elution solvent, type and volume of extraction solvent, salt concentration as well as sample solution pH, were investigated in detail. Under optimal conditions, the proposed method has good repeatability and reproducibility with intraday and interday relative standard deviations lower than 5.44 and 5.75%, respectively. The recoveries of the aconitum alkaloids ranged from 73.81 to 101.82%, and the detection limits were achieved within the range of 1.6–2.1 ng/mL. The proposed method offered the advantages of good applicability, sensitivity, simplicity, and feasibility, which makes it suitable for the determination of trace amounts of aconitum alkaloids in human plasma samples.     

Ionic‐liquid‐based dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography for the forensic determination of methamphetamine in human urine

Determination of methamphetamine in forensic laboratories is a major issue due to its health and social harm. In this work, a simple, sensitive, and environmentally friendly method based on ionic liquid dispersive liquid–liquid microextraction combined with high‐performance liquid chromatography was established for the analysis of methamphetamine in human urine. 1‐Octyl‐3‐methylimidazolium hexafluorophosphate with the help of disperser solvent methanol was selected as the microextraction solvent in this process. Various parameters affecting the extraction efficiency of methamphetamine were investigated systemically, including extraction solvent and its volume, disperser solvent and its volume, sample pH, extraction temperature, and centrifugal time. Under the optimized conditions, a good linearity was obtained in the concentration range of 10–1000 ng/mL with determination coefficient >0.99. The limit of detection calculated at a signal‐to‐noise ratio of 3 was 1.7 ng/mL and the relative standard deviations for six replicate experiments at three different concentration levels of 100, 500, and 1000 ng/mL were 6.4, 4.5, and 4.7%, respectively. Meanwhile, up to 220‐fold enrichment factor of methamphetamine and acceptable extraction recovery (>80.0%) could be achieved. Furthermore, this method has been successfully employed for the sensitive detection of a urine sample from a suspected drug abuser.     

Up‐and‐down shaker‐assisted ionic liquid‐based dispersive liquid—liquid microextraction of benzophenone‐type ultraviolet filters

Sun protection is an important part of our lives. UV filters are widely used to absorb solar radiation in sunscreens. However, excess UV filters constitute persistent groups of organic micropollutants present in the environment. An environmentally friendly ionic‐liquid‐based up‐and‐down shaker‐assisted dispersive liquid?liquid microextraction device combined with ultra‐performance liquid chromatography coupled with photodiode‐array detection has been developed to preconcentrate three UV filters (benzophenone, 2‐hydroxy‐4‐methoxybenzophenone, 2,2′‐dihydroxy‐4‐methoxybenzophenone) from field water samples. In this method, the optimal conditions for the proposed extraction method were: 40 μL [C₈MIM][PF₆] as extraction solvent and 200 μL methanol as disperser solvent were used to extract the UV filters. After up‐and‐down shaking for 3 min, the aqueous solution was centrifuged at 5000 rpm speed, then using microtube to collect the settled extraction solvent and using ultra‐performance liquid chromatography for further analysis. Quantification results indicated that the linear range was 2–1000 ng/mL. The LOD of this method was in the range 0.2–1.3 ng/mL with r² ≥ 0.9993. The relative recovery in studies of different types of field water samples was in the range 92–120%, and the RSD was 2.3–7.1%. The proposed method was also applied to the analysis of field samples.     

Application of ultrasound‐assisted liquid–liquid microextraction coupled with gas chromatography and mass spectrometry for the rapid determination of synthetic cannabinoids and metabolites in biological samples

The constant emergence of new psychoactive substances is a challenge to clinical and forensic toxicologists who need to constantly update analytical techniques to detect them. A large portion of these substances are synthetic cannabinoids. The aim of this study was to develop a rapid and simple method for the determination of synthetic cannabinoids and their metabolites in urine and blood using gas chromatography–mass spectrometry. The method involves an ultrasound‐assisted dispersive liquid–liquid microextraction that implies a rapid procedure, giving excellent extraction efficiencies with minimal use of toxic solvents. This is followed by silylation and analysis with gas chromatography–mass spectrometry. The chromatographic method allows for the separation and identification of 29 selected synthetic cannabinoids and some metabolites. The method was validated on urine and blood samples with the ability to detect and quantify all analytes with satisfactory limits of detection (from 1 to 5 ng/mL), limits of quantification (5 ng/mL), and selectivity and linearity (in the range of 5–200 ng/mL). The developed assay is highly applicable to laboratories with limited instrumental availability, due to the use of efficient and low‐cost sample preparation and instrumental equipment. The latter may contribute to enhance the detection of new psychoactive substances in clinical and forensic toxicology laboratories.