Determination of fungicides in sediments using a dispersive liquid–liquid microextraction procedure based on solidification of floating organic drop

A dispersive liquid–liquid microextraction procedure based on solidification of floating organic droplet has been investigated for the determination of fungicides (cyprodinil, difenoconazole, myclobutanil, and spiroxamine) in sediments by HPLC with diode array detection. In the overall extraction process, the extraction solvents can be separated easily from the sample solution, and the experiment time was shortened. Moreover, several parameters such as the type and volume of the extraction solvent and dispersive solvent, centrifugal speed, extraction time, and salt effect that affect the extraction efficiencies of the target fungicides were studied and optimized. Under the optimized conditions, the LOD for the target analytes were in the range of 0.1–0.5 μg/g. Satisfactory recoveries of the target analytes in the sediment samples were 81.00–99.00%, with RSDs (n = 5) that ranged from 1.8 to 6.5%. Finally, the simple, sensitive, and environmentally friendly method was successfully applied to determine the target fungicides in actual sediment samples.     

Sensitive determination of atorvastatin in human plasma by dispersive liquid–liquid microextraction and solidification of floating organic drop followed by high‐performance liquid chromatography

A novel and sensitive dispersive liquid–liquid microextraction method based on the solidification of the floating organic drop combined with high‐performance liquid chromatography and ultraviolet detection was used for the determination of atorvastatine in blood serum samples. The chromatographic separation of atorvastatin was carried out using methanol as the mobile phase organic modifier. Various parameters affecting the extraction efficiency were optimized, such as the kind and volume of extraction solvent (1‐undecanol) and disperser solvent (acetonitrile), pH, and the extraction time. The calibration curve was linear in the range of 0.2–6000 μg/L of atorvastatin (r² = 0.995) with a limit of detection of 0.07 μg/L. The relative standard deviation for 100 μg/L of atorvastatin in human plasma was 8.4% (n = 4). The recoveries of plasma samples spiked with atorvastatin were in the range of 98.8–113.8%. The obtained results showed that the proposed method is fast, simple, and reliable for the determination of very low concentrations of atorvastatin in human plasma samples.     

Sensitive determination of methadone in human serum and urine by dispersive liquid–liquid microextraction based on the solidification of a floating organic droplet followed by HPLC–UV

Dispersive liquid–liquid microextraction based on solidification of floating organic droplet was developed for the extraction of methadone and determination by high‐performance liquid chromatography with UV detection. In this method, no microsyringe or fiber is required to support the organic microdrop due to the usage of an organic solvent with a low density and appropriate melting point. Furthermore, the extractant droplet can be collected easily by solidifying it at low temperature. 1‐Undecanol and methanol were chosen as extraction and disperser solvents, respectively. Parameters that influence extraction efficiency, i.e. volumes of extracting and dispersing solvents, pH, and salt effect, were optimized by using response surface methodology. Under optimal conditions, enrichment factor for methadone was 134 and 160 in serum and urine samples, respectively. The limit of detection was 3.34 ng/mmL in serum and 1.67 ng/mL in urine samples. Compared with the traditional dispersive liquid–liquid microextraction, the proposed method obtained lower limit of detection. Moreover, the solidification of floating organic solvent facilitated the phase transfer. And most importantly, it avoided using high‐density and toxic solvents of traditional dispersive liquid–liquid microextraction method. The proposed method was successfully applied to the determination of methadone in serum and urine samples of an addicted individual under methadone therapy.     

Preconcentration and determination of methyl methacrylate by dispersive liquid–liquid microextraction

This article describes the preconcentration of methyl methacrylate in produced water by the dispersive liquid–liquid microextraction using extraction solvents lighter than water followed by gas chromatography. In the present experiments, 0.4 mL dispersive solvent (ethanol) containing 15.0 μL extraction solvent (toluene) was rapidly injected into the samples and followed by centrifuging and direct injection into the gas chromatograph equipped with flame ionization detector. The parameters affecting the extraction efficiency were evaluated and optimized including toluene (as extraction solvent), ethanol (as dispersive solvent), 15 μL and 0.4 mL (as the volume of extraction and dispersive solvents, respectively), pH 7, 20% ionic strength, and extraction's temperature and time of 20°C and 10 min, respectively. Under the optimum conditions, the figures of merits were determined to be LOD = 10 μg/L, dynamic range = 20–180 μg/L, RSD = 11% (n = 6). The maximum recovery under the optimized condition was determined to be 79.4%.     

Application of dispersive liquid–liquid microextraction based on solidification of floating organic drop for simultaneous determination of alachlor and atrazine in aqueous samples

Dispersive liquid–liquid microextraction based on solidification of floating organic drop coupled with HPLC‐UV detection as a fast and inexpensive technique was applied to the simultaneous extraction and determination of traces of two common herbicides, alachlor and atrazine, in aqueous samples. The critical experimental parameters, including type of the extraction and disperser solvents as well as their volumes, sample pH, salt addition, and extraction time were investigated and optimized. Under the optimum conditions, the calibration graphs found to be linear in the range of 0.1–200 μg/L with LOD in the range of 0.02–0.05 μg/L. The RSDs were in the range of 4.2–5.3% (n = 5). The relative recoveries of well, tap, and river water samples which have been spiked with different levels of herbicides were 94.0–106.0, 99.0–105.0, and 88.5–97.0%, respectively.     

Optimization of dispersive liquid–liquid microextraction with central composite design for preconcentration of chlordiazepoxide drug and its determination by HPLC‐UV

A simple, rapid, and sensitive method based on dispersive liquid–liquid microextraction combined with HPLC‐UV detection applied for the quantification of chlordiazepoxide in some real samples. The effect of different extraction conditions on the extraction efficiency of the chlordiazepoxide drug was investigated and optimized using central composite design as a conventional efficient tool. Optimum extraction condition values of variables were set as 210 μL chloroform, 1.8 mL methanol, 1.0 min extraction time, 5.0 min centrifugation at 5000 rpm min^?1, neutral pH, 7.0% w/v NaCl. The separation was reached in less than 8.0 min using a C₁₈ column using isocratic binary mobile phase (acetonitrile/water (60:40, v/v)) with flow rate of 1.0 mL min^?1. The linear response (r² > 0.998) was achieved in the range of 0.005–10 μg mL^?1 with detection limit 0.0005 μg mL^?1. The applicability of this method for simultaneous extraction and determination of chlordiazepoxide in four different matrices (water, urine, plasma, and chlordiazepoxide tablet) were investigated using standard addition method. Average recoveries at two spiking levels were over the range of 91.3–102.5% with RSD < 5.0% (n = 3). The obtained results show that dispersive liquid–liquid microextraction combined with HPLC‐UV is a fast and simple method for the determination of chlordiazepoxide in real samples.     

Dispersion‐solidification liquid–liquid microextraction for volatile aromatic hydrocarbons determination: Comparison with liquid phase microextraction based on the solidification of a floating drop

Two microextraction techniques – liquid phase microextraction based on solidification of a floating organic drop (LPME‐SFO) and dispersive liquid–liquid microextraction combined with a solidification of a floating organic drop (DLLME‐SFO) – are explored for benzene, toluene, ethylbenzene and o‐xylene sampling and preconcentration. The investigation covers the effects of extraction solvent type, extraction and disperser solvents' volume, and the extraction time. For both techniques 1‐undecanol containing n‐heptane as internal standard was used as an extracting solvent. For DLLME‐SFO acetone was used as a disperser solvent. The calibration curves for both techniques and for all the analytes were linear up to 10 μg/mL, correlation coefficients were in the range 0.997–0.998, enrichment factors were from 87 for benzene to 290 for o‐xylene, detection limits were from 0.31 and 0.35 μg/L for benzene to 0.15 and 0.10 μg/L for o‐xylene for LPME‐SFO and DLLME‐SFO, respectively. Repeatabilities of the results were acceptable with RSDs up to 12%. Being comparable with LPME‐SFO in the analytical characteristics, DLLME‐SFO is superior to LPME‐SFO in the extraction time. A possibility to apply the proposed techniques for volatile aromatic hydrocarbons determination in tap water and snow was demonstrated.     

Optimization of dispersive liquid–liquid microextraction based on the solidification of floating organic droplets using an orthogonal array design and its application for the determination of fungicide concentrations in environmental water samples

A dispersive liquid–liquid microextraction method based on the solidification of floating organic droplets was developed as a simple and sensitive method for the simultaneous determination of the concentrations of multiple fungicides (triazolone, chlorothalonil, cyprodinil, and trifloxystrobin) in water by high‐performance liquid chromatography with variable‐wavelength detection. After an approach varying one factor at a time was used, an orthogonal array design [L₂₅ (5⁵)] was employed to optimize the method and to determine the interactions between the parameters. The significance of the effects of the different factors was determined using analysis of variance. The results indicated that the extraction solvent volume significantly affects the efficiency of the extraction. Under optimal conditions, the relative standard deviation (n = 5) varied from 2.3 to 5.5% at 0.1 μg/mL for each analyte. Low limits of detection were obtained and ranged from 0.02 to 0.2 ng/mL. In addition, the proposed method was applied to the analysis of fungicides in real water samples. The results show that the dispersive liquid–liquid microextraction based on the solidification of floating organic droplets is a potential method for detecting fungicides in environmental water samples, with recoveries of the target analytes ranging from 70.1 to 102.5%.     

Preconcentration of organochlorine pesticides in aqueous samples by dispersive liquid–liquid microextraction based on solidification of floating organic drop after SPE with multiwalled carbon nanotubes

SPE joined with dispersive liquid–liquid microextraction based on solidification of floating organic drop (DLLME‐SFO) as a novel technique combined with GC with electron‐capture detection has been developed as a preconcentration technique for the determination of organochlorine pesticides (OCPs) in water samples. Aqueous samples were loaded onto multiwalled carbon nanotubes as sorbent. After the elution of the desired compounds from the sorbent by using acetone, the DLLME‐SFO technique was performed on the obtained solution. Variables affecting the performance of both steps such as sample solution flow rate, breakthrough volume, type and volume of the elution, type and volume of extraction solvent and salt addition were studied and optimized. The new method provided an ultra enrichment factor (8280–28221) for nine OCPs. The calibration curves were linear in the range of 0.5–1000 ng/L, and the LODs ranged from 0.1–0.39 ng/L. The RSD, for 0.01 μg/L of OCPs, was in the range of 1.39–13.50% (n = 7). The recoveries of method in water samples were 70–113%.     

Development of an ionic‐liquid‐based dispersive liquid–liquid microextraction method for the determination of antichagasic drugs in human breast milk: Optimization by central composite design

Chagas disease constitutes a major public health problem in Latin America. Human breast milk is a biological sample of great importance for the analysis of therapeutic drugs, as unwanted exposure through breast milk could result in pharmacological effects in the nursing infant. Thus, the goal of breast milk drug analysis is to inquire to which extent a neonate may be exposed to a drug during lactation. In this work, we developed an analytical technique to quantify benznidazole and nifurtimox (the two antichagasic drugs currently available for medical treatment) in human breast milk, with a simple sample pretreatment followed by an ionic‐liquid‐based dispersive liquid–liquid microextraction combined with high‐performance liquid chromatography and UV detection. For this technique, the ionic liquid 1‐octyl‐3‐methylimidazolium hexafluorophosphate has been used as the “extraction solvent.” A central composite design was used to find the optimum values for the significant variables affecting the extraction process: volume of ionic liquid, volume of dispersant solvent, ionic strength, and pH. At the optimum working conditions, the average recoveries were 77.5 and 89.7%, the limits of detection were 0.06 and 0.09 μg/mL and the interday reproducibilities were 6.25 and 5.77% for benznidazole and nifurtimox, respectively. The proposed methodology can be considered sensitive, simple, robust, accurate, and green.     

Preconcentration and determination of 2‐mercaptobenzimidazole by dispersive liquid–liquid microextraction and experimental design

A method was developed to determine 2‐mercaptobenzimidazole in water and urine samples using dispersive liquid–liquid microextraction technique coupled with ultraviolet–visible spectrophotometry. It was essential to peruse the effect of all parameters that can likely influence the performance of extraction. The influence of parameters, such as dispersive and extraction solvent volume and sample volume, on dispersive liquid–liquid microextraction was studied. The optimization was carried out by the central composite design method. The central composite design optimization method resulted in 1.10 mL dispersive solvent, 138.46 μL extraction solvent, and 4.46 mL sample volume. Under the optimal terms, the calibration curve was linear over the range of 0.003–0.18 and 0.007–0.18 μg/mL in water and urine samples, respectively. The limit of detection and quantification of the proposed approach for 2‐mercaptobenzimidazole were 0.013 and 0.044 μg/mL in water samples and 0.016 and 0.052 μg/mL in urine samples, respectively. The method was successfully applied to determination of 2‐mercaptobenzimidazole in urine and water samples.     

Dispersive liquid–liquid microextraction based on solidification of floating organic drop combined with field‐amplified sample injection in capillary electrophoresis for the determination of beta(2)‐agonists in bovine urine

Dispersive liquid–liquid microextraction based on solidification of floating organic drop (DLLME–SFO) was for the first time combined with field‐amplified sample injection (FASI) in CE to determine four β₂‐agonists (cimbuterol, clenbuterol, mabuterol, and mapenterol) in bovine urine. Optimum BGE consisted of 20 mM borate buffer and 0.1 mM SDS. Using salting‐out extraction, β₂‐agonists were extracted into ACN that was then used as the disperser solvent in DLLME–SFO. Optimum DLLME–SFO conditions were: 1.0 mL ACN, 50 μL 1‐undecanol (extraction solvent), total extraction time 1.5 min, no salt addition. Back extraction into an aqueous solution (pH 2.0) facilitated direct injection of β₂‐agonists into CE. Compared to conventional CZE, DLLME–SFO–FASI–CE achieved sensitivity enhancement factors of 41–1046 resulting in LODs in the range of 1.80–37.0 μg L^?1. Linear dynamic ranges of 0.15–10.0 mg L^?1 for cimbuterol and 15–1000 μg L^?1 for the other analytes were obtained with coefficients of determination (R²) ≥ 0.9901 and RSD% ≤5.5 (n = 5). Finally, the applicability of the proposed method was successfully confirmed by determination of the four β₂‐agonists in spiked bovine urine samples and accuracy higher than 96.0% was obtained.     

Dispersive liquid–liquid microextraction based on solidification of floating organic droplet for the determination of triazine and triazoles in mineral water samples

A simple, rapid, and sensitive method for the determination of atrazine, simazine, cyproconazole, tebuconazole, and epoxiconazole in mineral water employing the dispersive liquid–liquid microextraction with solidification of a floating organic drop with determination by liquid chromatography tandem mass spectrometry has been developed. A mixed solution of 250 μL 1‐dodecanol and 1250 μL methanol was injected rapidly into 10 mL aqueous solution (pH 7.0) with 2% w/v NaCl. After centrifugation for 5 min at 2000 rpm, the organic solvent droplets floated on the surface of the aqueous solution and the floating solvent solidified. The method limits of detection were between 3.75 and 37.5 ng/L and limits of quantification were between 12.5 and 125 ng/L. The recoveries ranged from 70 to 118% for repeatability and between 76 and 95% for intermediate precision with a relative standard deviation from 2 to 18% for all compounds. Low matrix effect was observed. The proposed method can be successfully applied in routine analysis for determination of pesticide residues in mineral water samples, allowing for monitoring of triazine and triazoles at levels below the regulatory limits set by international and national legislations.     

Determination of four acidic nonsteroidal anti‐inflammatory drugs in wastewater samples by dispersive liquid–liquid microextraction based on solidification of floating organic droplet and high‐performance liquid chromatography

A simple, environmentally friendly, and sensitive dispersive liquid–liquid microextraction based on solidification of floating organic droplet for the extraction of four acidic nonsteroidal anti‐inflammatory drugs (ketoprofen, naproxen, ibuprofen, and diclofenac) from wastewater samples subsequent by high‐performance liquid chromatography analysis was developed. The influence of extraction parameters such as pH, the effect of solution ionic strength, type of extraction solvent, disperser solvent, and extraction solvent volume were studied. High enrichment factors (283–302) were obtained through the developed method. The method provides good linearity (r > 0.999) in a concentration range of 1–100 μg/L, good intra‐ and inter‐day precision (relative standard deviation < 7%) and low limits of quantification. The relative recoveries of the selected compounds were situated over 80% both in synthetic and real water samples. The developed method has been successfully applied for the analysis of the selected compounds in wastewater samples.     

Optimization of modified dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography for the simultaneous preconcentration and determination of nitrazepam and midazolam drugs: An experimental design

A simple, sensitive, and rapid microextraction method, namely, ultrasound‐assisted surfactant‐enhanced emulsification microextraction based on the solidification of floating organic droplet method coupled with high‐performance liquid chromatography was developed for the simultaneous preconcentration and determination of nitrazepam and midazolam. The significant parameters affecting the extraction efficiency were considered using Plackett–Burman design as a screening method. To obtain the optimum conditions with consideration of the selected significant variables, a Box–Behnken design was used. The microextraction procedure was performed using 29.1 μL of 1‐undecanol, 1.36% (w/v) of NaCl, 10.0 μL of sodium dodecyl sulfate (25.0 μg mL^?1), and 1.0 μL of Tween80 (25.0 μg mL^?1) as an emulsifier in an extraction time of 20.0 min at pH 7.88. In order to investigate the validation of the developed method, some validation parameters including the linear dynamic range, repeatability, limit of detection, and recoveries were studied under the optimum conditions. The detection limits of the method were 0.017 and 0.086 ng mL^?1 for nitrazepam and midazolam, respectively. The extraction recovery percentages for the drugs studied were above 91.0 with acceptable relative standard deviation. The proposed methodology was successfully applied for the determination of these drugs in a number of human serum samples.     

SPE coupled with dispersive liquid–liquid microextraction followed by GC with flame ionization detection for the determination of ultra‐trace amounts of benzodiazepines

SPE combined with dispersive liquid–liquid microextration was used for the extraction of ultra‐trace amounts of benzodiazepines (BZPs) including, diazepam, midazolam, and alprazolam, from ultra‐pure water, tap water, fruit juices, and urine samples. The analytes were adsorbed from large volume samples (60 mL) onto octadecyl silica SPE columns. After the elution of the desired compounds from sorbents with 2.0 mL acetone, 0.5 mL of eluent containing 40.0 μL chloroform was injected rapidly into 4.5 mL pure water. After extraction and centrifugation, 2 μL of the sedimented phase was injected into a GC equipped with a flame ionization detector. Several parameters affecting this process were investigated and optimized. Under the optimal conditions, LODs ranged from 0.02 to 0.05 μg/L, a linear dynamic range of 0.1–100 μg/L and relative SDs in the range of 4.4–10.7% were attained. Very high preconcentration factors ranging from 3895–7222 were achieved. The applicability of the method for the extraction of BZPs from different types of complicated matrices, such as tap water, fruit juices, and urine samples, was studied. The obtained results reveal that the proposed method is a good technique for the extraction and determination of BZPs in complex matrices.     

Speciation of methyltins by dispersive liquid–liquid microextraction and gas chromatography with mass spectrometry

Dispersive liquid–liquid microextraction in combination with an in situ derivatization is suggested for methyltin compound sampling and preconcentration from water solutions. The derivatization was carried out with sodium tetraethylborate at pH 3. The effects of extraction and disperser solvents type, volume, and extraction time on the extraction efficiency were investigated. 1,2‐Dichlorobenzene was used as an extraction solvent and ethanol was used as a disperser solvent. The calibration graphs for all the analytes were linear up to 2 μg (Sn) L^?1, correlation coefficients were 0.998–0.999, LODs were 0.13, 0.05, and 0.06 ng (Sn) L^?1 for trimethyltin, DMT, and monomethyltin, respectively. Repeatabilities of the results were acceptable with RSDs up to 12.1%. A possibility to apply the proposed method for methyltin compound determination in water samples was demonstrated.     

Optimization of a novel method based on solidification of floating organic droplet by high-performance liquid chromatography for evaluation of antifungal drugs in biological samples

In this study, a simple, rapid, and highly efficient liquid-phase microextraction method based on solidification of floating organic droplet was coupled with high performance liquid chromatography-photo diode array detection (HPLC-PDA) for determination of ketoconazole, clotrimazole, and miconazole as antifungal drugs. Central composite design (CCD) was used for optimization of several factors affecting the extraction efficiency. The optimized conditions were established to be 550 rpm for stirring rate, 35 min for extraction time, 57 °C for extraction temperature, 8.5 for solution pH, 10 μl for organic solvent volume, and 7% (w/v) of NaCl for ionic strength. Limit of detections (LODs) of the extraction method ranged from 0.01 to 0.1 μg L⁻¹ and the linear dynamic ranges (LDRs) ranged from 0.1 to 300 μg L⁻¹ for the three antifungal drugs. Relative standard deviations (RSDs) of the proposed method were 5-11%. Preconcentration factors in the range of 306-1350 were obtained at extraction time of 35 min. Finally, performance of the proposed method was evaluated for the extraction and determination of the drugs’ levels in microgram per liter in samples and satisfactory results were obtained.     

Ionic liquids dispersive liquid–liquid microextraction and high‐performance liquid chromatographic determination of irbesartan and valsartan in human urine

An environmentally friendly ionic liquids dispersive liquid–liquid microextraction (IL‐DLLME) method coupled with high‐performance liquid chromatography (HPLC) for the determination of antihypertensive drugs irbesartan and valsartan in human urine samples was developed. The HPLC separations were accomplished in less than 10 min using a reversed‐phase C₁₈ column (250 × 4.60 mm i.d., 5 µm) with a mobile phase containing 0.3 % formic acid solution and methanol (v/v, 3:7; flow rate, 1.0 mL/min). UV absorption responses at 236 nm were linear over a wide concentration range from 50 µg/mL to the detection limits of 3.3 µg/L for valsartan and 1.5 µg/L for irbesartan. The effective parameters on IL‐DLLME, such as ionic liquid types and their amounts, disperser solvent types and their volume, pH of the sample and extraction time were studied and optimized. The developed IL‐DLLME‐HPLC was successfully applied for evaluation of the urine irbesartan and valsartan profile following oral capsules administration. Copyright © 2012 John Wiley & Sons, Ltd.     

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.