Isotope dilution gas chromatography with mass spectrometry for the analysis of 4‐octyl phenol, 4‐nonylphenol,and bisphenol A in vegetable oils

By the combination of solid‐phase extraction as well as isotope dilution gas chromatography with mass spectrometry, a sensitive and reliable method for the determination of endocrine‐disrupting chemicals including bisphenol A, 4‐octylphenol, and 4‐nonylphenol in vegetable oils was established. The application of a silica/N‐(n‐propyl)ethylenediamine mixed solid‐phase extraction cartridge achieved relatively low matrix effects for bisphenol A, 4‐octylphenol, and 4‐nonylphenol in vegetable oils. Experiments were designed to evaluate the effects of derivatization, and the extraction parameters were optimized. The estimated limits of detection and quantification for bisphenol A, 4‐octylphenol, and 4‐nonylphenol were 0.83 and 2.5 μg/kg, respectively. In a spiked experiment in vegetable oils, the recovery of the added bisphenol A was 97.5–110.3%, recovery of the added 4‐octylphenol was 64.4–87.4%, and that of 4‐nonylphenol was 68.2–89.3%. This sensitive method was then applied to real vegetable oil samples from Zhejiang Province of China, and none of the target compounds were detected.     

Dispersive liquid–liquid microextraction of phenolic compounds from vegetable oils using a magnetic ionic liquid

A novel method was developed for the determination of two endocrine‐disrupting chemicals, bisphenol A and 4‐nonylphenol, in vegetable oil by dispersive liquid–liquid microextraction followed by ultra high performance liquid chromatography with tandem mass spectrometry. Using a magnetic liquid as the microextraction solvent, several key parameters were optimized, including the type and volume of the magnetic liquid, extraction time, amount of dispersant, and the type of reverse extractant. The detection limits for bisphenol A and 4‐nonylphenol were 0.1 and 0.06 μg/kg, respectively. The recoveries were 70.4–112.3%, and the relative standard deviations were less than 4.2%. The method is simple for the extraction of bisphenol A and 4‐nonylphenol from vegetable oil and suitable for routine analysis.     

高效液相色谱法测定饮料类食品中的类雌激素

利用OASIS HLB固相萃取柱富集和净化样品,采用高效液相色谱分离,紫外及荧光检测,建立了不同饮料基质中的壬基酚(NP)、辛基酚(OP)和双酚A(BPA)等类雌激素的测定方法,并用该方法对市售部分产品进行了测定。不同加标水平的BPA,NP和OP的回收率为91.08%~103.19%,其相对标准偏差为0.5%~5.49%。该方法具有操作简单、灵敏度高和重现性好等优点。     

Two polydimethylsiloxane rod extraction methods for the sensitive determination of phenolic compounds in water samples

Simple, precise, and low‐cost methods for the simultaneous determination of phenolic endocrine disrupting compounds such as bisphenol A, trichlorophenol, pentachlorophenol, 4‐nonylphenol, and 4‐octylphenol in water samples were developed. The Direct, in situ derivatization methods are based on polydimethylsiloxane rod extraction followed by liquid desorption and chromatographic analysis by liquid chromatography and diode array detection. Several parameters affecting the extraction and desorption of the phenolic compounds and their acetylated derivates were studied, as well as the chromatographic and detection conditions. For the direct method, determination coefficients (r²) > 0.990 and LODs in the 0.6–2 μg/L range were obtained for all compounds except bisphenol A (9.5 μg/L). With the derivatization‐based method, based on in situ acetylation, lower limits of detection (0.3–0.9 μg/L) were obtained for all the compounds with r² > 0.988 and RSDs in the 2–9% range. The developed methods were applied to the analysis of spiked water samples obtaining recoveries of between 60.2 and 131.7% for the direct method, and of between 76.6 and 108.2% for the derivatization‐based method. The results demonstrate the feasibility of using these two methods for determining bisphenol A, trichlorophenol, pentachlorophenol, 4‐nonylphenol, and 4‐octylphenol in water.     

Rapid determination of alkylphenols in aqueous samples by in situ acetylation and microwave-assisted headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry

A rapid and solvent‐free procedure for the determination of 4‐tert‐octylphenol and 4‐nonylphenol isomers in aqueous samples is described. The method involves in‐situ acetylation and microwave‐assisted headspace solid‐phase microextraction prior to their determination using gas chromatography–ion trap mass spectrometry operated in the selected ion storage mode. The dual experimental protocols to evaluate the effects of various derivatization and extraction parameters were investigated and the conditions optimized. Under optimized conditions, 300 μL of acetic anhydride mixed with 1 g of potassium hydrogencarbonate and 2 g of sodium chloride in a 20 mL aqueous sample were efficiently extracted by a 65 μm polydimethylsiloxane‐divinylbenzene fiber that was located in the headspace when the system was microwave irradiated at 80 W for 5 min. The limits of quantitation were 5 and 50 ng/L for 4‐tert‐octylphenol and 4‐nonylphenol isomers, respectively. The precision for these analytes, as indicated by relative standard deviations, were less than 8% for both intra‐ and inter‐day analysis. Accuracy, expressed as the mean extraction recovery, was between 74 to 88%. A standard addition method was used to quantitate 4‐tert‐octylphenol and 4‐nonylphenol isomers, and the concentrations ranged from 120 to 930 ng/L in various environmental water samples.     

Selenium speciation in tea by dispersive liquid–liquid microextraction coupled to high‐performance liquid chromatography after derivatization with 2,3‐diaminonaphthalene

Selenium is an important element for human health, and it is present in many natural drinks and foods. Present study described a new method using dispersive liquid–liquid microextraction prior to high‐performance liquid chromatography with a UV variable wavelength detector for the determination of the total selenium, Se(IV), Se(VI), and total organoselenium in tea samples. In the procedure, 2,3‐diaminonaphthalene was used as the chelating reagent, 400 μL acetonitrile was used as the disperser solvent and 60 μL chlorobenzene was used as the extraction solvent. The complex of Se(IV) and 2,3‐diaminonaphthalene in the final extracted phase was analyzed by high‐performance liquid chromatography. The factors influencing the derivatization and microextraction were investigated. Under the optimal conditions, the limit of detection was 0.11 μg/L for Se(IV) and the linearity range was in the range of 0.5–40 μg/L. This method was successfully applied to the determination of selenium in four tea samples with spiked recoveries ranging from 91.3 to 100%.     

Ionic‐liquid‐based surfactant‐emulsified microextraction procedure accelerated by ultrasound radiation followed by high‐performance liquid chromatography for the simultaneous determination of antidepressant and antipsychotic drugs

In the present work, an efficient and environmental friendly method of ionic‐liquid‐based emulsified microextraction procedure accelerated by ultrasound radiation has been developed. Subsequently, its performance was compared with dispersive liquid–liquid microextraction and ultrasound‐assisted surfactant‐based emulsification microextraction methods. The optimization of experimental conditions was carried out by combination of central composite design and response surface methodology. The optimum conditions of variables were set as follows: 50 μL of 1‐hexyl‐3‐methylimidazolium hexafluorophosphate (extracting solvent), 10 min ultrasound time, and 10 min vortex time for agitating 6 mL sample solution in pH 3 in the presence of 4 mg sodium dodecyl sulfate without addition of salt and 200 μL of methanol as diluent solvent. Under these conditions, the responses are linear for doxepin and perphenazine in the range of 0.3–1000 and 5–1000 μg/L, respectively. The limits of detection were 0.1 μg/L for doxepin and 1 μg/L for perphenazine. Relative standard deviations were lower than 3.5 for the determination of both species. Finally, the method was used for the preconcentration and determination of doxepin and perphenazine in urine sample with relative recoveries in the range of 89–98%.     

Rapid pretreatment and determination of bisphenol A in water samples based on vortex‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with fluorescence detection

A method for the rapid pretreatment and determination of bisphenol A in water samples based on vortex‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with fluorescence detection was proposed in this paper. A simple apparatus consisting of a test tube and a cut‐glass dropper was designed and applied to collect the floating extraction drop in liquid–liquid microextraction when low‐density organic solvent was used as the extraction solvent. Solidification and melting steps that were tedious but necessary once the low‐density organic solvent used as extraction solvent could be avoided by using this apparatus. Bisphenol A was selected as model pollutant and vortex‐assisted liquid–liquid microextraction was employed to investigate the usefulness of the apparatus. High‐performance liquid chromatography with fluorescence detection was selected as the analytical tool for the detection of bisphenol A. The linear dynamic range was from 0.10 to 100 μg/L for bisphenol A, with good squared regression coefficient (r² = 0.9990). The relative standard deviation (n = 7) was 4.7% and the limit of detection was 0.02 μg/L. The proposed method had been applied to the determination of bisphenol A in natural water samples and was shown to be economical, fast, and convenient.     

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 herbicides in environmental water samples by simultaneous in‐syringe magnetic stirring‐assisted dispersive liquid–liquid microextraction and silylation followed by GC–MS

An on‐line, fast, simple, selective, and sensitive method has been developed for the determination of three herbicides belonging to the following families: triazines (atrazine), chloroacetamide (alachlor), and phenoxy (2,4‐dichlorophenoxyacetic acid) in water samples. The method involves an in‐syringe magnetic stirring‐assisted dispersive liquid–liquid microextraction along with simultaneous silylation prior to their determination by gas chromatography with mass spectrometry. Extraction, derivatization, and preconcentration have been simultaneously performed using acetone as dispersive solvent, N‐methyl‐N‐tert‐butyldimethylsilyltrifluoroacetamide as derivatization agent and trichloroethylene as extraction solvent. After stirring for 180 s, the sedimented phase was transferred to a rotary micro‐volume injection valve (3 μL) and introduced by an air stream into gas chromatograph with mass spectrometry detector. Recovery and enrichment factors were 87.2–111.2% and 7.4–10.4, respectively. Relative standard deviations were in the ranges of 6.6–7.4 for intraday and 9.2–9.6 for interday precision. The detection limits were in the range of 0.045–0.03 μg/L, and good linearity was observed up to 200 μg/L, with R² ranging between 0.9905 and 0.9964. The developed method was satisfactorily applied to assess the occurrence of the studied herbicides in groundwater samples. The recovery test was also performed with values between 77 and 117%.     

Vortex‐assisted liquid–liquid microextraction of strontium from water samples using 4′,4″(5″)‐di‐(tert‐butylcyclohexano)‐18‐crown‐6 and tetraphenylborate

A vortex‐assisted liquid–liquid microextraction method was developed for the chromatographic determination of strontium in aqueous samples. In the method, strontium was complexed with 4′,4″(5″)‐di‐(tert‐butylcyclohexano)‐18‐crown‐6 in the presence of tetraphenylborate as the counter anion, which increased the hydrophobicity of the ion‐association complex, resulting in its improved extraction into 1‐octanol. Strontium from the organic phase was stripped with nitric acid back to aqueous solution and determined by ion chromatography. The optimum microextraction conditions were as follows: 2.0 mL aqueous samples with 3 mM tetraphenylborate; 150 μL of 1‐octanol as the extractant phase with 10 mM DtBuCH18C6; vortex extraction time for 10 s; centrifugation at 6000 rpm for 4 min; stripping by 0.1 M nitric acid. Under the optimum conditions, the detection limit for strontium was 0.005 mg/L. The calibration curves showed good linearity over the range between 0.01 and 2.5 mg/L. Intra‐ and interday precisions of the present method were satisfactory with relative standard deviations of 1.7 and 2.1%, respectively.     

Determination of triazine herbicides in juice samples by microwave‐assisted ionic liquid/ionic liquid dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography

A novel microextraction method, termed microwave‐assisted ionic liquid/ionic liquid dispersive liquid–liquid microextraction, has been developed for the rapid enrichment and analysis of triazine herbicides in fruit juice samples by high‐performance liquid chromatography. Instead of using hazardous organic solvents, two kinds of ionic liquids, a hydrophobic ionic liquid (1‐hexyl‐3‐methylimidazolium hexafluorophosphate) and a hydrophilic ionic liquid (1‐butyl‐3‐methylimidazolium tetrafluoroborate), were used as the extraction solvent and dispersion agent, respectively, in this method. The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of 1‐hexyl‐3‐methylimidazolium hexafluorophosphate dispersed entirely into sample solution with the help of 1‐butyl‐3‐methylimidazolium tetrafluoroborate. In addition, an ion‐pairing agent (NH₄PF₆) was introduced to improve recoveries of the ionic liquid phase. Several experimental parameters that might affect the extraction efficiency were investigated. Under the optimum experimental conditions, the linearity for determining the analytes was in the range of 5.00–250.00 μg/L, with the correlation coefficients of 0.9982–0.9997. The practical application of this effective and green method is demonstrated by the successful analysis of triazine herbicides in four juice samples, with satisfactory recoveries (76.7–105.7%) and relative standard deviations (lower than 6.6%). In general, this method is fast, effective, and robust to determine triazine herbicides in juice samples.     

Ionic‐liquid‐based dispersive liquid–liquid microextraction combined with magnetic solid‐phase extraction for the determination of aflatoxins B1, B2, G1, and G2 in animal feeds by high‐performance liquid chromatography with fluorescence detection

A novel two‐step extraction technique combining ionic‐liquid‐based dispersive liquid–liquid microextraction with magnetic solid‐phase extraction was developed for the preconcentration and separation of aflatoxins in animal feedstuffs before high‐performance liquid chromatography coupled with fluorescence detection. In this work, ionic liquid 1‐octyl‐3‐methylimidazolium hexafluorophosphate was used as the extractant in dispersive liquid–liquid microextraction, and hydrophobic pelargonic acid modified Fe₃O₄ magnetic nanoparticles as an efficient adsorbent were applied to retrieve the aflatoxins‐containing ionic liquid. Notably, the target of magnetic nanoparticles was the ionic liquid rather than the aflatoxins. Because of the rapid mass transfer associated with the dispersive liquid–liquid microextraction and magnetic solid phase steps, fast extraction could be achieved. The main parameters affecting the extraction recoveries of aflatoxins were investigated and optimized. Under the optimum conditions, vortexing at 2500 rpm for 1 min in the dispersive liquid–liquid microextraction and magnetic solid‐phase extraction and then desorption by sonication for 2 min with acetonitrile as eluent. The recoveries were 90.3–103.7% with relative standard deviations of 3.2–6.4%. Good linearity was observed with correlation coefficients ranged from 0.9986 to 0.9995. The detection limits were 0.632, 0.087, 0.422 and 0.146 ng/mL for aflatoxins B₁, B2, G1, and G2, respectively. The results were also compared with the pretreatment method carried out by conventional immunoaffinity columns.     

Simultaneous preconcentration and determination of 2,4‐D,alachlor and atrazine in aqueous samples using dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography ultraviolet detection

Dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography‐ultraviolet detection as a fast and inexpensive technique was applied to the simultaneous extraction and determination of traces of three common herbicides, 2,4‐D, 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, extraction time and centrifuging time, and speed were investigated and optimized. Under the optimum conditions, the calibration graphs found to be linear in the range of 0.3–200 μg/L with limits of detection in the range of 0.05–0.1 μg/L. The relative standard deviations were in the range of 4.5–6.2% (n = 7). The relative recoveries of well, tap, and river water samples which have been spiked with different levels of herbicides were 92.0–107.0, 82.0–104.0, and 82.0–86.0%, respectively.     

Automated hollow‐fiber liquid‐phase microextraction followed by liquid chromatography with mass spectrometry for the determination of benzodiazepine drugs in biological samples

In this study, two‐phase hollow‐fiber liquid‐phase microextraction and three‐phase hollow‐fiber liquid‐phase microextraction based on two immiscible organic solvents were compared for extraction of oxazepam and Lorazepam. Separations were performed on a liquid chromatography with mass spectrometry instrument. Under optimal conditions, three‐phase hollow‐fiber liquid‐phase microextraction based on two immiscible organic solvents has a better extraction efficiency. In a urine sample, for three‐phase hollow fiber liquid‐phase microextraction based on two immiscible organic solvents, the calibration curves were found to be linear in the range of 0.6–200 and 0.9–200 μg L^?1 and the limits of detection were 0.2 and 0.3 μg L^?1 for oxazepam and lorazepam, respectively. For two‐phase hollow fiber liquid‐phase microextraction, the calibration curves were found to be linear in the range of 1–200 and 1.5–200 μg L^?1 and the limits of detection were 0.3 and 0.5 μg L^?1 for oxazepam and lorazepam, respectively. In a urine sample, for three‐phase hollow‐fiber‐based liquid‐phase microextraction based on two immiscible organic solvents, relative standard deviations in the range of 4.2–4.5% and preconcentration factors in the range of 70–180 were obtained for oxazepam and lorazepam, respectively. Also for the two‐phase hollow‐fiber liquid‐phase microextraction, preconcentration factors in the range of 101–257 were obtained for oxazepam and lorazepam, respectively.     

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.     

A sensitive and efficient method for trace analysis of some phenolic compounds using simultaneous derivatization and air‐assisted liquid–liquid microextraction from human urine and plasma samples followed by gas chromatography–nitrogen phosphorous detection

In present study, a simultaneous derivatization and air‐assisted liquid–liquid microextraction method combined with gas chromatography–nitrogen phosphorous detection has been developed for the determination of some phenolic compounds in biological samples. The analytes are derivatized and extracted simultaneously by a fast reaction with 1‐flouro‐2,4‐dinitrobenzene under mild conditions. Under optimal conditions low limits of detection in the range of 0.05–0.34 ng mL^?1 are achievable. The obtained extraction recoveries are between 84 and 97% and the relative standard deviations are less than 7.2% for intraday (n = 6) and interday (n = 4) precisions. The proposed method was demonstrated to be a simple and efficient method for the analysis of phenols in biological samples. Copyright © 2015 John Wiley & Sons, Ltd.     

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%.     

Dispersive liquid–liquid microextraction based on amine‐functionalized Fe3O4 nanoparticles for the determination of phenolic acids in vegetable oils by high‐performance liquid chromatography with UV detection

A novel dispersive liquid–liquid microextraction method based on amine‐functionalized Fe₃O₄ magnetic nanoparticles was developed for the determination of six phenolic acids in vegetable oils by high‐performance liquid chromatography. Amine‐functionalized Fe₃O₄ was synthesized by a one‐pot solvothermal reaction between Fe₃O₄ and 1,6‐hexanediamine and characterized by transmission electron microscopy and Fourier transform infrared spectrophotometry. A trace amount of phosphate buffer solution (extractant) was adsorbed on bare Fe₃O₄‐NH₂ nanoparticles by hydrophilic interaction to form the “magnetic extractant”. Rapid extraction could be achieved while the “magnetic extractant” on amine‐functionalized Fe₃O₄ nanoparticles was dispersed in the sample solution by vortexing. After extraction, the “magnetic extractant” was collected by application of an external magnet. Some important parameters, such as pH and volume of extraction and desorption solvents, the extraction and desorption time needed were carefully investigated and optimized to achieve the best extraction efficiency. Under the optimal conditions, satisfactory extraction recoveries were obtained for the six phenolic acids in the range of 84.2–106.3%. Relative standard deviations for intra‐ and inter‐day precisions were less than 6.3 and 10.0%, respectively. Finally, the established method was successfully applied for the determination of six phenolic acids in eight kinds of vegetable oils.     

Switchable‐hydrophilicity solvent liquid‐liquid microextraction versus dispersive liquid‐liquid microextraction prior to HPLC‐UV for the determination and isolation of piperine from Piper nigrum L

Switchable‐hydrophilicity solvent liquid‐liquid microextraction and dispersive liquid‐liquid microextraction were compared for the extraction of piperine from Piper nigrum L. prior to its analysis by using high‐performance liquid chromatography with UV detection. Under optimum conditions, limits of detection and quantitation were found as 0.2–0.6 and 0.7–2.0 μg/mg with the two methods, respectively. Calibration graphs showed good linearity with coefficients of determination (R²) higher than 0.9962 and percentage relative standard deviations lower than 6.8%. Both methods were efficiently used for the extraction of piperine from black and white pepper samples from different origins and percentage relative recoveries ranged between 90.0 and 106.0%. The results showed that switchable‐hydrophilicity solvent liquid‐liquid microextraction is a better alternative to dispersive liquid‐liquid microextraction for the routine analysis of piperine in food samples. A novel scaled‐up dispersive liquid‐liquid microextraction method was also proposed for the isolation of piperine providing a yield of 102.9 ± 4.9% and purity higher than 98.0% as revealed by NMR spectroscopy.