Headspace single-drop microextraction with in-drop derivatization and capillary electrophoretic determination for free cyanide analysis

A new method involving headspace single-drop microextraction (SDME) with in-drop derivatization and CE is developed for the preconcentration and determination of free cyanide. An aqueous microdrop (5 microL) containing Ni(II)-NH(3) (as derivatization agent), sodium carbonate and ammonium pyromellitate (as internal standard) was used as the acceptor phase. The extracted cyanide forms a stable Ni(CN)(4) (2-) complex which is then determined by CE. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time and sample ionic strength) affecting the extraction efficiency were investigated. Using headspace SDME, free cyanide can be effectively extracted from the neutral solutions, i.e. without the acidification of the sample which often is prone to errors due to incomplete liberation and artefactual cyanide production. Proposed SDME-CE method provided about 58-fold enrichment in 20 min. The calibration curve was linear for concentrations of CN(-) in the range from 0.25 to 20 micromol/L (R(2) = 0.997). The LOD (S/N = 3) was estimated to be 0.08 micromol/L of CN(-). Such a detection sensitivity is high enough for free cyanide determination in common environmental and physiological samples. Finally, headspace SDME was applied to determine free cyanide in human saliva and urine samples with spiked recoveries in the range of 91.7-105.6%. The main advantage of this method is that sample clean-up, preconcentration and derivatization procedures can be completed in a single step. In addition, the proposed technique does not require any sample pretreatment and thus is much less susceptible to interferences compared to existing methods.     

Capillary electrophoretic determination of ammonia using headspace single-drop microextraction

A new method involving headspace single-drop microextraction (SDME) and capillary electrophoresis (CE) is developed for the preconcentration and determination of ammonia (as dissolved NH₃ and ammonium ion). An aqueous microdrop (5 μL) containing 1 mmol/L H₃PO₄ and 0.5 mmol/L KH₂PO₄ (as internal standard) was used as the acceptor phase. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time) affecting the extraction efficiency were investigated. Proposed SDME-CE method provided about 14-fold enrichment in about 20 min. The calibration curve was linear for concentrations of NH₄⁺ in the range from 5 to 100 μmol/L (R² = 0.996). The LOD (S / N = 3) was estimated to be 1.5 μmol/L of NH₄⁺. Such detection sensitivity is high enough for ammonia determination in common environmental and biological samples. Finally, headspace SDME was applied to determine ammonia in human blood, seawater and milk samples with spiked recoveries in the range of 96-107%.     

基于离子液体的单滴微萃取-毛细管电泳在线联用测定水体中3种溴酚类化合物

建立了基于离子液体的单滴微萃取-毛细管电泳联用测定溴酚类化合物的方法。考察了萃取剂种类与体积、萃取时间、有机溶剂、盐浓度及萃取温度对萃取效率的影响。确定了最佳萃取条件为:以1-丁基-3-甲基咪唑六氟磷酸盐([C₄MIM]PF₆])离子液体作为萃取剂,萃取时间为8 min,样品溶液中NaCl浓度为10%(质量分数),萃取温度为20 ℃。在最佳条件下,3种溴酚(4-溴酚、2,6-二溴酚和2,4,6-三溴酚)在1~100 mg/L范围内呈良好的线性关系,线性相关系数为0.9939~0.9988;检出限为0.3 mg/L (S/N=3);该方法对3种溴酚的富集倍数分别为115.8、327.0和569.8; 6次平行测定的相对标准偏差为5.21%~6.47%;对本地区自来水、河水和湖水的加标回收率为87.8%~96.7%。结果表明,该方法稳定可靠,适合于水体中溴酚类污染物的测定。     

Combining gold nanoparticle-based headspace single-drop microextraction and a paper-based colorimetric assay for selenium determination

Analytical and Bioanalytical Chemistry - A novel method combining headspace single-drop microextraction with a paper-based colorimetric assay was developed. Headspace single-drop microextraction...     

Ionic liquid-based headspace single-drop microextraction coupled to gas chromatography for the determination of chlorobenzene derivatives

A novel method, based on the coupling of ionic liquid-based headspace single-drop microextraction (SDME) with gas chromatography (GC), is developed for the determination of chlorobenzene derivatives. For the SDME of five chlorobenzene derivatives, a 1.0 μL 1-octyl-3-methylimidazolium hexafluorophosphate microdrop is exposed for 20 min to the headspace of a 15 ml aqueous sample containing 20% (w/v) NaCl placed in 25 ml vial at 40 °C. Then, the extractant is directly injected into the injector block of the GC instrument. To avoid ionic liquid leaking into the chromatographic column, a small glass tube is placed in the injection block. Under optimized operation conditions, linear relation between peak areas and analyte concentrations up to 1.5 mg L^?1 has been obtained The detection limits range from 0.1 to 0.5 μg L^?1 for the various analytes. The relative standard deviations at 1.0 μg L^?1 range from 7.7 to 12.4%, and the enrichment factors from 41 to 127. The method is simple and sensitive, and does not suffer from the influence of a solvent peak. Its applicability is demonstrated by the determination of chlorobenzenes in wastewater samples.     

On-line coupling of ionic liquid-based single-drop microextraction with capillary electrophoresis for sensitive detection of phenols

An ionic liquid-based single-drop microextraction (IL-SDME) procedure using IL as an extractant on-line coupled to capillary electrophoresis (CE) is proposed. The method is capable of quantifying trace amounts of phenols in environmental water samples. For the SDME of three phenols, a 2.40 nL IL microdrop was exposed for 10 min to the aqueous sample and then was directly injected into the capillary column for analysis. Extraction parameters such as the extraction time, the IL single-drop volume, pH of the sample solution, ionic strength, volume of the sample solution and the extraction temperature were systematically investigated. Detection limits to three phenols were less than 0.05 μg mL⁻¹, and their calibration curves were all linear (R² ≥ 0.9994) in the range from 0.05 to 50 μg mL⁻¹. And enrichment factors for three phenols were 156, 107 and 257 without agitation, respectively. This method was then utilized to analyze two real environmental samples from Yellow River and tap water, obtaining satisfactory results. Compared with the usual SDME for CE, IL-SDME–CE is a simple, low-cost, fast and environmentally friendly preconcentration technique.     

Active single-drop microextraction for the determination of gaseous diisocyanates

Heterocyclic amines (HAs) were analysed in meat extract samples using a new method based on pressurised liquid extraction (PLE) and liquid chromatography-tandem mass spectrometry. This method combines the use of a pressurised fluid with a triple quadrupole MS/MS system, resulting in benefits from both systems: high extraction efficiency and sensitivity. The effects of solvent type and PLE operational parameters, such as temperature and extraction time, were studied to obtain maximum recovery of the analytes with minimum contamination. HA extraction was best achieved using dichloromethane/acetone (50/50, v/v) at 80 degrees C for 10 min. Recoveries ranged from 45% to 79% with good quality parameters: limit of detection values between 0.02 and 1 ng g(-1), linearity (r(2)>0.997), and run-to-run and day-to-day precisions with relative standard deviations lower than 13% achieved at both low (0.20 microg g(-1)) and medium (1.0 microg g(-1)) concentrations. This method reduces sample manipulation and total extraction time by nearly four-fold compared to conventional solid phase extraction. The optimised method was validated using laboratory reference material based on a meat extract, and was successfully applied to HA analysis in several cooked beef samples.     

Headspace single-drop microextraction and cuvetteless microspectrophotometry for the selective determination of free and total cyanide involving reaction with ninhydrin

Headspace single-drop microextraction has been used for the determination of cyanide with ninhydrin in combination with fibre-optic-based cuvetteless microspectrophotometry which accommodates sample volume of 1 μL placed between the two ends of optical fibres, and has been found to avoid salient drawbacks of batch methods. This method involved hydrocyanic acid formation in a closed vial, and simultaneous extraction and reaction with 2 μL drop of ninhydrin in carbonate medium suspended at the tip of a microsyringe needle held in the headspace of the acidified sample solution. The method was linear in range 0.025-0.5 mg L⁻¹ of cyanide. The headspace reaction was free from the interference of substances, e.g., thiocyanate, hydrazine sulphate, hydroxylammonium chloride and ascorbic acid. Sulphide was masked by cadmium sulphate, nitrite by sulphamic acid, sulphite by N-ethylmaleimide, and halogens by ascorbic acid. The limit of detection was found to be 4.3 μg L⁻¹ of cyanide which was comparable to existing most sensitive methods for cyanide. However, the present method is far more simple. The method was applied to acid-labile and metal cyanides complexes by treatment with sulphide when metal sulphides were precipitated setting cyanide ion free, and to iron(II) and (III) cyanide complexes by their decomposition with mercury(II), the mercury(II) cyanide formed was then determined. These pre-treatment methods avoided cumbersome pre-separation of cyanide by methods such as distillation or gas diffusion. The overall recovery of cyanide in diverse samples was 97% with RSD of 3.9%.     

Development of microwave-assisted extraction followed by headspace single-drop microextraction for fast determination of paeonol in traditional Chinese medicines

Paeonol is an important active component present in traditional Chinese medicines (TCMs), which was used for the treatment of many diseases such as eczema. In this work, microwave-assisted extraction (MAE) was firstly combined with headspace single-drop microextraction (HS-SDME), and applied to rapid determination of paeonol in two TCMs of Cynanchum paniculatum and Paeonia suffruticosa. In the proposed method, paeonol in TCMs was isolated by using MAE, followed by extraction and concentration by HS-SDME, and detected by gas chromatography-mass spectrometry (GC-MS). The experiment parameters of MAE and HS-SDME were discussed, and the method precision, recovery and detection limit were also studied. To further demonstrate the reliability of the quantification, both the proposed method and a standard method of steam distillation (SD) were simultaneously applied to quantitative analysis of paeonol in TCM samples from different growing areas. The experimental results show that MAE-HS-SDME is a simple and rapid method for the quantitative analysis of paeonol in TCMs, and is also a potential and alternative tool for quality monitoring for the two TCMs of C. paniculatum and P. suffruticosa.     

Fast determination of Z-ligustilide in plasma by gas chromatography/mass spectrometry following headspace single-drop microextraction

Angelica sinensis (danggui in Chinese) is a common traditional Chinese medicine (TCM), and its essential oil has been used for the treatment of many diseases such as hepatic fibrosis. Z-Ligustilide has been found to be an important active component in the TCM essential oil. In this work, for the first time, headspace single-drop microextraction (HS-SDME) followed by gas chromatography-mass spectrometry (GC-MS) was developed for the determination of Z-ligustilide in rabbit plasma after oral administration of essential oil of danggui. The extraction parameters of solvent selection, solvent volume, sample temperature, extraction time, stirring rate, and ion strength were systemically optimized. Furthermore, the method linearity, detection limit, and precision were also investigated. It was shown that the proposed method provided good linearity (0.02-20 microg/mL, R2 = 0.997), low detection limit (10 ng/mL), and good precision (RSD value less than 9%). Finally, HS-SDME followed by GC/MS was used for fast determination of Z-ligustilide in rabbit plasma at different time intervals after oral administration of danggui essential oil. The experimental results suggest that HS-SDME followed by GC/MS is a simple, sensitive, and low-cost method for the determination of Z-ligustilide in plasma, and a low-cost approach to pharmacokinetics studies of active components in TCMs.     

Multiple headspace single-drop microextraction coupled with gas chromatography for direct determination of residual solvents in solid drug product

This paper proposed a multiple headspace single-drop microextraction (MHS-SDME) method coupled to gas chromatography with flame-ionization detection (GC-FID) for direct determination of residual solvents in solid drug product. The MHS-SDME technique is based on extrapolation to an exhaustive extraction of consecutive extractions from the same sample which eliminates the matrix effect on the quantitative analysis of solid samples. The total peak area of analyte is calculated with a beta constant which can be obtained from the slope of the linear regression that related to the peak area of each extraction and the number of extraction times. In this work, a model drug powder was chosen and the amounts of residues of two solvents, methanol and ethanol, were investigated. The factors influencing the extraction process including extraction solvent, microdrop volume, extraction time, sample amount, thermostatting temperature and incubation time were studied. 10 mg of drug powder was incubated for 3 h at 140 °C prior to the first extraction and thermostatted for 15 min at 140 °C between each extraction. Extraction was carried out with 2 μL of dimethyl sulfoxide (DMSO) as the microdrop for 5 min. The features of the method were established using standard solutions. Validation of the proposed method showed good agreement with the traditional dissolution method for analysis of residual solvents in drug product. The results indicated that MHS-SDME has a great potential for the quantitative determination of residual solvents directly from the solid drug products due to its low cost, ease of operation, sensitivity, reliability and environmental protection.     

Coupling of ionic liquid-based headspace single-drop microextraction with GC for sensitive detection of phenols

A headspace single-drop microextraction (SDME) based on ionic liquid (IL) has been developed for the gas chromatographic determination of phenols. The volume of IL microdrop used was 1 microL. After extraction, the analytes were desorbed from the drop in the injection port and the involatile IL was withdrawn into the microsyringe. To facilitate the withdrawal of IL the upper diameter of the split inlet liner was enlarged to some extent. Some parameters were optimized for the determination of phenols. Under the selected conditions, i.e., desorption for 100 s at 210 degrees C after extraction for 25 min at 50 degrees C in solutions (pH 3) containing 0.36 g/mL sodium chloride, the LODs, RSDs, and the average enrichment factors of phenols were 0.1-0.4 ng/mL, 3.6-9.5% (n=5), and 35-794, respectively. The proposed procedure was applied to the determination of phenols in lake water and wastewater samples, and the spiked recoveries were in the range of 81-111% at a spiked level of 0.4 microg/mL. This method is a promising alternative for the sensitive determination of phenolic compounds.     

Molecularly imprinted dispersive solid-phase microextraction for determination of sulfamethazine by capillary electrophoresis

We have developed a rapid, selective and efficient method for dispersive solid-phase microextraction (DSPME) using microbeads of a molecularly imprinted polymer (MIP). It enables the pre-concentration of sulfamethazine and sample clean-up prior to capillary electrophoresis with UV detection. The microbeads were synthesized via precipitation polymerization using sulfamethazine, methacrylic acid and ethylene glycol dimethacrylate (EGDMA) as the template molecule, the functional monomer and the cross-linking monomer, respectively. Characterization by SEM displayed the high uniformity and dispersibility of the MIP microbeads. The adsorption and desorption of sulfamethazine and the parameters for CE were optimized to result in a limit of detection of 1.1?μg?L^?1, which is 373-fold lower than that of direct CE detection. The equilibration time of extraction was reduced to 5?min, and the selectivity of the microbeads was significantly improved compared to the non-imprinted polymer. The method was successfully applied to the determination of trace sulfamethazine in several milk samples, with recoveries in the range of 89?% to 110?%.

Gas chromatographic determination of carbonyl compounds in biological and oil samples by headspace single-drop microextraction with in-drop derivatisation

A suitable method for the gas chromatographic determination of 10 characteristic carbonyls in biological and oil samples based on the in-drop formation of hydrazones by using 2,4,6-trichlorophenylhydrazine (TCPH), has been developed. The derivatisation-extraction procedure was optimized separately for aqueous and oil samples with respect to the appropriate organic drop solvent, drop volume, in-drop TCPH concentration, sample stirring rate, temperature during single-drop microextraction (SDME), reaction time and headspace-to-sample volume ratio. The optimization showed differentiation of optimum values between the studied matrices. The limits of detection were found to range from 0.001 to 0.003 μg mL⁻¹ for the aqueous biological samples and from 0.06 to 0.20 μg mL⁻¹ for the oil samples. The limits of quantification were in the range of 0.003-0.010 μg mL⁻¹ and 0.020-0.059 μg mL⁻¹ for aqueous and oil samples, respectively. The overall relative standard deviations of the within-day repeatability and between-day reproducibility were <4.4% and <8.2% for the aqueous biological samples and <3.9% and <7.4% for the oxidized oil samples.     

Determination of preservatives by integrative coupling method of headspace liquid-phase microextraction and capillary zone electrophoresis

An integrative coupling method of headspace liquid-phase microextraction (HS-LPME) and capillary zone electrophoresis (CZE) was proposed in this paper. In the method, a separation capillary was used to create a microextraction droplet of the running buffer solution of CZE, hold the droplet at the capillary inlet, extract analytes of sample solutions in the headspace of a sample vial, inject concentrated analytes into the capillary and separate the analytes by CZE. The proposed method was applied to determine the preservatives of benzoic acid and sorbic acid in soy sauce and soft drink samples, in which the running buffer solution of 50 mmol/L tetraborate (pH 9.2) was directly used to form the acceptor droplet at the capillary inlet by pressure, and the preservatives in a 6-mL sample solution containing 0.25 g/mL NaCl were extracted at 90°C for 30 min in the headspace of a 14-mL sample vial. Then the concentrated preservatives were injected into the capillary at 10 cm height difference for 20 s and separated by CZE. The enrichment factors of benzoic acid and sorbic acid achieved 266 and 404, and the limits of detection (LODs) were 0.03 and 0.01 μg/mL (S/N=3), respectively. The recoveries were in the range of 88.7-105%. The integrative coupling method of HS-LPME and CZE was simple, convenient, reliable and suitable for concentrating volatile and semi-volatile organic acids and eliminating matrix interferences of real samples.     

Dispersive liquid-liquid microextraction versus single-drop microextraction for the determination of several endocrine-disrupting phenols from seawaters

Two liquid-phase microextraction procedures: single-drop microextraction (SDME) and dispersive liquid-liquid microextraction (DLLME), have been developed for the determination of several endocrine-disrupting phenols (EDPs) in seawaters, in combination with high-performance liquid chromatography (HPLC) with UV detection. The EDPs studied were bisphenol-A, 4-cumylphenol, 4-tertbutylphenol, 4-octylphenol and 4-n-nonylphenol. The optimized SDME method used 2.5 μL of decanol suspended at the tip of a micro-syringe immersed in 5 mL of seawater sample, and 60 min for the extraction time. The performance of the SDME is characterized for average relative recoveries of 102 ± 11%, precision values (RSD) < 9.4% (spiked level of 50 ng mL⁻¹), and detection limits between 4 and 9 ng mL⁻¹. The optimized DLLME method used 150 μL of a mixture acetonitrile:decanol (ratio 15.7, v/v), which is quickly added to 5 mL of seawater sample, then subjected to vortex during 4 min and centrifuged at 2000 rpm for another 5 min. The performance of the DLLME is characterized for average relative recoveries of 98.7 ± 3.7%, precision values (RSD) < 7.2% (spiked level of 20 ng mL⁻¹), and detection limits between 0.2 and 1.6 ng mL⁻¹. The efficiencies of both methods have also been compared with spiked real seawater samples. The DLLME method has shown to be a more efficient approach for the determination of EDPs in seawater matrices, presenting enrichment factors ranging from 123 to 275, average relative recoveries of 110 ± 11%, and precision values (RSD) < 14%, when using a real seawaters (spiked level of 3.5 ng mL⁻¹).     

Novel approach to improve the detection of colchicine via online coupling of ionic liquid-based single-drop microextraction with capillary electrophoresis

A novel approach based on ionic liquid‐single‐drop microextraction (IL‐SDME) online coupling with capillary electrophoresis (CE) was used to determine a toxic alkaloid – colchicine. The IL‐SDME procedure was optimized by extraction solvent, drop volume controlling, sample volume and pH, extraction time, and ionic strength. Under optimum conditions, enrichment factor was as much as 41‐fold with a relative standard deviation of 2.8% (n=3). Linear range of response was observed from 1 to 100 μg/mL, with detection limit of 0.25 μg/mL and correlation coefficient (R²) of 0.9994. The extraction of colchicine from spiked Lanzhou lily sample was performed and obtaining good result with an average recovery rate of 102.4 and 98.8% at 5 and 50 μg/mL, respectively. Comparing with the previous methods, IL‐SDME‐CE is really a convenient, economical, and environmentally benign way for determining colchicine.     

Comparison of efficiencies between single-drop microextraction and continuous-flow microextraction for the determination of methomyl in natural waters

Two liquid-phase microextraction (LPME) approaches, static direct-immersed single-drop microextraction (DI-SDME) and continuous-flow microextraction (CFME), were used to extract methomyl in water samples and their respective extraction efficiencies were compared. Several important parameters affecting extraction efficiency such as the type of extraction solvent, solvent drop volume, stirring speed or flow rate, extraction time and salt concentration were optimised. The optimised conditions were as follows: 3.0-µL tetrachloroethane (C₂H₂Cl₄) as the extraction solvent, 15% NaCl (w/v), 15 min extraction time and stirring speed at 600 rpm for DI-SDME; 3.5-µL C₂H₂Cl₄ as the extraction solvent, 15% NaCl (w/v), 21 min extraction time and flowing rate at 0.8 mL min^?1 for CFME. Under the previous optimal conditions, the linear range, detection limit (S/N = 3) and precision (RSD, n = 6) were 5.0-5000 ng mL^?1, 1.5 ng mL^?1, 6.9% for DI-SDME, and 4.0–10000 ng mL^?1, 2.5 ng mL^?1, 4.6% for CFME, respectively. Lake and river water samples were successfully analysed by DI-SDME and CFME. The result demonstrated that both SDME and CFME techniques are simple, low cost and amity to environment. As a result, the two approaches have tremendous potential in trace analysis of methomyl in natural waters.     

Use of single-drop microextraction for determination of fentanyl in water samples

Fentanyl is a very potent synthetic narcotic analgesic. Because of its strong sedative properties, it has become an analogue of illicit drugs such as heroin. Its unambiguous detection and identification in environmental samples can be regarded as strong evidence of its illicit preparation. In this paper we report application of single-drop microextraction (SDME) for analysis of water samples spiked with fentanyl. Experimental conditions which affect the performance of SDME, for example the nature of the extracting solvent, sample stirring speed, extraction time, ionic strength, and solution pH, were optimized. The method was found to be linear in the concentration range 0.10–10 ng mL⁻¹. The limits of quantitation and detection of the method were 100 pg mL⁻¹ and <75 pg mL⁻¹, respectively. This technique is superior to other sample-preparation techniques because of the simple experimental set-up, short analysis time, high sensitivity, and minimum use of organic solvent.     

Photoassisted vapor generation in the presence of organic acids for ultrasensitive determination of Se by electrothermal-atomic absorption spectrometry following headspace single-drop microextraction

A method is described for the determination of selenium at the pg/mL level by electrothermal-atomic absorption spectrometry using in situ photogeneration of Se vapors, headspace sequestration onto an aqueous microdrop containing Pd(II) and subsequent injection in a graphite tube. Several organic acids (formic, oxalic, acetic, citric and ethylenediaminetetraacetic) have been tried for photoreduction of Se(IV) into volatile Se compounds under UV irradiation. Experimental variables such as UV irradiation time, organic acid concentration, Pd(II) concentration in the drop, sample and drop volumes, extraction time and pH were fully optimized. Low-molecular weight acids such as formic and acetic provided optimal photogeneration of volatile Se species at a 0.6 mol/L concentration. Citric and ethylenediaminetetraacetic acid allowed to use a concentration as low as 1 mmol/L, but extraction times were longer than for formic and acetic acids. Photogeneration of (CH₃)₂Se from Se(IV) in the presence of acetic acid provided a detection limit of 20 pg/mL, a preconcentration factor of nearly 285 and a precision, expressed as relative standard deviation, of 4%. Analytical performance seemed to depend not only on the photogeneration efficiency obtained with each acid but also on the stability of the vapors in the headspace. The method showed a high freedom from interferences caused by saline matrices, but interferences were observed for transition metals at a relatively low concentration.