Multiple headspace single-drop micro-extraction for quantitative determination of lactide in thermally-oxidized polylactide

Single-drop micro-extraction (SDME), an emerging micro-extraction technique, was combined with multiple headspace (MHS) extraction to allow quantitative determination of lactide in thermally-oxidized polylactide. Different solvents, drop sizes and extraction times were tested to obtain best extraction efficiency and the method was further developed to obtain a linear regression plot for the multiple extractions. The combination of SDME and MHS extraction offered several advantages over traditional liquid-solid and headspace extraction techniques. No concentration step was needed and loss of volatiles was prevented as the ageing and extraction were performed in a closed system. Matrix effects, that disturb the quantitation of analytes in solid samples, were removed by the multiple headspace extraction.     

Toluene solvent system for the headspace gas chromatographic determination of styrene monomer in polystyrene

The use of toluene as a solvent to dissolve polystyrene for the determination of styrene monomers is studied. Compared with the modified solution headspace method using dimethylacetamide as solvent, with toluene the system is slightly less sensitive. However, there appeared to be minimal matrix effect when toluene is used, so a simpler external calibration method can be applied.     

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%.     

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.     

Multiple headspace solid-phase microextraction for the quantitative determination of volatile organic compounds in multilayer packagings

The theory of multiple headspace solid-phase microextraction (HS-SPME) and a method based on multiple HS-SPME for the quantitative determination of volatile organic compounds (VOCs) in packaging materials is presented. The method allows the direct analysis of solid samples without using organic solvents to extract analytes. Multiple headspace solid-phase microextraction is a stepwise method proposed to eliminate the influence of the sample matrix on the quantitative analysis of solid samples by HS-SPME. Different amounts of packaging and different volumes of standard solution were studied in order to remove a substantial quantity of analytes from the headspace at each extraction and obtain the theoretical exponential decay of the peak area of the four successive extractions and, thus, the total area was calculated from these four extractions. In addition, two fibres were compared: carboxen-polydimethylsiloxane (CAR-PDMS) and divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS), as they showed differences in the linearity of the exponential decay with the number of extractions depending on the compound. The CAR-PDMS fibre was better for the VOCs with a low molecular mass, whereas the DVB-CAR-PDMS fibre was better for the VOCs with a high molecular mass. Finally, the method was characterised in terms of linearity, detection limit and reproducibility and applied to analyse four multilayer packaging samples with different VOCs contents.     

Multiple headspace solid-phase microextraction using a new fiber for avoiding matrix interferences in the quantitative determination of ethyl carbamate in pickles

Multiple headspace solid-phase microextraction (HS-SPME) using a novel fiber coated with anilino-methyl triethoxy silicane-methacrylic acid/terminated silicone oil has been introduced as a useful pretreatment technique coupled to gas chromatography-flame ionization detector for the detection of ethyl carbamate in pickles. Anilino-methyl triethoxy silicane and methacrylic acid are put into use simultaneously with the aim to increase the hydrogen interaction strength between ethyl carbamate and the coating. In addition, the new fiber exhibits high thermal stability, good reproducibility, and long lifetime. Extraction temperature, extraction time, amount of desiccant, and amount of sample were well optimized to guarantee the suitability of multiple HS-SPME. Significant matrix interference was observed among various types of pickles and the multiple HS-SPME procedure was proved to be effective in avoiding the matrix effect by a complete recovery of the analyte. The method showed satisfactory linearity (0.1-100 mg kg(-1)), precision (4.25%, n = 5), and detection limit (0.038 mg kg(-1)). The accuracy of the method was evaluated by comparison with standard addition method and the results were statistically equivalent. The study indicates that the multiple HS-SPME procedure is simple, convenient, accurate, and low-cost, and most of all, can be used for quantitative analysis in complex matrix without matrix effect.     

顶空气相色谱法测定聚苯乙烯日用品中可溶性苯乙烯单体

应用带有顶空进样器气相色谱仪,采用外标法定量,分别以乙醇、乙醇 水作提取剂,分析了聚苯乙烯日用品中可溶性苯乙烯的含量,并对其提取温度、时间进行了研究。在选择的色谱条件下,用乙醇、乙醇 水提取苯乙烯标准溶液分别在0.8～5000mg L、0.1～200mg L浓度间呈现良好的线性关系,检出限<0.1mg L,其相对标准偏差分别为3.2%、5.9%。     

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.     

Multiple headspace extraction-capillary gas chromatography (MHE-CGC) for the quantitative determination of volatiles in contaminated soils

A multiple headspace extraction-capillary gas chromatographic method for the quantitative, accurate, and rapid determination of volatiles in multicontaminated soil samples has been developed. A thick film fused silica column has been used and a nine-step multiple headspace extraction (MHE) determination performed. Calibration was achieved by introducing 1 μl of a standard solution of mixed volatiles into empty headspace vials, the presence of the matrix being unnecessary in multiple headspace extraction. Accuracy of determination by MHE-CGC and a simple method employing standard additions have been compared.     

An electrochemical method for the determination of residual styrene in polystyrene

A rapid electroanalytical method for the determination of residual styrene in polystyrene is described. The sample of polymer was dissolved in toluene and, following the addition of 10% DMF and electrolyte, a square-wave voltammogram was recorded at a gold microdisc electrode (radius, 6 mum). A standard addition technique was used to relate the peak current to the styrene concentration in solution and, hence, the styrene content of the polymer. The method gave results which are similar to those of the accepted standard procedure. It does not, however, require the precipitation of the polymer and hence is quicker and more convenient.     

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.     

Ligand displacement, headspace single-drop microextraction, and capillary electrophoresis for the determination of weak acid dissociable cyanide

A new method involving ligand displacement, headspace single-drop microextraction (SDME) with in-drop derivatization and capillary electrophoresis (CE) was developed for the determination of weak acid dissociable (WAD) cyanide. WAD metal-cyanide complexes (Ag(CN)(2)(-), Cd(CN)(4)(2-), Cu(CN)(3)(2-), Hg(CN)(2), Hg(CN)(4)(2-), Ni(CN)(4)(2-) and Zn(CN)(4)(2-)) are decomposed with ligand-displacing reagent and the released hydrogen cyanide is extracted from neutral solution (pH 6.5) with an aqueous microdrop (5 microl) containing Ni(II)-NH(3) as derivatization agent. The hydrogen cyanide extracted reacts with Ni(2+) to form a stable and highly UV absorbing tetracyanonickelate anion which is then determined by CE. Among the three different ligand-displacing reagents (i.e., ethylenediamine, dithizone and polyethileneimine) studied none of the reagents used alone releases cyanide completely from all WAD cyanide complexes. Complete recoveries were obtained by the extraction of WAD cyanide from 0.4 mol l(-1) ethylenediamine chloride buffer (pH 6.5) containing 0.001% (wt) dithizone. Proposed system was applied to determine WAD cyanide in industrial wastewater and river waters samples with spiked recoveries in the range of 95.8-104.7%.     

Microwave-assisted headspace single-drop microextration of chlorobenzenes from water samples

A one-step and in-situ sample preparation method used for quantifying chlorobenzene compounds in water samples has been developed, coupling microwave and headspace single-drop microextraction (MW-HS-SDME). The chlorobenzenes in water samples were extracted directly onto an ionic liquid single-drop in headspace mode under the aid of microwave radiation. For optimization, a Plackett-Burman screening design was initially used, followed by a mixed-level factorial design. The factors considered were: drop volume, aqueous sample volume, stirring speed, ionic strength, extraction time, ionic liquid type, microwave power and length of the Y-shaped glass-tube. The optimum experimental conditions found from this statistical evaluation were: a 5 μL microdrop of 1-hexyl-3-methylimidazolium hexafluorophosphate exposed for 20 min to the headspace of a 30 mL aqueous sample, irradiated by microwaves at 200 W and placed in a 50 mL spherical flask connected to a 25 cm Y-shaped glass-tube. Under the optimised experimental conditions, the response of a high performance liquid chromatographic system was found to be linear over the range studied and with correlation coefficients ranging between 0.9995 and 0.9999. The method showed a good level of repeatability, with relative standard deviations varying between 2.3 and 8.3% (n = 5). Detection limits were found in the low μg L⁻¹ range varying between 0.016 and 0.039 μg L⁻¹. Overall, the performance of the proposed method demonstrated the favourable effect of microwave sample irradiation upon HS-SDME. Finally, recovery studies from different types of environmental water samples revealed that matrix had little effect upon extraction.     

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.     

Comparison of solid-phase and single-drop microextractions for headspace analysis of herbal essential oils

The analytical microextraction methods of gas chromatography coupled with flame ionisation detector (GC-FID) for determination of selected essential oils in herbs were proposed. Two microextraction methods for the isolation of essential oils from plants such as Lavandula spica L., Melissa officinalis L., Mentha piperita L. and Salvia officinalis L. were used. The methods of solid-phase and single-drop microextractions, were optimised and compared. The obtained LOD values for all studied essential oils were found to be within 2.5–20.5 μg for SDME and 57.0–139.8 μg for SPME method per 100 g of dried sample leaves. The appropriate LOQ values were then 8.4–68.4 μg for SDME and 189.8–466.1 μg for SPME of target analytes per 100 g of dried sample leaves.      

Multiple headspace extraction—A procedure for eliminating the influence of the sample matrix in quantitative headspace,gas chromatography

Summary A stepwise gas extraction procedure is described for the quantitative gas chromatographic analysis of volatile compounds in solid and liquid samples. This procedure is a modification of the usual headspace analysis and can be carried out with the same equipment, provided a pressure and time controlled sampling system is used. This procedure is called Multiple Headspace Extraction (MHE) therefore. This method has first been developed for the analysis of monomers in polymers and residual solvents in printed films, but it is shown that can be applied to various other sample types also including even liquid samples.Dedicated to L. S. Ettre on the occasion of his 60th birthday.     

AMicro-sized headspace GC technique for determination of organic volatile impurities in water-insoluble pharmaceuticals

Summary A micro-sized headspace technique is presented for determination of organic volatile impurities (OVIs) in water-insoluble pharmaceuticals. Its main features include reduction of the amounts of sample of drug and sample dissolution medium, from 100–200 mg and 1–5 mL, respectively, in the traditional headspace method to 5–30 mg and 100 μL in the micro-sized headspace method, and shortening the headspace equilibration time from 45–60 min to 5–10 min. The validity of method has been examined both experimentally and theoretically. The relative standard deviation of the analysis and the linearity of method satisfied the requirements of the United States Pharmacopoeia. It was found that headspace equilibrium conditions have little influence on the sensitivity of the method, and that the presence of different amounts of drug substance in the sampling solution has little effect on the analytical results, in contrast with the traditional headspace GC method.     

Development of gas chromatography-mass spectrometry following headspace single-drop microextraction and simultaneous derivatization for fast determination of short-chain aliphatic amines in water samples

In this work, for the first time, gas chromatography-mass spectrometry (GC-MS) following headspace single-drop microextraction (HS-SDME) and simultaneous derivatization was developed for fast determination of short-chain aliphatic amines (SCAAs) in water samples. In the proposed method, SCAAs in water samples were headspace extracted and concentrated by suspending a microdrop of solvent, and SCAAs extracted in the microdrop of solvent were simultaneously and rapidly reacted with pentafluorobenzaldehyde (PFBAY). The formed SCAA derivatives were analyzed by GC-MS. The HS-SDME parameters of solvent selection, solvent volume, sample temperature, extraction time and stirring rate were studied, and the method linearity, precision and detection limits, were also studied. The results show that the proposed method provided good linearity (R(2)>0.99, 5.0-500 ng/ml), low detection limit (0.6-1.1 ng/ml), and good precision (RSD value less than 10%). The proposed method was further tested by its application to quantitative analysis of SCAAs in four wastewater samples. The experiment results have demonstrated that GC-MS following HS-SDME and simultaneous derivatization is a simple, rapid and low-cost method for the determination of SCAAs in water samples.