Automation and optimization of liquid-phase microextraction by gas chromatography

Several fully automated liquid-phase microextraction (LPME) techniques, including static headspace LPME (HS-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and exposed to the headspace of the sample solution), exposed dynamic HS-LPME (the solvent is exposed in the headspace of sample vial for different time, and then withdrawn into the barrel of the syringe. This procedure is repeated a number of times), unexposed dynamic HS-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the gaseous sample is withdrawn into the barrel and then ejected), static direct-immersed LPME (DI-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and directly immersed into the sample solution), dynamic DI-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the sample solution is withdrawn and ejected), and two phase hollow fiber-protected LPME (HF-LPME) (a hollow fiber is used to stabilize and protect the solvent), auto-performed with a commercial CTC CombiPal autosampler, are described in this paper. Critical experimental factors, including temperature, choice of extraction solvent, solvent volume, plunger movement rate, and extraction time were investigated. Among the three HS-LPME techniques that were evaluated, the exposed dynamic HS-LPME technique provided the best performance, compared to the unexposed dynamic HS-LPME and static HS-LPME approaches. For DI-LPME, the dynamic process can enhance the extraction efficiency and the achieved method precision is comparable with the static DI-LPME technique. The precision of the fully automated HF-LPME is quite acceptable (RSD values below 6.8%), and the concentration enrichment factors are better than the DI-LPME approaches. The fully automated LPME techniques are more accurate and more convenient, and the reproducibility achieved eliminates the need for an internal standard to improve the method precision.     

Rapid determination of acetone in human blood by derivatization with pentafluorobenzyl hydroxylamine followed by headspace liquid-phase microextraction and gas chromatography/mass spectrometry

In the current work, a simple, rapid, accurate and inexpensive method was developed for the determination of acetone in human blood. The proposed method is based on derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA), followed by headspace liquid-phase microextraction (HS-LPME) and gas chromatography/mass spectrometry (GC/MS). In the present method, acetone in blood samples was derivatized with PFBHA and acetone oxime formed in several seconds. The formed oxime was enriched by HS-LPME using the organic solvent film (OSF) formed in a microsyringe barrel as extraction interface. Finally, the enriched oxime was analyzed by GC/MS in electron ionization (EI) mode. HS-LPME parameters including solvent, syringe plunger withdrawal rate, sampling volume, and extraction cycle were optimized and the method reproducibility, linearity, recovery and detection limit were studied. The proposed method was applied to determination of acetone in diabetes blood and normal blood. It has been shown that derivatization with HS-LPME and GC/MS is an alternative method for determination of the diabetes biomarker, acetone, in blood samples.     

Separation and identification of volatile constituents in Artemisia argyi flowers by GC-MS with SPME and steam distillation

Artemisia argyi leaf is a widely used traditional Chinese medicine (TCM). In this work, for the first time, the separation and identification of volatile constituents in Artemisia argyi flowers is performed. Gas chromatography-mass spectrometry (GC-MS) with solid-phase microextraction (SPME) is developed for the fast analysis of volatile constituents in the flowers. Several headspace SPME parameters, including fiber coating, extraction temperature, and extraction time, are optimized. Forty-nine compounds in the flowers are re-identified by SPME-GC-MS. At the same time, in order to compare with the SPME, steam distillation is used for analysis of the volatile constituents in the flowers, and forty-seven are detected. The total fifty-three compounds in the flowers, which mainly include cylcofenchene, alpha-pinene, alpha-myrcene, D-limonene, caryophyllene, and germacrene D, are identified by the two methods. Compared to the volatile components in Artemisia argyi leaves, the main components (including the two active compounds of borneol and borneol acetate) are also found in Artemisia argyi flowers. These results show that Artemisia argyi flowers as well as leaves might be used as TCM.     

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.     

Comparison of different extraction methods: steam distillation, simultaneous distillation and extraction and headspace co-distillation, used for the analysis of the volatile components in aged flue-cured tobacco leaves

Steam distillation (SD), simultaneous distillation and extraction (SDE) and headspace co-distillation (HCD) were compared here for their effectiveness in the extraction of volatile compounds from tobacco. The different grades of aged flue-cured tobacco leaves extracted by the three methods respectively were analyzed using GC-MS. Mass spectra or authentic compounds were used to identify around 408 components in various volatile fractions. On the one hand, the qualitative comparison showed that more compounds were detected in HCD extract (391 components) than in SDE extract (377 components), and the approximately quantitative analysis showed that the total amount of volatile components in SDE extract (445.48 microg/g) was much more than that in HCD extract (315.72 microg/g). But on the other hand, HCD was the most efficient for nearly all the highly volatile compounds among the three methods. As to low-volatile compounds such as lactones, long chain aldehydes, ketones, alcohols, and esters, more was detected in SDE extract than in HCD extract. The SD method (322 components, total amount 228.42 microg/g) was the lowest sensitive to all compounds except semi-volatile fatty acids among the three methods.     

Rapid determination of volatile constituents of Michelia alba flowers by gas chromatography-mass spectrometry with solid-phase microextraction

The volatile constituents of Michelia alba flowers, including fresh flowers, frozen flowers and withered flowers, were investigated by GC-MS. The volatiles in a simulated natural environment were sampled by solid-phase microextraction (SPME), with a 100 microm polydimethylsiloxane fiber at 25+/-5 degrees C for 4 h. The fibers were desorbed in a GC injection liner at 250 degrees C for 3 min. With headspace SPME-GC-MS analysis, 61 peaks were separated. The main compounds in headspace of fresh Michelia alba flowers included alpha-myrcene, (S)-limonene, (R)-fenchone, linalool, camphor, caryophyllene, germacrene D, etc., a greater number of compounds than for frozen flowers and withered flowers. At the same time, the biomarkers of fresh flowers were compared with the frozen flowers and withered flowers. In this study, headspace SPME-GC-MS afforded a simple and more sensitive sampling method for fresh Michelia alba flowers and other fresh flowers.     

Residual Solvents Determination in Pharmaceuticals by Static Headspace-Gas Chromatography and Headspace Liquid-Phase Microextraction Gas Chromatography

A headspace liquid phase microextraction (HS-LPME) method has been developed and optimized for the residual solvent determination in pharmaceutical products. A microdrop of n-hexanol containing isopropanol (as internal standard) was suspended at the tip of a gas chromatographic syringe and exposed to the headspace of the sample solution. After extraction for an optimized time, the microdrop was retracted into the syringe and injected directly into a GC injection port. Critical experimental factors, including extraction solvent, temperature, ionic strength, stirring rate, extraction time, equilibrium time, drop volume, and sample volume were investigated and optimized. Compared with the static headspace technique, HS-LPME method showed superior results, being compatible with the pharmaceutical samples.     

Identification of volatile basic components in tobacco by headspace liquid-phase microextraction coupled to matrix-assisted laser desorption/ionization with Fourier transform mass spectrometry

A method incorporating headspace liquid-phase microextraction (HS-LPME) coupled to matrix-assisted laser desorption/ionization (MALDI) with Fourier transform mass spectrometry (FTMS) was established to analyze volatile basic components in tobacco. The sample preparation volume for MALDI-MS was compatible with the volume of the solvent microdrop in the HS-LPME procedure. The pH and the polarity of the solvent for HS-LPME were adjusted by choice of the MALDI matrix and matrix additive. Based on the elemental composition and tandem mass spectrometry information, 25 volatile nitrogenous compounds in tobacco were detected and identified. The approach is fast and sensitive, and has the potential for automation for high-throughput analysis. This approach offers an alternative method for analysis of trace volatile organic compounds in complex samples.     

Determination of volatile organic acids in oriental tobacco by needle-based derivatization headspace liquid-phase microextraction coupled to gas chromatography/mass spectrometry

A method coupling needle-based derivatization headspace liquid-phase microextraction with gas chromatography-mass spectrometry (HS-LPME/GC-MS) was developed to determine volatile organic acids in tobacco. The mixture of N,O-bis(trimethylsilyl)trifluoroacetamide and decane was utilized as the solvent for HS-LPME, resulting that extraction and derivatization were simultaneously completed in one step. The solvent served two purposes. First, it pre-concentrated volatile organic acids in the headspace of tobacco sample. Second, the volatile organic acids extracted were derivatized to form silyl derivatives in the drop. The main parameters affecting needle-based derivatization HS-LPME procedure such as extraction and derivatization reagent, microdrop volume, extraction and derivatization time, and preheating temperature and preheating time were optimized. The standard addition approach was essential to obtain accurate measurements by minimizing matrix effects. Good linearity (R(2)> or =0.9804) and good repeatability (RSDs< or =15.3%, n=5) for 16 analytes in spiked standard analytes sample were achieved. The method has the additional advantages that at the same time it is simple, fast, effective, sensitive, selective, and provides an overall profile of volatile organic acids in the oriental tobacco. This paper does offer an alternative approach to determine volatile organic acids in tobacco.     

In-tube extraction for enrichment of volatile organic hydrocarbons from aqueous samples

In-tube extraction (ITEX) is a novel solventless extraction technique in which a headspace syringe with a needle body filled with a sorbent (here: Tenax TA) is used. The analytes are extracted from sample headspace by dynamic extraction. The needle body is surrounded by a separate heater, which is used for thermal desorption of analytes into the injection port of a GC system. We report here for the first time the optimization and evaluation of a fully automated analytical method based on ITEX. As target analytes, 19 common groundwater contaminants such as halogenated volatiles and monoaromatic compounds have been chosen. Method related parameters such as extraction temperature, number of extraction cycles, extraction and desorption volume as well as extraction and desorption flow rates were investigated in detail. The linear dynamic range of the ITEX method ranged over six orders of magnitude between 0.028 microg/L and 1218 microg/L with linear correlation coefficients between 0.990 and 0.998 for the investigated compounds. Method detection limits for monoaromatic compounds were between 28 ng/L (ethylbenzene) and 68 ng/L (1,2,4-trimethylbenzene). For halogenated volatile organic compounds, method detection limits between 48 ng/L (chloroform) and 799 ng/L (dichloromethane) were obtained. The precision of the method with external calibration was between 3.1% (chloroform ethylbenzene) and 7.4% (1,2,3-trimethylbenzene).     

Temperature-controlled headspace liquid-phase microextraction device using volatile solvents

A novel temperature-controlled headspace liquid-phase microextraction (TC-HS-LPME) device was established in which volatile solvents could be used as extractant. In this device, a PTFE vial cap with a cylindrical cavity was used as the holder of the extraction solvent. Up to 40 μl of extraction solvent could be suspended in the cavity over the headspace of aqueous sample in the vial. A cooling system based on thermoelectric cooler (TEC) was used to lower the temperature of extractant in PTFE vial cap to reduce the loss of volatile solvent during extraction process and increase the extraction efficiency. The selection of solvents for HS-LPME was then extended to volatile solvents, such as dichloromethane, ethyl acetate and acetone. The use of volatile extraction solvents instead of semi-volatile solvent reduced the interference of the large solvent peak to the analytes peaks, and enhanced the compatibility of HS-LPME with gas chromatograph (GC). Moreover, the use of larger volume of extractant solvent increases the extraction capacity and the injection volume of GC after extraction, thus improving detection limits. Several critical parameters of this technique were investigated by using chlorobenzenes (CBs) as the model analytes. High enrichment factors (498–915), low limits of detection (0.004–0.008 μg/L) and precision (3.93–5.27%) were obtained by using TC-HS-LPME/GC-FID. Relative recoveries for real samples were more than 83%.     

Application of Headspace Liquid-Phase Microextraction to the Analysis of Volatile Halocarbons in Water

The determination of four volatile halocarbons (CHCl₃, CCl₄, C₂HCl₃ and C₂Cl₄) in water by headspace liquid-phase microextraction (HS-LPME) with gas chromatography using a micro electron capture detector (GC-μECD) is described. The effects of the type and volume of the extraction solvent, headspace volume, stirring rate, extraction temperature and time and ionic strength on the extraction performance are investigated and optimized. The developed protocol yields a linear calibration curve in the concentration range from 0.05 to 50 µg L^?1 for the target analytes; the detection limits ranged from 0.003 to 0.146 µg L^?1 and the relative standard deviation (R.S.D.) values below 8.45%. The results demonstrate that HS-LPME followed with GC-μECD is a simple and reliable technique for the determination of volatile halocarbons in water samples.     

Characterization of volatile components of tea flowers (Camellia sinensis) growing in Kangra by GC/MS

Volatile flavour components of tea flowers (Camellia sinensis) were isolated by two methods viz. simultaneous distillation extraction (SDE), supercritical fluid extraction (SFE), analyzed by GC and GC/MS and compared with headspace analysis (HS). The composition of the volatile components extracted by the three methods differed considerably. In SFE, phenylethanol (14.7%), linalool (7.9%), (E)-linalool oxide furanoid (3.5%), epoxy linalool (1.6%), geraniol (2.3%) and hotrienol (1.5%) were major components. m-Xylene (2.6%), (E)-linalool oxide pyranoid (5.4%), p-myrcene (5.2%), alpha-cadinol (4.3%) and methyl palmitate (2.9%) were major compounds isolated by SDE. 3-hexenol (2.1%) (E)-4,8-dimethyl-1,3,7-nonatriene (20.9%) and linalool (35.1%) are major components in headspace analysis. Acetophenone and pheromone germacrene D is detected in tea flowers by all the methods studied. Floral, fresh and fruity odour of tea flowers is retained by SFE as there is very little loss of heat sensitive volatiles in SFE. The flavour isolated from SFE has superior quality compared to SDE.     

Comparison of direct thermal desorption with water distillation and superheated water extraction for the analysis of volatile components of Rosa damascena Mill. using GCxGC-TOF/MS

The composition of the volatile components from Rosa damascena Mill. was investigated using comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (TOF/MS). The samples were collected from Turkey and were extracted by water distillation (WD), superheated water extraction (SWE) and direct thermal desorption (DTD). It was found that superheated water extraction gave a slightly higher oil yield than water distillation. The major compounds found in volatiles of R. damascena Mill. were linalool, phenylethylalcohol, citronellol, nerol and geraniol. Phenylethylalcohol content was significantly higher using the DTD (36.52%) and SWE (38.14%) techniques compared to the WD (1.92%) technique. A lower content of monoterpene alcohols was found in volatiles extracted using the DTD method (73.69%) compared to the SWE (86.51%) and WD (86.56%) techniques reflecting the main finding that DTD extracts showed a greater total number of different components than either of the other two methods. The number of volatile components identified with a percentage higher than 0.05% were 54, 37, and 34 for the DTD, SWE and WD techniques, respectively. This highlighted DTD as a promising method for qualitative analysis of rose oil which can yield comprehensive results without the traditional obligation for costly and time consuming extraction techniques.     

Analysis of the Volatile Components in the Leaves of Cinna-momum camphora by Static Headspace Gas Chromatography Mass Spectrometry Combined with Accurate Weight Measurement

The volatile components in the leaves of C. camphora were analyzed by static headspace‐gas chromatography/mass spectrometry (HS‐GC‐MS) combined with accurate weight measurement. Accurate weight measurement obtained by Time‐of‐Flight mass spectrometry (TOF‐MS) helped to confirm the identification of volatiles in the analysis. 59 volatile components in the leaves of C. camphora were identified, which mainly included cis‐3‐hexen‐1‐ol (5.6%), 3‐hexen‐1‐ol, acetate (Z) (11.1%), β‐caryophyllene (15.4%), bicyclogermarene (8.4%), trans‐nerolidol (19.5%) and 9‐oxofarnesol (7.7%). The results show that method using HS‐GC‐MS combined with accurate weight measurement achieves reliable identification and has extensive application in the analysis of volatile components present in complex samples.     

顶空固相微萃取-气相色谱-质谱法用于白术中挥发性成分的分析

采用顶空固相微萃取-气相色谱-质谱法(HS-SPME-GC-MS)分离鉴定了白术中的挥发性成分,并与采用传统的水蒸气蒸馏法(SD)提取的挥发性成分进行了比较。实验中筛选了固相微萃取纤维头,优化了SPME的操作条件。样品在70 ℃下平衡30 min后,用65 μm聚二甲基硅氧烷-二乙烯基苯(PDMS-DVB)纤维头对白术样品顶空吸附30 min,于250 ℃下解吸4 min, 然后采用GC-MS对解吸物进行分离鉴定;采用HS-SPME-GC-MS鉴定出41种组分,占总峰面积的90.81%;采用SD-GC-MS鉴定出31个组分,占总峰面积的88.19%,且采用SD所提取的组分基本上都被固相微萃取所提取。结果表明, HS-SPME可取代耗时的SD用于白术中挥发性物质的提取。     

In-line coupling headspace liquid-phase microextraction with capillary electrophoresis

An analytical technique of in-line coupling headspace liquid-phase microextraction (HS-LPME) with capillary electrophoresis (CE) was proposed to determine volatile analytes. A special cover unit of the sample vial was adopted in the coupling method. To evaluate the proposed method, phenols were used as model analytes. The parameters affecting the extraction efficiency were investigated, including the configuration of acceptor phase, kind and concentration of acceptor solution, extraction temperature and time, salt-out effect, sample volume, etc. The optimal enrichment factors of HS-LPME were obtained with the sample volume of about half of sample vials, which were confirmed by both the theoretical prediction and experimental results. The enrichment factors were obtained from 520 to 1270. The limits of detection (LODs, S/N = 3) were in the range from 0.5 to 1 ng/mL each phenol. The recoveries were from 87.2% to 92.7% and the relative standard deviations (RSDs) were lower than 5.7% (n = 6). The proposed method was successfully applied to the quantitative analysis of the phenols in tap water, and proved to be a simple, convenient and reliable sample preconcentration and determination method for volatile analytes in water samples.     

Headspace liquid phase microextraction for quantitation of hexanal in potato crisps by gas chromatography

A simple and rapid method using headspace liquid-phase microextraction (HS-LPME) was developed for the determination of hexanal at low levels in potato crisp samples. Parameters such as extraction solvent, agitation of the sample, salt addition, organic drop volume, exposure time, and extraction time were controlled and optimised. The developed protocol was found to yield a linear calibration curve in the concentration range from 0.001 to 2 mg/L and a limit of detection of 0.1 microg/L with a good enrichment factor of > 107 for the analyte. The repeatability of the method was satisfactory (4%). The results demonstrate that HS-LPME is a rapid, accurate, and effective preparation method and could be successfully used for the determination of hexanal in potato crisp samples.     

LC-Ultrasound-Assisted Headspace Liquid Microextraction for the Analysis of Phenols in Water

An ultrasound-assisted headspace liquid microextraction method is presented. The organic solvent droplet is suspended at the bottom of a polychloroprene rubber tube. More extractant can be held and the stability of microdrop is better than by using a syringe needle so that extraction aided by ultrasonication can be carried out. Compared with traditional methods, the extraction efficiency is about ten times higher. The method has been used to determine phenols in real water samples, and good recoveries were obtained. It is a promising alternative for analyzing volatile or semivolatile pollutants in environmental samples due to its simplicity, rapidity and stability.     

Determination of Geosmin and 2-Methylisoborneol in Water by Headspace Liquid-Phase Microextraction Coupled with Gas Chromatography-Mass Spectrometry

Geosmin (GSM) and 2-methylisoborneol (MIB) were extracted from water samples, adsorbed in organic solvent microdrop by headspace liquid-phase microextraction (HS-LPME), and were analyzed by gas chromatography-mass spectrometry (GC-MS). Influence factors such as the extraction solvent types, headspace and microdrop volumes, stirring rate, equilibrium and extraction time, and ionic strength for HS-LPME efficiency were thoroughly evaluated. Under optimized extraction and detection conditions, the calibration curves of GSM and MIB were linear in the range of 5–1000 ng/L. The detection limits of GSM and MIB were 1.1 and 1.0 ng/L, respectively. Average recoveries of 95.45–113.7% (n = 5) were obtained and method precisions were also satisfactory. Trace levels of the off-flavor compounds at ng/L in tap water and raw water were successfully quantified.