Conventional Microsyringe Research Articles

Present state and applications of single drop microextraction for the determination of harmful organic compounds and pollutants

Abstract Single drop microextraction (SDME) nowadays earns an increasing attention by scientists due to its simplicity, low cost and the need for only common laboratory equipment. This microextraction technique combines sample cleanup and pre-concentration of analytes in one step. Furthermore, a significant reduction in the amount of organic solvents needed comparing to standard LLE techniques places SDME into the position of environmental friendly extraction techniques. SDME is a straightforward technique in which a micro-drop of solvent is suspended from the tip of a conventional micro-syringe and then it is in a direct contact with a sample solution in which it is immiscible or it could be suspended in the headspace above the sample. The paper overviews developments of the state-of-the-art SDME techniques for the extraction of harmful organic compound and pollutants from environmental, food and biological matrices. Key extraction parameters essential for SDME performance were described and discussed.

Water-based gas purge microsyringe extraction coupled with liquid chromatography for determination of alkylphenols from sea food Laminaria japonica Aresh

A novel organic solvent-free mode of gas purge microsyringe extraction, termed water-based gas purge microsyringe extraction, was developed. This technique can directly extract target compounds in wet samples without any drying process. Parameters affecting the extraction efficiency were investigated. Under optimal extraction conditions, the recoveries of alkylphenols were between 87.6 and 105.8%, and reproducibility was between 5.2 and 12.1%. The technique was also used to determine six kinds of alkylphenols (APs) from samples of Laminaria japonica Aresh. The OP and NP were detected in all the samples, and concentrations ranged from 26.0 to 54.5ngg−1 and 45.0–180.4ngg−1, respectively. The 4-n-butylphenol was detected in only one sample and its concentration was very low. Other APs were not detected in L. japonica Aresh samples. The experimental results demonstrated that the technique is fast, simple, non-polluting, allows for quantitative extraction, and a drying process was not required for wet samples. Since only aqueous solution and a conventional microsyringe were used, this technique proved affordable, efficient, and convenient for the extraction of volatile and semivolatile ionizable compounds.

Gas purge microsyringe extraction for quantitative direct gas chromatographic–mass spectrometric analysis of volatile and semivolatile chemicals

Sample pretreatment before chromatographic analysis is the most time consuming and error prone part of analytical procedures, yet it is a key factor in the final success of the analysis. A quantitative and fast liquid phase microextraction technique termed as gas purge microsyringe extraction (GP-MSE) has been developed for simultaneous direct gas chromatography–mass spectrometry (GC–MS) analysis of volatile and semivolatile chemicals without cleanup process. Use of a gas flowing system, temperature control and a conventional microsyringe greatly increased the surface area of the liquid phase micro solvent, and led to quantitative recoveries of both volatile and semivolatile chemicals within short extraction time of only 2 min. Recoveries of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and alkylphenols (APs) determined were 85–107%, and reproducibility was between 2.8% and 8.5%. In particular, the technique shows high sensitivity for semivolatile chemicals which is difficult to achieve in other sample pretreatment techniques such as headspace-liquid phase microextraction. The variables affecting extraction efficiency such as gas flow rate, extraction time, extracting solvent type, temperature of sample and extracting solvent were investigated. Finally, the technique was evaluated to determine PAHs, APs and OCPs from plant and soil samples. The experimental results demonstrated that the technique is economic, sensitive to both volatile and semivolatile chemicals, is fast, simple to operate, and allows quantitative extraction. On-site monitoring of volatile and semivolatile chemicals is now possible using this technique due to the simplification and speed of sample treatment.

Dynamic hollow fiber protected liquid phase microextraction and quantification using gas chromatography combined with electron capture detection of organochlorine pesticides in green tea leaves and ready-to-drink tea

The dynamic hollow fiber protected liquid phase microextraction (DHFP-LPME) technique was evaluated for the extraction of organochlorine pesticides (OCPs) in green tea leaves and ready-to-drink tea prior to gas chromatography combined-electron capture detection (GC–ECD) analysis. A conventional microsyringe with a 1.5 cm length of hollow fiber attached to its needle was connected to a syringe pump to perform the extraction. The microsyringe was used as both the microextraction device and the sample introduction device for GC–ECD analysis. In this work, the organochlorine pesticides were extracted and condensed to a volume of 3 μl of organic extracting solvent (1-octanol) confined within a 1.5 cm length of hollow fiber. The effects of extraction solvent, extraction time, sample agitation, plunger speed, and extraction temperature and salt concentration content on the extraction performance were also investigated. Good enrichments were achieved (34–297-fold) with this method, and good repeatabilities of extraction were obtained, with full name (RSDs) below 12.57%. Detection limits were much below 1 μg l −1 for ready-to-drink tea and much below 1 μg g −1 for green tea leaves.

Headspace Water-Based Liquid-Phase Microextraction

A new organic-free mode of headspace liquid-phase microextraction termed headspace water-based liquid-phase microextraction has been developed. Five phenols were used as model compounds in the development and evaluation of the procedure. Parameters affecting the extraction efficiency were investigated. Under optimal extraction conditions, very high enrichment factors were achieved. Since only water (with sodium hydroxide to adjust the pH) and a conventional microsyringe were used, this new technique is affordable, efficient, and convenient for extraction of volatile and semivolatile ionizable compounds. In addition, in combination with capillary electrophoresis, the entire analytical process is totally organic solvent-free and is thus environmentally friendly.

Dynamic Liquid−Liquid−Liquid Microextraction with Automated Movement of the Acceptor Phase

A new dynamic liquid-liquid-liquid microextraction procedure, with the automated movement of acceptor phase (LLLME/AMAP) to facilitate mass transfer, was developed in this study. Four compounds, 3-nitrophenol, 4-nitrophenol, 3,4-dinitrophenol, and 2,4-dichlorophenol, were used as model compounds to be preconcentrated from water samples. The extraction involved filling a 2-cm length of hollow fiber with 4 muL of acceptor solution using a conventional microsyringe, followed by impregnation of the pores of the fiber wall with 1-octanol. The fiber was then immersed in 4 mL of aqueous sample solution. The analytes in the sample solution were extracted into the organic solvent and then back-extracted into the acceptor solution. During extraction, the acceptor phase was repeatedly moved in and out of the hollow fiber channel and the syringe controlled by a syringe pump. Separation and quantitative analyses were then performed by using high-performance liquid chromatography. The results indicated that up to 400-fold enrichment of the analytes could be obtained under the optimized conditions. The enrichment factors were two times those of static liquid-liquid-liquid microextraction. Good repeatabilities (RSD values below 9.30%) were obtained. The calibration linear range was from 10 to 1000 ng/mL with the square of the correlation coefficient (r2) >0.9916. Detection limits were in the range of 0.45-0.98 ng/mL. In addition, as compared with the previously reported dynamic three-phase microextraction in which there was no relative movement between the acceptor and the organic phase (which is not conducive to effective mass transfer), this new method shows much higher extraction efficiency. All these results suggest that this new dynamic LLLME/AMAP technique could be a better alternative to the previous LLLME for the extraction of analytes from aqueous samples.

Automated hollow fiber-protected dynamic liquid-phase microextraction of pesticides for gas chromatography–mass spectrometric analysis

Dynamic liquid-phase microextraction (LPME) controlled by a programmable syringe pump was evaluated for extracting pesticides in water prior to GC–MS analysis. A conventional microsyringe with a 1.3-cm length of hollow fiber attached to its needle was connected to a syringe pump to perform the extraction. The microsyringe was used as both the microextraction device as well as the sample introduction device for GC–MS analysis. The attached hollow fiber served as the “holder” and “protector” of 3 μl of organic solvent. The solvent was repeatedly withdrawn into and discharged from the hollow fiber by the syringe pump. Pesticides were extracted from 4-ml water samples into the organic solvent impregnated in the hollow fiber. The effects of organic solvents, plunger movement pattern, agitation and extraction time were investigated. Good repeatabilities of extraction performance were obtained, with the RSD values ranging from 3.0% (alachlor) to 9.8% (4-chlorophenol) for the 14 pesticides; most RSD values were under 5.0%. The method provided a 490-fold preconcentration of the target pesticides. The limits of detection were in the range of 0.01–5.1 μg/l ( S/ N=3) in the GC–MS selected ion monitoring mode. In addition, sample clean-up was achieved during LPME because of the selectivity of the hollow fiber, which prevented undesirable large molecules from being extracted. A slurry sample (mixture of 40 mg soil/ml of water) containing seven pesticides was extracted using this method which also gave good linearity and precision (most RSDs<7.0%, n=3).

Application of static liquid-phase microextraction to the analysis of organochlorine pesticides in water

Static liquid-phase microextraction, with subsequent analysis by gas chromatography–electron-capture detection, has been applied to extract eight organochlorine pesticides from water. A conventional microsyringe was used to extract analytes from water samples over a concentration range of 0.05–100 μg/l. Factors relevant to the extraction process were investigated. The sensitivity of the method was enhanced with agitation, and increasing the extraction temperature, of the sample solution. Concentration factors of >50-fold were easily achieved within 25 min of extraction. The analytical data exhibited a relative standard deviation (RSD) range of 3.2% (lindane) to 10.7% (methoxychlor) for the eight pesticides; most RSD values were under 7%. Water samples collected from a reservoir, and from tap water in a chemical laboratory were analyzed using the procedure.

Application of dynamic liquid-phase microextraction to the analysis of chlorobenzenes in water by using a conventional microsyringe.

A dynamic liquid-phase microextraction technique combined with gas chromatography/mass spectrometry (GC/MS) is described for the extraction of 10 chlorobenzenes from water samples into 1 microL of organic solvent by using a conventional microsyringe. The effects of extraction solvent, plunger movement pattern, sampling volume, number of samplings, and salt concentration on the extraction performance were investigated. Good repeatabilities of extraction were obtained, with the RSD values below 5.3% except for hexachlorobenzene (9.3%). By using a sampling volume of 6 microL and 15 samplings, detection limits were found to be between 0.02 and 0.05 microgram/L under GC/MS-selective ion monitoring mode.

Liquid-Phase Microextraction in a Single Drop of Organic Solvent by Using a Conventional Microsyringe

Two modes of liquid-phase microextraction (LPME) were developed for capillary gas chromatography. Both methodologies, i.e., static LPME and dynamic LPME, involve the use of very small amounts of organic solvent (<2 μL) in a conventional microsyringe. The performance of the two techniques is demonstrated in the determination of two chlorobenzenes extracted into a single drop of toluene by the use of a 10-μL syringe. Static LPME provided some enrichment (∼12-fold), good reproducibility (9.7%), and simplicity but suffered relatively long extraction time (15 min). Dynamic LPME provided higher (∼27-fold) enrichment within much shorter extraction time (∼3 min), and relatively poorer precision (12.8%), primarily due to repeated manual manipulation. Both methods allow the direct transfer of extracted analytes into a gas chromatograph.