Search

As sample sizes get smaller and analyte concentrations lower, techniques that provide efficient extractions are needed. Liquid-phase microextraction (LPME) has become an area of increasing interest. Coupled with the use of hollow fibers that serve as a support for immobilized liquids and as a barrier between the donor and acceptor phases allows complex extractions, especially of aqueous samples, to be performed with high enrichment factors. In this installment, the subject of LPME is reviewed with emphasis on the use of hollow fibers. Applications examples will be provided., Sample preparation is a key step in chemical analysis because it is, in some cases, the slowest and most complicated step overall. Sample preparation is necessary to extract, isolate, and [...]

A ubiquitous electrochemical sensor which can detect pollutants in nonconducting aqueous solutions is prepared using a triple layer design, comprising a polyelectrolyte entrapped within micrometer-length nanochannels and sandwiched between two nanometer-thick electrode layers. Replacement of the polyelectrolyte with an enzyme-polyelectrolyte mixture within the nanochannels confers excellent biosensing characteristics. Its superior analytical performance of quantitating copper ions and formaldehyde at trace levels without additional sample treatment steps is demonstrated in freshwater samples derived from a local reservoir. 10.1021/ac100776p

A new two-step microextraction technique, combining dispersive liquid-liquid microextraction (DLLME) and dispersive microsolid-phase extraction (Do[mu]-SPE), was developed for the fast gas chromatographic-mass spectrometric determination of polycyclic aromatic hydrocarbons (PAHs) in environmental samples. A feature of the new procedure lies in that any organic solvent immiscible with water can be used as extractant in DLLME. A special apparatus, such as conical-bottom test tubes, and tedious procedures of centrifugation, refrigeration of the solvent, and then thawing it, associated with classical DLLME or similar techniques are not necessary in the new procedure, which potentially lends itself to possible automation. In the present D-[micro]-SPE approach, hydrophobic magnetic nanoparticles were used to retrieve the extractant of 1-octanol in the DLLME step. It is noteworthy that the target of D-[micro]-SPE was the 1-octanol rather than the PAHs. Because of the rapid mass transfer associated with the DLLME and the D-[micro]-SPE steps, fast extraction could be achieved. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: vortex at 3200 rpm in the DLLME step for 2 min and in D-[micro]-SPE for 1 min and then desorption by sonication for 4 min with acetenitrile as the solvent. The results demonstrated that enrichment factors ranging from 110- to 186-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 11.7 61.4 pg/mL and 0.04-0.21 ng/mL, respectively. The linearities were 0.5-50, 1-50, or 2-50 ng/mL for different PAHs. Finally, the two-step extraction method was successfully used for the fast determination of PAHs in river water samples. This two-step method, combining two different and efficient miniaturized techniques, provides a fast means of sample pretreatment for environmental water samples. 10.1021/ac9023632

This report describes the use of a porous membrane-protected micro-solid-phase extraction ([micro]-SPE) procedure to extract acidic drugs from wastewater that are then determined by high-performance liquid chromatography with ultraviolet detection. The [micro]-SPE device consists of [C.sub.18] sorbent held within a membrane envelope made of polypropylene. Ketoprofen and ibuprofen were selected as model compounds, and extraction parameters were optimized. Correlation coefficients of 0.9980 and 0.9953 were obtained for ketoprofen and ibuprofen, respectively, across a concentration range of 1-250 [micro]g/L. Relative extraction recoveries were between 94 and 112%. The relative standard deviation of the analytical method ranged between 2 and 10%, respectively. The method detection limits for these target analytes in wastewater ranged from 0.03 to 0.08 [micro]g/L. When compared to conventional solid-phase extraction (SPE), this new method showed better detection limits with good reproducibility. The results shows that this [micro]-SPE technique is a feasible alternative to multistep SPE for the extraction of analytes in complex samples.

A zirconia hollow fiber membrane in the macrorange was for the first time successfully synthesized via a template method coupled with a sol-gel process. A polypropylene hollow fiber was employed as the template. The preparation procedure includes repeated impregnation of the template in the proper zirconia sol precursor, and calcination to burn off the template, producing the zirconia hollow fiber. The resulting hollow fiber membrane is almost identical to its template in terms of morphology, exhibiting a hollow core structure. In addition to that, it has a bimodal porous substructure that is different from its template, narrowly distributed nanoskeleton pores, and uniform textural pores or throughpores. The wall thickness and substructures can be conveniently controlled by the synthetic conditions and postheat treatment. Moreover, the thus-prepared zirconia hollow fiber was applied for the microextraction and concentration of a nerve agent degradation product followed by liquid chromatography-mass spectrometric analysis. Since the zirconia fiber exists as an individual device and is directly usable for extracting, handling is more convenient than, for example, an adsorbent in powder form that needs to be coated on a rod for the extraction process. In addition, it is easily prepared and is superior to the monolithic material in this sense. Pinacolyl methylphosphonic acid, one degradation product of organophosphorus nerve agent (soman), was used as the model analyte. Zirconia hollow fiber was demonstrated to be a highly selective adsorbent for the phosphonic acid-containing compounds with high sensitivity. Limit of detection was as low as 0.07 ng/mL (0.39 nM).

Injection port derivatization following ion-pair hollow fiber-protected liquid-phase microextraction (LPME) for the trace determination of acidic herbicides (2,4-dichlorobenzoic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 3,5-dichlorobenzoic acid, 2-(2,4,5-trichlorophenoxy)propionic acid) in aqueous samples by gas chromatography/mass spectrometry (GC/ MS) was developed. Prior to GC injection port derivatization, acidic herbicides were converted into their ion-pair complexes with tetrabutylammonium chloride in aqueous samples and then extracted by 1-octanol impregnated in the hollow fiber. Upon injection, ion pairs of acidic herbicides were quantitatively derivatized to their butyl esters in the GC injection port. Thus, several parameters related to the derivatization process (i.e., injection temperature, purge-off time) were evaluated, and main parameters affecting the hollow fiber-protected LPME procedure such as extraction organic solvent, ion-pair reagent type, pH of aqueous medium, concentration of ion-pair reagent, sodium chloride concentration added to the aqueous medium, stirring speed, and extraction time profile, optimized. At the selected extraction and derivatization conditions, no matrix effects were observed. This method proved good repeatability (RSDs < 12.3%, n = 6) and good linearity ([r.sup.2] [greater than or equal to] 0.9939) for spiked deionized water samples for five analytes. The limits of detection were in the range of 0.51-13.7 ng x [L-.sup.-1] (S/N =3) under GC/MS selected ion monitoring mode. The results demonstrated that injection port derivatization following ion-pair hollow fiber-protected LPME was a simple, rapid, and accurate method for the determination of trace acidic herbicides from aqueous samples. In addition, this method proved to be environmentally friendly since it completely avoided open derivatization with potentially hazardous reagents.

A novel, multiwalled carbon nanotube (MWCNT)-supported micro-solid-phase extraction ([micro]-SPE) procedure has been developed. A 6-mg sample of MWCNTs was packed inside a (2 cm x 1.5 cm) sheet of porous polypropylene membrane whose edges were heat-sealed to secure the contents. The [micro]-SPE device, which was wetted with dichloromethane, was then placed in a stirred sewage sludge sample solution to extract organophosporous pesticides, used here as model compounds. Tumbling of the extraction device within the sample solution facilitated extraction, and the porous membrane acted as a filter to exclude the extraction of extraneous materials. After extraction, analytes were desorbed in hexane and analyzed using gas chromatography/mass spectrometry. Since the porous membrane afforded protection of the MWCNTs, no further cleanup of the extract was required. The [pi]--[pi] electrostatic interaction with the analytes and the large surface area of MWCNTs facilitated the adsorption of analytes, with good selectivity and reproducibility. Under the optimized extraction conditions, the method showed good linearity in the range of 0.1-50/[micro]g/L, repeatability of the extractions (RSD 2-8%, n = 4), and low limits of detection (1-7 pg/g). No analyte carryover effect was observed, and each [micro]-SPE device could be used for up to 30 extractions. Comparison was made with hollow fiber protected solid-phase microextraction and headspace solid-phase microextraction; [micro]-SPE was demonstrated to be a fast, accurate, and cost-effective pretreatment method for sewage sludge samples.

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.

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 [micro]L 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 ([r.sup.2]) > 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.

A simple and novel two-step liquid-liquid-liquid microextraction technique combined with reversed-phase HPLC has been developed for the determination of the nonsteroidal antiinflammatory drugs ibuprofen and 2-(4-chloropbenoxy) -2-methylpropionic acid in wastewater samples. In the first step, the analytes were extracted from an acidified sample (donor solution) into 1-octanol immobilized in the pores of 10 pieces of polypropylene hollow fiber and further into a basic acceptor phase inside the hollow fiber channels. This first extraction step, using 0.01 M NaOH as the acceptor phase and 0.1 M HCl within the donor phase, had a 100% relative recovery with an enrichment factor of 100-fold. The extract in the first step was then adjusted to acidic condition with HCl. It now represented the donor phase for the second step of the extraction, using a single piece of hollow fiber, with 2 [micro]L of 0.01 M NaOH solution as the acceptor phase. This analyte-enriched acceptor phase was subsequently withdrawn into a microsyringe and directly injected into an HPLC system for analysis. With this two-step microextraction, sensitivity enhancement of > 15 000-fold could be obtained. Detection limits of [less than or equal to] 100 ng/L could be achieved for both compounds. The method was applied to the analysis of wastewater.

Dynamic three-phase (liquid-liquid-liquid) microextraction was developed for capillary electrophoresis. Four aromatic amines as model compounds were extracted from 4-mL aqueous samples adjusted to basic condition (donor solution) through a small volume of organic solvent impregnated in a hollow fiber, which was held by the needle of a conventional syringe, and retracted into a 5-#L acidic acceptor solution inside the syringe. A renewable organic film and aqueous sample plug were formed inside the hollow fiber with the repeated movement of the syringe plunger enabled by a programmable syringe pump. This is believed to be the first reported instance of a semi-automated dynamic liquid-liquid-liquid microextraction (LLLME) procedure. Following this microextraction, the 5-[micro]L acceptor solution was analyzed by capillary zone electrophoresis (CE). This new technique provided ~140-fold enrichment in 20 min. Utilizing 4-chloroaniline as internal standard, dynamic LLLME could provide good reproducibility (

Two novel types of substituted cyclam-capped [beta]-cyclodextrin ([beta]-CD)-bonded silica particles have been prepared and used as chiral stationary phases in capillary electrochromatography (CEC). The two stationary phases have a chiral selector with three recognition sites: [beta]-CD, cyclam, and the latter's sidearm. They exhibit excellent enantioselectivities in CEC for a wide range of compounds as a result of the cooperative functioning of the anchored [beta]-CD and cyclam. After inclusion of the metal ion ([Ni.sup.2+]) from the running buffer into the substituted cyclams and their sidearm ligands, the bonded stationary phases become positively charged and can provide extra electrostatic interactions with ionizable solutes and enhance the dipolar interactions with some polar neutral solutes. This enhances the host-guest interaction with some solutes and improves chiral recognition and enantioselectivity. These new types of stationary phases exhibit great potential for fast chiral separations in CEC.

The organic solvent film formed in a microsyringe barrel vas used as an extraction interface in headspace liquid-phase microextraction (HS-LPME) of chlorobenzenes. Some common organic solvents with different vapor pressures (9.33-12 918.9 Pa) were studied as extractants. The results indicated that even the solvent with the highest vapor pressure (cyclohexane) can be used to carry out the extraction successfully. In general, the reasons for successful extraction are the very small space (5 [mm.sup.3]) within the microsyringe barrel and the fast equilibrium between gaseous analytes and organic solvent film. Both of these factors significantly reduced the risk of solvent loss during extraction. Thus, the choice of extraction solvent for the present method was very flexible. From the viewpoint of extraction efficiency, toluene (which has relatively low vapor pressure) was found to provide the best extraction efficiency. The effects of sampling volume, organic solvent volume, syringe withdrawal rate, and number of extraction cycles were also investigated. The procedure with respect to repeatability and limits of detection was evaluated by soil spiked with chlorobenzenes. Repeatability was between 5.7 and 17.7%, and the limits of detection were 6-14 ng/g. HS-LPME was shown to be an inexpensive, fast, and simple sample preparation method for volatile compounds.

An easy, simple, and highly efficient on-line preconcentration method for acidic compounds in capillary electro-phoresis was investigated. It combined two on-line concentration techniques, field-amplified sample injection (FASI) and sweeping. A low-pH (2.5) background electrolyte was used to suppress the electroosmotic flow (EOF), obviating the need of a coated capillary, as well as to neutralize the weakly acidic analytes. After injection of a plug of water inside the separation capillary, negative voltage was applied to initialize FASI for a much longer time than usual. The anions experienced a high electric field and moved quickly to the boundary of the water and the low-pH nonmicellar electrolyte. When the anions encountered the low-pH electrolyte, they were neutralized and a focused sample zone was formed. Then both inlet and outlet vials were changed to those containing the low-pH micellar background electrolyte. As negative voltage was applied, the anionic micelles moved into the capillary, and sweeping and separation began. The novelty in the present procedure is that a low-pH buffer is used to suppress the EOF and also the ionization of the analytes, without need of any other additives or use of a coated capillary. This method afforded 100 000-fold improvement in peak heights for some phenoxy acidic herbicides. The detection limits for these compounds could be low as 100 pg/mL.

Two modes of liquid-phase microextraction (LPME) combined with hollow fiber (HF) were developed for gas chromatography/mass spectrometry (GC/MS). Both methodologies, that is, static LPME with HF and dynamic LPME with HF, involved the use of a small volume of organic solvent impregnated in the hollow fiber, which was held by the needle of a conventional GC syringe. In static LPME/HF, the hollow fiber impregnated with solvent was immersed in the aqueous sample, and the extraction processed under stirring; in dynamic LPME/HF, the solvent was repeatedly withdrawn into and discharged from the hollow fiber by a syringe pump. This is believed to be the first reported instance of a semiautomated liquid microextraction procedure. The performance of the two techniques was demonstrated in the analysis of two PAH compounds in an aqueous sample. Static LPME/HF provided ~35-fold enrichment in 10 min and good reproducibility (~4%). Dynamic LPME/HF could provide higher enrichment (~75-fold) in 10 min and even better reproducibility (~3%). Both methods allow the direct transfer of extracted analytes to a GC/MS system for analysis.

A new microextraction technique termed hollow fiber-protected liquid-phase microextraction (LPME) was developed. Triazines were employed as model compounds to assess the extraction procedure and were determined by gas chromatography/mass spectrometry. Toluene functioned as both the extraction solvent and the impregnation solvent. Some important extraction parameters, such as effect of salt, agitation, pH, and exposure time were optimized. The new method provided good average enrichment factors of > 150 for eight analytes, good repeatability (RSDs