Reduction of extraction times in liquid-phase microextraction

Recently, we introduced a simple and inexpensive disposable device for liquid-phase microextraction (LPME) based on porous polypropylene hollow fibres. In the present paper, extraction times were significantly reduced by an increase in the surface of the hollow fibres. The model compounds methamphetamine and citalopram, were extracted from 2.5 ml of urine, plasma, and whole blood after dilution with water and alkalisation with 125 μl of 2 M NaOH though a porous polypropylene hollow fibre impregnated with hexyl ether and into an aqueous acceptor phase consisting of 0.1 M HCl. Two commercially available hollow fibres, which differed in surface area, wall thickness and internal diameter, were compared. An increase in the contact area of the hollow fibre with the sample solution by a factor of approximately two resulted in reduction in equilibrium times by approximately the same factor. Thus, the model compounds were extracted to equilibrium within 15 min from both urine and plasma, and within 30 min from whole blood. For the first time LPME was utilised to extract drugs from whole blood, and the extracts were comparable with plasma both with regard to sample clean-up and extraction recoveries. Extraction recoveries for methamphetamine and citalopram varied from 60 to 100% using the two fibres and the different matrices.     

Three-phase liquid-phase microextraction of weakly basic drugs from whole blood

The behaviour of weak basic analytes in liquid-phase microextraction (LPME) and the optimisation of parameters in whole blood are described. Benzodiazepines and non-benzodiazepine drugs were chosen as model substances. Liquid-phase microextraction based on disposable polypropylene hollow fibres was used in the three-phase extraction of five weak bases from whole blood. The sample work up with the liquid-phase microextraction technique can be impeded by low recovery due to incomplete trapping in the acceptor phase of weakly basic drugs and the complexity of the whole blood matrix. Different parameters related to this problem were experimentally studied. Additionally the stability of the analytes was examined because of low pH in the acceptor phase. The investigation resulted in optimised LPME conditions for the extraction of weak bases from whole blood. The parameters limiting the recovery were evaluated.     

Fiber-based liquid-phase micro-extraction of mebeverine enantiomers followed by chiral high-performance liquid chromatography analysis and its application to pharmacokinetics study in rat plasma

The applicability of two-phase liquid-phase micro-extraction (LPME) in porous hollow polypropylene fiber for the sample preparation and the stereoselective pharmacokinetics of mebeverine (MEB) enantiomers (an antispasmodic drug) in rat after intramuscular administration were studied. Plasma was assayed for MEB enantiomer concentrations using stereospecific high-performance liquid chromatography with ultraviolet detection after a simple, inexpensive, and efficient preconcentration and clean-up hollow fiber-based LPME. Under optimized micro-extraction conditions, MEB enantiomers were extracted with 25 μl of 1-octanol within a lumen of a hollow fiber from 0.5 ml of plasma previously diluted with 4.5 ml alkalized water (pH 10). The chromatographic analysis was carried out through chiral liquid chromatography using a DELTA S column and hexane-isopropyl alcohol (85:15 v/v) containing 0.2% triethylamine as mobile phase. The mean recoveries of (+)-MEB and (-)-MEB were 75.5% and 71.0%, respectively. The limit of detection (LOD) was 3.0 ng/ml with linear response over the concentration range of 10-2500 ng/ml with correlation coefficient higher than 0.993 for both enantiomers. The pharmacokinetic studies showed that the mean plasma levels of (+)-MEB were higher than those of (-)-MEB at almost all time points. Also, (+)-MEB exhibited greater t(max) (peak time in concentration-time profile), C(max) (peak concentration in concentration-time profile), t(1/2) (elimination half-life), and AUC(0-240 min) (area under the curve for concentration versus time) and smaller CL (clearance) and V(d) (apparent distribution volume) than its antipode. The obtained results implied that the absorption, distribution, and elimination of (-)-MEB were more rapid than those of (+)-MEB and there were stereoselective differences in pharmacokinetics.     

Hollow fiber-liquid phase microextraction combined with gas chromatography for the determination of phenothiazine drugs in urine

A simple method of hollow fiber-liquid phase microextraction (HF-LPME) combined with gas chromatography (GC) was developed for the analysis of four phenothiazine drugs (promethazine, promazine, chlorpromazine and trifluoperazine) in human urine samples. All variables affecting the extraction of target analytes including organic solvent type, stirring rate, extraction time, extraction temperature, pH of sample solution and ionic strength were carefully studied and optimized. Under the optimal conditions, the analytical performance of HF-LPME-GC-flame photometric detector (FPD) and HF-LPME-GC-flame ionization detector (FID) were evaluated and compared. The results showed that the HF-LPME-GC-FID was more sensitive than HF-LPME-GC-FPD for the determination of four target phenothiazine drugs, while the signal peak shape and resolution obtained by HF-LPME-GC-FPD was better than that obtained by HF-LPME-GC-FID. HF-LPME-GC-FPD/FID was successfully applied for the assay of the interested phenothiazine drugs in urine sample, and the excretion of the drugs was also investigated by monitoring the variation of the concentration of chlorpromazine in urine of a psychopath within 8 h after drug-taking. The proposed method provided an effective and fast way for the therapeutic drug monitoring (TDM) of phenothiazine.     

Equilibrium sampling through membrane based on a single hollow fibre for determination of drug-protein binding and free drug concentration in plasma

The determination of drug-protein binding and free drug concentration in plasma applying the equilibrium sampling through membrane (ESTM) technique has been studied using supported liquid membrane extraction in a single hollow fibre without any membrane carrier. In the extraction setup, the donor phase (plasma or buffer) was placed in the vial, into which was immersed the hollow fibre with the acceptor phase situated in the lumen. This proposed technique was applied to study the drug-protein binding of five local anaesthetics and two antidepressants as model substances, and the influence of the total drug concentration on the drug-protein binding was investigated. The brief theoretical background for determination of the drug-protein binding under equilibrium conditions is described. The developed method shows a new, improved and simple procedure for determination of free drug concentration in plasma and extent of drug-protein binding.     

Determination of aconitine,hypaconitine and mesaconitine in urine using hollow fiber liquid-phase microextraction combined with high-performance liquid chromatography

Hollow fiber liquid-phase microextraction (HF-LPME) coupled with high-performance liquid chromatography was used to simultaneously determine three Aconitum alkaloids, including aconitine (AC), hypaconitine (HA) and mesaconitine (MA) in human urine sample. Analytes were extracted from 5 mL urine sample containing 1.0 mmol/L NaOH into 1-octanol membrane phase impregnated in the pores of hollow fiber wall, and then back extracted into acidified aqueous solution in the lumen of the hollow fiber. After extraction, 10 μL of the acceptor phase was analyzed directly by HPLC. In this method, some important extraction parameters, such as organic solvent, extraction time, stirring rate, pH of donor phase and acceptor phase, temperature, and the volume of acceptor phase were optimized. This method provided 98- to 288-fold enrichment factors within 60 min of extraction and good repeatability with RSDs of 0.99–7.22%. The calibration curves were linear over the ranges of 16.0–128.0 μg/L for AC, 11.0–88.0 μg/L for HA and 8.1–64.8 μg/L for MA in human urine sample, with correlation coefficients of 0.9949, 0.9969 and 0.9904, respectively. Limits of detection were from 0.7 to 1.5 μg/L, and recoveries from spiked urine sample varied from 84.4% to 106.2% for AC, 77.3% to 85.6% for HA and 90.1% to 100.8% for MA.     

Electromembrane extraction of trace amounts of naltrexone and nalmefene from untreated biological fluids

Nalmefene and naltrexone are used to block the effects of narcotics and alcohol. In the present work, for the first time a microextraction technique was presented to reduce matrix interferences and improve detection limits of the drugs in urine and plasma samples. Electromembrane extraction (EME) followed by high performance liquid chromatography (HPLC) coupled with ultraviolet (UV) detection was optimized and validated for quantification of nalmefene and naltrexone from biological fluids. The membrane consists 85% of 2-nitrophenyl octyl ether (NPOE) and 15% di-(2-ethylhexyl) phosphate (DEHP) immobilized in the pores of a hollow fiber. A 100 V electrical field was applied to make the analytes migrate from sample solution with pH 2.0, through the supported liquid membrane (SLM) into an acidic acceptor solution with pH 1.0 which was located inside the lumen of hollow fiber. Extraction recoveries in the range of 54% and 75% were obtained in different biological matrices which resulted in preconcentration factors in the range of 109-149 and satisfactory repeatability (2.0相似文献   

Urine sample preparation of tricyclic antidepressants by means of a supported liquid membrane technique for high-performance liquid chromatographic analysis

Supported liquid membrane (SLM) technique for sample work-up and enrichment was used for determination of tricyclic antidepressant drugs in urine by high-performance liquid chromatography (HPLC) with UV detection. The studied antidepressant drugs were amitriptyline, opipramol, noxiptyline and additionally diethazine was used as possible internal standard. Alkaline phosphoric buffer with urine sample, as the donor solution, was passed over the liquid membrane into which investigated substances were extracted. On the other side of the membrane, analyzed compounds were trapped due to creating non-extractable form in acidic acceptor solution. Enriched and cleaned up drugs were then injected into a HPLC system with ultraviolet detection to analyze of their concentration in acceptor solution. Optimum extraction efficiency was determined by changing acceptor and donor solutions pH, application of different flow rates of donor solution and by using different solvents in the membrane. Also, donor solution volume, extraction time and concentration of analytes were varied to check the linearity of extraction process. The highest extraction efficiency: 43% for opipramol, 56% for noxiptyline, 43% for amitriptyline and 42% for diethazine (R.S.D. values were <6% and n=3) was achieved when 0.05 M phosphate buffer pH 4.0 and 9.5 were used as donor and acceptor solutions, respectively, n-undecane with 5% tri-n-octylphosphine oxide (TOPO) was used as liquid membrane. Limit of quantification (LOQ) for tricyclic antidepressants after enrichment of 100ml of urine sample was about 1 ng/ml.     

Liquid-phase and dispersive liquid-liquid microextraction techniques with derivatization: recent applications in bioanalysis

Liquid phase microextraction (LPME), especially hollow fiber liquid-phase microextraction (HF-LPME), and dispersive liquid-liquid microextraction (DLLME) offer high enrichments of target analytes in a single step. The analytical usefulness of these techniques is significantly enhanced by coupling them with suitable derivatization methods. Due to their simplicity, diverse bioanalytical applications have recently been reported. This review focuses on the recent developments of the combined LPME (mainly HF-LPME and single drop microextraction (SDME)) and DLLME techniques with derivatization for the analysis of biological samples. A broad range of sample matrices such as urine, blood, plasma and human hair samples with various derivatization methods for polar or ionizable organic compounds will be considered. These techniques can also be extended to the determination of trace metal ions, such as the heavy metal ions (Hg, Pb, and Co) and Se. Future trends of the techniques will also be discussed.     

Three phases hollow fiber LPME combined with HPLC-UV for extraction, preconcentration and determination of valerenic acid in Valeriana officinalis

In the present work, the applicability of hollow fiber-based liquid phase microextraction (HF-LPME) was evaluated for the extraction and preconcentration of valerenic acid prior to its determination by reversed-phase HPLC/UV. The target drug was extracted from 5.0 mL of aqueous solution with pH 3.5 into an organic extracting solvent (dihexyl ether) impregnated in the pores of a hollow fiber and finally back extracted into 10 μ L of aqueous solution with pH 9.5 located inside the lumen of the hollow fiber. In order to obtain high extraction efficiency, the parameters affecting the HF-LPME, including pH of the donor and acceptor phases, type of organic phase, ionic strength, the volume ratio of donor to acceptor phase, stirring rate and extraction time were studied and optimized. Under the optimized conditions, enrichment factor up to 446 was achieved and the relative standard deviation (RSD) of the method was 4.36% (n = 9). The linear range was 7.5-850 μg L?1 with correlation coefficient (r2=0.999), detection limits was 2.5 μg L?1 and the LOQ was 7.5 μg L?1. The proposed method was evaluated by extraction and determination of valerenic acid in some Iranian wild species of Valerianaceae.     

Analysis of enzymatic steroid conversions by high pressure liquid chromatography.

Enzyme catalyzed introduction of the 1–2 double bond into a steroid can be monitored through spectrophotometric changes accompanying electron acceptor reduction or through paper or thin-layer chromatographic analysis of the reaction product. The spectrophotometric method is not applicable to cases in which the oxidized form of the electron acceptor is continually regenerated. In studying such cases, we have found high pressure liquid chromatography (HPLC) to be a method of direct analysis more convenient than paper chromatography or tlc. Use of a water based eluant and a reverse phase column for the HPLC analysis allows direct injection of a sample of the aqueous reaction solution after acidification, and no extraction with an organic solvent is necessary.     

Three phase liquid phase microextraction of phenylacetic acid and phenylpropionic acid from biological fluids

Three phase liquid phase microextraction (three phase LPME) technique coupled with HPLC-UV has been applied as a sensitive and efficient sample preparation method to determine phenylacetic acid (PAA) as a biomarker of depressive disorders and phenylpropionic acid (PPA) in biological fluids. The compounds were extracted from 3.0 ml aqueous solution with the adjustment of pH at a fixed value in the range of 2.0-3.5 (donor solution) into an organic phase (1-hexanol) layered on the surface of the donor solution and finally back-extracted into 4.0 microl of the acceptor microdrop (pH 11.1) located at the end of the microsyringe needle. After a prescribed back-extraction time, the acceptor microdrop was withdrawn into the microsyringe and then directly injected into the HPLC system. In order to achieve maximum extraction efficiency, different parameters affecting the extraction conditions were optimized. At the optimum conditions (donor solution: 2.3M Na(2)SO(4), pH 2.0-3.5; organic membrane: 95 microl of 1-hexanol; acceptor solution: 4.0 microl of 0.1M NH(3)/NH(4)(+) with pH 11.1; donor solution temperature: 45-50 degrees C; extraction time: 20 min and back-extraction time: 12 min), up to 110-fold enrichment factor was obtained. The calibration curve for these analytes was linear in the range of 1-5000 microg/l with r(2)>0.998. The intraday and interday RSD% were below 6.5% and the limits of detection (LODs) for both analytes were 0.2 microg/l (based on S/N=3). The proposed technique is a low cost, simple and sensitive method with highly clean-up effect. Finally, this technique was successfully utilized for the detection of target analytes in human urine, serum and plasma.     

Electrically Assisted Liquid‐Phase Microextraction Combined With Capillary Electrophoresis for Quantification of Propranolol Enantiomers in Human Body Fluids

In this study, electromembrane extraction (EME) combined with cyclodextrin (CD)‐modified capillary electrophoresis (CE) was applied for the extraction, separation, and quantification of propranolol (PRO) enantiomers from biological samples. The PRO enantiomers were extracted from aqueous donor solutions, through a supported liquid membrane (SLM) consisting of 2‐nitrophenyl octyl ether (NPOE) impregnated on the wall of the hollow fiber, and into a 20‐μL acidic aqueous acceptor solution into the lumen of hollow fiber. Important parameters affecting EME efficiency such as extraction voltage, extraction time, pH of the donor and acceptor solutions were optimized using a Box‐Behnken design (BBD). Then, under these optimized conditions, the acceptor solution was analyzed using an optimized CD‐modified CE. Several types of CD were evaluated and best results were obtained using a fused‐silica capillary with ammonium acetate (80 mM, pH 2.5) containing 8 mM hydroxypropyl‐β‐CD as a chiral selector, applied voltage of 18 kV, and temperature of 20°C. The relative recoveries were obtained in the range of 78–95%. Finally, the performance of the present method was evaluated for the extraction and determination of PRO enantiomers in real biological samples. Chirality 26:260–267, 2014. © 2014 Wiley Periodicals, Inc.     

Extraction of trace amounts of pioglitazone as an anti-diabetic drug with hollow fiber liquid phase microextraction and determination by high-performance liquid chromatography-ultraviolet detection in biological fluids

The applicability of hollow fiber liquid phase microextraction (HF-LPME) for extraction and preconcentration of trace amounts of pioglitazone (PGL) as an anti-diabetic drug in biological fluids, prior to determination by high-performance liquid chromatography (HPLC), was evaluated. In this technique, the target drug was extracted into di-n-hexyl ether immobilized in the wall pores of a porous hollow fiber from 10 mL of the aqueous sample (source phase, SP) with pH 8.0, and then back extracted into the receiving phase (RP) with pH 2.2 located in the lumen of the hollow fiber. The extraction occurred due to a pH gradient between the two sides of the hollow fiber. After extracting for a prescribed time, 24 μL of the RP solution was taken back into the syringe and injected directly into a HPLC instrument for quantification. The Taguchi orthogonal array (OAD) experimental design with an OA₁₆ (4⁵) matrix was employed to optimize the HF-LPME conditions. Different factors affecting the HF-LPME efficiency such as the nature of organic solvent used to impregnate the membrane, pH of the SP and RP, stirring speed, extraction time and ionic strength were studied and optimized. Under the optimum conditions (di-n-hexyl ether as membrane impregnation solvent, pHs of the SP and RP equal to 8.0 and 2.2, respectively, extraction time of 30 min, stirring speed of 500 rpm and 10% (w/v) NaCl for adjusting the ionic strength), preconcentration factor of 180, linear dynamic range (LDR) of 2.5–250 μg L^?1 with good correlation of determination (r² > 0.998) and limit of detection (LOD) of 1.0 μg L^?1 were obtained for the target drug. The percent relative intra-day and inter-day standard deviations (RSDs%) based on five replicate determinations were 4.7 and 15%, respectively. Once LPME was optimized, the performance of the proposed technique was evaluated for the determination of PGL in different types of biological fluids such as plasma and urine samples. The results showed that the proposed HF-LPME method could be successfully applied to determine trace amounts of PGL in biological samples.     

Enzyme-linked bridging assay method for the quantification of oligonucleotide-based drugs in biological matrices

With ongoing efforts to develop oligonucleotide-based (ODN-based) therapeutics, there is a need for a sensitive, high-throughput method of quantification of ODN-based drugs in biological matrices. To overcome the insufficient sensitivity and time-consuming sample extraction procedures involved in conventional capillary gel electrophoresis (CGE) and high-performance liquid chromatography (HPLC), we developed a nucleic acid hybridization-based enzyme-linked bridging assay (ELBA), which shows significant advantages over CGE methods in evaluating ODN-based drugs in plasma and tissue: (1) It has higher sensitivity; (2) it involves easier sample extraction procedures; (3) it is suitable for many ODN-based drugs, even those with different secondary structures and modifications, including phosphorothioate oligonucleotide (PSODN), mixed backbones with 2'-O-Me (MBO), locked nucleic acid (LNA) modifications, and B- and C-type CpG sequences; and (4) it is highly selective, even during simultaneous quantification, with regard to intact ODNs and their 3'-metabolites. This universal design produces a rapid, sensitive, specific assay with minimal method development time. It is well suited to high-throughput analysis of various ODN-based drugs.     

Determination of N-acetylator phenotype using caffeine as a probe compound: a comparison of high-performance liquid chromatography and capillary electrophoresis methods

A test for determining N-acetylator metabolic phenotype has been developed using caffeine as a probe drug. A spot sample of urine is taken, and the unextracted urine is then analysed by micellar electrokinetic capillary chromatography. Phenotype is determined from the peak-area ratio of urinary 5-acetylamino-6-formylamino-3-methyluracil to 1-methylxanthine. Phenotype assignments using this method were compared with those made using a standard high-performance liquid chromatography assay, with good agreement between the two methods. The advantage of the capillary electrophoresis analysis is that no sample extraction is necessary, resulting in a total analysis time of around 20 min, and removing a potential source of error.     

Analysis of amantadine in biological fluids using hollow fiber-based liquid-liquid-liquid microextraction followed by corona discharge ion mobility spectrometry

A method based on liquid-liquid-liquid microextraction combined with corona discharge ion mobility spectrometry was developed for the analysis of amantadine in human urine and plasma samples. Amantadine was extracted from alkaline aqueous sample as donor phase through a thin phase of organic solvent (n-dodecane) filling the pores of the hollow fiber wall and then back extracted into the organic acceptor phase (methanol) located in the lumen of the hollow fiber. All variables affecting the extraction of analyte including acceptor organic solvent type, concentration of NaOH in donor phase, ionic strength of the sample and extraction time were studied. The linear range was 20-1000 and 5-250 ng/mL for plasma and urine, respectively (r(2)≥0.990). The limits of detection were calculated to be 7.2 and 1.6 ng/mL for plasma and urine, respectively. The relative standard deviation was lower than 8.2% for both urine and plasma samples. The enrichment factors were between 45 and 54. The method was successfully applied for the analysis of amantadine in urine and plasma samples.     

A long-term stable and adjustable osmotic pump for small volume flow based on principles of phloem loading

An adjustable pump for microfluidics employing principles of osmoregulation analogous to those of phloem loading in plant leaves has been constructed and tested. Volume flow arises in a hollow fibre with vapour-permeable hydrophobic membrane. The fibre is connected to a source chamber filled with salt crystals and saturated salt solution. The source chamber takes up water through a relatively small membrane area and delivers saturated salt solution to one end of the capillary flow path within the hollow fibre. A stationary osmotic gradient is sustained in the hollow fibre lumen by constant input of saturated salt solution and radial osmotic water absorption. The strong temperature dependence of isothermal membrane distillation enables adjustment of the flow rate up to 20 nL/s. The pump provides pulse-free flow of any liquid with constant rate for at least 26 days without recharging the source chamber. Backpressures up to 1 bar decrease the flow rate by less than 4%. The volume delivered at a constant rate is more than 40 times larger than the volume of the source chamber. Osmoregulatory pumps of the described type may be useful for microinfusion, microdialysis and analytical microsystems.