Gel-electromembrane extraction of peptides: Determination of five hypothalamic agents in human plasma samples.

Agarose gel as a green membrane has been proposed for use in electromembrane extraction of five hypothalamic-related peptides without an ionic carrier. Octreotide, goserelin, triptorelin, cetrorelix, and somatostatin were extracted from 5.0 mL of sample solution (adjusted to pH 5.0) into a microvolume acceptor solution (HCl, 100 mM) under the applied voltage of 30 V in 15 min. The pH of the agarose gel 3.0% (w/v) was adjusted to 4.0 to facilitate the movement of peptides through the membrane. Quantification was performed using an HPLC-UV system on a C18 column. Quantification and detection limits were found to be in the range of 15.0-20.0 ng mL-1 and 4.5-6.0 ng mL-1, respectively. Dynamic linear ranges were found to be in the range of 15.0-1000 ng mL-1 (R2 > 0.995) and recoveries were in the range of 62.3-77.6%. The optimized method was applied to spiked human plasma samples. The method showed relative recoveries in the range of 44.8-66.0%. Finally, the proposed method was compared with and shown to have higher recoveries than, the conventional electromembrane extraction method for the peptides under study.

Developing a miniaturized setup for in-tube simultaneous determination of three alkaloids using electromembrane extraction in combination with ultraviolet spectrophotometry.

Herein, electromembrane extraction was combined with ultraviolet spectrophotometry using a customized manifold for preconcentration and simultaneous determination of morphine, codeine, and papaverine in water and human urine samples. Absorption spectra of the extracts were recorded inside the lumen of the hollow fiber using two fiber optics connected to a miniature spectrophotometer. Partial least squares regression was applied to resolve the overlapped spectra of the analytes. Performance of the model was validated by an independent test set. Central composite design was applied to optimize the extraction parameters. The optimized extraction conditions are as follows; supporting liquid membrane: 2-nitrophenyl octyl ether containing 15% v/v bis(2-ethylhexyl) phosphate, applied voltage: 80 V, donor pH: 3.0, acceptor pH: 1.0, extraction time: 20 min. Finally, the optimized extraction method was validated for determination of the mentioned alkaloids in human urine samples. The method showed good linearity (R2  > 0.995) for all of the mentioned alkaloids. The limits of detection for morphine, codeine, and papaverine in diluted human urine were found to be 0.6, 1.1, and 0.6 ng/mL, respectively with acceptable relative standard deviations. Enrichment factors of 104, 108, and 102 were achieved for morphine, codeine, and papaverine, respectively.

Quantification of controlled release leuprolide and triptorelin in rabbit plasma using electromembrane extraction coupled with HPLC-UV.

An electromembrane extraction followed by HPLC-UV technique was developed and validated for quantification of leuprolide and triptorelin in rabbit plasma. The influencing parameters on the extraction efficiency were optimized using experimental design methodology. The optimized conditions were found to be; supported liquid membrane: a mixture of 1-octanol and 2-ethyl hexanol (1:1) containing 10% v/v di(2-ethylhexyl) phosphate, applied voltage: 5 V, extraction time: 5 min, pH of the donor phase: 4.5 and pH of the acceptor phase: 1.0. The optimized method was validated for linearity, intraday and interday precision, and accuracy in rabbit plasma. The range of quantification for both peptides was 0.5-1000 ng/mL with regression coefficients higher than 0.994. Relative recoveries of leuprolide and triptorelin were found to be 80.3 and 75.5%, respectively. Limits of quantification and detection for both peptides were found to be 0.5 and 0.15 ng/mL, respectively. The validated method was successfully applied to pharmacokinetic study of the 1-month depot formulations of each peptide after subcutaneous administration to rabbits.

Electrically enhanced liquid-phase microextraction of three textile azo dyes from wastewater and plant samples.

An electromembrane extraction procedure coupled with HPLC and visible detection was applied for the extraction of three textile azo dyes as organic salts. The extraction parameters such as extraction time, applied voltage, pH range, and concentration of salt added were optimized. A driving force of 60 V was applied to extract the analytes through 2-nitrophenyl octyl ether, used as the supported liquid membrane, into a neutral aqueous solution. This method required 20 min extraction time from a neutral sample solution. The proposed microextraction technique provided good linearity with correlation coefficients from 0.996 to 0.998 over a concentration range of 1.0-1000.0 ng/mL. The LODs of dyes were 0.30-0.75 ng/mL, while the reproducibility ranged from 6.7 to 12.9% (n = 6). Also, enrichment factors of 96-162 that corresponded to the recoveries ranging from 48 to 81% were achieved. Finally, the application of this new method was demonstrated on wastewater samples and some plants grown in contaminated environments. Excellent selectivity was obtained as no interfering peaks were detected.

Solid-phase microextraction of phthalate esters from aqueous media by electrophoretically deposited TiO2 nanoparticles on a stainless steel fiber.

A novel SPME fiber was prepared by electrophoretic deposition of titanium dioxide nanoparticles (nano-TiO2) on a stainless steel wire. It was used in the direct immersion solid-phase microextraction (DI-SPME) of four phthalate esters from aqueous samples prior to gas chromatographic (GC) analysis. The effects of various parameters on the efficiency of the SPME process such as the mode of extraction, extraction temperature, film thickness of the SPME fiber, salt content, extraction time and stirring rate were investigated. The comparison of the fiber with another homemade poly(3,4-ethylenedioxythiophene)-TiO2 (PEDOT-TiO2) nanocomposite fiber and a commercial polydimethylsiloxane (PDMS) fiber showed the better extraction efficiency of the nano-TiO2 fiber for phthalate esters. Under optimized conditions, the limit of detection (LOD) for the phthalate esters varied between 0.05 and 0.12µgL(-1). The inter-day and intra-day relative standard deviations for various phthalate esters at 10µgL(-1) concentration level (n=6) using a single fiber were 6.6-7.5% and 8.3-11.1%, respectively. The fiber to fiber repeatabilities (n=4), expressed as relative standard deviation (RSD%), were between 8.9% and 10.2% at 10µgL(-1) concentration level. The linear ranges varied between 0.5 and 1000µgL(-1). The method was successfully applied to the analysis of the bottled mineral water sample with recoveries from 86 to 107%.

Two-phase electromembrane extraction followed by gas chromatography-mass spectrometry analysis.

A two-phase electromembrane extraction (EME) was developed and directly coupled with gas chromatography mass spectrometry (GC-MS) analysis. The proposed method was successfully applied to the simultaneous determination of imipramine, desipramine, citalopram and sertraline. The model compounds were extracted from neutral aqueous sample solutions into the organic phase filled in the lumen of the hollow fiber. This method was accomplished with 1-heptanol as organic phase, by means of 60 V applied voltage and with the extraction time of 15 min. Experiments reported recoveries in the range of 69-87% from 1.2 mL neutral sample solution. The compounds were quantified by GC-MS instrument, with acceptable linearity ranging from 1 to 500 ng mL(-1) (R(2) in the range of 0.989 to 0.998), and repeatability (RSD) ranging between 7.5 and 11.5% (n = 5). The estimated detection limits (S/N ratio of 3:1) were less than 0.25 ng mL(-1). This novel approach based on two-phase EME brought advantages such as simplicity, low-costing, low detection limit and fast extraction with a total analysis time less than 25 min. These experimental findings were highly interesting and demonstrated the possibility of solving ionic species in the organic phase at the presence of electrical potential.

Electromembrane extraction of zwitterionic compounds as acid or base: comparison of extraction behavior at acidic and basic pHs.

This study has performed on electromembrane extraction (EME) of some zwitterionic compounds based on their acidic and basic properties. High performance liquid chromatography (HPLC) equipped with UV detection was used for determination of model compounds. Cetirizine (CTZ) and mesalazine (MS) were chosen as model compounds, and each of them was extracted from acidic (as a cation) and basic (as an anion) sample solutions, separately. 1-Octanol and 2-nitrophenyl octylether (NPOE) were used as the common supported liquid membrane (SLM) solvents. EME parameters, such as extraction time, extraction voltage and pH of donor and acceptor solutions were studied in details for cationic and anionic forms of each model compound and obtained results for two ionic forms (cationic and anionic) of each compound were compared together. Results showed that zwitterionic compounds could be extracted in both cationic and anionic forms. Moreover, it was found that the extraction of anionic form of each model compound could be done in low voltages when 1-octanol was used as the SLM solvent. Results showed that charge type was not highly effective on the extraction efficiency of model compounds whereas the position of charge within the molecule was the key parameter. In optimized conditions, enrichment factors (EF) of 27-60 that corresponded to recoveries ranging from 39 to 86% were achieved.

Electro membrane extraction of sodium diclofenac as an acidic compound from wastewater, urine, bovine milk, and plasma samples and quantification by high-performance liquid chromatography.

Electro membrane extraction (EME) as a new microextraction method was applied for extraction of sodium diclofenac (SDF) as an acidic compound from wastewater, urine, bovine milk and plasma samples. Under applied potential of 20 V during the extraction, SDF migrated from a 2.1 mL of sample solution (1mM NaOH), through a supported liquid membrane (SLM), into a 30 µL acceptor solution (10 mM NaOH), exist inside the lumen of the hollow fiber. The negative electrode was placed in the donor solution, and the positive electrode was placed in the acceptor solution. 1-octanol was immobilized in the pores of a porous hollow fiber of polypropylene as SLM. Then the extract was analyzed by means of high-performance liquid chromatography (HPLC) with UV-detection for quantification of SDF. Best results were obtained using a phosphate running electrolyte (10 mM, pH 2.5). The ranges of quantitation for different samples were 8-500 ngmL(-1). Intra- and inter-day RSDs were less than 14.5%. Under the optimized conditions, the preconcentration factors were between 31 and 66 and also the limit of detections (LODs) ranged from 2.7 ng mL(-1) to 5 ng mL(-1) in different samples. This procedure was applied to determine SDF in wastewater, bovine milk, urine and plasma samples (spiked and real samples). Extraction recoveries for different samples were between 44-95% after 5 min of extraction.