Electromembrane Extraction of Posaconazole for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometric Detection.

A new mode of electromembrane extraction (EME) has been developed for detection via matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS). Posaconazole, extracted from 8 mL of a 10 mM trifluoroacetic acid solution onto a thin polyvinylidene difluoride (PVDF) membrane, was used as a model analyte. The transport was forced by an electrical potential difference between two electrodes inside the lumen of a hollow fiber and glass tube. Under an application of 80 V, cationic posaconazole in the sample solution moved toward the negative electrode inside the glass tube and was trapped by the PVDF membrane on the side. After 15 min of extraction, 3 µL of α-cyano-4-hydroxycinnamic acid (CHCA) solution was applied on top of the membrane, which was then analyzed by MALDI/MS. Under optimal extraction conditions, the calibration curve of posaconazole was linear over a concentration range of 0.10-100.00 nM. The limit of detection (LOD) at a signal-to-noise ratio of 3 was 0.03 nM with an enhancement factor of 138 for posaconazole. The application of this method to the determination of posaconazole in human serum samples was also successfully demonstrated.

Solvent-free electromembrane extraction: A new concept in electro-driven extraction.

A solvent-free electromembrane extraction (SF-EME) device was developed. A thin polyvinylidene difluoride (PVDF) membrane placed at the end of an L-shaped glass tube acted as an analyte collector and was inserted into the sample solution. Under an applied voltage of 110 V, cationic peptides in the sample solution moved toward the negative electrode inside the L-shaped glass tube and were trapped by the membrane at the end of the tube. After 1 min of extraction, 3 µL of α-cyano-4-hydroxycinnamic acid (CHCA) solution was applied on top of the membrane, and then the membrane was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS). The parameters affecting the extraction efficiency, such as the type of membrane, applied voltage, pH range, and extraction time, were optimized. Under optimal extraction conditions, the calibration curves of angiotensin II and Arg-vasopressin were linear over concentration ranges of 0.50-30.00 nM and 0.20-25.00 nM, respectively. The limits of detection (LODs) at a signal-to-noise ratio of 3 were 0.15 and 0.06 nM with enhancement factors of 209 and 118 for angiotensin II and Arg-vasopressin, respectively. The application of this method to the determination of peptides in complex matrix solutions was also successfully demonstrated.

Cyclodextrin-assisted dispersive liquid-liquid microextraction for the preconcentration of carbamazepine and clobazam with subsequent sweeping micellar electrokinetic chromatography.

A new version of dispersive liquid-liquid microextraction, namely, cyclodextrin-assisted dispersive liquid-liquid microextraction, with subsequent sweeping micellar electrokinetic chromatography has been developed for the preconcentration and sensitive detection of carbamazepine and clobazam. α-Cyclodextrin and chloroform were used as the dispersive agent and extraction solvent, respectively. After the extraction, carbamazepine and clobazam were analyzed using micellar electrokinetic chromatography with ultraviolet detection. The detection sensitivity was further enhanced using the sweeping technique. Under optimal extraction and stacking conditions, the calibration curves of carbamazepine and clobazam were linear over a concentration range of 2.0-200.0 ng/mL. The method detection limits at a signal-to-noise ratio of 3 were 0.6 and 0.5 ng/mL with sensitivity enhancement factors of 3575 and 4675 for carbamazepine and clobazam, respectively. This developed method demonstrated high sensitivity enhancement factors and was successfully applied to the determination of carbamazepine and clobazam in human urine samples. The precision and accuracy for urine samples were less than 4.2 and 6.9%, respectively.

Surfactant-assisted dispersive liquid-liquid microextraction combined with field-amplified sample stacking in capillary electrophoresis for the determination of mexiletine and lidocaine.

A sensitive method for the determination of mexiletine and lidocaine using surfactant-assisted dispersive liquid-liquid microextraction coupled with capillary electrophoresis was developed. Triton X-100 and dichloromethane were used as the dispersive agent and extraction solvent, respectively. After the extraction, mexiletine and lidocaine were analyzed using capillary electrophoresis with ultraviolet detection. The detection sensitivity was further enhanced through the use of field-amplified sample stacking. Under optimal extraction and stacking conditions, the calibration curves were linear over a concentration range of 0.05-1.00 µM for mexiletine and 0.03-1.00 µM for lidocaine. The limits of detection (signal-to-noise ratio of 3) were 0.01 and 0.01 µM for mexiletine and lidocaine, respectively. An approximately 1141- to 1250-fold improvement in sensitivity was observed for the two analytes compared with the injection of a standard solution without the surfactant-assisted dispersive liquid-liquid microextraction and field-amplified sample stacking procedures. This developed method was successfully applied to the determination of mexiletine and lidocaine in human urine and serum samples. Both precision and accuracy for urine and serum samples were less than 8.7 and 6.7%, respectively. The recoveries of the two analytes from urine and serum samples were 54.7-64.9% and 16.1-56.5%, respectively.

Determination of immunosuppressive drugs in human urine and serum by surface-assisted laser desorption/ionization mass spectrometry with dispersive liquid-liquid microextraction.

A rapid and sensitive method for the determination of immunosuppressive drugs through surface-assisted laser desorption/ionization mass spectrometric detection (SALDI/MS) was developed. Colloidal Pd and α-cyano-4-hydroxycinnamic acid (CHCA) were used as the SALDI co-matrix. To eliminate interference and enhance the sensitivity, dispersive liquid-liquid microextraction (DLLME) was employed to extract the immunosuppressive drugs from the aqueous solutions. Under optimal extraction and detection conditions, calibration curves for cyclosporine and everolimus in aqueous solutions were linear over a concentration range from 0.01 to 1.20 µM. For sirolimus, the linear concentration range of the calibration curve was from 0.05 to 2.00 µM. The limits of detection (LODs) were calculated to be 3, 3, and 14 nM for cyclosporine, everolimus, and sirolimus, respectively. The enrichment factors of DLLME were calculated to be 108, 122, and 101 for cyclosporine, everolimus, and sirolimus, respectively. This novel method was successfully applied for the determination of immunosuppressive drugs in human urine and serum samples.

Rapid determination of rivaroxaban in human urine and serum using colloidal palladium surface-assisted laser desorption/ionization mass spectrometry.

RATIONALE: Rivaroxaban is a new anticoagulant drug that has recently been introduced for clinical applications. To ensure optimum efficacy while minimizing the risk of toxicity and other adverse effects, a simple and sensitive analytical procedure for monitoring the concentration of rivaroxaban in biological fluids is required. METHODS: Rivaroxaban was extracted from aqueous solutions by dispersive liquid-liquid microextraction (DLLME). Detection of rivaroxaban was achieved through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using colloidal palladium as the SALDI matrix. RESULTS: The calibration curve for rivaroxaban in aqueous solutions was linear over the concentration range from 5 to 500 nM. The limit of detection (LOD) for rivaroxaban at a signal-to-noise ratio of 3 was 2 nM. With a sample-to-extract volume ratio of 200, the enrichment factors were calculated to be 141. This method was successfully applied for the determination of rivaroxaban in human urine and serum samples. The LODs for rivaroxaban in urine and serum were calculated to be 6 nM and 60 nM, respectively. CONCLUSIONS: The analysis speed, together with the ease of operation and high sensitivity, allows SALDI-MS method to be particularly suitable for the high-throughput screening of rivaroxaban levels in human urine and serum samples.

Sensitive detection of piperazinyl phenothiazine drugs by field-amplified sample stacking in capillary electrophoresis with dispersive liquid-liquid microextraction.

A rapid, simple and sensitive method for the detection of piperazinyl phenothiazine drugs using dispersive liquid-liquid microextraction (DLLME) combined with field-amplified sample stacking (FASS) in CE was developed. Sensitivity parameters that affect the extraction and FASS efficiency, such as the type and volume of disperser solvent, extraction time, addition of salt, and efficiency of FASS, were investigated and optimized. Note that the conductivity ratio between BGE and sample zone was measured to be 2300. Under optimal extraction and stacking conditions, the calibration curve, which ranged from 0.3 to 160 ng/mL, demonstrated good linearity with a correlation coefficient r≧ 0.9900. The LODs of prochlorperazine (Pcp), trifluoperazine (Tfp), perphenazine (Ppa), and fluphenazine (Fpa) at an S/N of 3 were 0.1, 0.1, 0.07, and 0.08 ng/mL, respectively. An approximately 1000-fold to 2500-fold improvement in sensitivity was achieved for the four tested analytes compared to conventional CZE without DLLME. The recoveries of all phenothiazines in urine and plasma ranged from 85.7 to 107.6% and 95.6 to 105.4%, respectively. The proposed method was demonstrated to be a rapid and convenient method for the determination of four piperazinyl phenothiazine drugs in human urine and plasma.

Detection of posaconazole by surface-assisted laser desorption/ionization mass spectrometry with dispersive liquid-liquid microextraction.

A simple, rapid, and sensitive method for the detection of posaconazole using dispersive liquid-liquid microextraction (DLLME) coupled to surface-assisted laser desorption/ionization mass spectrometric detection (SALDI/MS) was developed. After the DLLME, posaconazole was detected using SALDI/MS with colloidal gold and α-cyano-4-hydroxycinnamic acid (CHCA) as the co-matrix. Under optimal extraction and detection conditions, the calibration curve, which ranged from 1.0 to 100.0 nM for posaconazole, was observed to be linear. The limit of detection (LOD) at a signal-to-noise ratio of 3 was 0.3 nM for posaconazole. This novel method was successfully applied to the determination of posaconazole in human urine samples.

Detection of digoxin in urine samples by surface-assisted laser desorption/ionization mass spectrometry with dispersive liquid-liquid microextraction.

A novel method for the detection of digoxin using dispersive liquid-liquid microextraction (DLLME) coupled to the surface-assisted laser desorption/ionization mass spectrometric detection (SALDI/MS) was developed. Acetone and chloroform were used as the disperser solvent and extraction solvents, respectively. After the extraction, digoxin was detected using SALDI/MS with colloidal palladium as the matrix. Under optimal extraction and detection conditions, the calibration curve, which ranged from 0.01 to 0.50 µM, was observed to be linear. The limit of detection (LOD) at a signal-to-noise ratio of 3 was 2 nM for digoxin. With a sample-to-extract volume ratio of 400, the enrichment factor for digoxin was calculated to be 252. This novel method was successfully applied for the determination of digoxin in human urine samples.

Excitation-dependent visible fluorescence in decameric nanoparticles with monoacylglycerol cluster chromophores.

Organic fluorescent nanoparticles, excitation-dependent photoluminescence, hydrogen-bonded clusters and lysobisphosphatidic acid are four interesting individual topics in materials and biological sciences. They have attracted much attention not only because of their unique properties and important applications, but also because the nature of their intriguing phenomena remained unclear. Here we report a new type of organic fluorescent nanoparticles with intense blue and excitation-dependent visible fluorescence in the range of 410-620 nm. The nanoparticles are composed of ten bis(monoacylglycerol)bisphenol-A molecules and the self-assembly occurs only in elevated concentrations of 2-monoacylglycerol via radical-catalysed 3,2-acyl migration from 3-monoacylglycerol in neat conditions. The excitation-dependent fluorescence behaviour is caused by chromophores composed of hydrogen-bonded monoacylglycerol clusters, which are linked by an extensive hydrogen-bonding network between the ester carbonyl groups and the protons of the alcohols with collective proton motion and HO···C=O (n→π) interactions.

Sensitive determination of sertraline by capillary electrophoresis with dispersive liquid-liquid microextraction and field-amplified sample stacking.

A novel method for the determination of sertraline using dispersive liquid-liquid microextraction (DLLME) coupled with capillary electrophoresis (CE) was developed. Acetone and dichloromethane were used as the disperser solvent and extraction solvent, respectively. A mixture of the extraction and disperser solvents was rapidly injected into a 1.0 mL aqueous sample to form a cloudy solution. After the extraction, sertraline was analyzed using CE that was equipped with UV detection. A 74-fold improvement in the sensitivity was observed when DLLME was used to extract sertraline. Since the DLLME extract residue was redissolved with 5 µL of water that contained 20% methanol, the detection sensitivity was further enhanced through the use of field-amplified sample stacking (FASS). A 11-fold improvement in the sensitivity was obtained when FASS was used to on-line concentrate sertraline. Under optimal extraction and stacking conditions, the calibration curve, which ranged from 0.01 to 1 µM was observed to be linear. The limit of detection (LOD) at a signal-to-noise ratio of 3 was 2.5 nM for sertraline. An approximately 814-fold improvement in the sensitivity was observed for sertraline compare with injection of standard solution without the DLLME and FASS procedures. This developed method was successfully applied to the determination of sertraline in human urine samples.

Determination of macrolide antibiotics using dispersive liquid-liquid microextraction followed by surface-assisted laser desorption/ionization mass spectrometry.

A novel method for the determination of macrolide antibiotics using dispersive liquid-liquid microextraction coupled to surface-assisted laser desorption/ionization mass spectrometric detection was developed. Acetone and dichloromethane were used as the disperser solvent and extraction solvent, respectively. A mixture of extraction solvent and disperser solvent were rapidly injected into a 1.0 mL aqueous sample to form a cloudy solution. After the extraction, macrolide antibiotics were detected using surface-assisted laser desorption/ionization mass spectrometry (SALDI/MS) with colloidal silver as the matrix. Under optimum conditions, the limits of detection (LODs) at a signal-to-noise ratio of 3 were 2, 3, 3, and 2 nM for erythromycin (ERY), spiramycin (SPI), tilmicosin (TILM), and tylosin (TYL), respectively. This developed method was successfully applied to the determination of macrolide antibiotics in human urine samples.

Silver-coated gold nanoparticles as concentrating probes and matrices for surface-assisted laser desorption/ionization mass spectrometric analysis of aminoglycosides.

A novel method for the determination of aminoglycosides by surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) with the aid of silver-coated gold nanoparticles (Au@AgNPs) has been developed. The Au@AgNPs with surface capped by anionic citrate were used as concentrating probes as well as matrices in SALDI MS. Adsorption of aminoglycosides onto the nanoparticles was mainly through electrostatic attraction. The aminoglycoside-adsorbed nanoparticles were directly characterized by SALDI MS after a simple washing. Using Au@AgNPs to preconcentrate the aminoglycosides from 500 microL buffer solution, the limits of detection (LODs) at signal-to-noise ratio of 3 were 3, 25, 15, 30, and 38 nM for paromomycin, kanamycin A, neomycin, gentamicin, and apramycin, respectively. This method was successfully applied to the determination of aminoglycosides in human plasma samples. The LODs of aminoglycosides in plasma samples were 9, 130, 81, and 180 nM for paromomycin, kanamycin A, neomycin, and gentamicin, respectively. Recoveries of aminoglycosides in plasma samples were about 80%.

Orexin-A modulates glutamatergic NMDA-dependent spinal reflex potentiation via inhibition of NR2B subunit.

Glucose-sensitive neurons in the lateral hypothalamic area produce orexin-A (OxA) as well as orexin-B (OxB) and send their axons to the spinal dorsal horn, which predominantly expresses orexin receptor-1 (OX-1), showing a higher sensitivity to OxA. The purpose of the present study was to assess the effects of OxA on the induction of a novel form of activity-dependent reflex potentiation, spinal reflex potentiation (SRP), in the pelvic-urethral reflex activity. External urethra sphincter electromyogram in response to pelvic afferent nerve test stimulation (TS; 1/30 Hz) or repetitive stimulation (RS; 1 Hz) was recorded in anesthetized rats. TS evoked a baseline reflex activity, whereas RS produced SRP, which was abolished by intrathecal OxA (30 nM, 10 mul). Intrathecal SB-408124 (10 muM, 10 mul), an OX-1 antagonist, reversed the abolition on SRP caused by OxA. Although there is, so far, no NR2A- and NR2B-specific agonist available, N-methyl-d-aspartate (NMDA) reversed the abolition on the RS-induced SRP caused by the co-administration of OxA and Co-101244 (30 nM, 10 mul; an NMDA NR2B subunit antagonist), but it did not reverse the abolition by the co-administration of OxA and PPPA (300 nM, 10 mul; an NMDA NR2A subunit antagonist). In conclusion, the activation of descending orexinergic fibers may inhibit the repetitive afferent input-induced central sensitization of pelvic-urethral reflex activity and urethra hyperactivity, indicating that spinal orexinergic neural transmission may be a novel target for the treatment of patients with neuropathetic or postinflammatory pain of pelvic origin.

Capillary electrophoresis of aminoglycosides with argon-ion laser-induced fluorescence detection.

A new analytical method for aminoglycosides (kanamycin, bekanamycin, paromomycin and tobramycin) based on capillary electrophoretic separation and argon-ion laser-induced fluorescence detection has been developed. 6-Carboxyfluorescein succinimidyl ester (CFSE) was used for precolumn derivatization of the non-fluorescent aminoglycosides. Optimal separation and detection were obtained with an electrophoretic buffer of 30 mM sodium borate (pH 9.0) and an air-cooled argon-ion laser (excitation at 488 nm, emission at 520 nm). The concentration limits of detection in aqueous solution were 3.9-8.2 nM. Combined with a simple cleanup procedure, this method can be applied to the determination of aminoglycosides in human plasma. A calibration curve ranging from 0.15 to 30 microM was shown to be linear. The limits of detection of aminoglycosides in human plasma were between 14.4 and 24.0 nM. Recoveries of spiked aminoglycosides in human plasma were between 92 and 105%.

Analysis of peptides and proteins affinity-bound to iron oxide nanoparticles by MALDI MS.

Iron oxide nanoparticles modified with oleate have been employed for the extraction of peptides and proteins from aqueous solution before matrix-assisted laser desorption/ionization (MALDI) mass spectrometric (MS) analysis. Adsorption of peptides and proteins onto the nanoparticles were mainly through electrostatic attraction and hydrophobic interaction. The analyte-adsorbed iron oxide nanoparticles could be efficiently collected from solution using a magnet. No elution step was needed. With this preconcentration strategy, the lowest detectable concentration of angiotensin I, insulin, and myoglobin in 500 microL of aqueous solution were 0.1 nM, 0.1 nM, and 10.0 nM, respectively. In addition, the nanoparticles could extract the analytes from solution with a high content of salt and surfactant, thus eliminating suppression effect during MALDI MS analysis. This method was successfully applied to concentrate the tryptic digest products of cytochrome c. In addition, the tryptic digestion of cytochrome c can be directly conducted on the iron oxide nanoparticles.

Determination of small phosphorus-containing compounds by capillary electrophoresis.

The review focuses on the analysis of small phosphorus-containing compounds by capillary electrophoresis (CE) with different detection modes including UV absorption, laser-induced fluorescence, conductometry, amperometry, atomic spectrometry, and mass spectrometry. Determinations of phosphates, organophosphate, and chemical warfare agents in environmental samples such as water, soil and grains are emphasized. To achieve better sensitivity, high-resolving power, and reproducibility, the optimum separation conditions for various analytes (samples) are different. We compare the merits and demerits of the different detection modes for the detection of the analytes. Although the present methods are successful in many cases, there is still a need to develop high-throughput CE techniques for screening numerous environmental samples and sample stacking techniques in CE for the analysis of trace analytes.

Determination of gabapentin in human plasma by capillary electrophoresis with laser-induced fluorescence detection and acetonitrile stacking technique.

A sensitive analytical method for gabapentin [1-(aminomethyl) cyclohexaneacetic acid] (GBP) in human plasma based on capillary electrophoretic separation and laser-induced fluorescence (LIF) detection has been developed. 6-Carboxyfluorescein succinimidyl ester (CFSE) was used for precolumn derivatization of the non-fluorescent drug in plasma. Optimal separation and detection were obtained with an electrophoretic buffer of 50mM sodium borate (pH 9.5) and an air-cooled argon-ion laser (excitation at 488 nm, emission at 520 nm). A calibration curve ranging from 0.3 to 150 microM was shown to be linear. The concentration limit of detection (LOD) in plasma was 60 nM. We also demonstrate how the detection limit can be enhanced by using acetonitrile stacking technique. With stacking, the limit of detection for gabapentin in plasma was 4.8 nM. A calibration curve ranging from 0.03 to 15 microM was shown to be linear. Both the within-day and day-to-day reproducibility and accuracy were

Determination of vigabatrin by capillary electrophoresis with laser-induced fluorescence detection.

A new analytical method for vigabatrin based on capillary electrophoretic separation and laser-induced fluorescence detection has been developed. 5-Carboxytetramethylrhodamine succinimidyl ester was used for precolumn derivatization of the non-fluorescent drug. Optimal separation and detection were obtained with an electrophoretic buffer of 50 mM sodium borate (pH9.5) containing 10 mM sodium dodecyl sulfate and a green He-Ne laser (excitation at 543.5 nm, emission at 589 nm). The concentration limit of detection in aqueous solution was 24 nM. Combined with a simple cleanup procedure, this method can be applied to the determination of vigabatrin in human plasma. A calibration curve ranging from 1.5 to 200 microM shown to be linear. Both the within-day and day-to-day reproducibilities and accuracies were less then 14.3% and 4.9% respectively. The limit of detection of vigabatrin in plasma was about 0.13 microM

Simultaneous determination of selenium and antimony compounds by capillary electrophoresis with indirect fluorescence detection.

Capillary electrophoresis (CE) with indirect fluorescence detection was used to analyze selenium (selenite, selenate, selenomethionine, and selenocystine) and antimony (antimonite and antimonate) compounds. The separation was achieved by CE in 6 min with a 1.2 mM fluorescein solution at pH 9.5. Fluorescein also functioned as a background fluorophore for the indirect detection of these nonfluorescent species. Linearity of more than two orders of magnitude was generally obtained. Precision of migration times and peak areas was less than 1.0% and 7.2%, respectively. The concentration limits of detection (CLODs) was in the microM range. The detection sensitivity was generally dependent upon the transfer ratio (TR, defined as the number of moles of fluorescein ions displaced by one mole of analyte ions) of each species.