Aqueous Potassium Phosphate Research Articles

Aqueous arsenic(V) remediation and redox transformation of arsenic(III) to arsenic(V) using Fe3O4/Douglas fir biochar

Magnetite nanoparticles were deposited on Douglas fir biochar (Fe3O4/DFBC) using aqueous, NaOH-induced chemical co-precipitation from Fe2+/Fe3+ salt solutions. Fe3O4/DFBC was used to remediate As(V)-contaminated water. Kinetics and isotherms were studied. pH 5 was selected as the optimized pH due to low iron leaching and closeness to groundwater pH. Adsorption equilibrium was reached after 3 h, 2 h, and 1 h for 0.5, 5, and 50 mg/L initial As(V) concentrations, respectively. Adsorption was endothermic, and the Langmuir capacity was 6.33 mg/g at 25 °C. Ionic strength, impacts of Fe3O4/DFBC particle size, and competitive ion/molecule effects during As(V) adsorption were studied. Continuous-flow fixed-bed column breakthrough studies performed at 0.5, 5, and 50 mg/L of As(V) at pH 5 exhibited maximum capacities of 3.47, 3.99, and 3.72 mg/g, respectively. Aqueous potassium phosphate was used successfully for column regeneration. Fe3O4/DFBC was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Mössbauer spectroscopy before and after As(III) and As(V) adsorption. Mössbauer found the “Fe3O4” was composed of several phases. A key target was the study of simultaneous toxic As(III) adsorption and its transformation to As(V) from pH 1–13. The highest removal of As(III) and oxidized As(V) was obtained at pH 3. The relationship between iron leaching and pH was investigated and the pH-dependent surface adsorption was monitored using X-ray photoelectron spectroscopy (XPS) from pH 1 to 13. One goal of this study was to enhance the understanding of the adsorption characteristics needed for initial scaling of a treatment facility that can efficiently remediate arsenic-contaminated wastewater. Experiments were conducted using batch and fixed bed continuous flow columns to optimize adsorption process parameters under various circumstances and solution matrices. Another goal was to further establish the surface structures of the chemisorbed arsenates versus pH.

(Digital Presentation) Electrochemical Single Impact Method for Electroactive Bacterial Detection Onto Carbon Ultramicroelectrode

This work aims to design a high sensitivity and selectivity biosensor based on the electrochemistry of single impacts onto ultramicroelectrode (UME) to detect and identify various bacterial strains. The main objective is to establish a unique electrochemical signature for each bacterial cell through the individual impact event signal on the surface of the UME [1, 2]. First, we focus on the detection of well-known electroactive Gram-negative bacteria such as Shewanella oneidensis in order to be able to selectively detect these different single cells. In this case, the strategy currently used is to record a chronoamperometric curve in an aqueous potassium phosphate buffer (pH = 7.4) solution containing a redox probe at an UME polarized at the oxidation or reduction potential of the electrochemical active aqueous species and to observe a “current step” when one bacterium impacts the UME, corresponding to a “blocking effect” [3] (Figure A). The response signal expected from single bacterium collision may also be a “current spike” corresponding to either the own electrochemical activity of the bacterium toward the redox probe and the UME applied potential or a “bouncing effect” of the bacterium which does not stick onto UME surface (Figure B).In order to be able to identify the type of bacterial cell striking the UME surface, an adapted functionalization (covalent grafting via reduction of diazonium aryl salts) with appropriate affinity (bio)chemical species such as antibodies or aptamers could be performed. This strategy could confer to the UME surface a selectivity of the signal generated during single impacts. For example, the electro-grafting of diazo-pyridinium cations for microbial fuel cell electrodes showed to promote and improve the development of bacterial electroactive films [4].[1] E. Lebègue, N. L. Costa, R. O. Louro, F. Barrière, J. Electrochem. Soc. 16 (2020) 105501[2] A. T. Ronspees, S. N.Thorgaard, Electrochimica Acta. 278 (2018) 412-420[3] G. Guanyue, W. Dengchao, B. Ricardo, Z. Jinfang, M. Michael V. Anal. Chem. 90 (2018) 12123−12130[4] H. Smida, E. Lebègue, J-F. Bergamini, F. Barrière, C. Lagrost, Bioelectrochemistry. 120 (2018) 157-165 Figure 1

A Deep Eutectic Solvent Thermomorphic Multiphasic System for Biocatalytic Applications.

The applicability of a thermomorphic multiphasic system (TMS) composed of a hydrophobic deep eutectic solvent (DES) and an aqueous potassium phosphate buffer with a lower critical solution temperature (LCST) phase change for homogeneous biocatalysis was investigated. A lidocaine‐based DES with the fatty acid oleic acid as a hydrogen‐bond donor was studied. Phase diagrams were determined and presented within this study. We tested different additional components to the solvent system and observed a decrease in the cloud point of approximately 0.026 °C per concentration unit. Distribution studies revealed a clear distribution of the protein in the aqueous buffer phase (>95 %), whereas the hydrophobic substrate and educt accumulated (>95 %) in the DES‐enriched layer. Finally, a reduction catalyzed by horse liver alcohol dehydrogenase was performed in a larger‐scale experiment, and the biocatalyst could be recycled by simply removing the DES phase for three recycling runs.

Communication—Electrochemical Single Nano-Impacts of Electroactive Shewanella Oneidensis Bacteria onto Carbon Ultramicroelectrode

Electrochemical single nano-impacts of electroactive Shewanella oneidensis bacteria at a 7 μm diameter carbon fibre ultramicroelectrode in an aqueous potassium phosphate buffer (pH = 7.2) solution containing a redox active probe (potassium ferro- or ferricyanide) is reported. We present chronoamperometric measurements recorded at the ultramicroelectrode polarized at the potential of the steady-state current of the redox probe in solution (oxidation for K4Fe(CN)6 or reduction for K3Fe(CN)6) in the presence of bacteria. The shape of current transients associated to single bacteria nano-impacts is compared and discussed as a function of the redox probe in solution and of the ultramicroelectrode applied potential.

Water Activities and Equilibrium Phase Behavior for the Binary K3PO4(aq), K2SO4(aq) and the Ternary K3PO4 + K2SO4 + H2O Systems at Various Temperatures from 298.15 to 353.15 K

Thermodynamic properties of the aqueous binary and ternary potassium phosphate or/and sulfate solutions were studied at various temperatures from 298.15 to 353.15 K. The water activity measurements for the binary K2SO4(aq), K3PO4(aq) and the ternary K3PO4 + K2SO4 + H2O systems were performed from dilute to saturated solution using the hygrometric method. The modeling approach based on the ion interaction model was developed to evaluate the thermodynamic properties. From these measurements of phosphate and sulfate salts, the ion-interaction parameters β(0), β(1), and C ϕ in binary solutions were determined at various temperatures, and used to calculate the osmotic and activity coefficients of these aqueous solutions. The water activity of mixed salts solutions and related properties such as osmotic and activity coefficients are reported at four different temperatures. The osmotic coefficients and binary parameters were used to evaluate the mixing parameters $$ \theta_{{{\text{PO}}_{ 4} , {\text{SO}}_{ 4} }} $$ and $$ \psi_{{{\text{K,PO}}_{ 4} , {\text{SO}}_{ 4} }} $$ in the mixed K3PO4 + K2SO4 + H2O solutions. The solubility measurements of the binary systems were carried out for K2SO4(s) and K3PO4(s) from 298.15 to 353.15 K, up to mmax(K3PO4(s)) = 8.90 mol·kg−1 and mmax(K2SO4(s)) = 1.20 mol·kg−1 at 353.15 K, respectively. The thermodynamic characteristics, solubility products $$ K_{\text{SP}}^{^\circ } $$ and the excess Gibbs energies of K2SO4(aq) and K3PO4(aq) are also reported.

Light-Induced Surface Reactions at the Bismuth Vanadate/Potassium Phosphate Interface.

Bismuth vanadate has recently drawn significant research attention as a light-absorbing photoanode due to its performance for photoelectrochemical water splitting. In this study, we use in situ ambient pressure X-ray photoelectron spectroscopy with "tender" X-rays (4.0 keV) to investigate a polycrystalline bismuth vanadate (BiVO4) electrode in contact with an aqueous potassium phosphate (KPi) solution at open circuit potential under both dark and light conditions. This is facilitated by the creation of a 25 to 30 nm thick electrolyte layer using the "dip-and-pull" method. We observe that under illumination bismuth phosphate forms on the BiVO4 surface leading to an increase of the surface negative charge. The bismuth phosphate layer may act to passivate surface states observed in photoelectrochemical measurements. The repulsive interaction between the negatively charged surface under illumination and the phosphate ions in solution causes a shift in the distribution of ions in the thin aqueous electrolyte film, which is observed as an increase in their photoelectron signals. Interestingly, we find that such changes at the BiVO4/KPi electrolyte interface are reversible upon returning to dark conditions. By measuring the oxygen 1s photoelectron peak intensities from the phosphate ions and liquid water as a function of time under dark and light conditions, we determine the time scales for the forward and reverse reactions. Our results provide direct evidence for light-induced chemical modification of the BiVO4/KPi electrolyte interface.

Vortex Fluidic Device-Intensified Aqueous Two Phase Extraction of C-Phycocyanin from Spirulina maxima

A vortex fluidic device (VFD) is effective for downstream processing of C-phycocyanin (C-PC) from blue-green microalga Spirulina maxima using an aqueous two phase system (ATPS): polyethylene glycol (PEG) and aqueous potassium phosphate. The VFD-intensified ATPS continuous flow processing (VFD-ATPS) has spontaneous phase separation of the liquid exiting the 20 mm diameter tube inclined at 45° and rotating at 6550 rpm, for a 0.2 mL/min flow rate. This processing results in at least a 9.3-fold increase in phase demixing efficiency, 1.18-fold increase in C-PC purity, and 22% increase in yield compared to conventional ATPS methods. Multistage counter current distribution (CCD) using VFD-ATPS followed by removal of PEG and salt increased C-PC purity by 6-fold compared to the crude extract, with triple TOF mass spectrometry showing more than 95% sequence coverage for both subunits. This work establishes the utility of using VFD-intensified ATPS processing for protein purification and its potential as an effectiv...

Calorimetric and isentropic compressibility studies on (saccharide/methyl glycoside/deoxy-derivative + KH2PO4 + H2O) solutions at different temperatures

Heats of dilution (q) of various saccharides and their methyl-/deoxy-derivatives (solutes) have been measured in water and in (0.05, 0.15, 0.25 and 0.35) molkg−1 aqueous potassium phosphate monobasic (KH2PO4) solutions at (288.15, 298.15, 308.15, and 318.15) K. Limiting standard enthalpies of dilution (ΔdilH°) for the solutes were calculated from data q measured using isothermal titration micro calorimeter. The speed of sound (u) of solutes was measured in water and in (0.25, 0.50, 1.00 and 1.25) molkg−1 KH2PO4 solutions at (288.15–318.15) K. From these data, the apparent molar isentropic compressibilities (Ks,2,ϕ), interaction coefficients, hydration numbers and transfer parameters (ΔtΔdilH°, ∆tK°s,2) have been calculated. These parameters have been discussed in terms of solute–solvent/cosolute interactions occurring in these solutions. The results suggest that saccharides and their derivatives act as kosmotropes in mixed aqueous solvent.

Effect of potassium phosphate buffer on volumetric behavior of glycine in aqueous solutions at different temperatures

The apparent molar volume (V∅) of glycine in water and in 100, 500 and 1000mM aqueous potassium phosphate buffer (KPB) solutions have been obtained from density measurements at different temperatures (288.15 to 328.15K, including physiological temperature) and at different pH values (1.00, 7.40 and 14.00) by using vibrating-tube digital density meter. The estimated partial molar volumes at infinite dilution (V2o) have been used to obtain the corresponding transfer volume (∆trV2o) from water to aqueous potassium phosphate buffer solutions. Interaction parameters have been calculated from ∆trV2o data. The partial molar expansibilities (∂V2o|∂T)P at infinite dilution and (∂2V2o|∂T2)P values have also been determined from the V2o data at different temperatures. The hydration numbers (nH) of glycine at pH7.4 have been determined from the V2o data in the presence of KPB at different temperatures. The results have been discussed in terms of various interactions operating in these systems.

Ion hydration and association in aqueous potassium phosphate solutions.

Ionic hydration and ion association in aqueous solutions of KH2PO4, K2HPO4, and K3PO4 at 25 °C up to high concentrations have been investigated using dielectric relaxation spectroscopy (DRS). The three phosphate anions were found to be extensively hydrated, with total hydration numbers at infinite dilution of ~11 (for H2PO4(-)), ~20 (HPO4(2-)), and ~39 (PO4(3-)). These values are indicative of the existence of a second hydration shell around HPO4(2-) and especially PO4(3-). Two types of hydrating water molecules could be quantified: irrotationally bound (ib, H2O molecules essentially "frozen" on the DRS time scale) and "slow" (loosely bound water molecules with identifiably slower dynamics than bulk water). For H2PO4(-) over the entire concentration range and for HPO4(2-) and PO4(3-) at concentrations c ≲ 1 mol L(-1), only "slow" H2O was detected; however, at higher concentrations of the latter two anions, an increasing fraction of ib water appears, making up ~50% of the total hydration number close to the saturation limit of K2HPO4. Contrary to common belief, all three salts showed significant ion pair formation, with standard association constants of the 1:1 species increasing in the order: KH2PO4(0)(aq) < KHPO4(-)(aq) < KPO4(2-)(aq). The main type of ion pair in solution shifted from solvent-shared ion pairs (SIPs) to double-solvent-separated ion pairs (2SIPs) in the same sequence.

Study on interactions of saccharides and their derivatives with potassium phosphate monobasic (1:1 electrolyte) in aqueous solutions at different temperatures

The densities (ρ) of monosaccharides, their methyl and deoxy derivatives, disaccharides and trisaccharides have been measured in water and in (0.25, 0.50, 1.00 and 1.25)molkg−1 aqueous potassium phosphate monobasic (KH2PO4) solutions at (288.15, 298.15, 308.15 and 318.15)K and atmospheric pressure. The standard partial molar volumes (V2°) at infinite dilution and the corresponding volumes of transfer (∆tV2°) of solutes (saccharides and derivatives) from water to aqueous solutions of KH2PO4 have been calculated. The interaction coefficients (using the McMillan–Mayer theory) and standard partial molar expansibilities (VE°) have also been calculated. The results suggested the dominance of hydrophilic–ionic interactions due to the great affinity of phosphate (H2PO4−) anions for hydrogen bonding with hydrophilic sites of the saccharide molecules.

EFFICACY AND SAFETY OF ADJUNCTIVE BITOPERTIN VERSUS PLACEBO IN SUBJECTS WITH PERSISTENT PREDOMINANT NEGATIVE SYMPTOMS OF SCHIZOPHRENIA TREATED WITH ANTIPSYCHOTICS – UPDATE FROM THE SEARCHLYTE PROGRAMME

The densities (ρ) of monosaccharides, their methyl and deoxy derivatives, disaccharides and trisaccharides have been measured in water and in (0.25, 0.50, 1.00 and 1.25) mol kg− 1 aqueous potassium phosphate monobasic (KH2PO4) solutions at (288.15, 298.15, 308.15 and 318.15) K and atmospheric pressure. The standard partial molar volumes (V2°) at infinite dilution and the corresponding volumes of transfer (∆tV2°) of solutes (saccharides and derivatives) from water to aqueous solutions of KH2PO4 have been calculated. The interaction coefficients (using the McMillan–Mayer theory) and standard partial molar expansibilities (VE°) have also been calculated. The results suggested the dominance of hydrophilic–ionic interactions due to the great affinity of phosphate (H2PO4−) anions for hydrogen bonding with hydrophilic sites of the saccharide molecules.

The rapid simultaneous tricyclic antidepressant determination by plasma deproteinization and liquid chromatography

Background: Imipramine, desipramine, amitriptyline and nortriptyline are widely prescribed antidepressant drugs in Asia because of their low price and high efficacy. The concentrations of these drugs in plasma need to be monitored for achieving efficient therapy. A simple, rapid and practical analytical method is required. Objective: To develop a plasma deproteinization process for rapid determination of imipramine, desipramine, amitriptyline or nortriptyline in plasma using high-performance liquid chromatography (HPLC). Methods: A deproteinizing agent, with an acceptable accuracy and sensitivity, to precipitate plasma protein containing imipramine, desipramine, amitriptyline and nortriptyline was investigated along with the HPLC condition for resolving each of these compounds. The developed method was verified by performing a bio-analytical method validation, and by analyzing plasma samples from volunteers who received imipramine or amitriptyline. Results: Using clomipramine as an internal standard, the concentrations of imipramine, desipramine, amitriptyline and nortriptyline in plasma could easily be determined by precipitating plasma protein with acetonitrile and concentrated aqueous potassium phosphate solution prior to HPLC analysis. The mobile phase comprised of acetonitrile and 70 mM phosphate buffer (pH 6.1) (60/40 v/v). A separation was achieved on a C 18 column, and the effluent was measured by UV absorption at 251 nm or by EC detection at +1.0 V of glassy carbon against silver/ silver chloride reference electrode. The chromatographic separation was excellent, without interference from endogenous plasma constituents. All compounds were resolved in a run time of 12 minutes. The method was suitable for quantifying drug concentrations in the ranges of 40-900 ng/ml for UV detection or 4-900 ng/mL for EC detection. The relative standard intra-day and inter-day deviations for each compound in the plasma were less than 8%. The percentage of bias was within ±4% which confirmed the accuracy of the method. The method proved to be efficient and practical for determining the plasma concentrations of each compound, following the administration of imipramine or amitriptyline to volunteers. Conclusion: This developed method is very simple, rapid and inexpensive and is practical for routine therapeutic drug monitoring and forensic toxicological screening.

Identification of naphthoquinonic and anthraquinonic dyes via sequential potential steps applied to the voltammetry of microparticles methodology

An electrochemical method for identifying anthraquinonic, naphthoquinonic, and related dyes in microsamples is reported. This method is based on the sequential application of oxidative and reductive constant-potential polarization steps coupled with the record of square wave voltammograms to solid microsamples of dyes in contact with aqueous electrolytes. As a result, oxidized/reduced products form a layer on the lateral faces of the dye crystals as suggested by attenuated total reflectance-Fourier transform infrared spectroscopy and atomic force microscopy data. This methodology is applied for characterizing alizarin, purpurin, and natural dyes aloe, cochineal red, madder lake, kermes, shellac, and henna attached to paraffin-impregnated graphite electrodes in contact with aqueous potassium phosphate buffer.

Investigation of folic acid stability in fortified instant noodles by use of capillary electrophoresis and reversed-phase high performance liquid chromatography

A single enzyme treatment with α-amylase, prior to the quantification of added folic acid (FA) in fortified instant fried Asian noodles with analysis performed by capillary zone electrophoresis (CZE) and reversed-phase high performance liquid chromatography (RP-HPLC) with UV detection, is described. The method was validated and optimized for capillary electrophoresis (CE) with separation achieved using a 8 mM phosphate–12 mM borate run buffer with 5% MeOH at pH 9.5. FA was well separated from matrix components with nicotinic acid (NA) employed as an internal standard. In a comparative study, separation of FA was performed using HPLC with a mobile phase consisting of 27% MeOH (v/v) in aqueous potassium phosphate buffer (3.5 mM KH 2PO 4 and 3.2 mM K 2HPO 4), pH 8.5, and containing 5 mM tetrabutylammonium dihydrogen phosphate as an ion-pairing agent. For both methods, excellent results were obtained for various analytical parameters including linearity, accuracy and precision. The limit of detection was calculated to be 2.2 mg/L for CE without sample stacking and 0.10 mg/L with high performance liquid chromatography (HPLC). Sample extraction involved homogenization and enzymatic extraction with α-amylase. Results indicated that FA was stable during four main stages of instant fried noodle manufacturing (dough crumbs, cut sheets, steaming and frying).

L-Galactose replaces l-fucose in the pectic polysaccharide rhamnogalacturonan II synthesized by the l-fucose-deficient mur1 Arabidopsis mutant.

Arabidopsis thaliana mur1 is a dwarf mutant with altered cell-wall properties, in which l-fucose is partially replaced by l-galactose in the xyloglucan and glycoproteins. We found that the mur1 mutation also affects the primary structure of the pectic polysaccharide rhamnogalacturonan II (RG-II). In mur1 RG-II a non-reducing terminal 2- O-methyl l-galactosyl residue and a 3,4-linked l-galactosyl residue replace the non-reducing terminal 2- O-methyl l-fucosyl residue and the 3,4-linked l-fucosyl residue, respectively, that are present in wild-type RG-II. Furthermore, we found that a terminal non-reducing l-galactosyl residue, rather than the previously reported d-galactosyl residue, is present on the 2- O-methyl xylose-containing side chain of RG-II in both wild type and mur1 plants. Approximately 95% of the RG-II from wild type and mur1 plants is solubilized as a high-molecular-weight (>100 kDa) complex, by treating walls with aqueous potassium phosphate. The molecular mass of RG-II in this complex was reduced to 5-10 kDa by treatment with endopolygalacturonase, providing additional evidence that RG-II is covalently linked to homogalacturonan. The results of this study provide additional information on the structure of RG-II and the role of this pectic polysaccharide in the plant cell wall.

Rapid Method for Analysis of Aspirin–Butalbital in Serum Utilizing a Monolithic C18 Column

A fast and sensitive high performance liquid chromatography (HPLC) assay was developed for the simultaneous determination of aspirin–butalbital in human serum. Serum samples were treated with a solid phase extraction procedure. The analytes were separated using a mobile phase of 90:10 (v/v) 0.1 M aqueous potassium phosphate monobasic (pH 4)‐acetonitrile on a monolithic C18 column with UV detection at 220 nm. Benzoic acid was used as the internal standard (IS). The method was validated over the range of 0.5–100 µg mL−1 for each drug. The method proved to be accurate (percent bias for all calibration samples varied from −13 to 6.6%) and precise (range from 0.1% to 10%). The mean percent absolute recoveries were 104 ± 6.3 for aspirin, 92.6 ± 5.5 for butalbital and 106 ± 6.9 for the internal standard. The assay should be applicable for use in pharmacokinetic studies and routine serum monitoring of these drugs.

Comparative Study of Silylation Methods to Improve the Stability of Silicate MCM-41 in Aqueous Solutions

The stability of silicate MCM-41 in aqueous solutions for up to 12 days has been dramatically improved by silylation with hexamethyldisilazane (HMDS). Mesoporous molecular sieves including MCM-41 show promise for application as selective media for separations of large molecules such as proteins, which are important in the food and pharmaceutical industries. However, many such applications involve aqueous solutions in which MCM-41 has limited stability. Thus, hexamethyldisilazane has been used to create a hydrophobic surface coating on both flat silica and MCM-41 in order to improve their stability in aqueous solutions. This coating was shown to persist on the flat surfaces after aging in water for up to 7 days, using contact angle measurements and atomic force microscopy, unlike a coating applied using trichloromethylsilane which was removed by water. The HMDS-coated MCM-41 showed much greater structural stability than uncoated MCM-41 in both water and an aqueous potassium phosphate buffer solution of pH 6 for extended periods.

Automated determination of amisulpride by liquid chromatography with column switching and spectrophotometric detection

A fully automated chromatographic method including on-line blood serum or plasma clean-up, isocratic high-performance liquid chromatography (HPLC) and spectrophotometric detection was developed for quantitative analysis of the new antipsychotic drug amisulpride. After injection of serum or plasma onto the HPLC system and clean-up on a pre-column (10×4.0 mm I.D.) filled with Silica CN 20 μm (pore size 10 nm) by an eluent consisting of 8% acetonitrile in deionized water, the chromatographic separation was performed on Lichrospher CN (5 μm; 250×4.6 mm I.D.) by an eluent consisting of 50% acetonitrile and 50% aqueous potassium phosphate buffer (0.008 M, pH 6.4). The UV detector was set at 254 nm. The limit of quantification was about 10 μg/l. The method revealed linearity between 10 and 600 μg/l (correlation coefficients R 2>0.9996). The inter-assay reproducibility (coefficient of variation) of quality control samples was between 2.8 and 11.3%. Inaccuracy was between −0.6 and +9.1%. The performance of daily calibration standards revealed an imprecision always below 15% and maximum inaccuracy of 7.7%. The method can be applied to therapeutic drug monitoring as well as pharmacokinetic studies of amisulpride.

Automated determination of reboxetine by high-performance liquid chromatography with column-switching and ultraviolet detection

A fully automated method including column-switching and isocratic high-performance liquid chromatography (HPLC) was developed for quantitative analysis of the new antidepressant reboxetine, a noradrenaline reuptake inhibitor. After serum injection into the HPLC system and on-line sample clean-up on a silica C 8 (10×4.0 mm I.D.) clean-up column with an eluent consisting of 2.5% acetonitrile in deionized water, the chromatographic separation was performed on an analytical column (Lichrospher CN; 250×4.6 mm I.D.) with an eluent of acetonitrile–aqueous potassium phosphate buffer (0.008 M, pH 6.4) (50:50). The UV detector was set at 273 or 226 nm. The limit of quantification was about 15 ng/ml at 273 nm and about 4 ng/ml at 226 nm. The day-to-day relative standard deviation ranged between 2.7 and 6.7% with recovery rates ≥90%. Linear regression analyses revealed correlation coefficients >0.998. The method can be applied to therapeutic drug monitoring of reboxetine as well as pharmacokinetic studies.