Borate Buffer pH Research Articles

Comparison of Electrophoretic Methods for Determination of Critical Micelle Concentration of Anionic Alkylsulfate Surfactants in Water/Organic Environment

The methods for determination of critical micelle concentration of anionic surfactants using capillary electrophoresis instrumentation were compared in this work. We have focused on the determination of critical micelle concentration of homological series of n-alkyl sulfates using four different methods: the electrical current-based method, and method using migration times, retention factors and effective mobilities of n-alkylbenzenes as probe molecules. We have studied the effects of operation conditions (capillary dimensions, applied voltage) and composition of probe samples on the values of critical micelle concentration. The values of critical micelle concentration determined in water and in 25 mmol L−1 borate buffer pH 8.5 without and with addition of 20% (v/v) of acetonitrile ranged from 60 mmol L−1 for sodium nonyl sulfate to 6.1 mmol L−1 for sodium tridecyl sulfate, with higher values for electrolyte containing acetonitrile. The concentration and solvent of probe molecules have significant effect on the determined value of critical micelle concentration. We have studied in detail critical micelle concentration of sodium dodecyl sulfate in mixtures with low concentration of acetonitrile up to the 6% (v/v). In this region, higher uncertainty of determination of critical micelle concentration was experienced.

Spectrophotometric method for determination of Glucosamine Sulphate in dosage forms by derivatization using Quality by Design approach

A Quality by Design approach was used to develop a sensitive spectrophotometric method for determination of glucosamine Sulphate in pharmaceutical dosage forms and optimize a derivatization reaction of glucosamine with o-phthalaldhyde. This strategy was focused on derivatization process understanding and analytical method development and validation. Both of them were evaluated by applying risk assessment and Design Space tools. The scouting step was carried out by analyzing different derivatizing agents, type of buffers, pH of buffers, and time of reaction. Five critical process parameters (CPPs) were selected related to, pH of borate buffer, volume of 2-mercaptoethanol (ME), volume of o-phthalaldhyde (OPA), and the time of reaction. The effect of different levels of CPPs on critical quality attributes (CQAs) (the absorbance of derivative) was evaluated in the screening design using fractional factorial design. Using response surface methodology and contour plots the optimum values of the selected factors were determined and the design space of the method was defined. Finally, control strategy was designed and the method was validated and applied to a real sample of glucosamine dosage forms using the optimum derivatization conditions of the reaction; pH of borate buffer 10.5, concentration of buffer 0.05M, Time of reaction 10.7 minutes, volume of ME 100μL, and volume of OPA 5.1mL at room temperature. The results of the present study clearly shown that the developed method was sensitive relative to the other published spectrophotometric and HPLC methods with identification of the most significant factors affecting the derivatization reaction.

Optimization of a Precolumn OPA Derivatization HPLC Assay for Monitoring of l-Asparagine Depletion in Serum during l-Asparaginase Therapy.

A method for monitoring l-asparagine (ASN) depletion in patients' serum using reversed-phase high-performance liquid chromatography with precolumn o-phthalaldehyde and ethanethiol (ET) derivatization is described. In order to improve the signal and stability of analytes, several important factors including precipitant reagent, derivatization conditions and detection wavelengths were optimized. The recovery of the analytes in biological matrix was the highest when 4% sulfosalicylic acid (1:1, v/v) was used as a precipitant reagent. Optimal fluorescence detection parameters were determined as λex = 340 nm and λem = 444 nm for maximal signal. The signal of analytes was the highest when the reagent ET and borate buffer of pH 9.9 were used in the derivatization solution. And the corresponding derivative products were stable up to 19 h. The validated method had been successfully applied to monitor ASN depletion and l-aspartic acid, l-glutamine, l-glutamic acid levels in pediatric patients during l-asparaginase therapy.

Separation of Nucleobases Using High‐performance Liquid Chromatography Coupled with Voltammetric Scanning

AbstractIn this paper, a method based on chromatographic separation of analytes and their quantification using on‐line cyclic voltammetry is reported. The method based on high performance liquid chromatography on reverse phase column was optimized using free nucleobases‐guanine, adenine, thymine, and cytosine. The optimal separation of nucleobases was detected when using 0.05 M borate buffer (pH 9.0) as the mobile phase, at isocratic flow rate 1 mL min−1, and at separation column temperature of 30 °C. The accurate timing of the cyclic voltammetry enabled us to quantify the concentrations of individual nucleobases by oxidation on glassy carbon electrode.

Reactivity differences of O‐aryl O‐(4‐nitrophenyl) thionocarbonates versus their homolog carbonates: Micellar catalysis in hydrolysis reactions

AbstractThe alkaline hydrolysis reaction of O‐(4‐cyanophenyl), O‐(4‐methylphenyl), and phenyl O‐(4‐nitrophenyl) thionocarbonates (1, 2, and 3, respectively) and O‐(4‐cyanophenyl) and phenyl O‐(4‐nitrophenyl) carbonates (4 and 5, respectively) has been spectrophotometrically studied in aqueous borate buffer media, in the presence of the cationic surfactant CTAB. The pseudophase model successfully explained the results obtained, in the presence of this cationic micelle, and various kinetic parameters were determined. Results show that the catalytic efficiency increases in carbonates and thionocarbonates. In fact, a catalytic efficiency ( ) of 485‐fold was found in the hydrolysis reaction of thionocarbonate 1, while in the carbonate homolog 4, the effect was of 146‐fold. In addition, we found that at the same experimental conditions (Borate buffer pH = 9.0 and 25°C), an increase in the concentration of the buffer led to a decrease of the hydrolysis rate.

Regulation of Hydrogen Sulfide Levels by Cannabinoids in the Bovine Isolated Retina

Both endocannabinoids and hydrogen sulfide (H2S) have been reported to exert neuroprotective actions in neural tissues (Biermann et al., Mol Vis. 2011;17:1275–86; Nucci et al., Invest Ophthalmol Vis Sci. 2007;48(7):2997–3004). It remains to be determined if these modulators can interact with each other and/or share a common pathway in their neuroprotective actions.PurposeThe aim of the present study was, therefore, to investigate the pharmacological actions of endocannabinoids on the biosynthesis of H2S in isolated bovine neural retina.MethodsIsolated bovine retinae were homogenized and exposed to different concentrations of methanandamide (1 nM – 10 uM) and 2‐arachidonyl glycerol (2‐AG) (1 – 3 uM) for 90 minutes at 37ºC. Retinal homogenates were then incubated with ethylenediaminetetraacetic acid (EDTA) (1%), Zinc acetate (1%), and Borate buffer (pH 11) for 30 mins followed by 10‐minute incubation with N, N dimethyl p‐phenylenediamine (20 mM) and FeCl3 (300 mM). Samples were then centrifuged at 5000 g for three minutes and supernatant was assessed for H2S content using the well‐established Methylene Blue method.ResultsBoth methanandamide and 2‐AG elicited a concentration‐dependent decrease in basal H2S production in the isolated retina. For instance, methanandamide (10 μM) significantly (p <0.05) reduced basal production of H2S by 30% when compared to controls. Likewise, 2‐AG (10 μM) also elicited a 30% decrease in basal retinal H2S concentration when compared to controls.ConclusionsWe conclude that exogenously applied endocannabinoids can alter the basal production of H2S in the isolated neural retina. The observed effect of endocannabinoids on the pathway leading to H2S biosynthesis suggests that a cross‐talk exists between both neuromodulators in the retina.Support or Funding InformationSupported by NIH/NEI Research Grant 1R15EY022215‐01This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Facile and Selective Determination of Dipeptides Using 3-Methylcatechol as a Novel Fluorogenic Reagent

Selective determination of peptides in mixtures or biological samples requires specific techniques for analysis. Herein, we report 3-methylcatechol (3-MC) as a novel fluorogenic reagent for the selective determination of dipeptides by a simple fluorescence (FL) derivatization reaction. After extensive screening of 31 different catechol analogues, 3-MC was found to generate FL with peptides. The reaction was performed at 100 °C for 10 min in the presence of borate buffer (pH 7) and sodium periodate. The resulting FL intensities were measured by spectrofluorometer at excitation wavelengths of 380 nm and emission wavelengths of 500 nm. Different reaction conditions such as concentration of sodium periodate, reaction time and pH of the borate buffer were studied to determine the optimum reaction conditions. Linearity was obtained between FL intensity and peptide concentrations from 10 to 160 µM with a lower detection limit of 10 µM (S/N = 3). Dipeptides containing Ala, Phe, Leu and Val at the N-termini generated significant FL in comparison to the reagent blank (**p < 0.005, ***p < 0.0005). The reaction is simple, rapid, selective and sensitive which can be applied for the determination of the dipeptides as biomarkers or to determine enzyme activity.

Enantioselective determination of aspartate and glutamate in biological samples by ultrasonic-assisted derivatization coupled with capillary electrophoresis and linked to Alzheimer’s disease progression

A simple cyclodextrin-mediated capillary zone electrophoresis method equipped with a laser-induced fluorescence detector was developed for chiral analysis of the excitatory amino acids aspartate (Asp) and glutamate (Glu). Plasma and cerebrospinal fluid (CSF) samples were pretreated with centrifugal filter devices before analysis to remove high-molecular-weight proteins (molecular weight cut-off: 3000) and then derivatized using 10 mM 6-carboxyfluorescein N-hydroxysuccinimide ester in DMSO under sonication at 25 °C for 2 h. After the derivatization reaction, reacted samples were diluted 100-fold with 5-([4,6-dichlorotriazin-2-yl]amino)fluorescein hydrochloride (DTAF) solution and then hydrodynamically subjected to capillary electrophoresis (0.5 psi for 5 s, injection volume 8.27 nL). The separation buffer consisted of 50 mM borate buffer (pH 9.0) with 6 mM γ-CD and 0.1% polyvinylpyrrolidone, and the separation voltage was set at 20 kV. In the linearity calculations for the determination of d/l-Asp and d/l-Glu in plasma and CSF, a standard addition method was utilized to spike solutions with 0–20.0 μg mL−1l-Glu and 0–2.0 μg mL−1d-Glu and d/l-Asp to construct calibration curves. Correlation coefficients were above 0.998 for every analyte. The limits of detection (S/N = 3) for d/l-Asp and d/l-Glu standard solutions were 0.85–0.96 μg mL−1. The proposed method was applied successfully to determine d/l-Asp and d/l-Glu concentrations in the plasma and CSF samples of 26 patients with Alzheimer’s disease (AD), and the association between these concentrations and disease severity was investigated. Statistical analysis showed a moderately negative correlation (r = −0.158) between plasma l-Asp concentration and AD severity.

Determination of peptide antibiotics in animal food by capillary electrochromatography coupled with laser induced fluorescence

A rapid and sensitive method was established for the analysis of peptide antibiotics (bacitracin, polymyxin B and colistin) in animal food by capillary electrochromatography (CEC) coupled with laser induced fluorescence (LIF) using 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as fluorogenic reagent. Peptide antibiotics were derivatized by NBD-F in 50 mmol/L borate buffer (pH 7.5) for 45 min at 60℃. The fluorescence derivatives of peptide antibiotics were separated on a packed phenyl capillary column with a mobile phase consisting of acetonitrile-potassium phosphate (pH 5.0, 10 mmol/L) (55:45, v/v) at the flow rate of 0.02 mL/min. A supplementary pressure of 3.8 MPa and a separation voltage of -10 kV were applied. The limits of detection (LODs, S/N=3) were 5.0-10.0 ng/mL, which fulfilled the requirement of maximum residue limits for examined peptide antibiotics. The method was applied to detect peptide antibiotics in milk and feed stuffs. The spiked recoveries of the three peptide antibiotics were 72.9%-112.4%. The method shows some advantages on the simpler pretreatment and higher sensitivity, which can be of great benefit to the residual analysis of the veterinary drugs.

Simultaneous detection of 5-fluorocytosine and 5-fluorouracil in human cells carrying CD/5-FC suicide gene system by using capillary zone electrophoresis

A well-known suicide gene therapy approach, cytosine deaminase (CD) in combination with prodrug 5-flurocytosine (5-FC), has become an effective strategy of tumor treatment. However, there are short of simple and convenient detection methods to evaluate the efficiency of 5-FC conversion to 5-fluorouracil (5-FU) in human cells carrying various CD/5-FC systems. In this study, we developed an effective capillary zone electrophoresis (CZE) method to simultaneously measure 5-FC and 5-FU in cells carrying CD/5-FC suicide gene system. Under the condition of 60 mM borate buffer (pH 9.5) and 25 kV separation voltage with 0.5 psi × 15 s injection in 210 nm, the separation of 5-FC and 5-FU could be completely achieved within 15 min. The linearity of the calibration curve of standard 5-FC and 5-FU was in the range from 1 to 1000 μM (r2 > 0.999) and their recoveries were 98.4% and 96.0%, respectively. Due to the simple sample preparation and easy detection, this method is suitable for the study of the conversion efficiency of CD/5-FC suicide gene system. It aims to intuitively evaluate CD/5-FC systems and helps to guide the improvement of more effective CD/5-FC suicide gene systems.

Separation of amino acids and β-blockers enantiomers by capillary electrophoresis with 1-butyl-3-methylimidazolium L-prolinate [C4MIm][L-Pro] as a chiral selector

The current study is devoted to the synthesis of amino acid ionic 1-butyl-3-methylimidazolium L-prolinate [C 4 MIm][L-Pro] liquid and the investigation of its possibilities as a chiral selector for the separation of amino acids (tryptophan and tyrosine) and β-blockers (carvedilol and propranolol) enantiomers. The following factors affecting the resolution of amino acids stereoisomers under ligand exchange capillary electrophoresis were established: background electrolyte pH, concentration of chelate complex, molar ratio of metal and ligand and its nature. The enantioselectivity values of 1.25 for tryptophan enantiomers and 1.17 for tyrosine enantiomers were observed when the background electrolyte consisted of 50 mM borate buffer (pH = 12.2), 20 mM [C 4 MIm][L-Pro], and 10 mM CuSO 4 . The synergetic effect of the synthesized ionic liquid and (2-hydroxypropyl)-β-cyclodextrine when added to the background electrolyte content (20 мМ NaH 2 PO 4, pH = 2.5) was discovered during the separation of carvedilol and propranolol enantiomers. The achieved resolution for carvedilol ( R s = 1.1) and propranolol ( R s = 1.6) enantiomers allowed determining the enantiomers ratio of active ingredients in drug formulations. Keywords : ligand exchange capillary electrophoresis, amino acid ionic liquids, chiral selector, amino acids, β-blockers, synergetic effect, enantioseparation (Russian) DOI: http://dx.doi.org/10.15826/analitika.2018.22.1.004 Kolobova E.A. 1 , Kartsova L.A. 2 , Alopina E.V. 2 , Smirnova N.A. 2 1 The Nikiforov Russian Center of Emergency and Radiation Medicine, 54 Optikov st., St. Petersburg, 199034, Russian Federation 2 Saint-Petersburg State University, Institute of Chemistry, 26 Universitetskii prospect, St. Petersburg, Petergof, 198504, Russian Federation

Integrated quality by design (QbD) and design of experiments (DoE) approach for UFLC determination of telaprevir in rat serum

ABSTRACTAn ultrafast liquid chromatographic bioanalytical method was developed and validated for the determination of telaprevir in Wistar albino rat serum. Principles of quality by design (QbD) were implemented for enhancing the bioanalytical liquid–liquid extraction of telaprevir from rat serum. A Box–Behnken design was utilized in the studies by selecting extraction time, centrifugation speed, and vortex time as the critical method variables for evaluating their effect on the critical analytical attribute, i.e., %recovery of telaprevir. Chromatographic separation was achieved within a run time of 10 min using a C-18 column and mobile phase comprising of methanol:borate buffer of pH 9 (90:10 v/v) flowing at 1.2 mL/min. Photodiode array detection was performed at 270 nm. Results of validation studies were satisfactory. The method was linear over a concentration of 25–10,000 ng/mL. Limit of detection for the developed method was 10 ng/mL. Further, design of experiments (DoE) used for inter-day accuracy and precision study suggested superior method reliability. This integrated QbD- and DoE-based approach ensured the development of a validated and reliable analytical method for optimum bioanalysis of telaprevir in biological matrix.

Covalent linking peptide to hydrothermally reduced graphene oxide for ultrasensitive detection of matrix metalloproteinase 9

Exact assay of matrix metalloproteinase 9 (MMP9) has attracted considerable attentions for the clinical diagnosis of disease in early stage. In this report, we covalently engineer a fluorescein isothiocyanate-labeled peptide (Pep-FITC) linker containing the specific cleavage substrate of MMP9 onto the surface of hydrothermally reduced nano-graphene oxide (nrGO) to develop a FRET-based nrGO-Pep-FITC nanoprobe for ultrasensitive detection of MMP9. Upon cleavage of the Pep-FITC at the amide bond between Ser and Leu by MMP9, FITC was separated from nrGO, and fluorescence recovery of FITC was proportional to the MMP9 concentration within 0.01–0.06 nM and 0.06–0.15 nM ranges, respectively, in an aqueous solution, exhibiting 0.83 pM of detection limit. This nanoprobe is stable under borate buffer (pH = 7.4) with bovine serum albumin or 0.1% surfactant Triton 100 or Tween 20, and has good specificity for MMP9 detection, which is meaningful for MMP9-related clinical and bioanalytical applications.

Polyoxometalate-based catalysts for photocatalytic, chemical catalytic and electrocatalytic water oxidation

Complex [Fe11 (H2O)14(OH)2(W3O10)2(α-SbW9O33)6]27−(2) has been studied independently under photocatalytic or chemical catalytic or electrocatalytic conditions by our group. (1) Under the optimal photocatalytic conditions (photoirradiation at λ = 420 nm, [Ru(bpy)3](ClO4)2 as the photosensor, Na2S2O8 as the oxidant in borate buffer (pH = 10.0)], the turnover number (TON) can reach as high as 1815, the initial quantum yield and the initial turnover frequency (TOF) for the first 60 s was 47% and 6.3 s−1, respectively. (2) We report herein that 2 are highly active homogeneous water oxidation catalysts when [Ru(bpy)3]3+ is used as the terminal oxidant, with a turnover number (TON) of higher than 78. (3) The current densities achieved during cyclic voltammetry (CV) show that 2 exhibit no electrocatalytic activity at pH 10.0. This study discusses the catalytic behaviors and mechanism of 2 in different experimental conditions (driving forces) for water oxidation.

Dynamic Kinetic Resolution of Ethyl 1,2,3,4‐Tetrahydro‐β‐carboline‐1‐carboxylate: Use of Different Hydrolases for Stereocomplementary Processes

Both enantiomers of 1,2,3,4‐tetrahydro‐β‐carboline‐1‐carboxylic acid have been prepared by dynamic kinetic resolution of the corresponding ethyl ester (±)‐1. CAL‐B‐catalysed hydrolysis of (±)‐1·HCl in NH4OAc buffer (pH 8.0, 30 °C) provided amino acid (R)‐2·HCl with 98 % ee and 90 % yield in 20 min. The hydrolysis with Alcalase in borate buffer (pH 8.0, 30 °C) showed S selectivity and the product (S)‐2·HCl was obtained with 60 % ee and 66 % yield in 45 h. The absolute configuration of (S)‐2 was determined by TDDFT electronic circular dichroism and optical rotation calculations.

Microwave assisted synthesis of metal-organic framework MIL-101 nanocrystals as sorbent and pseudostationary phase in capillary electrophoresis for the separation of anthraquinones in environmental water samples.

In this work, a CE method was developed to separate five anthraquinones: aloe-emodin, rhein, emodin, chrysophanol, and physcion. The CE method used a nano-sized metal organic framework MIL-101 (nMIL-101) as pseudostationary phase (PSP) and sorbent for dispersed particle extraction (DPE). The nMIL-101 was synthesized by microwave technique and was characterized by UV-vis, TEM, Zeta potential, X-ray diffraction spectrometry and micropore physisorption. In this method, anthraquinones were adsorbed by nMIL-101 of a fast kinetics within 10 min and then separated by CE. The CE conditions were optimized considering time, pH, buffer ionic strength, and nanoparticles concentration. The optimal CE condition is using 20 mM sodium borate buffer (pH 9.1) containing 15% methanol (v/v) and 400 mg/L nMIL-101 as additives within 8 min. The LODs varied from 24 to 57 μg/L, which were lower than those previously reported. Our method has been successfully applied to determine trace anthraquinones in environmental water samples.

Substituted benzotriazoles as inhibitors of copper corrosion in borate buffer solutions

The adsorption of substituted 1,2,3-benzotriazoles (R-BTAs) onto copper is measured via ellipsometry in a pure borate buffer (pH 7.4) and satisfactorily described by Temkin’s isotherm. The adsorption free energy (−ΔG a 0 ) values of these azoles are determined. The (−ΔG a 0 ) values are found to rise as their hydrophobicity, characterized by the logarithm of the partition coefficient of a substituted BTA in a model octanol–water system (logP), grows. The minimum concentration sufficient for the spontaneous passivation of copper (C min) and a shift in the potential of local copper depassivation with chlorides (E pt) after an azole is added to the solution (i.e., ΔE = E pt in − E pt backgr characterizing the ability of its adsorption to stabilize passivation) are determined in the same solution containing a corrosion additive (0.01М NaCl) for each azole under study. Both criteria of the passivating properties of azoles (logC min and ΔE) are shown to correlate linearly with logP, testifying to the role played by surface activity of this family of organic inhibitors in protecting copper in an aqueous solution.

Application of capillary electrophoresis to the separation of rhenium complex of 1,2,3-trihydroxybenzene

A capillary zone electrophoretic method has been developed for a separation of a reaction mixture of a rhenium complex. The rhenium complex was synthesized in a reaction of a rhenium precursor and 1,2,3-trihydroxybenzene in acetonitrile with triethylamine addition. The capillary electrophoretic method has been used for the separation in borate and phosphate buffer (pH 6.30–11.80). All components in the reaction mixture (unreacted precursor, ligand, and final rhenium complex) have been determined by capillary zone electrophoresis with UV–Vis detection in an aqueous running electrolyte within 10 min. Dependencies of effective electrophoretic ion mobility on the pH value have been determined for the ligand, unreacted precursor, and final complex in both electrolytes.

Stacking-cyclodextrin-microchip electrokinetic chromatographic determination of gabapentinoid drugs in pharmaceutical and biological matrices

A facile, rapid, and highly sensitive microchip-based electrokinetic chromatographic method was developed for the simultaneous analysis of two gabapentinoid drugs, gabapentin (GPN) and pregabalin (PGN). Both drugs were first reacted with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) via nucleophilic substitution reactions to yield highly fluorescent products with λex/em 470/540nm. Analyses of both fluorescently labeled compounds were achieved within 200s in a poly(methyl methacrylate) (PMMA) microchip with a 30mm separation channel. Optimum separation was achieved using a borate buffer (pH 9.0) solution containing methylcellulose and β-cyclodextrin (β-CD) as buffer additives. Methylcellulose acted as a dynamic coating to prevent adsorption of the studied compounds on the inner surfaces of the microchannels, while β-CD acted as a pseudo-stationary phase to improve the separation efficiency between the labeled drugs with high resolution (Rs>7). The fluorescence intensities of the labeled drugs were measured using a light emitting diode-induced fluorescence detector at 540nm after excitation at 470nm. The sensitivity of the method was enhanced 14- and 17-fold for PGN and GPN, respectively by field-amplified stacking relative to traditional pinched injection so that it could quantify 10ngmL−1 for both analytes, with a detection limit lower than 3ngmL−1. The developed method was efficiently applied to analyze PGN and GPN in their pharmaceutical dosage forms and in biological fluids. The extraction recoveries of the studied drugs from plasma and urine samples were more than 89% with%RSD values lower than 6.2.

Online stacking of carboxylated magnetite core-shell nanoparticles in capillary electrophoresis.

The stacking effect on carboxylated magnetite core-shell nanoparticles using sodium borate buffer pH 9.5 as the background electrolyte is presented. The ionic strength of the background electrolyte ranged from 5 to 100mM, and the ionic strength of a sample zone ranged from 5 to 100mM. Moreover, water was used as the sample dispersant. Both stacking and de-stacking effects were observed when conductivities of the sample zone and the background electrolyte differed. An explanation of carboxylated magnetic core-shell nanoparticles behavior was suggested based on the Derjaguin-Landau-Verwey-Overbeek theory supposing that the aggregation point is defined by the energetic barrier as the sum of energies given by electrostatic interactions and Van der Waals interactions. Moreover, the stacking conditions were applied for the evaluation of the lowest detectable dilution of magnetic nanoparticles. The carboxylated magnetic nanoparticles were dispersed in 10mM borate/NaOH pH 9.5 and injected for 60s to the background electrolyte composed of 100mM borate/NaOH pH 9.5 that allowed the detection of 100-fold diluted nanoparticles.