Open-tubular Capillary Electrochromatography Research Articles

Enantioselective open-tubular capillary electrochromatography using cyclodextrin-modified gold nanoparticles as stationary phase

Enantioselective open-tubular CEC (OTCEC) with thiolated β-CD modified gold nanoparticles (CD-GNPs) as stationary phase was developed. The enantioselective OT capillary column was fabricated by electrostatic assembly of poly(diallydimethylammonium chloride) (PDDA) followed by self-adsorption of negatively charged CD-GNPs. The enantioselective capillary column has a steady EOF mobility over a wide pH range of 3.0 to 9.2 (RSD 4.8%), and is quite stable over 240 min with very good column to column reproducibility. Efficient enantioseparation of the presented method was demonstrated by analyzing three drug enantiomers. Our results show that the column exhibits good run-to-run repeatability for enantioseparations and can maintain the enantioselectivity for more than 1 month if the column was stored in CD-GNPs solution at 4 °C.

Polydopamine as an adhesive coating for open tubular capillary electrochromatography

Polydopamine (PolyD) coating was used as an adhesive layer in the preparation of biological stationary phases for open tubular capillary electrochromatography (OT-CEC). The influence of coating solution freshness, coating time, temperature and dopamine hydrochloride concentration on the PolyD layer formation was studied. The performance of the polyD coating was monitored by measuring the electro-osmotic flow in coated capillaries. Following polyD coating of the capillary, secondary layer material (e.g. cell membrane solutions, phospholipid mixtures or mitochondria) was inserted into the capillary for at least 1 h. The performance of these double-coated capillaries (a polyD layer+a biological material layer) was compared with capillaries containing the respective biological material directly attached to the capillary wall. The study reveals that the presence of polyD layer in fused silica capillaries improves the performance of lipid and membrane fragment coatings in capillaries. At the same time, the thickness of the polyD layer does not have marked impact on the secondary coatings. Analysis with test analytes demonstrated that double-coated capillaries can be applied to study membrane-drug interactions.

A novel amphipathic block copolymer coating forming micelle-like aggregates for separation of steroids in open tubular capillary electrochromatography

A new amphipathic block copolymer, poly(tert-butyl acrylate)127-block-poly(glycidyl methacrylate)86, was developed for the coating in open tubular capillary electrochromatography. The self-assembly characters of the coating, which could form micelle-like aggregates under proper conditions, were observed by atomic force microscopy. Compared with bare capillary, this coating could act as surfactant and lead to improve the separation of steroids. In addition, the influence of pH, buffer concentration and organic solvents on the separation was investigated. The best separation of the three model steroid analytes could be achieved using 20.0mM borate buffer at pH 10.5. For covalent bonding, the coating showed good repeatability and stability with RSD of uEOF less than 3.3%. Then, this proposed method was well validated with good linearity (≥0.999), recovery (91.0–94.0%) and repeatability, and was successfully used for separation of steroids in spiked serum samples, which indicated that this new OT-CEC method could provide a potential tool to determine steroids in real biological system without interference.

Studying the interaction between triazines and humic substances—A new approach using open tubular capillary eletrochromatography

The strength of the interaction between a pesticide and the soil organic matter is a key parameter to assess the risk of it reaching to groundwater with potentially harmful effects to human health. In this work, a new approach that allows measuring such interactions in a few minutes using a purified fraction of the soil organic matter (humic substances) is detailed. The strength of sorption is assessed via the normalised difference of elution (retention factor, k′) between the chemical of interest and a neutral marker transported via electroosmotic flow through an open tubular column supporting the immobilised humic substances (open tubular capillary electrochromatography). The immobilisation was achieved by incubating a capillary, pre-coated with a monolayer of humic acid, with an acidic solution of humic substances. This induces the formation of a supramolecular structure of humic substances as it occurs in soils. This aggregate can easily be removed using alkaline solutions, and a new structure assembled using other humic substances (HS) or different incubations conditions. The whole procedure takes 2h. This approach has been tested using five triazines and three types of humic substances. The order of the strength of sorption of the triazines as expected from relevant literature and the relative standard deviation of k′ was between 1 and 6%. Good repeatability was also observed after long period of wash, between re-coating and repeating of the full coating with a new capillary.

Cover Picture: Electrophoresis 23‐24'2010

AbstractIssue no. 23–24 is a regular issue with an “Emphasis on Proteomics” and comprises 20 contributions assembled into 5 distinct parts. Part I is on innovation in proteomics and has 9 research articles describing novel proteomics methodologies and applications. Part II is on innovative assays and applications, and contains 5 full research articles on in‐capillary CE assay, electrophoretically mediated microanalysis, genotyping, SNP, STR and CE of polyphenols. Two research articles on preconcentration of peptides and melamine are included in Part III. Part IV has two articles on enantioseparations of amino acids by ligand exchange CE and on sensitized phosphorescence in the chiral separation of bupropion by CE. Part V is on open tubular CEC with 2 articles describing novel wall coated stationary phases.Featured articles include:Generation and characterization of a specific polyclonal antibody against the mouse serotonin receptor 1A: A state of the art‐recommendation how to characterize antibody specificity (10.1002/elps.201000374))Electrophoretically‐mediated microanalysis assay for sirtuin enzymes (10.1002/elps.201000336))

Polyacrylamide grafted on multi‐walled carbon nanotubes for open‐tubular capillary electrochromatography: Comparison with silica hydride and polyacrylate phase matrices

A new nanoparticle-bound polymer stationary phase was prepared by in situ polymerization of methacrylamide (MAA), bis-acrylamide crosslinker, and carboxylated multi-walled carbon nanotubes (multi-walled CNTs; MWNTs), using the abundant double bonds in the cyclopentadienyl rings in MWNT structure, on a silanized capillary. Each intermediate capillary between the synthesis steps was characterized by SEM, by ATR-IR, and by EOF measurements varying the pH, concentration, and volumetric ratios of ACN in running buffers. The resulting EOF profile was comparable to those of two other capillaries with different phase matrices, silica hydride and polybutyl methacrylate (BMA) phases. With the complex functionality of MWNTs on the hydrophilic polyacrylamide network, the MAA-CNT capillary was capable of separating diverse samples with a wide range of polarity and dissociation properties using open-tubular CEC. Besides optimizing CEC conditions, the migration times of samples were analyzed with respect to velocity and retention factors to evaluate electrophoretic and chromatographic contributions to the CEC mechanism. The migration rates of benzoic acids were determined by the electrophoretic mobilities of the various phenolate ions, while phenolic aldehydes and ketones were additionally influenced by chromatographic interactions, such as π-π, electrostatic effects, hydrogen bonding, and hydrophobic interactions. The retention factors were greater for flavonoids, which are polyphenolic, than for simple phenols, but were smaller than those obtained from the hydrophobic BMA-CNT column. A complete well-resolved separation of the cationic forms of tetracyclines was acheived either by electrophoresis or by chromatography in the MAA-CNT capillary, but not in the BMA-CNT and silica hydride-CNT capillaries.

Carboxymethylchitosan covalently modified capillary column for open tubular capillary electrochromatography of basic proteins and opium alkaloids

A novel open tubular (OT) column covalently modified with hydrophilic polysaccharide, carboxymethylchitosan (CMC) as stationary phase has been developed, and employed for the separations of basic proteins and opium alkaloids by capillary electrochromatography (CEC). With the procedures including the silanization of 3-aminopropyltrimethoxysilane (APTS) and the combination of glutaraldehyde with amino-silylated silica surface and CMC, CMC was covalently bonded on the capillary inner wall and exhibited a remarkable tolerance and chemical stability against 0.1 mol/L HCl, 0.1 mol/L NaOH or some organic solvents. By varying the pH values of running buffer, a cathodic or anodic EOF could be gained in CMC modified column. With anodic EOF mode (pH < 4.3), favorable separations of basic proteins (trypsin, ribonuclease A, lysozyme and cytochrome C) were successfully achieved with high column efficiencies ranging from 97,000 to 182,000 plates/m, and the undesired adsorptions of basic proteins on the inter-wall of capillary could be avoided. Good repeatability was gained with RSD of the migration time less than 1.3% for run-to-run ( n = 5) and less than 3.2% for day-to-day ( n = 3), RSD of peak area was less than 5.6% for run-to-run ( n = 5) and less than 8.8% for day-to-day ( n = 3). With cathodic EOF mode (pH > 4.3), four opium alkaloids were also baseline separated in phosphate buffer (50 mmol/L, pH 6.0) with column efficiencies ranging from 92,000 to 132,000 plates/m. CMC-bonded OT capillary column might be used as an alternative medium for the further analysis of basic proteins and alkaline analytes.

The role of methacrylate polymerized as porous‐layered and nanoparticle‐bound phases for open‐tubular capillary electrochromatography: Substitution of a charged monomer for a bulk monomer

The bulk monomer, butyl methacrylate (BMA), was copolymerized with an ionizable monomer (mono-(2-(methacryloyloxy)ethyl) succinate (MES)) and carbon nanotubes (CNTs) by ethylene dimethacrylate (EDMA) crosslinking to form the porous-layered and nanoparticle-bound stationary phases for open-tubular CEC. Here, two new phases were synthesized to check the role of BMA on the BMA-MES and BMA-CNT phases and the suitability of the MES monomer for concurrently acting as a bulk monomer. One phase, MES-EDMA, was simply composed of MES monomer and EDMA crosslinker and exhibited a phase construction of molecular layers, in contrast to the polymeric phases of BMA-MES. Another phase studied was MES-CNT, which SEM images showed that MES could be a good bulk monomer for a CNT-polyacrylate composite phase with embedded CNTs. For all the modified capillaries, the EOF profiles observed in phosphate buffers between pH 3.6 and 9.6 were comparable with each other and conformed to their corresponding SEM images. The residual silanols retained their influence on the EOF profiles in the MES-EDMA and BMA-MES capillaries, but diminished in the CNT-bound capillaries. In a comparison with the MES-EDMA capillary, the BMA-MES capillary afforded a stronger interaction with flavonoids and phenolic acids and still retained positive capacity factor values. Additionally, the capacity factors obtained from the BMA-CNT capillary were higher than those from the MES-CNT capillary, as the BMA-CNT phase had hydrophobic BMA units and a high surface contact area of bound CNTs.

Microwave-Assisted Preparation of a β-Cyclodextrin-Based Stationary Phase for Open Tubular Capillary Electrochromatography

Fluorescein isothiocyanate was used as a label to show that a 3-aminopropylmethyldimethoxysilane (KH 550)-modified capillary column was prepared by microwave irradiation. A bromoacetate-substituted β-cyclodextrin (Br-β-CD) was successfully bound to the KH 550-modified column as a chiral stationary phase for open tubular capillary electrochromatography. Compared with conventional synthesis, the microwave-assisted process significantly decreased the preparation time of the stationary phase from 16 h to 40 min. Baseline chiral separation of 1-phenyl-1,2-ethanediol was achieved using the Br-β-CD modified column.

Triamine‐bonded stationary phase for open tubular capillary electrochromatography

A multi-functional separation column modified with 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane was developed for open tubular capillary electrochromatography. This functional hydrophilic triamine-bonded open tubular column could generate both anodic and cathodic EOF. When the pH of the running buffer was below 5.3 (30% 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane, v/v), the anodic EOF was exhibited, which greatly prevented the undesired adsorptions of basic proteins on the capillary inner wall. Favorable separation of four basic proteins (viz. trypsin, ribonuclease A, lysozyme and cytochrome c) was successfully achieved at pH 3.5 of 10 mmol/L phosphate buffer. The column efficiencies of proteins were in the range from 87,000 to 110,000 plates/m, and the RSD values for migration time of four proteins were less than 1.2% (run-to-run, n=5). The ionic analytes were also separated efficiently in the co-electroosmotic mode. The average efficiencies ranged from 81,000 to 190,000 plates/m for seven aromatic acids and 186,000-245,000 plates/m for four nucleoside monophosphates, respectively, and good capillary column repeatability was gained with RSD of the migration time not more than 3.0%. The triamine-bonded open tubular capillary column is favorable to be an alternative functional medium for the further analysis of basic proteins and anionic analytes.

Permanent gold nanoparticle coatings on polyelectrolyte multilayer modified capillaries for open-tubular capillary electrochromatography

This paper reports on a new strategy to coat fused silica capillaries through ionic adsorption of gold nanoparticles (AuNPs) on a polyelectrolyte multilayer (PEM) modified capillary wall. The coating was constructed in situ by alternating rinses with positively charged poly(diallydimethylammonium chloride), negatively charged poly(sodium-4-styrenesulfonate), and positively charged AuNPs. After self-assembly of n-octadecanethiol onto the surface of AuNPs, the modified capillary was investigated as a new medium for the separation of neutral analytes and proteins in open-tubular capillary electrochromatography (OT-CEC). The surface coverage of the capillary wall was increased using the high density of AuNPs which were dynamically capped with 4-dimethylaminopyridine (DMAP). The chromatographic performance of the column coated with positively charged AuNPs was remarkably improved compared with a column modified with negatively charged AuNPs. The coating was robust over more than 810 runs in this study and also showed high stability against 0.01 M NaOH, 0.01 M HCl, and electrolyte concentrations up to 70 mM. The run-to-run, day-to-day, and capillary-to-capillary reproducibilities of electroosmotic flow were satisfying with relative standard deviation values of less than 1% in all cases. The AuNP-coated PEM modified capillary column not only showed good performance for neutral analytes but also was suitable for the analysis of both basic and acidic proteins.

Potential role of gold nanoparticles for improved analytical methods: an introduction to characterizations and applications

Nanoparticle-based material is a revolutionary scientific and engineering venture that will invariably impact the existing analytical separation and preconcentration for a variety of analytes. Nanoparticles can be regarded as a hybrid between small molecule and bulk material. A material on the nanoscale produces considerable changes on various properties, making them size- and shape-dependent. Gold nanoparticles (Au NPs), one of the wide variety of core materials available, coupled with tunable surface properties in the form of inorganic or inorganic-organic hybrid have been reported as an excellent platform for a broad range of analytical methods. This review aims to introduce the basic principles, examples, and descriptions of methods for the characterization of Au NPs by using chromatography, electrophoresis, and self-assembly strategies for separation science. Some of the latest important applications of using Au NPs as stationary phases toward open-tubular capillary electrochromatography, gas chromatography, and liquid chromatography as well as roles of run buffer additive to enhance separation and preconcentration in the field of chromatographic, electrophoretic and in chip-based systems are reviewed. Additionally, we review Au NPs-assisted state-of-the-art techniques involving the use of micellar electrokinetic chromatography, an online diode array detector, solid-phase extraction, and mass spectrometry for the preconcentration of some chemical compounds and biomolecules.

Lysine-based zwitterionic molecular micelle for simultaneous separation of acidic and basic proteins using open tubular capillary electrochromatography.

In this work, a zwitterionic molecular micelle, poly-epsilon-sodium-undecanoyl lysinate (poly-epsilon-SUK), was synthesized and employed as a coating in open tubular capillary electrochromatography (OT-CEC) for protein separation. The zwitterionic poly-epsilon-SUK containing both carboxylic acid and amine groups can be either protonated or deprotonated depending on the pH of the background electrolyte; therefore, either an overall positively or negatively charged coating can be achieved. This zwitterionic coating allows protein separations in either normal or reverse polarity mode depending on the pH of the background electrolyte. The protein mixtures contained four basic proteins (lysozyme, cytochrome c, alpha-chymotrypsinogen A, and ribonuclease A) and six acidic proteins (myoglobin, deoxyribonuclease I, beta-lactoglobulin A, beta-lactoglobulin B, alpha-lactalbumin, and albumin). Protein separations were optimized specifically for acidic (reverse mode) and basic (normal mode) pH values. Varying the polymer thickness by changing the polymer and salt concentration had a great influence on protein resolution, while nearly all peaks were also baseline resolved in both modes using the optimized poly-epsilon-SUK coating concentration of 0.4% (w/v). Proteins in human sera were separated under optimized acidic and basic conditions in order to demonstrate the general utility of this coating. Nanoscale characterizations of the poly-epsilon-SUK micellar coatings on silicon surfaces were accomplished using atomic force microscopy (AFM) to gain insight into the morphology and thickness of the zwitterionic coating. The thickness of the polymer coating ranged from 0.9 to 2.4 nm based on local measurements using nanoshaving, an AFM-based method of nanolithography.

New capillary coatings in open tubular CEC as models for biological membranes

Novel stationary phases in open tubular CEC were investigated. The coating procedure was fast and simple. The coating material contained membrane suspension of different neuronal cell lines. The performance and stability of three cell lines: human neuroblastoma SH-SY5Y, murine microglia Bv-2 and human glioma U87-MG cells were studied. The coating solution was expected to contain both membrane proteins and membrane lipids. The presence of membrane proteins was tested by Western blotting and the presence of phospholipids by the analysis of phosphorus content. The stability of the coating was estimated by monitoring the mobility of EOF over successive runs. The effects of pH, storage time and temperature on the coating stability were also studied. The results showed that the cell membrane-based coating was stable over pH range of 6.5-8.5. Coatings derived from different cells yielded similar stability and EOF mobility. Capillary coated with a membrane solution was stable over 3-day period. The same coating solution could be used for 3 weeks.

Succinyl methacrylate polymerized in porous-layered phases for open-tubular capillary electrochromatography: Comparison with silica hydride monolayered phases

A polymer phase, which was constructed with butyl methacrylate (BMA), an ionizable monomer (mono-(2-(methacryloyloxy)ethyl) succinate (MES)), and a crosslinking agent (ethylene dimethacrylate), was first formed in a porous-layered open-tubular (PLOT) capillary. The PLOT capillary was characterized with SEM and electrophoretic flow as the pH level, ionic strength and addition of organic modifiers in the running buffers changed. In addition, a bare capillary and a silica hydride based capillary (SiH-MES), which bore a monolayered MES phase on it, were used to compared with the BMA-MES capillary. Besides optimizing the capillary electrochromatographic (CEC) conditions for each group of analytes, which were a mixture of nucleosides and thymine, flavonoids, and phenolic acids,comparison of the separation selectivity among analytes between the BMA-MES and SiH-MES capillaries was done according to the velocity and retention factors obtained from the CEC data. Overall, the polymeric phase formed in the PLOT mode was capable of preventing blockage of the columns and was superior to the monolayered phase bonding with the same ionizable ligands for application in CEC as well as to the bare silica phase in CE.

Open tubular capillary electrochromatography: A useful microreactor for collagen I glycation and interaction studies with low-density lipoprotein particles

Diabetes, a multifunctional disease and a major cause of morbidity and mortality in the industrialized countries, strongly associates with the development and progression of atherosclerosis. One of the consequences of high level of glucose in the blood circulation is glycation of long-lived proteins, such as collagen I, the most abundant component of the extracellular matrix (ECM) in the arterial wall. Glycation is a long-lasting process that involves the reaction between a carbonyl group of the sugar and an amino group of the protein, usually a lysine residue. This reaction generates an Amadori product that may evolve in advanced glycation end products (AGEs). AGEs, as reactive molecules, can provoke cross-linking of collagen I fibrils. Since binding of low-density lipoproteins (LDLs) to the ECM of the inner layer of the arterial wall, the intima, has been implicated to be involved in the onset of the development of an atherosclerotic plaque, collagen modifications, which can affect the affinity of native and oxidized LDL for collagen I, can promote the entrapment of LDLs in the intima and accelerate the progression of atherosclerosis. In this study, open tubular capillary electrochromatography is proposed as a new microreactor to study in situ glycation of collagen I. The kinetics of glycation was first investigated in a fused silica collagen I-coated capillary. Dimethyl sulphoxide, injected as an electroosmotic flow marker, gave information about the charge of coating. Native and oxidized LDL, and selected peptide fragments from apolipoprotein B-100, the protein covering LDL particles, were injected as marker compounds to clarify the interactions between LDLs and the glycated collagen I coating. The method proposed is simple and inexpensive, since only small amounts of collagen and LDL are required. Atomic force microscopy images complemented our studies, highlighting the difference between unmodified and glycated collagen I surfaces.

Multi-wall carbon nanotubes bonding on silica-hydride surfaces for open-tubular capillary electrochromatography

Prepared multi-wall carbon nanotube (MWNT) materials, including untreated MWNT, HNO 3-treated MWNT and HNO 3-HCl-treated MWNT were covalently attached onto a silica-hydride-modified capillary by hydrosilation, using the abundant double bonds between the pentagon carbons in the MWNT structure. These MWNT-incorporated capillaries were characterized by SEM, ATR-IR and electroosmotic flow (EOF) measurements in phosphate buffers with a pH range of 3.7–9.3 and in the mixtures of acetonitrile modifier. The untreated capillary was assumed to carry some carboxylate groups formed on the non-acid-treated MWNTs, as it had higher EOF values than the hydride capillary. As the MWNTs were treated with HNO 3 and HCl solutions, the capillaries had increasingly higher EOF values. To examine the existence of an electrochromatography mechanism in the modified capillaries, a mixture of nucleosides and thymine was probed to check the velocity factor and retention factor. In addition to the π–π interaction between the probe solutes and the MWNT immobilized stationary phases; a reversed-phase mechanism could contribute to the chromatographic retention. For acidic tetracyclines, increasing the loadability of MWNTs resulted in a high retention factor and improved the separation resolution.

Separation of tryptic peptides of native and glycated BSA using open-tubular CEC with salophene–lanthanide–Zn2+complex as stationary phase

Open-tubular CEC (OT-CEC) with a new stationary phase, salophene-lanthanide-Zn(2+) complex, has been applied to the separation of tryptic peptides of native BSA and BSA glycated by glucose and ribose. Glycation of proteins (non-enzymatic modification by sugars) significantly affects their properties and it is of great importance from a physiological point of view. Separation of tryptic peptides of glycated BSA by CZE was poor because of their strong adsorption to the bare fused silica capillary. An improved separation of tryptic peptides of both native and glycated BSA was achieved by OT-CEC in the fused silica capillary non-covalently coated with salophene-lanthanide-Zn(2+) complex, which suppressed the adsorption of peptides to the capillary and via specific interactions with some (glyco)peptides enhanced selectivity of the separation. Significant differences have been found in OT-CEC analyses of tryptic hydrolysates of native and glycated BSA. In OT-CEC-UV profile of tryptic peptides of native BSA, 44 peaks could be resolved, whereas a reduced number of 38 peaks were observed in the profile of tryptic peptides of glucose-glycated BSA and only 30 peaks were found in the case of ribose-glycated BSA. The developed OT-CEC can be potentially used for monitoring of protein glycation.

Etched succinate‐functionalized silica hydride stationary phase for open‐tubular CEC

An open-tubular (OT) CEC column was designed to anchor ionizable succinate-functionalized ligands onto a silica hydride-based stationary phase through surface etching, silanization, and hydrosilation reactions beginning from a bare fused-silica tube. The modified columns that were produced in each step were monitored by analysis of the effect of performance of EOF on the changes of pH values, concentrations, and the amount of ACN added in the running buffers. By tracking the EOF patterns between columns, the author determined that the surface composition of the final product column was a combination of silanols, silica hydrides, and succinate ligands. Furthermore, lower loading volumes of the succinate ligands prepared for the hydrosilation reaction served to complete the mixed-mode OT-CEC columns, and subsequently to carry out the separation of six phenyl alcohols. Studies on the elution order of these alcohols identified the presence of chromatographic interactions in addition to electrophoresis. Based on the employment of a solvation parameter model, these interactions likely included dispersion interactions, dipole-type interactions, and interactions arising through the polarizable electrons in the solute. The optimum buffer conditions for CEC separations of phenyl alcohols, carbonyl-substituted phenols, and a mixture of nucleosides and thymine were a phosphate buffer (50 mM, pH 10.51), a borate buffer (50 mM, pH 8.62), and a borate buffer (50 mM, pH 9.50), respectively. Overall, the hydride-based stationary phases with ionizable ligands were successfully applied to the OT-CEC separations, and these results confidently propose an ideal route to the synthesis of novel OT-CEC columns.

Open tubular CEC with novel block copolymer coatings for separation of aromatic amines

A new type of block copolymer, which was synthesized by styrene and maleic anhydride, P(MAn-alt-St)(119)-b-PSt(558), was successfully developed as the capillary coatings in open tubular CEC. It is interesting that the covalently bonded coatings are porous and the coatings can play the role of surfactants in the separation of aromatic amines when the buffer solution was composed of 30.0 mM ammonium acetate at pH 7.7 with 20% THF. Thus, successful baseline separation of five kinds of aromatic amines has been achieved. As validated by both artificially prepared solutions of aromatic amines and four real samples of commercially available permanent hair dyes, this proposed method was successfully applicable to the quantitative analysis of p-phenylenediamine (PPD) and o-phenylenediamine (OPD) ingredients in these commercial products, with a linear range between 8.3 microM and 6.0 mM, correlation coefficient above 0.990 and recovery between 83.5 and 110.9%. The detection limit obtained from calculations based on signal-to-noise ratio (S/N=3) was 4.2 microM for PPD and 6.0 microM for OPD, respectively. Furthermore, the role of the surfactants played by the block copolymer coatings has been primarily explored.