Solute adsorption on polymer-coated fused-silica capillary electrophoresis columns using selected protein and peptide standards

Suberin as a green surfactant additive for peptide analysis using capillary electrophoresis

Capillary electrophoresis is a powerful separation technique for analysis of proteins and peptides, with benefits like low consumption of reagents, solvents and sample. The separation efficiency and resolution can be deteriorated by adsorption of analytes to the inner capillary wall, though. Many methods to circumvent this obstacle have been reported, including background electrolyte addition of surfactants that aggregate as protective coatings at the wall. In this work, anionic suberin surfactant was used together with the cationic surfactant cetyltrimethylammonium bromide (CTAB) for analysis of trypsin digested lysozyme as a model sample. Suberin fatty acids were extracted from birch bark, which is a side-stream product originating from pulp and paper waste streams. Different adjustments of the solvent extraction protocol, and the method to neutralize the suberin fatty acids to obtain surface active sodium salts were evaluated regarding number of peaks observed, separation repeatability, and analysis time. The influence of background electrolyte pH was also studied. The potential of the surface-active sodium salts of suberin fatty acids as an additive enhancer in combination with CTAB is illustrated by excellent repeatability, especially at lower pH values. The number of peaks observed was also higher at lower pH, while the analysis time was shorter.

Rapid Purification of Immunoglobulin G Using a Protein A-​immobilized Monolithic Spin Column with Hydrophilic Polymers

A rapid purification method was developed for antibody production in Chinese hamster ovary (CHO) cells using a Protein A-immobilized monolithic silica spin column with hydrophilic polymers. Monolithic silica modified with copolymers of 2-hydroxyethylmethacrylate (HEMA) and glycidyl methacrylate (GMA) showed lower non-specific protein absorption than that modified with a silane reagent. The epoxy group of GMA was converted to an amino group, and Protein A was modified by the coupling reagent. The amount of immobilized Protein A was controlled by changing the ratio of GMA to HEMA and the mesopore size of monolith. A modified monolith disk was fixed to a spin column for rapid antibody purification. The linear curves (for the antibody concentrations over 10 - 300 μg/mL) had a correlation coefficient of >0.999. Our column had various analytical advantages over previously reported columns, including a shorter preparation time (<10 min) and smaller sample volumes for purification with Protein A-immobilized agarose.

Recent trends of capillary electrophoresis-mass spectrometry in proteomics research

Progress in proteomics research has led to a demand for powerful analytical tools with high separation efficiency and sensitivity for confident identification and quantification of proteins, posttranslational modifications, and protein complexes expressed in cells and tissues. This demand has significantly increased interest in capillary electrophoresis-mass spectrometry (CE-MS) in the past few years. This review provides highlights of recent advances in CE-MS for proteomics research, including a short introduction to top-down mass spectrometry and native mass spectrometry (native MS), as well as a detailed overview of CE methods. Both the potential and limitations of these methods for the analysis of proteins and peptides in synthetic and biological samples and the challenges of CE methods are discussed, along with perspectives about the future direction of CE-MS. @ 2019 Wiley Periodicals, Inc. Mass Spec Rev 00:1-16, 2019.

All-in-one solid-phase microextraction: Development of a selective solid-phase microextraction fiber assembly for the simultaneous and efficient extraction of analytes with different polarities

In the present work, for the first time, an all-in-one solid-phase microextraction technique was developed for the simultaneous and efficient extraction of analytes within a vast polarity range. A novel fiber assembly composed of two different steel components each coated with different coatings (polydimethylsiloxane and polyethylene glycol) in terms of polarity by sol-gel technology was employed for the extraction of model compounds of different polarity in a single run followed by gas chromatography with mass spectrometry. Effective parameters in the extraction step and gas chromatography with mass spectrometry analysis were optimized for all model compounds. The detection limits of the developed method for model compounds were below 0.2 ng/L. The repeatability and reproducibility of the proposed method, explained by relative standard deviation, varied between 7.22 and 9.15% and between 7.95 and 14.90 (n = 5), respectively. Results showed that, under random conditions, compared to separate extractions performed by two other differently end-coated components that had not been assembled as the final dual fiber, as two individual fibers; simultaneous, efficient and relatively selective extraction of all model compounds was obtained in a single run by the proposed all-in-one technique. Finally, the optimized procedure was applied to extraction and determination of the model compounds in spiked water samples.

Neutral hydrophilic coatings for capillary electrophoresis prepared by controlled radical polymerization

In the present study, porous silica particles as well as impervious fused-silica wafers and capillary tubes were modified with hydrophilic polymers (hydroxylated polyacrylamides and polyacrylates), using a surface-confined grafting procedure based on atom transfer radical polymerization (ATRP) which was also surface-initiated from α-bromoisobutyryl groups. Initiator immobilization was achieved by hydrosilylation of allyl alcohol on hydride silica followed by esterification of the resulting propanol-bonded surface with α-bromoisobutyryl bromide. Elemental analysis, IR and NMR spectroscopies on silica micro-particles, atomic force microscopy, ellipsometry and profilometry on fused-silica wafers, as well as CE on fused-silica tubes were used to characterize the chemically modified silica substrate at different stages. We studied the effect of monomer concentration as well as cross-linker on the ability of the polymer film to reduce electroosmosis and to prevent protein adsorption (i. e., its non-fouling capabilities) and found that the former was rather insensitive to both parameters. Surface deactivation towards adsorption was somewhat more susceptible to monomer concentration and appeared also to be favored by a low concentration of the cross-linker. The results show that hydrophilic polyacrylamide and polyacrylate coatings of controlled thickness can be prepared by ATRP under very mild polymerization conditions (aqueous solvent, room temperature and short reaction times) and that the coated capillary tubes exhibit high efficiencies for protein separations (0.3-0.6 million theoretical plates per meter) as well as long-term hydrolytic stability under the inherently harsh conditions of capillary isoelectric focusing. Additionally, there was no adsorption of lysozyme on the coated surface as indicated by a complete recovery of the basic enzyme. Furthermore, since polymerization is confined to the inner capillary surface, simple precautions (e.g., solution filtration) during the surface modification process are sufficient to prevent capillary clogging.

Biocompatible polymeric monoliths for protein and peptide separations

The concept of biocompatibility with reference to chromatographic stationary phases for separation of biomolecules (including proteins and peptides) is introduced. Biocompatible is a characteristic that indicates resistance to nonspecific adsorption of biomolecules and preservation of their structures and biochemical functions. Two types of biocompatible polymeric monoliths [i. e., polyacrylamide- and poly(meth)acrylate-based monoliths] used for protein and peptide separations are reviewed in detail, with emphasis on size exclusion, ion exchange, and hydrophobic interaction chromatographic modes. Biocompatible monoliths for enzyme reactors are also included. The two main synthetic approaches to produce biocompatible monoliths are summarized, i. e., surface modification of a monolith that is not inherently biocompatible and direct copolymerization of hydrophilic monomers to form a biocompatible monolith directly. Integration of polyethylene glycol into the poly(meth)acrylate monolith network is becoming popular for reduction of non-specific protein interactions.

CE separation of proteins and yeasts dynamically modified by PEG pyrenebutanoate with fluorescence detection

The optimized protocols of the bioanalytes separation, proteins and yeasts, dynamically modified by the nonionogenic tenside PEG pyrenebutanoate, were applied in CZE and CIEF with the acidic gradient in pH range 2-5.5, both with fluorescence detection. PEG pyrenebutanoate was used as a buffer additive for a dynamic modification of proteins and/or yeast samples. The narrow peaks of modified analytes were detected. The values of the pI's of the labeled proteins were calculated using new fluorescent pI markers in CIEF and they were found to be comparable with pI's of the native compounds. As an example of the possible use of the suggested CIEF technique, the mixed cultures of yeasts, Candida albicans, Candida glabrata, Candida kefyr, Candida krusei, Candida lusitaniae, Candida parapsilosis, Candida tropicalis, Candida zeylanoides, Geotrichum candidum, Saccharomyces cerevisiae, Trichosporon asahii and Yarrowia lipolytica, were reproducibly focused and separated with high sensitivity. Using UV excitation for the on-column fluorometric detection, the minimum detectable amounts of analytes, femtograms of proteins and down to ten cells injected on the separation capillary, were estimated.

Surface modification of poly(methyl methacrylate) microfluidic devices for high-resolution separations of single-stranded DNA

While polymer-based microfluidic devices offer some unique opportunities in developing low-cost systems for a variety of application areas, the ability to sort electrophoretically with high efficiency a number of different targets has remained somewhat elusive with an example consisting of achieving single base resolution as required for DNA sequencing. While the reasons for this are many-fold, it is clear that some type of coating is required on the polymer substrate to suppress the EOF and/or minimize potential solute/wall interactions. To this end, we report on a simple grafting procedure to allow the formation of polymer coats, which in this example used linear polyarcylamides (LPAs), onto a poly(methyl methacrylate) (PMMA) microfluidic device. The procedure involved creating an amine-terminated PMMA surface by appropriately functionalizing the PMMA through either a chemical or photochemical process. The aminated surface could then be used to covalently anchor methacrylic acid, which was used as a scaffold to produce LPAs on the surface through radical polymerization of acrylamide. The resulting surfaces demonstrated EOFs that were nearly an order of magnitude smaller than native PMMA. In addition, these LPA-coated devices could produce highly reproducible migration times of over approximately 20 runs with plate numbers exceeding 10(5) m(-1). Using gel electrophoretic analysis of a single base track generated from an M13mp18 template using Sanger cycle sequencing and dye-primer chemistry, the resolution value obtained for bases 199 and 200 was 0.18 while for bases 208 and 209 it was 0.21. For the native PMMA, these bands were found to comigrate.

Highly efficient protein separations in capillary electrophoresis using a supported bilayer/diblock copolymer coating

A surfactant/polymer wall coating consisting of the doubly chained cationic surfactant dimethyldioctadecylammonium bromide (DODAB) and polyoxyethylene (POE) 40 stearate is investigated. The coating is formed by simply rinsing a capillary with a solution containing DODAB and POE 40 stearate. The resultant coating is semi-permanent--demonstrating stable electroosmotic flow (EOF) even after a 60 min high pressure rinse with buffer. The EOF (-0.45+/-(0.23) x 10(-4) cm(2) V(-1) s(-1) at pH 7.4) is suppressed by more than a factor of ten compared to that observed for DODAB alone. Model protein mixtures were separated over a pH range of 3-10 with efficiencies of up to greater than 1 million plates/m for the basic proteins cytochrome c, lysozyme, ribonuclease A and alpha-lactalbumin, and the acidic proteins insulin chain A, trypsin inhibitor, and alpha-chymotrypsinogen A. Migration time reproducibility was 0.5-4.0% from run to run and 0.6-4.3% from day to day. Protein recoveries with this coating ranged from 84% to 97%.

Permanent surface modification of polymeric capillary electrophoresis microchips for protein and peptide analysis

Because of their surface heterogeneity, proteins readily adsorb on polymeric substrates via various interactions, which adversely affects the performance of polymeric microfluidic devices in electrophoresis-based protein/peptide analysis. Therefore, it is necessary to use surface modification techniques such as dynamic coating or more complicated permanent surface modification, which has broader application and better performance, to render the polymeric microchannels protein-resistant. This manuscript is a review of the surface chemistry of microfluidic devices used for electrophoretic separations of proteins and peptides. The structural complexity of proteins as it relates to adsorption is described, followed by a review of the mechanisms and structural characteristics of protein-resistant surfaces. Permanent surface modification techniques used in grafting protein-resistant materials onto the surfaces of electrophoresis microchannels fabricated from polymer substrates are summarized and successful examples are presented.

Micellar electrokinetic chromatography of fluorescently labeled proteins on poly(dimethylsiloxane)-based microchips

MEKC of standard proteins was investigated on PDMS microfluidic devices. Standard proteins were labeled with AlexaFluor(R) 488 carboxylic acid tetrafluorophenyl ester and filtered through a size-exclusion column to remove any small peptides and unreacted label. High-efficiency MEKC separations of these standard proteins were performed using a buffer consisting of 10 mM sodium tetraborate, 25 mM SDS, and 20% v/v ACN. A separation of BSA using this buffer in a 3.0 cm long channel generated a peak with a plate height of 0.38 microm in <20 s. Additional fast separations of myoglobin, alpha-lactalbumin, lysozyme, and cytochrome c also yielded peaks with plate heights ranging from 0.54 to 0.72 microm. All proteins migrated with respect to their individual pIs. To improve the separations, we used a PDMS serpentine chip with tapered turns and a separation distance of 25 cm. The number of plates generated increased linearly with increasing separation distance on the extended separation channel chips; however, the resolution reached an asymptotic value after about 7 cm. This limited the peak capacity of the separation technique to 10-12.

Noncovalent coatings for the separation of synthetic polypeptides by nonaqueous capillary electrophoresis

Recently, we demonstrated the possibility to extend the range of capillary electrophoresis (CE) applications to the separation of non-water-soluble synthetic polymers. This work focuses on the control of the electro-osmotic flow (EOF) and on the limitation of the solute adsorption in nonaqueous electrolytes. For these purposes, different strategies were investigated. For the initial, a viscous additive (ethylene glycol or glycerol) was used in the electrolyte in order to decrease the EOF magnitude and, possibly, to compete with solute adsorption. A second strategy was to modify, before separation, the fused-silica capillary wall by the adsorption of poly(ethylene oxide) (PEO) via hydrogen bonding. The influence of the molecular mass of the adsorbed PEO on the EOF magnitude and direction was studied in electrolytes based on methanol/acetonitrile mixtures containing ammonium ions. For PEO molecular masses above 1000 g/mol, reversed (anodic) EOF were reported in accordance with previous results obtained with PEO covalently bonded capillaries. The influence of the nature and the concentration of the background electrolyte cation on the EOF magnitude and direction were also investigated. A third strategy consisted in modifying the capillary wall by the adsorption of a cationic polyelectrolyte layer. Advantageously, this polyelectrolyte layer suppressed the adsorption of the polymer solutes onto the capillary wall. The results obtained in this work confirm the high potential and the versatility of CE for the characterization of ionizable organic polymers in nonaqueous media.

Preparation and evaluation of poly(polyethylene glycol methyl ether acrylate-co-polyethylene glycol diacrylate) monolith for protein analysis

A poly(polyethylene glycol methyl ether acrylate-co-polyethylene glycol diacrylate) monolith was prepared by UV-initiated polymerization. Methanol and ethyl ether were selected as porogens from a variety of organic solvents to achieve the desirable characteristics of the monolith. The preparation of the monolith could be achieved within 10 min. The monolith was macroscopically homogeneous, had low flow resistance, and did not swell or shrink significantly in tetrahydrofuran. Inverse size-exclusion data indicate that the monolith had a total porosity of 75.4% and an internal porosity of 9.1%. The monolith could be used for size-exclusion separation of peptides, although it could not separate proteins with molecular masses between 10 and 100 K due to its unique pore size distribution. It was found to resist adsorption of proteins in capillary liquid chromatography when using 100 mM phosphate buffer (pH 7.0) containing 0.5 M NaCl. Complete recovery of both acidic and basic proteins was achieved. The monolith can be used for applications in which inert materials are required for protein analysis.

Dynamic modification of microorganisms by pyrenebutanoate for fluorometric detection in capillary zone electrophoresis

Pyrenebutanoate, a fluorescent amphiphilic probe, is suggested here as a capillary zone electrophoresis (CZE) buffer additive for dynamic modification and analysis of microbial cells. Mixed cultures of microorganisms Escherichia coli, Candida albicans, Enterococcus faecalis and Staphylococcus epidermidis were concentrated, resolved by CZE and detected. Using UV excitation for on-column fluorometric detection, a detection sensitivity for the microorganisms on the order of from one to tens of injected cells was achieved.

Separation of structurally related synthetic peptides by capillary zone electrophoresis

The separation of two different sets of synthetic peptides has been investigated by high-performance capillary zone electrophoresis utilising naked, fused silica capillaries. The effects of electrolyte pH, buffer concentration, capillary length and electric field strength on the separation efficiency and selectivity were systematically varied, with the highest resolution achieved with buffer electrolytes of low pH and relatively high ionic strength. Under optimised separation conditions utilising the "short end injection" separation approach with negative electric field polarity, a series of eight structurally-related synthetic peptides were baseline resolved within 4 min without addition of any modifier of the background electrolyte with separation efficiencies in the vicinity of 600000 theoretical plates/m. Further significant enhancement of separation efficiencies could be achieved by taking advantage of the "long end injection" approach with positive electric field polarity. The outcome of these experimental variations parallels the "sweeping" effect that has been observed in the capillary electrochromatographic and micellar electrokinetic separations of polar molecules and permits rapid resolution of peptides with focusing effects. In addition, small changes in the electrolyte buffer pH and concentration were found to have a significant impact on the selectivity of synthetic peptides of similar intrinsic charge. These observations indicate that multi-modal separation mechanisms operated under these conditions with the unmodified fused silica capillaries. This study, moreover, documents additional examples of peptide-specific multi-zoning behaviour in the high-performance capillary zone electrophoretic separation of synthetic peptides.

Separation of mixtures of acidic and basic peptides at neutral pH

Mixtures of acidic and basic peptides composed of the phosphorylated and nonphosphorylated forms of peptide substrates for kinases and a phosphatase were separated by capillary electrophoresis (CE) in buffer conditions compatible with live mammalian cells. The separation of such mixtures was especially challenging given the high salt and neutral pH of the requisite physiologic buffers. Due to poor peak reproducibility in bare capillaries, several strategies were implemented to improve the electrophoretic separation of the peptide mixtures. Covalent coating of the capillary with the neutral polymer poly(dimethylacrylamide) (PDMA) resulted in a 2-fold improvement in the migration time RSD, but required the use of hydrodynamic flow to overcome the differing electrophoretic mobilities (microeo) of the peptides at neutral pH. This parabolic fluid flow diminished separation efficiency almost 5-fold. Polarity switching during the CE run was used to overcome the opposed microeo, but required the retention of hydrodynamic flow and consequent reduction in separation efficiency. The most efficient separations were seen with the use of covalently-linked, charged polymer coatings to maintain electroosmotic flow and to reduce wall interactions. Two such coatings were tested in the current study. Relative to the PDMA coating, an anionic poly(acrylate) improved the average migration time RSD of six peptides from 1.3 to 0.85% and average separation efficiency from 4.8 to 18.0 (x 10(4) plates/m). Likewise, cationic poly([3-(methacryloylamino)propyl]-trimethylammonium) improved the average migration time RSD of eight peptides from 1.2 to 1.1% and average separation efficiency from 4.8 to 33.9 (x 10(4) plates/m). These findings will be of value to the growing number of applications for analytical techniques utilizing CE for cellular analysis and biochemical studies.

Capillary electrochromatographic study of sapphyrin-organophosphoric acid derivatives interaction

Interaction of phosphate moiety possessing compounds with sapphyrin was studied using open-tubular electrochromatography in sapphyrin-coated capillaries. It was revealed that phenylthiohydantoin (PTH)-phosphoserine and PTH-phosphothreonine exert such a strong interaction that they can not be eluted from the sapphyrin-coated capillary even at prolonged run times (70 min). Nucleoside polyphosphates show generally strong interaction (but weaker than the above mentioned serine and threonine derivatives) no matter whether they possess one or two bases. Also the number of phosphate residues present in nucleoside polyphosphates tested plays a secondary role only. p-Aminobenzylphosphoric (p-ABPA) acid exhibited an unexpected behavior. It was retained more in the phosphate containing buffer than in borate-acetate. This appears to indicate that other than complexing of the phosphate moiety may be involved in the interaction. As no such effects were observed with the PTH-derivatives of serine and threonine it was concluded that additional interaction (if involved) depends on the nature of the organic part of the molecule.

Characterization and applications of etched chemically modified capillaries for open-tubular capillary electrochromatography

In this article, the effects of the stationary phase, buffer pH, organic modifier type, organic modifier composition, applied voltage, and temperature on the migration of several synthetic peptides in etched chemically modified open-tubular capillaries are discussed. With these solutes, migration is due to two effects: electrophoretic mobility and solute/bonded phase interactions. In addition, relative migration rates are evaluated for the peptide samples as a function of these experimental variables in order to determine which parameters might be useful for optimizing separations in open-tubular capillary electrochromatography (OTCEC). Some examples of synthetic peptide separations are presented where the sample contains a major component and several minor species, demonstrating how the resolution of these mixtures can be affected by the appropriate choice of experimental variables.

Bonded dimethylacrylamide as a permanent coating for capillary electrophoresis

A method for coating capillaries for capillary electrophoresis with chemically bonded polydimethylacrylamide has been developed, and the properties of the capillaries have been evaluated. The coated capillaries provided high separation efficiency, 12 x 10(5) theoretical plates/m was obtained for cytochrome c. The electroosmotic flow at pH 8.0 was 10 x 10(-10) to 6 x 10(-10) m2 V(-1) s(-1). The coated capillaries were quite stable at high pH. At least 150 runs could be done at pH 10 without appreciable performance deterioration. The excellent performance of the coated capillaries was illustrated by separation of basic proteins, acidic proteins, 9-fluorenylmethyl chloroformate-derivatized neurotransmitter amino acids, peptide reference mixtures and peptides digested from a bacteria protein.

Toxinological and immunological studies of capillary electrophoresis fractionated Chrysaora quinquecirrha (Desor) fishing tentacle and Chironex fleckeri Southcott nematocyst venoms

Repeated runs of capillary electrophoresis (CE) were used to study partially-purified jellyfish nematocyst venom protein in concentrations sufficient to perform toxinological assays. Nematocyst venoms from Chironex fleckeri (Cf) and Chysaora quinquecirrha were processed. The CE eluate was divided into quadrants by scanning protein content. The fourth fraction of both jellyfish venoms, contained proteins with the smallest molecular weight components, which were responsible for the highest hemolysins and the humoral and cell-mediated immunological activity. Cytotoxic Cf lethal factor activity against human liver cells was widely dispersed throughout both venoms but more prominent in fraction 4. A V(beta) receptor human T-cell repertoire was not species-specific for either crude or fractionated jellyfish nematocyst venom.

Modified capillary electrophoresis system for peptide, protein and double-stranded DNA analysis

The results of high-performance capillary electrophoresis (HPCE) studies of peptide, protein and double-stranded DNA separations on a laboratory-made HPCE system are presented. Parameters of the HPCE system are given. The new method of capillary surface modification by grafting poly(glycidyl methacrylate) is described. The problems of HPCE biopolymer analysis connected with the sample-wall interactions are discussed.

Hydrophobic-phase-modified fused-silica columns for capillary electrophoresis

Coated capillaries modified with a hydrophobic layer were developed. Linear hydrocarbons and ethylbenzene modified surfaces greatly improved the electrophoretic performance of the capillaries. The column efficiency for organic compounds reached as high as 327 000 theoretical plate numbers per meter on a 50 microm I.D. linear hydrocarbon (C6) surface treated fused-silica capillary column. This value did not change during 50 repeated analyses and the columns showed strong stability against 0.1 M NaOH and 0.1 M HCl. The relative standard deviation of the run-to-run, day-to-day, and capillary-to-capillary coating with hydrophobic layer showed values of < or =2.5%, and good reproducibility. The separations of four aromatic amines and six pharmacological amines at pH 2.5 is reported.

Direct determination of small cations in proteinaceous samples using a flow injection-capillary electrophoresis system

A method is described for the direct determination of small inorganic cations in samples containing large amounts of proteins, such as milk or blood plasma. The method is based on electrokinetic injection in a flow injection analysis-capillary electrophoresis (CE) system. The selected CE-electrolyte, containing 5 mM 4-aminopyridine and 7 microM cetyltrimethylammonium bromide at pH 4.5, prevents detrimental protein adsorption on the capillary walls. Therefore, no sample pretreatment, except for dilution, is required. Up to 30 repeated injections in one electrophoretic run can be performed, yielding RSD values of the migration time of less than 1 and 2.5% (n=30) for milk and blood plasma samples, respectively.

Protein and peptide separations on high surface area capillaries

A 50 microm capillary that has been etched with ammonium hydrogen difluoride is evaluated as a separation medium for capillary electrochromatography. For a tryptic digest of transferrin, the etched capillary gave better resolution (more peaks in the overall peptide map) and longer retention than separations done under identical experimental conditions on an unetched fused-silica capillary. Resolution on the etched capillary was improved by lowering the voltage from 300 to 267 V/cm. A four-component protein sample also resulted in longer retention on an echted capillary than on an unetched fused-silica capillary that were both coated with Polybrene. After correction for differences in electroosmotic flow between the two capillaries, the calculated electrophoretic mobilities for all four proteins were lower on the etched capillary than on the unetched fused-silica capillary. The results of both the tryptic digest and protein experiments strongly indicate the presence of chromatographic effects on the etched capillary that contribute to the increased retention and improved resolution with respect to the unetched fused-silica capillary.

Microfabricated filters for microfluidic analytical systems

Solvent and reagent filters were micromachined into quartz wafers using deep reactive ion etching to create a network of intersecting 1.5 x 10 microns channels. When placed at the bottom of reservoirs with a side exit, this channel network behaved as a lateral percolation filter composed of an array of cubelike structures one layer deep. Flow through these filters was driven by electroosmotic flow (EOF). Silanol groups at the walls of channels in the network provided the requisite charge to trigger EOF when voltage was applied laterally to the filter. Adsorption of cationic proteins in this silanol-rich matrix was controlled by the application of a polyacrylamide coating prepared by bonding N-hydroxysuccinimide (NHS)-activated poly(acrylic acid) to (gamma-aminopropyl)silane-derivatized filters. Subsequent reaction of residual NHS groups in the coating with 2-(2-aminoethoxy)ethanol provided channels of low charge density and adsorptivity. These lateral percolation filters were shown to be efficacious in filtering solvents containing a variety of particulate materials, ranging from dust to cells.

Capillary electrophoresis using diol-bonded fused-silica capillaries

In this paper, 3-glycidoxypropyltrimethoxysilane was used to produce diol-bonded capillaries at room temperature for capillary electrophoresis (CE). A variety of standard reference compounds and authentic biological samples including ribonucleotides, peptides and proteins were used to test the columns. It was found that greatly suppressed electroosmotic flow was measured over a pH range of 3-10. Lower than 1.6% relative standard deviation (> 10 runs) in migration time was observed for the analysis of test proteins. For real samples of ribonucleotides in tumor cell extracts, approximately 1 million theoretical plates and excellent peak shapes were obtained. The high column efficiency and symmetrical peaks allowed the separation of samples with only 0.6% maximum difference in migration times. The diol-bonded fused-silica capillary columns were stable when used in a pH range of 2-8 under typical CE conditions. The column preparation method involved a simple dynamic coating procedure at room temperature, greatly simplifying the more typical static coating methods that require vacuum pumps and ovens.