High-performance capillary electrophoretic separation of bases, nucleosides, and oligonucleotides: retention manipulation via micellar solutions and metal additives

Advances in Chemical and Biological Methods to Identify Microorganisms-From Past to Present

Fast detection and identification of microorganisms is a challenging and significant feature from industry to medicine. Standard approaches are known to be very time-consuming and labor-intensive (e.g., culture media and biochemical tests). Conversely, screening techniques demand a quick and low-cost grouping of bacterial/fungal isolates and current analysis call for broad reports of microorganisms, involving the application of molecular techniques (e.g., 16S ribosomal RNA gene sequencing based on polymerase chain reaction). The goal of this review is to present the past and the present methods of detection and identification of microorganisms, and to discuss their advantages and their limitations.

dCas9-mediated Nanoelectrokinetic Direct Detection of Target Gene for Liquid Biopsy

The-state-of-the-art bio- and nanotechnology have opened up an avenue to noninvasive liquid biopsy for identifying diseases from biomolecules in bloodstream, especially DNA. In this work, we combined sequence-specific-labeling scheme using mutated clustered regularly interspaced short palindromic repeats associated protein 9 without endonuclease activity (CRISPR/dCas9) and ion concentration polarization (ICP) phenomenon as a mechanism to selectively preconcentrate targeted DNA molecules for rapid and direct detection. Theoretical analysis on ICP phenomenon figured out a critical mobility, elucidating two distinguishable concentrating behaviors near a nanojunction, a stacking and a propagating behavior. Through the modulation of the critical mobility to shift those behaviors, the C-C chemokine receptor type 5 ( CCR5) sequences were optically detected without PCR amplification. Conclusively, the proposed dCas9-mediated genetic detection methodology based on ICP would provide rapid and accurate micro/nanofluidic platform of liquid biopsies for disease diagnostics.

Evaluation of Type-A Endonucleases for the Quantitative Analysis of DNA Damage due to Exposure to Acetaldehyde Using Capillary Electrophoresis

The substrate selectivities of three endonucleases were studied quantitatively using capillary zone electrophoresis to find one giving N²-ethyl(Et)-2'-deoxyguanosine-5'-monophosphate (5'-dGMP) and cyclic 1,N²-propano(CPr)-5'-dGMP from DNAs damaged by acetaldehyde (AA). Six 2'-deoxyribonucleoside-5'-monophosphates to be quantified in the hydrolysis solutions of DNAs, namely, Et-5'-dGMP, CPr-5'-dGMP, and four authentic ones, were completely separated using a 100 mM borate running buffer solution having an optimized pH of 9.67. Using the present method, nuclease reactions of nuclease S1 (NS1), nuclease P1 (NP1), and nuclease Bal 31 to 2'-deoxyribonucleoside-5'-monophosphates from damaged Calf thymus (CT-) DNAs were monitored. The CT-DNAs were prepared by treatment with AA to generate Et-guanine or CPr-guanine internally. Bal 31 hydrolyzed the damaged CT-DNAs to yield Et-5'-dGMP and CPr-5'-dGMP quantitatively. The two 5'-dGMP adducts were not detected in the hydrolysis solutions using NS1 or NP1. Bal 31 can be a suitable nuclease for analyzing DNA damages caused by AA.

Quantum dot-DNA aptamer conjugates coupled with capillary electrophoresis: A universal strategy for ratiometric detection of organophosphorus pesticides

Based on the highly sensitivity and stable-fluorescence of water-soluble CdTe/CdS core-shell quantum dots (QDs) with broad-specificity DNA aptamers, a novel ratiometric detection strategy was proposed for the sensitive detection of organophosphorus pesticides by capillary electrophoresis with laser-induced fluorescence (CE-LIF). The as-prepared QDs were first conjugated with the amino-modified oligonucleotide (AMO) by amidation reaction, which is partial complementary to the DNA aptamer of organophosphorus pesticides. Then QD-labeled AMO (QD-AMO) was incubated with the DNA aptamer to form QD-AMO-aptamer duplex. When the target organophosphorus pesticides were added, they could specifically bind the DNA aptamer, leading to the cleavage of QD-AMO-aptamer duplex, accompany with the release of QD-AMO. As a result, the ratio of peak height between QD-AMO and QD-AMO-aptamer duplex changed in the detection process of CE-LIF. This strategy was subsequently applied for the detection of phorate, profenofos, isocarbophos, and omethoate with the detection limits of 0.20, 0.10, 0.17, and 0.23μM, respectively. This is the first report about using QDs as the signal indicators for organophosphorus pesticides detection based on broad-specificity DNA aptamers by CE-LIF, thus contributing to extend the scope of application of QDs in different fields. The proposed method has great potential to be a universal strategy for rapid detection of aptamer-specific small molecule targets by simply changing the types of aptamer sequences.

Neoglycoproteins as carbohydrate antigens: synthesis, analysis, and polyclonal antibody response

The analysis and polyclonal antibody response for newly synthesized maltose-BSA conjugate neoglycoproteins is described. In this first proof of concept study, a simple carbohydrate antigen, maltose, was linked to BSA by reductive amination. An aglycone spacer was utilized to conserve the intact annular maltose structure and to promote the accessibility of the carbohydrate immunogen hapten during immunization. The neoglycoproteins were investigated by CGE and the number of conjugated maltose residues was determined by MALDI-TOF MS. The neoglycoproteins were then evaluated by immunization of BALB/c mice and the polyclonal antibody response was tested by ELISA as evidence for the presence of sugar-containing epitope-specific antibodies. Selective antibody binding was demonstrated to the synthesized neoglycoproteins with different (low and high) glycosylation degrees suggesting the possible use of this approach to generate antibodies. Moreover, the polyclonal antibody response was not inhibited by maltose or other simple carbohydrates to confirm presence of the neoglycoprotein-specific antibodies.

Determination of association constants between 5'-guanosine monophosphate gel and aromatic compounds by capillary electrophoresis

Hydro gel formed by 5'-guanosine monophosphate (GMP) in the presence of a potassium ion is expected to exhibit interesting selectivity in capillary electrophoretic separations. Here, we estimated the conditional association constants between the hydro gel (G-gel) and aromatic compounds by capillary electrophoresis in order to investigate the separation selectivity that is induced by the G-gel. Several aromatic compounds were separated in a solution containing GMP and potassium ion at different concentrations. The association constants were calculated by correlating the electrophoretic mobilities of the analytes obtained experimentally using a concentration of G-gel. During semi-quantitative estimation, naphthalene derivatives had larger association constants (Kass=10.3-16.8) compared with those of benzene derivatives (Kass=3.91-5.31), which means that the binding sites of G-gel match better to a naphthalene ring than to a benzene ring. A hydrophobic interaction was also found when the association constants for alkyl resorcinol were compared with those of different hydrocarbon chains. The association constants of nucleobases and tryptophan ranged from 6.05 to 12.6, which approximated the intermediate values between benzene and naphthalene derivatives. Consequently, the selective interaction between G-gel and aromatic compounds was classified as one of three types: (1) an intercalation into stacked planar GMP tetramers; (2) a hydrophobic interaction with a long alkyl chain; or, (3) a small contribution of steric hindrance and/or hydrogen bonding with functional groups such as amino and hydroxyl groups.

Mechanism of signal suppression by anionic surfactants in capillary electrophoresis-electrospray ionization mass spectrometry

Micellar-mediated capillary electrophoresis (CE) is used for a wide variety of applications, including the separation of pharmaceuticals, environmental contaminants, illicit drugs, DNA fragments, and many other biological samples. The electrospray ionization interface is one of the most common CE-MS interfaces. Coupling micellar-mediated CE separations with MS detection combines two very powerful, widely applicable analytical techniques. Some types of surfactants strongly interfere with electrospray ionization mass spectrometric (ESI-MS) detection of analytes, and in many cases the ESI-MS analyte signals are completely quenched. Only a few reports have appeared that describe the ESI-MS detection of analytes in the presence of surfactants; however, the exact mechanism of ionization suppression has not yet been addressed. In this work, a modified aerosol ionic redistribution (AIR) model is presented that qualitatively explains the results of previous studies, including those using "polymeric surfactants". Analyte ionization suppression by surfactants appears to be caused by Coulombic interaction between oppositely charged solute and surfactant ions in the ESI-produced offspring droplets. It appears that the ability of surfactants to quench electrospray ionization is directly related to the surface activity and the charge of the surfactant. Also, highly surface active components tend to be enriched in ESI-produced offspring droplets. Analyte ion signals can be detected under conditions that lower the surface concentration of oppositely charged surfactant ions in aerosol droplets. The mechanistic information outlined here may be used to design micellar-mediated CE separations that allow detection of analyte ions by ESI-MS.

Electrochemical uranyl biosensor with DNA oligonucleotides as receptor layer

The feasibility of using gold electrodes modified with short-chain ssDNA oligonucleotides for determination of uranyl cation is examined. Interaction between UO(2)(2+) and proposed recognition layer was studied by means of voltammetric and quartz crystal microbalance measurements. It was postulated that ssDNA recognition layer functions via strong binding of UO(2)(2+) to phosphate DNA backbone. The methylene blue was used as a redox marker for analytical signal generation. Biosensor response was based on the difference in electrochemical signal before and after subjecting it to sample containing uranyl ion. The lower detection limit of 30 nmol L(-1) for UO(2)(2+) was observed for a sample incubation time of 60 min. Proposed ssDNA-modified electrodes demonstrated good selectivity towards UO(2)(2+) against common metal cations, with only Pb(2+) and Ca(2+) showing considerable interfering effect.

Metabolomic approach for determination of urinary nucleosides as potential tumor markers using electromigration techniques

In the postgenome-sequencing era, several large projects have been running recently. Proteomics and other analysis or structural biology are the most active today. Since the late 1990 s, metabolomics has been gaining importance in systems biology, as it provides real-world end points that complement and help in the interpretation of genomic and proteomic data. Comprehensive information about the level changes of numerous metabolites present in the analyzed samples is essential in metabolomic studies. Therefore, the applied analytical techniques must be suitable for the simultaneous analysis of a diverse range of low-molecular-mass endogenous metabolites such as nucleosides at various concentrations and in different matrices, in particular, in urine and serum. In the view of metabolomic study, this domain is obviously significant to understand specific humans' reactions and it can be perceived as a diagnostic and predictive tool in pathological reactions. Since the term "metabolom" has occurred in common scientific use, there have been many publications about possible ways of analysis of nucleosides as metabolites of either oxidative DNA damage or RNA's turnover that are used as the potential tumor markers. Besides, the availability of fast, reproducible and easy to apply analytical techniques that would allow the identification of a large number of metabolites is highly desirable since they may provide detailed information about the progression of a pathological process. This paper, which describes the most relevant electromigration techniques, covers the period starting from the review of Karl H. Schram (Mass Spectrom. Rev. 1998, 17, 131-251) up to the beginning of 2009.

Separation of corticosteroids by microemulsion EKC with diethylL-tartrate as the oil phase

A novel microemulsion based on a mixture of diethyl L-tartrate (DET) and SDS was developed for the microemulsion EKC (MEEKC) determination of structurally related steroids. The system consisted of 0.5% w/w DET, 1.7% w/w SDS, 1.2% w/w 1-butanol, 89.6% w/w phosphate buffer (40 mM, pH 7.0), and 7% w/w ACN. With an applied voltage of +10 kV, a baseline separation of aldosterone (A), cortisone acetate (CA), dexamethasone (D), hydrocortisone (H), hydrocortisone acetate (HA), prednisolone (P), prednisolone acetate (PA), prednisone (Ps), triamcinolone (T), and triamcinolone acetonide (TA) could be achieved. Under the optimized conditions, the reproducibility of the retention time (n = 4) for most of the compounds was less than +/-0.8% with the exception of A, Ps, and T. The average number of theoretical plates was 18 800 plates/m. The results were compared with those achieved by the modified micellar EKC (MEKC). MEEKC showed obvious advantages over MEKC for the separation of highly hydrophobic substances. To further evaluate the system, we tested the MEEKC method by analyzing corticosteroids in a spiked urine sample.

Control of electroosmotic flow by a cation additive to enhance the separation of amino acids by micellar electrokinetic chromatography

The effect of a divalent cation (Mg2+) and 3 monovalent cations (Na+, Li+, and K+) as buffer additives on the electroosmotic flow (EOF) was investigated in order to improve the separation performance of p-acetamidobenzenesulfonyl fluoride (PAABS-F) derivatives of 20 standard amino acids by micellar electrokinetic chromatography (MEKC). The EOF can be decreased with increasing concentration of cations with the order of cations as Mg2+>K+>Na+>Li+. However, it was found that the resolution cannot be improved easily using a buffer cation which is more capable of decreasing the EOF. Taking the migration time, resolution, and peak shape into account, Na+ is the best buffer additive, although the EOF decreased most using Mg2+. Using 20 mmol/L borate at pH 9.3 containing 140 mmol/L SDS and 20 mmol/L Na+ as electrolyte, 20 standard amino acids were successfully separated within 14 min.

Capillary electrophoretic method for nucleotide analysis in cells: application on inherited metabolic disorders

Purine and pyrimidine nucleotides influence many metabolic pathways and their analogs have been widely used in medicine. A capillary electrophoretic method was developed for measuring intracellular nucleotides. The final BGE consisted of 40 mM citric acid with addition of 0.8 mM CTAB titrated by gamma-aminobutyric acid to pH 4.4. The electrophoretic separations were carried out in an uncoated silica capillary (id/od - 75/375 microm; effective/total length - 90/97 cm). The method allows a complete separation of 21 nucleotides and deoxynucleotides within 15 min with separation efficiencies up to 400,000 theoretical plates per meter. Due to the use of an acidic separation medium, the method offers a high selectivity toward the studied analytes versus possible interferences from matrices. Sample preparation was optimized in order to shorten work-time and prevent analyte degradation. The method was applied for analyzing nucleotides in human erythrocytes and Chinese hamster ovary cells. Diagnostic potential for inherited metabolic disorders of nucleotide metabolism is presented.

Identification and quantification of GC-rich oligodeoxynucleotides in tissue extracts by capillary gel electrophoresis

Capillary gel electrophoresis (CGE) is a widely used method for quantification of oligonucleotide-based drugs, such as CpG oligodeoxynucleotides (CpG ODN), aptamers and small interfering ribonucleic acids (siRNAs) that allows accurate quantification of parent compound as well as metabolites. Stable secondary structure formation of these molecules frequently prevents analysis by conventional CGE methods and impedes pharmacokinetic assessment. Herein, we describe development of a CGE method for identification and quantification of complex mixtures of secondary structure forming GC-rich ODN in biological samples at dose levels of 0.5mg/kg and above. Samples containing GC-rich CpG ODN and metabolite markers were treated by solid-phase-extraction (SPE) and subsequently analyzed by CGE using a 50cm neutrally coated capillary at 60 degrees C together with a 7M urea buffer system containing 30% dimethylsulfoxide (DMSO). Peak resolutions >or=1 were typically achieved, enabling pharmacokinetic assessment of secondary structure forming oligonucleotides in biological samples that hitherto were unsusceptible to quantitative analysis.

Separation of purine and pyrimidine bases by capillary electrophoresis using β-cyclodextrin as an additive

Capillary electrophoresis was applied to separate purine and pyrimidine bases in the basis of their partial ionization in the alkaline buffer. The effects of buffer pH, buffer and beta-cylclodextrin concentration were systematically investigated using a commercial capillary electrophoresis instrument with UV detector at 254nm. We found that the resolutions of bases (especially for adenine and thymine) were significantly improved in the presence of beta-cylclodextrin. The satisfactory separation of five bases such as cytosine, thymine, adenine, guanine and uracil were achieved by capillary electrophoresis using beta-cylclodextrin as an additive. Under the optimal conditions, the linear range was from 2 to 200microg/ml for bases (R= 0,991-0,9977 ) and the detection limits were from 0.8 to 1.8microg/ml (S/N = 2). The detection limit of 0.05microg/ml ( S/N=2 ) for uracil was obtained by stacking injection mode. The assay was used to determine the deamination of cytosine to uracil by heating in the presence of sodium hydroxide. Our primarily results show that capillary electrophoresis is a very useful tool for determination of purine and pyrimidine bases and study on nucleic acids.

Continuous fractionation of enantiomer pairs in free solution using an electrophoretic analog of simulated moving bed chromatography

Continuous fractionation of the left and right enantiomers of Piperoxan was performed in free solution in a vortex-stabilized electrophoresis apparatus. Sulfated beta-cyclodextrin was used as the chiral selector. A capillary electrophoresis (CE) study of the separation of Piperoxan enantiomers was carried out in order to find the buffer conditions that produce the maximum peak separation time between the two enantiomers and the optimal chiral selector concentration. These peak separation times were then used to calculate the electrophoretic mobilities of the enantiomer-ligand complexes. The difference in electrophoretic mobilities, when used in a preliminary model of the enantiomer separation, indicated that, by imposing a fluid flow opposite the direction of electromigration, it would be possible to force the fast and slow enantiomers to move in opposite directions within the vortex-stabilized apparatus. Using the predictions of the preliminary separation model, the vortex stabilized electrophoresis apparatus was configured with a feed port at the center of the chamber axis and offtake ports near the cathode and anode. This allowed for continuous operation of the apparatus. Continuous fractionations were completed at throughputs of 1.5 and 4.0 mg/h with both offtakes showing greater than 99% enantiomeric purity at 4.0 mg/h using CE. Fractionation was achieved at a throughput of 10 mg/h, but while the slow enantiomer was recovered with greater than 99% purity, only 96% enantiomeric purity of the fast stereoisomer was achieved. The loss of resolution at higher volumetric throughputs supports our hypothesis that a mobility-dependent "window" of operation exists in which two solutes can be completely separated.

Screening method for inherited disorders of purine and pyrimidine metabolism by capillary electrophoresis with reversed electroosmotic flow

Capillary electrophoresis with electroosmotic flow reversed by cationic surfactant for diagnosis of purine and pyrimidine inherited enzyme deficiencies is reported. Final separation conditions consist of 45 mM borate, 55 mM N-tris[hydroxymethyl]methylglycine, 10 mM tartrate, 1 mM cetyltrimethylammonium bromide and 0.44% tetrabutylammonium hydroxide-2-amino-2-methyl-1,3-propanediol (pH 8.6). Average sensitivity (2.51 microM), reproducibility of migration times (run-to-run C.V. < or = 0.6%, day-to-day C.V. < or = 2.5%), linearity (R2>0.994) and imprecision (mean intra-assay RSD 4.7% and inter-assay RSD 6.6%) of the method are acceptable for diagnostic purposes. Applicability of the method is demonstrated on urine samples from patients with enzymatically proven enzyme deficiencies.

Discontinuous electrophoretic stacking system for cholate-based electrokinetic chromatographic separation of 8-hydroxy-2'-deoxyguanosine from unmodified deoxynucleosides

The stacking and baseline-resolved separation of the oxidative damage marker, 8-hydroxy-2'-deoxyguanosine (8-OHdG), from unmodified deoxynucleosides in under 4 min is reported. Separations of 8-OHdG from 2'-deoxyadenosine, 2'-deoxycytosine, 2'-deoxyguanosine, and thymidine are accomplished using micellar electrokinetic capillary chromatography with sodium cholate. Importantly, the use of sulfate, intentionally added to the sample matrix, results in effective stacking of 8-OHdG and other analytes. This work extends electrokinetic stacking injection of neutral analytes to include deoxynucleosides. The procedure works well with either electrokinetic or hydrodynamic injection. The separation buffer and sample matrix composition were optimized to effect stacking conditions with an uncoated 50 microm fused-silica capillary. The lower limit of detection for the analytes is in the nanomolar range, and is more than an order of magnitude lower than without stacking. With 30 s (5.7 cm) electrokinetic injections, stacking and baseline separation of 8-hydroxy-2'-deoxyguanosine from the unmodified nucleosides is accomplished, even in the presence of a 400-fold excess of unmodified deoxynucleosides.

Analysis of DNA adducts bases by capillary electrophoresis with amperometric detection

We have developed a method for the detection of DNA adducts by combining capillary electrophoresis (CE) with the specificity of amperometric detection. Guanine is the most easily damaged base of the four normal DNA bases and many adducts of guanine have been found in DNA. These guanine adducts are often electrochemically active, while the normal bases with the exception of guanine are not. Therefore, CE with amperometric detection will be a promising method to study DNA damage. The four normal deoxynucleosides and two damaged deoxnucleosides N2-ethyldeoxyguanosine (N2-ethyl-dG) and 8-hydroxydeoxyguanosine (8-OH-dG), were completely separated by micellar electrokinetic chromatography (MEKC). Deoxyguanosine and the two damaged deoxynucleosides were identified using amperometric detection. The sensitivity of our system was comparable to that of UV detection. Analysis of DNA hydrolysis products was also performed briefly using this method.

Highly sensitive and direct detection of DNA fragments using a laser-induced capillary vibration effect

A pulsed laser-induced stationary wave capillary vibration detection method was applied to the sensitive detection of capillary gel electrophoresis, and the direct detection of non-labeled nucleic acids, such as DNA sequencing products, was demonstrated. An excimer laser operating at 248 nm was used as a CVL excitation source, and polynucleotides were sensitively detected without derivatization. From an investigation on the endurance of several matrixes to pulsed laser irradiation, a polyacrylamide without a cross-linker (0%C) was found to have adequate endurance, and it exhibited no serious damage during an analysis. A cytosine-terminated sequence reaction product was detected with a sensitivity close to that of laser-induced fluorometry (LIF). These results suggest the feasibility of the highly sensitive detection of ultramicro amounts of biological materials without a pre- or post-column derivatization, which has usually been required in sensitive detection procedures, such as LIF. Furthermore, the feasibility of a novel DNA sequencing method is also suggested.

Determination at ppb level of an anti-human immunodeficiency virus nucleoside drug by capillary electrophoresis-electrospray ionization tandem mass spectrometry

Capillary electrophoresis coupled with tandem mass spectrometry was used to indirectly separate and quantify the active metabolite of the anti-human immunodeficiency virus (anti-HIV) didanosine drug. The influence of several parameters (pH and ionic strength of volatile formic acid-ammonia buffer) upon electroosmotic flow, electrophoretic mobility and peak efficiency of several nucleosides (A, dA, ddA, C) has been studied. This paper illustrates the current importance in CE-MS technique as a complementary or substituted method to the known HPLC-radioimmunoassay or HPLC-UV method to measure levels of anti-HIV drugs. The limit of detection for 2',3'-dideoxyadenosine by this method is 2 microg 1(-1) in a formic acid-ammonia buffer (pH 2.5, 10 mM ionic strength). This methodology could be used to perform simultaneous detection of two or more anti-HIV nucleosides, such as stavudine or didanosine in combination therapy.

Integrated electroosmotically-driven on-line sample purification system for nanoliter DNA sequencing by capillary electrophoresis

An integrated on-line system is developed for DNA sequencing at the nanoliter scale. The technique involves the use of a nanoreactor for small-volume cycle-sequencing reaction, capillary zone electrophoresis (CZE) for purification of the sequencing fragments, and capillary gel electrophoresis (CGE) for separation of the purified DNA fragments. The nanoreactor and CZE are integrated into one capillary, where a 100-nl dye-labeled terminator cycle-sequencing reaction is carried out followed by CZE to separate excess dye-labeled terminators from the sequencing fragments. On-line electrokinetic injection of the purified DNA fragments into the CGE system is accomplished at a small-volume tee connector by which the CZE capillary is interfaced to the CGE system. The utility of the system is demonstrated in sequencing nanoliter volumes of single-stranded DNA (M13mp18) and double-stranded DNA (pGEM). The use of voltage to drive both CZE and CGE makes it feasible for automation and future adaptation of the whole system to a microchip.

Application of capillary electrophoresis in clinical chemistry: the clinical value of urinary modified nucleosides

Urinary modified nucleosides were determined by capillary electrophoresis using a 300 mM SDS-25 mM sodium tetraborate-50 mM sodium dihydrogenphosphate buffer. The nucleosides were extracted from urine by phenylboronate affinity gel chromatography. In cancer patients the levels of the modified nucleosides are generally elevated. By an artificial neural network method breast cancer patients were differentiated from normal individuals, which indicates that the modified nucleosides could be of clinical value as tumor markers.

Rapid quantification of DNA methylation by high performance capillary electrophoresis

The actual methods to evaluate total DNA methylation based on high performance liquid chromatography (HPLC) are long and tedious due to the specific running buffers required. In this work, a new open-tube capillary electrophoresis system has been applied to the separation of acid hydrolyzed genomic DNA and so, to the evaluation of genomic DNA methylation. Several running conditions were tested but separation of cytosine and 5-methyl-cytosine was only possible by sodium dodecyl sulfate (SDS) micelle system. The importance of sample dissolution preparation has also been demonstrated. The results of this study open up the possibility of quantification of the relative methylation degree of rapid genomic DNA by a simple method based on high performance capillary electrophoresis (HPCE).

From small charged molecules to oligomers: a semiempirical approach to the modeling of actual mobility in free solution

According to Stokes' treatment, the ionic mobility of particles, which are small with respect to Debye length, is usually considered to be proportional to the nominal charge and inversely proportional to the hydrodynamic radius. Experimentally, it is well known, however, that the ionic mobility of a small multicharged molecule does not depend linearly on its nominal charge in a wide range. This behavior can be accounted for by a condensation of the charge or a modification of the friction coefficient with the charge. This paper presents a semiempirical modeling of the actual mobility based on the assumption of additivity of frictional contributions pertaining to the uncharged molecular backbone and to each charged or uncharged moiety. Condensation of the charge was not considered. The model first appeared to be suitable for multicharged analytes having a characteristic dimension smaller than the Debye length, such as benzene polycarboxylic acids and polysulfated disaccharides. This approach was then adapted to account for the actual mobilities of singly and evenly charged oligomers (N-mers) having a dimension smaller than or similar to the Debye length. Rather good experimental agreement was obtained for polyalanines and polyglycines (N < or = 6), fatty acid homologs, fully sulfonated polystyrene oligomers (N < or = 13), and polycytidines (N < or = 10). Especially the influence of the polymerization degree on the mobility of oligomers having identical charge densities was clarified. It is also shown that the electrophoretic contribution to the overall friction coefficient increases linearly with the nominal charge but hardly depends on the chemical nature of the charged moieties. This model should be of interest to evaluate the role of various physicochemical phenomena (hydrodynamic and electrophoretic frictions, hydrodynamic coupling, charge condensation) involved in the migration of charged oligomers.

Influence of ring opening-closure equilibrium of oxanine, a novel damaged nucleobase, on migration behavior in capillary electrophoresis

Oxanine (Oxa) is a novel damaged nucleobase which is generated from guanine by HNO2 or NO. As a fundamental study for detection of Oxa formed in vivo, capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) have been tested by changing the pH of the running buffer. At pH 7, CZE did not separate Oxa from seven other nucleobases, and MEKC separated Oxa but their peaks migrated close together. In both the techniques, an extreme peak broadening occurred for Oxa around pH 9 and a good peak separation was achieved at pH 12. The behavior of the Oxa peak is discussed in relation to the unique multistep acid-base equilibria of Oxa.

Selectivity in capillary electrokinetic separations

This review gives a survey of selectivity modes in capillary electrophoresis separations in pharmaceutical analysis and bioanalysis. Despite the high efficiencies of these separation techniques, good selectivity is required to allow quantitation or identification of a particular analyte. Selectivity in capillary electrophoresis is defined and described for different separation mechanisms, which are divided into two major areas: (i) capillary zone electrophoresis and (ii) electrokinetic chromatography. The first area describes aqueous (with or without organic modifiers) and nonaqueous modes. The second area discusses all capillary electrophoretic separation modes in which interaction with a (pseudo)stationary phase results in a change in migration rate of the analytes. These can be divided in micellar electrokinetic chromatography and capillary electrochromatography. The latter category can range from fully packed capillaries, via open-tubular coated capillaries to the addition of microparticles with multiple or single binding sites. Furthermore, an attempt is made to differentiate between methods in which molecular recognition plays a predominant role and methods in which the selectivity depends on overall differences in physicochemical properties between the analytes. The calculation of the resolution for the different separation modes and the requirements for qualitative and quantitative analysis are discussed. It is anticipated that selectivity tuning is easier in separation modes in which molecular recognition plays a role. However, sufficient attention needs to be paid to the efficiency of the system in that it not only affects resolution but also detectability of the analyte of interest.

Electrokinetic chromatography

The important features of electrokinetic chromatography are critically reviewed. Special emphasis is given to systems using micelles as pseudostationary phase. Short and comprehensive overviews are given on the subjects of separation, comparison with capillary electrochromatography, on-line coupling with mass spectrometry, and developments that are expected in the future. A greater coverage on the subject of improvement of detection sensitivity, specifically by on-line concentration was also contributed.