Recent developments in isotachophoresis

Isotachophoresis: Theory and Microfluidic Applications

Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.

Isotachophoresis applied to biomolecular reactions

This review discusses research developments and applications of isotachophoresis (ITP) to the initiation, control, and acceleration of chemical reactions, emphasizing reactions involving biomolecular reactants such as nucleic acids, proteins, and live cells. ITP is a versatile technique which requires no specific geometric design or material, and is compatible with a wide range of microfluidic and automated platforms. Though ITP has traditionally been used as a purification and separation technique, recent years have seen its emergence as a method to automate and speed up chemical reactions. ITP has been used to demonstrate up to 14 000-fold acceleration of nucleic acid assays, and has been used to enhance lateral flow and other immunoassays, and even whole bacterial cell detection assays. We here classify these studies into two categories: homogeneous (all reactants in solution) and heterogeneous (at least one reactant immobilized on a solid surface) assay configurations. For each category, we review and describe physical modeling and scaling of ITP-aided reaction assays, and elucidate key principles in ITP assay design. We summarize experimental advances, and identify common threads and approaches which researchers have used to optimize assay performance. Lastly, we propose unaddressed challenges and opportunities that could further improve these applications of ITP.

Multidimensional liquid phase separations for mass spectrometry

Large part of the current research in biology, medicine, and biotechnology depends on the analysis of DNA (genomics), proteins (proteomics), or metabolites (metabolomics). The advances in biotechnology also command development of adequate analytical instrumentation capable to analyze minute amounts of samples. The analysis of the content of single cells may serve as an example of ultimate analytical applications. Most of the separation techniques have been developed in the last three decades and alternative approaches are being investigated. At present, the main protocols for analyses of complex mixtures include 2-DE (IEF) followed by electrophoresis in SDS polyacrylamide gel (SDS-PAGE) and chromatographic techniques. Information-rich techniques such as MS and NMR are essential for the identification and structure analysis of the analyzed compounds. High resolution separation of the individual sample components is often a prerequisite for success. High resolution proteomic analysis in the majority of laboratories still relies on the time consuming and laborious offline methods. This review highlights some of the important aspects of 2-D separations including microfluidics.

Isotachophoretic determination of carboxylic acids in biodegradation samples

In the current study a method of isotachophoretic separation of selected carboxylic acids was developed. The method was used for the determination of carboxylated oligo(ethylene glycol)s and their degradation products in biodegradation tests of PEG 250 DA [a mixture of dicarboxylated oligo(ethylene glycol)s]. Two tests were performed in the studies: the Organization for Economic Cooperation and Development (OECD) screening test and the river water die-away test. Both the biodegradation tests proved relatively fast biodegradation of the studied compounds. In the OECD screening test the biodegradation was faster than in the river water die-away test which can be ascribed to a higher concentration of bacteria in the biodegradation liquor. The minimal sample pretreatment and relatively low cost of analysis by the isotachophoretic method used here make it a good alternative to existing methods of carboxylic acids analysis.

Electrophoretic methods in the analysis of beverages

A review of the applications of electrophoresis to the determination of various compounds in beverage samples, namely beer, hard drinks, juice, milk, soft drinks, tea and wine, is presented.

The use of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) polymers as spacers for isotachophoresis in sieving gel matrices

The electric field strength gradients generated in isotachophoresis (ITP) may be used for the separation of biomolecules. Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (polyAMPS) polymers of a uniform distribution of molecular mass were synthesized and used as novel spacers in ITP. Since these polymeric spacers are strongly acidic species, their ionic charges remain constant over a wide pH range, so that their ionic mobilities are governed solely by their molecular masses and not by the pH of the milieu. A modification of ITP known as telescope electrophoresis was used to separate a number of acidic dyes of varying ionic mobility, using polyAMPS polymers as spacers. The resolution obtained was superior to that obtained by polyacrylamide gel electrophoresis (PAGE), due to the focusing effect of the electric field strength gradient. Since these novel polymeric spacers are designed to operate within sieving medium, it was decided to test their suitability for the separation of DNA molecules. DNA molecules up to 1000 bp long were successfully resolved, with a similar resolution to that obtained with conventional PAGE.

Automated free-solution isotachophoresis: instrumentation and fractionation of human serum proteins

An automated free-solution isotachophoresis system (FS-ITP) for preparative fractionation of biopolymers is described, operated in a batch mode. The dimension of the separation chamber allows an up to 1200-fold higher sample load compared to separation in capillaries of 180 microm inner diameter as used in analytical capillary isotachophoresis (C-ITP). The preparative capacity of the system is within the milligram range. The method is fully compatible with analytical C-ITP, which is essential for preparative-scale isotachophoresis with regard to optimization of electrolyte systems and the search for suitable spacers. As a model application the fractionation of human serum proteins is reported. The collected fractions were analyzed by C-ITP and agarose gel electrophoresis.

Analysis of lipoproteins with analytical capillary isotachophoresis

An analytical free flow capillary isotachophoresis procedure, with a discontinuous electrolyte system, for the detailed analysis of lipoproteins in human body fluids has been developed. The technique is based on prestaining whole serum lipoproteins with a lipophilic dye before separation. Human serum lipoproteins are separated into 14 well-characterized subfractions according to their electrophoretic mobility. High density lipoproteins (fraction 1 to 6) are separated into three major subpopulations, the fast migrating high density lipoprotein (HDL) subpopulation, containing mainly apo AI and phosphatidylcholine, the subpopulation with intermediate mobility, consisting of particles rich in apo AII, apo E, and C apolipoproteins, and the slowly migrating HDL subfraction, containing mainly particles rich in apo AI, apo AIV, and lecithin: cholesterol acyltransferase (LCAT) activity. The apo B containing lipoproteins (fraction 7 to 14) can be subdivided into four major functional groups. The first represents chylomicron derived particles and large triglyceride-rich very low density lipoproteins (VLDL). The second group consists of small VLDL and intermediate density lipoprotein (IDL) particles, anf the third and fourth group represent the low density lipoproteins. The isotachophoretic analysis of human serum samples obtained from patients with hyperlipoproteinemias is compatible with the classification according to the Frederickson phenotypes and reflects the respective biochemical abnormalities. Furthermore, several genetic disorders of lipid and lipoprotein metabolism like HDL deficiency syndromes, familial LCAT deficiency, Fish eye disease, hypobetalipoproteinemia and abetalipoproteinemia can be well characterized by analytical capillary isotachophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Isotachophoresis of nucleic acid constituents

Determination methods for purine and pyrimidine bases, nucleosides, nucleotides and related compounds using analytical capillary isotachophoresis are reviewed. First, the isotachophoretic characterization of these compounds, as well as methods for sample preparation prior to analysis, and the different ways of detecting unknown substances in complex biological systems are described. Then applications of isotachophoretic analysis in medical diagnosis and biomedical research are reviewed. In particular, the analysis of purines, pyrimidines, nucleosides and related compounds in blood and serum for the diagnosis and treatment of inherited diseases and cancer is described. Selected applications of nucleotide analysis in biomedical research using different tissue extracts are also reviewed, and some examples of nucleotide-dependent enzymic reactions, which were performed by means of analytical isotachophoresis, are presented.

Analysis of leukotrienes, prostaglandins, thromboxane B2 and their metabolites by capillary isotachophoresis

An analytical capillary isotachophoretic method for the analysis of the eicosanoids leukotriene E4, leukotriene B4, prostaglandins E1 and E2, 6-keto-prostaglandin F1 alpha, thromboxane B2, and their metabolites of omega- and/or beta-oxidation is described. The method is based on anionic separation and detection by UV absorbance (254 nm) and conductivity and allows simultaneous analysis of the primary compounds and their corresponding major urinary metabolites. The method was applicable to the qualitative and quantitative analysis of prostaglandin E1 in a drug preparation.

Application of capillary isotachophoresis in peptide analysis

This paper gives a broad and detailed review of the applications of one of the modern high-performance electromigration separation techniques--capillary isotachophoresis (ITP)--in peptide analysis. Examples are presented of the utilization of capillary ITP for peptide analysis in the fields of chemistry, general and clinical biochemistry, biology, biotechnology, pharmacy and the food industry. The complete composition of all the electrolyte systems used for peptide ITP analyses in both cationic and anionic techniques is given in tabular form. According to the purpose of analysis the applications are divided into several sections: model studies, determination of physico-chemical characteristics, purity control of both intermediate and final peptide preparations, including the determination of low-molecular-mass ionogenic admixtures, and the analysis of peptides in biological fluids and tissue extracts. In addition to the main applications the theoretical and methodological aspects of peptide ITP analysis are discussed. The basic electromigration properties of peptides (their polyampholyte character, effective and absolute mobilities, acid-base equilibria) are explained and the selection of parameters for peptide ITP analysis is described in detail. The advantages and disadvantages of ITP compared with other electrophoretic and chromatographic methods used for peptide analysis are discussed.

Applications of capillary electrophoresis for industrial analysis

Capillary electrophoresis techniques, particularly isotachophoresis and zone electrophoresis, are useful for the determination of various analytes in a wide range of sample matrices. This paper reports applications of capillary electrophoresis developed for detergent, food additive, herbicide, animal nutrition and biotechnology samples. Major advantages of capillary electrophoresis include versatility and speed of method development. Options for small ion analysis using modern, fused silica capillary instruments are discussed.

Capillary zone electrophoresis of oligonucleotides. Factors affecting separation

The influence of various parameters affecting separation of oligonucleotides by capillary zone electrophoresis has been examined. The effects of pH, ionic strength, and various additives, including highly charged cations such as spermine, were studied. Using polycytidines as model compounds, it was demonstrated that pH in the range of 5-8 and ionic strength in the range of 20-200 mmol/l do not influence the separation of oligonucleotides substantially. However, with the addition of spermine to the background electrolyte, migration order was inverted as the effective mobilities of the larger oligonucleotides were greatly decreased. With the addition of spermine and sodium dodecyl sulfate, the separation+ of these model oligonucleotides was also significantly affected. The best separation of a homologous series of polycytidines was obtained with a background electrolyte containing 60 mmol/l histidine, 30 mmol/l glutamic acid, 50 mmol/l sodium dodecyl sulfate and 3 mmol/l spermine.

Determination of oxalate in human serum by multicolumn isotachophoresis

The practical usefulness of multicolumn isotachophoresis was demonstrated by the determination of oxalate levels in human serum. 10 mmol/L HCl and 100 mmol/L Na2HPO4 served as the leading and terminating electrolyte, respectively. For the stabilization of the isotachophoretic zones in large cross section channels a suspension of Bio-Gel P-300 in the leading electrolyte was used. For the analysis ca. 1 mL of fresh serum was required and 1.2 mL of 1:1 mixture of serum and the suspension of Bio-Gel P-300 in deionized water was applied as sample. The time of analysis ranged between 45-49 min. The detection limit of analysis was determined to be 50 nmol/L. Reproducibility of analysis of 1 mumol/L oxalate in water standard was found to be 2.6% (n = 6).

Photometric detection at 405 nm in trace analysis by capillary isotachophoresis

The possibilities of photometric detection at 405 nm were investigated for trace isotachophoretic analysis of various ionic constituents. Increased selectivity of the detection enabled, for example, the detection and determination of nitrophenols at 10(-8) M in a 25-microliter sample. 5-Nitrofurylacrylic acid, a wine stabilizer, could be detected with confidence at ca. 0.1 ppm in wine without any sample pretreatment. Approximately 250-fmol amounts of amino acids, labelled with 2,4-dinitrophenyl, were detectable with the technique employed. This is almost three decades lower in comparison to what is achievable with an high resolution universal detector. The adsorption of the analytes in the sample handling devices as well as in the separation compartment were problems in the analysis at this concentration level. The detection limit given above was achieved when these phenomena were suppressed by the addition of naphthalene-1,3,6-trisulphonate or pyrophosphate to the sample solution.