Simplified universal method for determining electrolyte temperatures in a capillary electrophoresis instrument with forced-air cooling.

Temperature increase due to resistive electrical heating is an inherent limitation of capillary electrophoresis (CE). Active cooling systems are used to decrease the temperature of the capillary, but their capacity is limited; and in addition, they leave "hot spots" at the detection interface and at the capillary ends. Until recently, the matter was complicated by the lack of a fast and generic method for temperature determination in efficiently and inefficiently cooled regions of the capillary.

Universal method for determining electrolyte temperatures in capillary electrophoresis.

Temperature increase in capillary electrophoresis (CE) due to Joule heating is an inherent limitation of this powerful separation technique. Active cooling systems can decrease the temperature of a large part of the capillary but they leave "hot spots" at the capillary ends which can completely ruin some CE analyses despite their short lengths. Here, we introduce a "universal method for determining electrolyte temperatures" (UMET) that can determine temperatures in both efficiently- and inefficiently-cooled parts of the capillary.

Milli-free flow electrophoresis: I. Fast prototyping of mFFE devices.

We coin a term of milli-free flow electrophoresis (mFFE) to describe mid-scale FFE with flow rates intermediate to macro-FFE and micro-FFE (μFFE). Introduced decades ago, mFFE did not find practical applications. We revive mFFE, as we view it as a viable purification complement to continuous synthesis in capillary reactors with product flow rates of ∼5 to 2000 μL/min, too small for macro-FFE but too large for μFFE.

Heat-associated field distortion in electro-migration techniques.

Electro-migration techniques, such as electrophoresis, are widely utilized in analytical sciences. If a single electrolyte is used, the field strength is typically assumed to be well-defined. Heat-associated field distortion (HAFD) has been suggested as a result of the nonuniform heat dissipation throughout the electrolyte; however, it has never been experimentally studied.

Non-orthogonal micro-free flow electrophoresis: from theory to design concept.

Micro-free flow electrophoresis (microFFE) is a technique that facilitates continuous separation of molecules in a shallow channel with a hydrodynamic flow and an electric field at an angle to the flow. We recently developed a general theory of microFFE that suggested that an electric field non-orthogonal to the flow could improve resolution. Here, we used computer modeling to study resolution as a function of the electric field strength and the angle between the electric field and the hydrodynamic flow.

Optimized ultrasound-assisted extraction procedure for the analysis of opium alkaloids in papaver plants by cyclodextrin-modified capillary electrophoresis.

This study investigated the use of ultrasound-assisted extraction to improve the extraction efficiency of morphine, codeine and thebaine from the papaver plants. Extraction conditions such as type of solvent, temperature, duration, frequency and power level of ultrasonic were optimized and the influences of different parameters on resolution of alkaloids in CE were studied. The optimized condition for CE separation includes a sodium phosphate buffer (100 mM, pH 3.

Non-orthogonal-to-the-flow electric field improves resolution in the orthogonal direction: hidden reserves for combining synthesis and purification in continuous flow.

There is a pressing need for continuous purification of products of synthesis conducted in continuous-flow microreactors. An existing technique, micro free-flow electrophoresis (microFFE), could fulfill this niche if its resolving power for similar molecules was improved. MicroFFE continuously separates ions in the hydrodynamic flow by an electric field orthogonal to the flow.

Determination of the surface heat-transfer coefficient in CE.

A knowledge of the heat-transfer coefficient, h(s), for the external surface of the capillary or the overall heat coefficient, h(OA), is of great value in predicting the mean increase in temperature of the electrolyte, DeltaT(Mean), during electrokinetic separations. For CE, traditional indirect methods of determining h(s) were time-consuming and tended to overestimate cooling efficiency; a novel method is introduced, which is based on curve-fitting of plots of conductance versus voltage to calculate several important parameters including DeltaT(Mean), h(s), the conductance free of Joule heating effects (G(0)) and the voltage that causes autothermal runaway, V(lim). The new method is superior to previously published methods in that it can be performed more quickly and that it corrects for systematic errors in the measurement of electric current for voltages <5 kV.

Joule heating effects and the experimental determination of temperature during CE.

Joule heating is ubiquitous in electrokinetic separations. This review is in two major parts. The first part documents the effects of Joule heating on the physical properties of the electrolyte and efficiency of separations and the second part focuses on advances in the determination of electrolyte temperatures that have been described in the literature over the past 5 years.

Separation of inorganic anions on a high capacity porous polymeric monolithic column and application to direct determination of anions in seawater.

A commercially available 4.6 mm id x 50 mm polymethacrylate-based monolithic strong anion exchange column (ProSwift SAX-1S) designed for the separation of proteins has been successfully used to separate small inorganic anions in the presence of a seawater sample matrix. Using a hydroxide eluent with suppressed conductivity detection the ion exchange capacity of this column declined over time; however, using KCl as the eluent, the column performance was stable with a capacity of 530 microequiv.

Reliable electrophoretic mobilities free from Joule heating effects using CE.

Ionic electrophoretic mobilities determined by means of CE experiments are sometimes different when compared to generally accepted values based on limiting ionic conductance measurements. While the effect of ionic strength on electrophoretic mobility has been long understood, the increase in the mobility that results from Joule heating (the resistive heating that occurs when a current passes through an electrolyte) has been largely overlooked. In this work, a simple method for obtaining reliable and reproducible values of electrophoretic mobility is described.

Fluorinated ethylenepropylene copolymer as a potential capillary material in CE.

In this work, a new generation UV-transparent polymer, fluorinated ethylenepropylene copolymer (FEP) exhibiting a low degree of crystallinity, extruded in dimensions similar to the most commonly used CE capillaries of approximately 80 mum id and about 360 mum od was investigated for its use as a CE capillary. FEP is transparent down to the low-UV region, and as fluorinated polymers in general are good electrical insulators and exhibit reasonable heat conductivity, it has considerable potential as a material for electrodriven analysis in capillary or microchip formats. The FEP capillary has been characterised with regard to some important aspects for its use as a CE capillary, including its profile of EOF versus pH, as well as procedures for manipulating EOF by coating the inner capillary wall with various semipermanent and dynamic layers.

Identification of inorganic improvised explosive devices by analysis of postblast residues using portable capillary electrophoresis instrumentation and indirect photometric detection with a light-emitting diode.

A commercial portable capillary electrophoresis (CE) instrument has been used to separate inorganic anions and cations found in postblast residues from improvised explosive devices (IEDs) of the type used frequently in terrorism attacks. The purpose of this analysis was to identify the type of explosive used. The CE instrument was modified for use with an in-house miniaturized light-emitting diode (LED) detector to enable sensitive indirect photometric detection to be employed for the detection of 15 anions (acetate, benzoate, carbonate, chlorate, chloride, chlorite, cyanate, fluoride, nitrate, nitrite, perchlorate, phosphate, sulfate, thiocyanate, thiosulfate) and 12 cations (ammonium, monomethylammonium, ethylammonium, potassium, sodium, barium, strontium, magnesium, manganese, calcium, zinc, lead) as the target analytes.

Temperature profiles and heat dissipation in capillary electrophoresis.

While temperature control is usually employed in capillary electrophoresis (CE) to aid heat dissipation and provide acceptable precision, internal electrolyte temperatures are almost never measured. In principle, this limits the accuracy, repeatability, and method robustness. This work presents a fundamental study that combines the development of new equations characterizing temperature profiles in CE with a new method of temperature determination.

Variation of zeta-potential with temperature in fused-silica capillaries used for capillary electrophoresis.

The temperature variation of electroosmotic mobility corrected for the effects of Joule heating (muEOF0) was employed to investigate the variation of the zeta-potential (zeta) with temperature in fused-silica capillaries. Experimentally determined values for zeta increased at 0.39% per degrees C, a rate that is about four to five times smaller than reported previously.

Internal electrolyte temperatures for polymer and fused-silica capillaries used in capillary electrophoresis.

Polymers are important as materials for manufacturing microfluidic devices for electrodriven separations, in which Joule heating is an unavoidable phenomenon. Heating effects were investigated in polymer capillaries using a CE setup. This study is the first step toward the longer-term objective of the study of heating effects occurring in polymeric microfluidic devices.

Conductivity detection for conventional and miniaturised capillary electrophoresis systems.

Since the introduction of capillary electrophoresis (CE), conductivity detection has been an attractive means of detection. No additional chemical properties are required for detection, and no loss in sensitivity is expected when miniaturising the detector to scale with narrow-bore capillaries or even to the microchip format. Integration of conductivity and CE, however, involves a challenging combination of engineering issues.

Determination of inorganic ions using microfluidic devices.

The separation and detection of inorganic ions on microfluidic devices has received little attention since the 'lab-on-a-chip' concept has revolutionised the field of electrokinetically driven analysis. This review presents a summary and discussion of the published literature on inorganic analysis using microfluidic devices and includes sections on electromigration separation methods, namely isotachophoresis (ITP), capillary electrophoresis (CE), and hyphenated ITP-CE, together with a brief account of flow injection analysis. The review concludes with the authors' perspective on future directions for inorganic analysis on microfluidic devices.