A water-activated pump for portable microfluidic applications

An on-chip micropump for portable microfluidic applications was investigated using mathematical modeling and experimental testing. This micropump is activated by the addition of water, via a dropper, to ionic polymer particles that swell due to osmotic effects when wetted. The resulting particle volume increase deflects a membrane, forcing a separate fluid from an adjacent reservoir. The micropump components, along with the microfluidic components, are fabricated using the contact liquid photolithographic polymerization (CLiPP) method. The maximum flow rate achieved with this pump is 17 microL per minute per mg of dry polymer particles of 355-425 microm in diameter. The pump flow rate may be controlled by adjusting the particle size and amount, the membrane properties, and the channel dimensions. The experimental results demonstrate good agreement with an analytical model describing the particle swelling and its coupling with resistive forces from the bending membrane, viscous flow in the microchannel, and interfacial effects. Key features of this micropump are that it can be placed directly on a microdevice, and that it requires only a small amount of water and no external power supply to function. Therefore, this pumping system is useful for applications in which a highly portable device is required.     

Assay of Bicarbonate Content in Certain Effervescent Formulations

Abstract

A quantitative method was developed for the assay of the bicarbonate content in a number of potassium-replacement effervescent tablets with citric acid. The method involved treatment of an aliquot of the crushed tablet with water, then with 0.5 N sulfuric acid, followed by quantitative absorption of the liberated carbon dioxide into 0.2 N sodium hydroxide in a closed system with a calcium chloride-protected vent. The sodium carbonate-sodium hydroxide solution was subjected to a two-step titration with standard acid using phenolphthalein and bromophenol blue indicators for the first and second step, respectively. Overall percent recovery (± SD) of potassium bicarbonate from simulated tablets were: 99.6 ± 0.9% (n = 4); in presence of potassium citrate, 100.0 ± 1.3% (n = 4); and in presence of potassium chloride and L-lysine hydrochloride, 101.5 ± 1.9% (n = 3). Application of the method to commercial products near the expiration date showed potassium bicarbonate contents of 80–90% of label claim. The method may be applied to the assay of any bicarbonate salt in other effervescent formulations.     

Carbon Dioxide Measurements with and without Barium Peroxide in Electrolytic Studies with and without a Supporting Electrolyte

Abstract

This research deals with the quantitative formation of carbon dioxide in electrolytic oxidation reactions. The electrolytic reactions were run with barium peroxide to generate the superoxide anion at the anode. With the organic compounds used in these electrolytic studies we needed to develop a method where we could determine the amount of carbon dioxide liberated from these compounds with the superoxide anion. This method degasses an acidified solution with dry nitrogen, which carries the carbon dioxide to a standard solution of sodium hydroxide. Titration of the sodium hydroxide solution with standardized hydrochloric acid revealed the amount of carbon dioxide formed in the reaction after precipitation of the carbonate ions with barium chloride. Blank runs with the apparatus using anhydrous sodium carbonate produced 99% plus results of recovered carbon dioxide from the sodium carbonate.     

Three-dimensional interconnected microporous poly(dimethylsiloxane) microfluidic devices

This technical note presents a fabrication method and applications of three-dimensional (3D) interconnected microporous poly(dimethylsiloxane) (PDMS) microfluidic devices. Based on soft lithography, the microporous PDMS microfluidic devices were fabricated by molding a mixture of PDMS pre-polymer and sugar particles in a microstructured mold. After curing and demolding, the sugar particles were dissolved and washed away from the microstructured PDMS replica revealing 3D interconnected microporous structures. Other than introducing microporous structures into the PDMS replica, different sizes of sugar particles can be used to alter the surface wettability of the microporous PDMS replica. Oxygen plasma assisted bonding was used to enclose the microstructured microporous PDMS replica using a non-porous PDMS with inlet and outlet holes. A gas absorption reaction using carbon dioxide (CO(2)) gas acidified water was used to demonstrate the advantages and potential applications of the microporous PDMS microfluidic devices. We demonstrated that the acidification rate in the microporous PDMS microfluidic device was approximately 10 times faster than the non-porous PDMS microfluidic device under similar experimental conditions. The microporous PDMS microfluidic devices can also be used in cell culture applications where gas perfusion can improve cell survival and functions.     

Simple and accurate method for determining dissolved inorganic carbon in environmental water by reaction headspace gas chromatography

We investigate a simple and accurate method for quantitatively analyzing dissolved inorganic carbon in environmental water by reaction headspace gas chromatography. The neutralization reaction between the inorganic carbon species (i.e. bicarbonate ions and carbonate ions) in environmental water and hydrochloric acid is carried out in a sealed headspace vial, and the carbon dioxide formed from the neutralization reaction, the self‐decomposition of carbonic acid, and dissolved carbon dioxide in environmental water is then analyzed by headspace gas chromatography. The data show that the headspace gas chromatography method has good precision (relative standard deviation ≤ 1.63%) and accuracy (relative differences ≤ 5.81% compared with the coulometric titration technique). The headspace gas chromatography method is simple, reliable, and can be well applied in the dissolved inorganic carbon detection in environmental water.     

Fuel cell-powered microfluidic platform for lab-on-a-chip applications

The achievement of a higher degree of integration of components--especially micropumps and power sources--is a challenge currently being pursued to obtain portable and totally autonomous microfluidic devices. This paper presents the integration of a micro direct methanol fuel cell (μDMFC) in a microfluidic platform as a smart solution to provide both electrical and pumping power to a Lab-on-a-Chip system. In this system the electric power produced by the fuel cell is available to enable most of the functionalites required by the microfluidic chip, while the generated CO(2) from the electrochemical reaction produces a pressure capable of pumping a liquid volume through a microchannel. The control of the fuel cell operating conditions allows regulation of the flow rate of a liquid sample through a microfluidic network. The relation between sample flow rate and the current generated by the fuel cell is practically linear, achieving values in the range of 4-18 μL min(-1) while having an available power between 1-4 mW. This permits adjusting the desired flow rate for a given application by controlling the fuel cell output conditions and foresees a fully autonomous analytical Lab-on-a-Chip in which the same device would provide the electrical power to a detection module and at the same time use the CO(2) pumping action to flow the required analytes through a particular microfluidic design.     

Continuous determination of carbon dioxide evolved during thermal decomposition reactions

A simple device suitable for continuous monitoring of carbon dioxide evolved during thermal decomposition reactions is described. Carbon dioxide is transported by a carrier gas through the device connected to thermoanalytical equipment and absorbed by soda lime reagent. The reaction heat released is linearly proportional to the amount of carbon dioxide absorbed.     

Cosorption effect in gas chromatography: flow fluctuations caused by adsorbing carrier gases

Adsorbing carrier gases have a number of advantages in analytical and preparative gas chromatography, such as clearer detector signals and higher column efficiencies. This work shows that adsorbing carrier gases also may be useful because they cause the mobile phase flow rate to become unsteady after injecting a small amount of sample. This work shows that a 100 microL sample of helium can liberate enough carbon dioxide carrier gas from a zeolite 5A packed column at 373 K, that the departure from the steady-state flow rate had an upper lobe area of 586 microL of carrier gas. This was confirmed by coupling a modified Langmuir kinetic model with the Ergun equation.     

Development of Microdroplet Generation Method for Organic Solvents Used in Chemical Synthesis

Recently, chemical operations with microfluidic devices, especially droplet-based operations, have attracted considerable attention because they can provide an isolated small-volume reaction field. However, analysis of these operations has been limited mostly to aqueous-phase reactions in water droplets due to device material restrictions. In this study, we have successfully demonstrated droplet formation of five common organic solvents frequently used in chemical synthesis by using a simple silicon/glass-based microfluidic device. When an immiscible liquid with surfactant was used as the continuous phase, the organic solvent formed droplets similar to water-in-oil droplets in the device. In contrast to conventional microfluidic devices composed of resins, which are susceptible to swelling in organic solvents, the developed microfluidic device did not undergo swelling owing to the high chemical resistance of the constituent materials. Therefore, the device has potential applications for various chemical reactions involving organic solvents. Furthermore, this droplet generation device enabled control of droplet size by adjusting the liquid flow rate. The droplet generation method proposed in this work will contribute to the study of organic reactions in microdroplets and will be useful for evaluating scaling effects in various chemical reactions.     

Ion chromatographic determination of organic acids in food samples using a permanent coating graphite carbon column

From the viewpoint of a graphite carbon column with excellent durability, it was applied to the ion chromatography (IC) of several organic acids. The carbon column was permanently coated with the cetyltrimethylammonium (CTMA) ion, and the elution behaviors of several organic acids (acetic acid, lactic acid, succinic acid, malic acid, tartaric acid, citric acid) and inorganic anions (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻) were examined according to a non-suppressed IC coupled with conductivity detector, when an ion-exchange ability was given to the graphite carbon column. When salicylic acid and sodium salicylate were used as a mobile phase, each organic acid are analyzed approximately 10 min. But the separation of malic acid, chloride and nitrite was difficult. When benzoic acid and 2-amino-2-hydroxymethyl-1,3-puropanediol (tris aminomethane) were used as a mobile phase, tartaric acid and citric acid, etc. with large valency showed tendency to which the width of each peaks extended and retention time increased. However, it was possible to separate excellently for the analytes detected within 10 min. The developed method was then applied to the determination of organic acids in several food samples.     

Spontaneous generation of emulsion droplets by autonomous fluid-pumping using the gas permeability of poly(dimethylsiloxane) (PDMS)

Conventional droplet-based microfluidic systems require expensive, bulky external apparatuses, such as electric power supplies and pressure-driven pumps for fluid transportation. This study demonstrates an alternative way to produce emulsion droplets by autonomous fluid-handling based on the gas permeability of poly(dimethylsiloxane) (PDMS). Furthermore, basic concepts of fluid-handling are expanded to control the direction of the microfluid in the microfluidic device. The alternative pumping energy resulting from the high gas permeability of PDMS is used to generate water-in-oil (W/O) emulsions, which require no additional structures apart from microchannels. We can produce emulsion droplets by simple loading of the oil and aqueous solutions into the inlet reservoirs. During the operation of the microfluidic device, changes in droplet size, volumetric flow rate, and droplet generation frequency were quantitatively analyzed. As a result, we found that changes in the wetting properties of the microchannel greatly influence the volumetric flow rate and droplet generation frequency. This alternative microfluidic approach for preparing emulsion droplets in a simple and efficient manner is designed to improve the availability of emulsion droplets for point of care bioanalytical applications, in situ synthesis of materials, and on-site sample preparation tools.     

Self‐acidity induced effervescence and manual shaking‐assisted microextraction of neonicotinoid insecticides in orange juice

A novel dispersive liquid‐liquid microextraction that combines self‐induced acid‐base effervescent reaction and manual shaking, coupled with ultra high performance liquid chromatography with tandem mass spectrometry was developed for simultaneous determination of ten neonicotinoid insecticides and metabolites in orange juice. An innovative aspect of this method was the utilization of the acidity of the juice for a self‐reaction between acidic components contained in the juice sample and added sodium carbonate which generated carbon dioxide bubbles in situ, accelerating the analytes transfer to the extractant of 1‐undecanol. The total acid content of juice sample was measured to produce the maximum amount of bubbles with minimum usage of carbonate. Manual shaking was subsequently adopted and was proven to enhance the extraction efficiency. The factors affecting the performance, including the type and the amount of the carbon dioxide source and extractant, and ionic strength were optimized. Compared with conventional methods, this approach exhibited low limits of detection (0.001–0.1 µg/L), good recoveries (86.2–103.6%), high enrichment factors (25–50), and negligible matrix effects (?12.3–13.7%). The proposed method was demonstrated to provide a rapid, practical, and environmentally friendly procedure due to no acid reagent, toxic solvent, or external energy requirement, giving rise to potential application on other high acid‐content matrices.     

Kinetics of Absorption of Carbon Dioxide into Sodium Metaborate Solution

Carbon dioxide capture potential of sodium metaborate, which is the main product of the process by means of which hydrogen is obtained from sodium borohydride, was investigated. This work aims at both carbon dioxide capture and finding an alternative use for sodium metaborate. The products of this chemical absorption are sodium carbonate, sodium bicarbonate, and boric acid; all of which are industrially important chemicals. In this study, the kinetics of the reaction between sodium metaborate and carbon dioxide was investigated at atmospheric pressure and temperatures between 17 and 50°C while initial sodium metaborate concentration was changed as 0.5, 1, and 2.5 wt%. The frequency factor and activation energy for this reaction were found as 1.97 × 10⁻³ m³/mol‐s and 18,062 J/mol, respectively.     

A method for the simultaneous detection of hydrogen fluoride and fluorine

A relatively simple and rapid method for detecting hydrogen fluoride and elemental fluorine is described. A solution containing sodium bicarbonate and potassium bromide is treated with the gas. Hydrogen fluoride immediately liberates carbon dioxide from the bicarbonate; elemental fluorine immediately colours the solution and then causes the evolution of oxygen, hydrogen peroxide and hydrogen fluoride. A mixture of fluorine and hydrogen fluoride simultaneously colours the solution and evolves carbon dioxide.     

苯甲酸钐的水热合成和热分解反应机理

用水热法合成了无水苯甲酸钐配合物,经元素分析、IR和X射线粉末衍射表征了该配合物,系层状结构,属单斜晶系。用TG、DTA、IR、色谱-质谱联用仪研究了它的热分解机理。在氮气氛下,热分解分两步进行:第一步分解生成钐的二碳酸一氧盐和有机化合物。生成的有机化合物成分比较复杂,主要成分为苯甲酸、二苯甲酮、9,10-蒽醌和1,3-二苯基异苯并呋喃等。第二步二碳酸一氧盐进一步分解生成氧化钐和二氧化碳。     

Novel headspace gas chromatographic method for determination of oxalate in oxygen delignification liquor

A novel headspace gas chromatographic (HS-GC) method is demonstrated for an indirect determination of oxalate in oxygen delignification liquors. A small volume (50-100 microL) of liquor sample is introduced into a sampling vial that contains 1.0 mL of 2 mol/L sulfuric acid. After removal of carbon dioxide (generated from carbonate in the acidic medium) by heating, the sample was mixed with a 0.5 mL of 0.02 mol/L potassium permanganate solution in a closed testing vial. At an elevated temperature (70 degrees C), the oxalate in the sample is rapidly converted to carbon dioxide by reacting with permanganate. The carbon dioxide in the headspace can be measured by gas chromatography with a thermal conductive detector. Using a multiple headspace extraction (MHE) measurement technique, the kinetics of formation of the carbon dioxide from the other organic species in the sample can be determined, and thus a correction can be made for minimizing the interferences. The present method is simple, accurate and can be easily automated.     

An evaporation-based microfluidic sample concentration method

We present a method for sample concentration within microfluidic devices using evaporation-induced flow. Evaporation-induced flow is easy to incorporate into microfluidic designs and can be used to concentrate a wide variety of molecules. The practicality of this method was demonstrated with 0.2 microm fluorescent spheres and FITC-labeled BSA. Thirty two percent of the 0.6 microL fluorescent sphere suspension was concentrated into a well within a microfluidic device. In the same amount of time, 93% of the 0.6 microL FITC-labeled BSA solution was concentrated.     

Flexible microfluidic devices with three-dimensional interconnected microporous walls for gas and liquid applications

This article presents a simple, low-cost method of fabrication and the applications of flexible polystyrene microfluidic devices with three-dimensional (3D) interconnected microporous walls based on treatment using a solvent/non-solvent mixture at room temperature. The complete fabrication process from device design concept to working device can be completed in less than an hour in a regular laboratory setting, without the need for expensive equipment. Microfluidic devices were used to demonstrate gas generation and absorption reactions by acidifying water with carbon dioxide (CO(2)) gas. By selectively treating the microporous structures with oxygen plasma, acidification of water by acetic acid (distilled white vinegar) perfusion was also demonstrated with the same device design.     

Microfluidic chip-based fabrication of PLGA microfiber scaffolds for tissue engineering

In this paper, we have developed a method to produce poly(lactic- co-glycolic acid) (PLGA) microfibers within a microfluidic chip for the generation of 3D tissue engineering scaffolds. The synthesis of PLGA fibers was achieved by using a polydimethylsiloxane (PDMS)-based microfluidic spinning device in which linear streams of PLGA dissolved in dimethyl sulfoxide (DMSO) were precipitated in a glycerol-containing water solution. By changing the flow rate of PLGA solution from 1 to 50 microL/min with a sheath flow rate of 250 or 1000 microL/min, fibers were formed with diameters that ranged from 20 to 230 microm. The PLGA fibers were comprised of a dense outer surface and a highly porous interior. To evaluate the applicability of PLGA microfibers generated in this process as a cell culture scaffold, L929 fibroblasts were seeded on the PLGA fibers either as-fabricated or coated with fibronectin. L929 fibroblasts showed no significant difference in proliferation on both PLGA microfibers after 5 days of culture. As a test for application as nerve guide, neural progenitor cells were cultured and the neural axons elongated along the PLGA microfibers. Thus our experiments suggest that microfluidic chip-based PLGA microfiber fabrication may be useful for 3D cell culture tissue engineering applications.     

Some investigations for a titrimetric determination of nanomoles of carbon

The ultramicrocoulometric acidimetric titration of carbon dioxide in an aqueous solution was compared with a simple volumetric titration in nonaqueous solution. The lower limit of determination was about 200 and 20 ng carbon, respectively. A determination of organic carbon (as benzoic acid or sucrose) in an aqueous solution takes less than 1 min.