Evaluation of depth profiling using laser resonant desorption as a method to measure diffusion coefficients in ice

Diffusion of gases in ice is involved in cloud, snow, and ice core chemistry, but few data exist on the relevant diffusion coefficients. A novel method to measure diffusion coefficients in ice has recently been proposed by Livingston et al. (Anal. Chem., 2000, 72, 5590-5599). It is based on depth profiling of doped ice crystals epitaxially grown on Ru(001) by laser resonant desorption (LRD). Using this method, Livingston et al. obtained a value of the diffusion coefficient of the HCl hydrate in ice at 190 K of about 5 x 10(-11) cm2/s. We argue here that this value is many orders of magnitude higher than what could be expected from literature values, which are not reported in sufficient detail by Livingston et al. We investigate the possibilities that their high value could be due to (1) diffusion in defects in the ice, which would be present in very high concentrations because of the ice growth method; and (2) the fact that diffusion of high concentrations of HCl in ice at 190 K forms an amorphous HCl:H2O solid mixture, where HCl diffusion is fast. We present new infrared spectroscopic data on solid HCl:H2O mixtures that confirm that such mixtures can indeed be formed in an amorphous state at 190 K. Our proposed interpretation is that by depositing large amounts of HCl on epitaxially grown ice, Livingston et al. created a superficial amorphous binary mixture and that fast diffusion of HCl in the ice, possibly accelerated by a high defect density, produced an amorphous HCl:H2O mixture. We conclude that the processes studied by Livingston et al. are different from those involved in the atmospheric and cryospheric sciences, and that their data, obtained by depth profiling using LRD, probably cannot be applied to those fields.     

The shear viscosity and mutual diffusion coefficients of binary mixtures using the modified Enskog Theory

We use an extended form of the modified Enskog Theory (MET) to calculate viscosity and mutual diffusion coefficients for several binary mixtures. Second and third virial coefficients are required for the calculations. We find that the extended MET provides predictions of the shear viscosity for He-Ar and Ne-Ar mixtures with an accuracy of 2% at densities up to 6 mol · L^–1. Extended MET values of mutual diffusion coefficients of binary mixtures in which the mole fraction of one component approaches zero were calculated for He-Ar and Kr-Ar mixtures. The MET values fall within 10–15% of the experimental data at densities up to 11 mol · L^–1.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

An extensible complex fast Fourier transform processor chip forreal-time spectrum analysis and measurement

This paper describes in detail the design of a CMOS custom fast Fourier transform (FFT) processor for computing a 256-point complex FFT. The FFT is well-suited for real-time spectrum analysis in instrumentation and measurement applications. The FFT butterfly processor reported here consists of one parallel-parallel multiplier and two adders. It is capable of computing one butterfly computation every 100 ns thus it can compute a 256-point complex FFT in 102.4 μs excluding data input and output processes     

Affinity analysis of a protein-aptamer complex using nonequilibrium capillary electrophoresis of equilibrium mixtures

We propose a new method that allows the use of low-affinity aptamers as affinity probes in quantitative analyses of proteins. The method is based on nonequilibrium capillary electrophoresis of the equilibrium mixture (NECEEM) of a protein with its fluorescently labeled aptamer. In general, NECEEM of a protein with a fluorescently labeled aptamer generates an electropherogram with three characteristic features: two peaks and an exponential curve. Two peaks correspond to (i) the equilibrium amount of free aptamer in the equilibrium mixture and (ii) the amount of the protein-aptamer complex that remains intact at the time of detection. The exponential part is ascribed to the complex decaying during separation under nonequilibrium conditions. Simple analysis of the three features in experiments with known concentrations of the protein can be used for the determination of the equilibrium dissociation constant, Kd, of the aptamer-protein complex. Similar analysis of the three features in the experiment with unknown concentration of the protein and known Kd value allows the determination of the protein concentration. In this proof-of-principle work, the NECEEM method was applied to the analysis of thrombin using a fluorescein-labeled aptamer under the conditions at which the protein-aptamer complex completely decayed during the separation. We demonstrated that, despite the decay, as few as 4 x 10(6) molecules of the protein could be detected with NECEEM without sacrificing the accuracy. This sensitivity is comparable with that reported by others for the aptamer-based equilibrium method. Thus, the proposed NECEEM-based method allows the use of aptamers for highly sensitive affinity analysis of proteins even when protein-aptamer complexes are unstable.     

Unsteady mass transfer to drops in liquid flow for appreciably different diffusion coefficients of the continuous and disperse gas phases

Scientific-Industrial Organization State Institute of Applied Chemistry, St. Petersburg. Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 62, No. 2, pp. 195–203, February, 1992.     

Measurement of the binding of proteins to polyelectrolytes by frontal analysis continuous capillary electrophoresis

We have developed a novel technique, frontal analysis continuous capillary electrophoresis (FACCE), to study the binding of proteins to polyelectrolytes. Compared with existing electrophoresis methods such as conventional frontal analysis and the Hummel-Dreyer method, FACCE offers enhanced lower detection limits and is free from effects due to slow binding kinetics, thus making it suitable for studying equilibrium systems. In addition, with a single calibration, FACCE provides for efficient quantitative analysis. Here we report results obtained with β-lactoglobulin as the ligand and sodium poly(styrenesulfonate) (NaPSS) as the ligand-binding substrate. For this model system, FACCE yields reproducible calibration curves and binding isotherms. The binding parameters so determined are compared with previous results for other protein-polyelectrolyte systems.     

Initial density dependence of experimental viscosities and of calculated diffusion coefficients of the binary vapor mixtures methanol-benzene and methanol-cyclohexane

The paper reports experimental results for the viscosity of the vapor mixtures methanol-benzene (five mole fractions with densities up to 1.5kg·m^–3 and 0.022 mol·L ^–1) and methanol-cyclohexane (four mole fractions with densities up to 1.9kg·m^–3 and 0.026 mol·L ^–1). In analogy to the pure components, the measurements on the mixtures were carried out with an oscillating-disk viscometer with small gaps, completely made of quartz, beginning as near as possible to room temperature and continuing to a maximum temperature of 630 K. A first evaluation by means of the Chapman-Enskog theory of dilute gases has shown differences in the resulting values of the interaction viscosity _ij ⁽⁰⁾ in the limit of zero density exceeding the experimental errors. Consistent results were obtained by taking into account the initial density dependence of the viscosity within the framework of the modified Enskog theory for gaseous mixtures. The values of _ij ⁽⁰⁾ were also used to estimate binary diffusion coefficients of the mixtures.     

pH-controlled diffusion of proteins with different pI values across a nanochannel on a chip

Electrostatic interactions dominate the diffusion of proteins in a nanochannel, which was measured and modeled for pH values above and below the isoelectric points of three lectin proteins. Maximal diffusion coefficients were obtained when the proteins were neutral at their pI. This pH-controlled transport led to a separation of biomolecules across the nanochannel. A pI shift was observed, due to reversible adsorption of proteins on the walls, which affects the pH in the nanochannel.     

Homogeneous immunoassay for detection of TNT and its analogues on a microfabricated capillary electrophoresis chip

A homogeneous immunoassay for TNT and its analogues is developed using a microfabricated capillary electrophoresis chip. The assay is based on the rapid electrophoretic separation of an equilibrated mixture of an anti-TNT antibody, fluorescein-labeled TNT, and unlabeled TNT or its analogue. The band intensities of the free fluorescein-labeled TNT and of the antibody-antigen complex reveal the relative equilibrated concentrations. Titration of the anti-TNT antibody with a fluorescein-labeled TNT derivative yields a binding constant of (3.9 +/- 1.3) x 10(9) M(-1). The dissociation rate constant of the complex is determined by kinetic capillary electrophoresis using a folded channel and a rotary scanner to interrogate the separation at multiple time points. The dissociation rate constant is found to be 0.035 +/- 0.005 s(-1), and the resulting binding rate constant is (1.4 +/- 0.7) x 10(7) M(-1) s(-1). Binding constants of TNT and five of its analogues are determined by competitive assays: TNT (4.3 +/- 2.6) x 10(8) M(-1); 1,3,5-trinitrobenzene (5.1 +/- 3.3) x 10(7) M(-1); picric acid (7.5 +/- 4.4) x 10(6) M(-1); 2,4-dinitrotoluene (7.9 +/- 4.0) x 10(6) M(-1); 1,3-dinitrobenzene (1.0 +/- 0.7) x 10(6) M(-1); and 2,4-dinitrophenol (5.1 +/- 3.0) x 10(4) M(-1). TNT and its analogues can be assayed with high sensitivity (LOD 1 ng/mL) and with a wide dynamic range (1-300 ng/mL) using this chip-based method.     

Condensation heat transfer coefficients of halogenated binary refrigerant mixtures on a smooth tube

In this study, external condensation heat transfer coefficients (HTCs) of nonazeotropic refrigerant mixtures of HFC32/HFC134a and HFC134a/HCFC123 at various compositions were measured on a horizontal smooth tube of a 19 mm outside diameter. All data were taken at the vapor temperature of 39 °C with a wall subcooling of 3–8 °C. Test results showed that HTCs of the tested mixtures were 19.4–85.1% lower than the ideal values calculated by the mole fraction weighting of the HTCs of the pure components. A thermal resistance due to the diffusion vapor film seemed to be partly responsible for the significant reduction of HTCs with these nonazeotropic mixtures.     

Gravitational sedimentation induced blood delamination for continuous plasma separation on a microfluidics chip

Continuous plasma separation will be greatly helpful for dynamic metabolite monitoring in kinetics research and drug development. In this work, we proposed a continuous on-chip plasma separation method based on the natural aggregating and sedimentation behavior of red blood cells at low shear rate. In this approach, a glass capillary was first used to realize quick and obvious delamination of blood cells from plasma. A novel "dual-elbow" connector was designed to change the direction of delamination. The blood was finally separated by laminar flow and bifurcation on the microchip. Results demonstrated that the present device can efficiently and stably separate plasma from blood in a continuous means, e.g., in a 4 h separation we did not observe clogging or a trend of clogging. In addition, the present approach can avoid the damage to cells which usually occurs in separation with high shear rate in a microchannel and possible contaminants to plasma. The proposed microchip device is robust, simple, and inexpensive for long time plasma separation with high plasma recovery and less sample consumption. The present work provides an effective tool for metabolite monitoring in pharmacokinetics research and drug development.     

Capillary electrophoresis separations on a planar chip with the column-coupling configuration of the separation channels

Some basic aspects of capillary electrophoresis (CE) separations on a poly(methyl methacrylate) chip provided with two separation channels in the column-coupling (CC) configuration and on-column conductivity detectors were studied. The CE methods employed in this study included isotachophoresis (ITP), capillary zone electrophoresis (CZE), and CZE with on-line ITP sample pretreatment (ITP-CZE). Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed, and electrophoresis was a dominant transport process in the separations performed by these methods. Very reproducible migration velocities of the separated constituents were typical under such transport conditions, and consequently, test analytes could be quantified by various ITP techniques with 1-2% RSD. The CC configuration of the separation channels provides means for an effective combination of an enhanced load capacity of the separation system with high detection sensitivities for the analytes in concentration-cascade ITP separations. In this way, for example, succinate, acetate, and benzoate could be separated also in instances when they were present in the loaded sample (1.2 microL) at 1 mmol/L concentrations while their limits of detection ranged from 8 to 12 micromol/L concentrations. A well-defined ITP concentration of the analyte(s) combined with an in-column sample cleanup (via an electrophoretically driven removal of the matrix constituents from the separation compartment) can be integrated into the separations performed on the CC chip. These sample pretreatment capabilities were investigated in ITP-CZE separations of model samples in which nitrite, phosphate, and fluoride (each at a 10 micromol/L concentration) accompanied matrix constituents (sulfate and chloride) at considerably higher concentrations. Here, both the concentration of the analytes and cleanup of the sample were included in the ITP separation in the first separation channel while the second separation channel served for the CZE separation of the ITP pretreated sample and the detection of the analytes.     

Integrating the digitized backscattered image to measure absorption and reduced-scattering coefficients in vivo

Measurement of absorption and reduced-scattering optical coefficients a and s is possible when a steady-state backscattered image is used on a sample surface. A new method for processing the backscattered image, acquired with a CCD, has been developed. The image is integrated to decrease sensitivity to noise. The resulting curve is defined as the integral reflectance. The curve is then fitted with a relaxation model to evaluate a and s . We have validated the method with calibrated scattering and absorption phantoms. The integral reflectance method is then applied to measurements of the a and s coefficients of human skin in vivo .     

焦耳热对芯片电泳分离效率影响的模拟分析和实验

采用CoventorWare有限元分析软件对电泳芯片管道内焦耳热效应进行了模拟计算和分析,以牛血清白蛋白和溶菌酶作为样品分析对象,通过考虑芯片不同绝缘层厚度、分离场强、缓冲液浓度条件下分离效能,来考察芯片电泳过程中管内焦耳热现象对样品分离的影响,明确了在综合电泳分离条件中限制焦耳热的必要性.     

Modeling of a diffusion process in intensive pressure-assisted electrosintering of powder mixtures to a metal base

A computer model is proposed for the diffusion process that occurs in the contact zone between a composite powder and a metal base during intensive pressure-assisted electrosintering of the powder onto the base. The model consists of two parts: (i) a model of the temperature field in the powder sample volumes under study, and (ii) a model of the diffusion process in the contact zone between the powder particles and the metal base during the sintering. The data on the time variation of the contact temperature, as calculated in the first part, are then used in the second one for solving the diffusion problem. The model adequacy has been verified by comparing the calculated data and the results of laboratory investigations of the diffusion between a titanium powder sample and a copper plate during the pressure-assisted sintering. The model proposed can be used to study structural alterations in powder composites being bonded to a metal base by intensive pressure-assisted electrosintering as well as to optimize the sintering process variables for powder composites.     

Continuous-flow pI-based sorting of proteins and peptides in a microfluidic chip using diffusion potential

Efficient sample preparation tools are the key to measuring molecular signals in a complex biological system. A novel continuous-flow isoelectric point (pI)-based sorting technique has been developed for proteins and peptides in a microfluidic chip format. It can sort biomolecules at a relatively high flow rate of up to 10 microL/min and does not require carrier ampholytes, which can create molecular backgrounds for subsequent analysis. Furthermore, the electrophoretic field required to run the pI-based sorting is generated by the diffusion of buffer ions in situ, at the liquid junction between two laminar flows within the microfluidic channel. Utilizing the diffusion potential in combination with a pH difference between the buffers, we demonstrated a separation of binary mixtures of pI markers and proteins without applying any external field. The sorting resolution and its efficiency are sufficiently high for sample preparation and could be further improved by optimizing buffers or with an additional transverse electric field. Once fully developed, it can potentially be a pI-based sample fractionation tool for proteomic analysis of complex biomolecule samples.     

Automated Fourier transform infrared analysis of urinary stones: technical aspects and example of procedures applied to carbapatite/weddellite mixtures

New software (ScanLith) was developed to provide an automated procedure for identifying and quantifying crystalline species in urinary calculi. The first step was to strictly define operative conditions of sample preparation because they have a significant influence on the stability of various crystalline phases. Second, we determined the quantification coefficients of a polynomial curve required to develop the automated procedure. This was illustrated by the study of carbapatite and weddellite, as both constituents represent one of the most frequent associations found in stones analyzed in our laboratory. The following quadratic equation was obtained with a correlation coefficient r2 = 0.9997: Y = -0.5144x2 + 1.5239x - 0.0141, where Y is the absorbance ratio carbapatite/weddellite and x is the percentage of carbapatite in the mixture. The absorbance of carbapatite and weddellite was measured at 1035 cm(-1) and 1325 cm(-1), respectively. The third step was to validate the ScanLith procedure in routine analysis by comparing computed results with those of an expert. Concordance (r2 = 0.9824) was better than that previously reported using various computerized systems with a mean deviation of 4%. Algorithms developed in ScanLith to identify main and minor components found in urinary stones, even in complex mixtures containing up to seven constituents, allowed us to lower the detection threshold down to 1 to 10% depending on the main component.     

Shah and sine convolution Fourier transform detection for microchannel electrophoresis with a charge coupled device

This paper describes an improved format for Shah convolution Fourier transform (SCOFT) detection that utilizes the spatial resolution of a charge-coupled device (CCD) rather than a fixed optical mask to perform a Shah or sine convolution over a fluorescence signal. The laser-induced fluorescence from a 9-mm section of microfabricated channel is collected with a CCD at 28 Hz. Each image frame is multiplied by a convolution function to modulate the collected signal through space. Each frame is then summed to generate an intensity-versus-time data set for Fourier analysis. The fluorescence signal oscillates at a frequency dependent upon both the convolution function multiplied across each data frame and the velocity of fluorescent microspheres or a plug of fluorescent dye flowing through the channel. This SCOFT technique affords more flexibility over formats that employ a physical mask and provides data that can be optimized for signal-to-noise (S/N) or resolution information. A 1,000-fold improvement in S/N is demonstrated for a plug of fluorescein dye. Detection of fluorescent beads exhibited frequency signals that were dependent upon the bead size distribution, the electric field, and the electrophoresis buffer concentration. Data are presented demonstrating the quantitation of fluorescent microspheres.