Bayesian Methods for Ion Selective Electrodes

With the increasing use of ion‐selective electrodes in environmental and health applications, it is important to know the precision of estimated concentrations. A Bayesian model for non‐linear calibration is introduced which provides estimates of measurement precision by incorporating uncertainty in calibration parameters and inherent random noise in emf response. The analysis of lead in 17 soil samples demonstrates that large gains in precision are possible when calibrations are extended to include multiple electrodes and standard addition data. The results highlight the need for improved calibration and routine use of standard addition as ion selective electrodes become increasingly popular for demanding, real world applications.     

Molecular-modulation spectrometry: CH3ONO photolysis and detection of nitroxyl

The method of molecular-modulation spectrometry for studying photochemical reactions has been applied to methyl nitrite photolysis. The infrared absorption of the nitroxyl radical HNO has been observed in the gas phase at 3300 cm^?1. Under the present experimental conditions the steady-state concentration of HNO under steady illumination was 1.1 × 10¹² particles/cc, and the observed modulation amplitude was 4.5 × 10¹⁰ particles/cc. At 25°C and 1 atm of nitrogen, the cross section for infrared absorption by HNO at 3300 cm^?1 is 1.7 × 10^?19 cm². The rate constant ratio b/c was found to be 8.0. From the literature value of the rate constant d , the observed rate constant for the reaction is e = (5 ± 1) × 10^?11 cc/particle sec.     

Nucleation near a critical temperature

In this paper we extend the conventional theory of nucleation to take in the effects of excluded-volume interference between the precritical droplets present prior to phase transformation. It is shown that, close to the critical point, the effect of excluded volume is to cause a sizable increase in the surface free energy of the critical nucleus. A corresponding increase in the barrier to nucleation explains the large undercoolings achieveable experimentally in this region. Our results are compared with recent experimental measurements of Heady and Cahn and favorable agreement is found.Supported in part by National Science Foundation Grant NSF CHE 76-21297.     

Homogeneous nucleation of metals in a plasma-quench reactor

We present a new and general application of the method of moments for modeling the nucleation of condensates in a steady-state supersonic nozzle flora generated in a plasma-quench reactor. A closed set of growth/evaporation rate equations has been employed to propagate the moments of the particle size distribution without invoking the usual coarse-graining or truncation approximations of conventional binning approaches. The method has been employed to calculate the nucleation rates, particle number density, and the particle-size distribution for 11 elemental metals (Ag, Al, Be, Ce, Cr, Fe, Gd, Ti, Th, U, and Zr) condensing in a model argon nozzle flow. We have identified the regions in the nozzle of maximum nucleation rate, and have shown how different particle-size distributions can develop in different regions.     

Performance impact of dynamic surface coatings on polymeric insulator-based dielectrophoretic particle separators

Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously, using insulator-based dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric microfluidic devices with surfactant coatings provide an affordable engineering strategy for selective particle enrichment and sorting. Figure Model generated image (COMSOL) depicting the electric field gradient divided by the electric field that occurs within an array of insulating posts