Measurement/data-processing method to improve the ruggedness of membrane-based sensors: Application to amperometric oxygen sensor

This paper describes alternative measurement and data-processing approaches that can reduce effects of experimental variables on results obtained with a membrane-based sensor for oxygen. In the new approaches, the membrane-based sensor is first equilibrated with the sample solution, after which a polarizing voltage is applied and current vs. time data are recorded as the response decays toward a steady-state condition. Current vs. time data are then processed by a fixed-time option and an integration option designed to determine the charge corresponding to the total amount of oxygen inside the membrane when a polarizing voltage is applied. The current measured at a fixed time and the total charge varied linearly with oxygen concentration between 0.05 and 0.26 mmol l(-1). Pooled relative standard deviations (N = 35) for the measurement/data-processing step were near 0.4% for the new pre-equilibrium options compared to a value of 0.3% for the steady-state option. Dependencies of the pre-equilibrium options on membrane thickness and stirring rate in the most sensitive regions were at least two orders of magnitude smaller than for the steady-state option.     

Kinetic aspects of analytical chemistry

A broad view of the role of kinetics in analytical chemistry is presented. Two principal themes are that the role of kinetic methods is much greater than is generally acknowledged and that the most commonly used kinetic approaches make inadequate use of information that is available. After a brief discussion of historical developments that date back to the latter part of the 1800s, primary attention is focused on a classification of measurement and data-processing approaches that have been developed. Approaches are grouped into methods for single components without and with error compensation and methods for resolving two or more components in mixtures. They are further grouped into direct-computation and curve-fitting approaches and into integral and derivative methods within these more general categories. Correlations are then drawn between these approaches as applied to chemical processes and to physicochemical and purely physical processes such as luminescence, electrode responses, and flow systems, including chromatographic processes. It is argued that all analytical methods are either kinetic or equilibrium in character and that kinetic-based methods represent a much larger fraction of the total than is generally recognized.     

Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part I: Creep constitutive relation and fatigue model

In this study, a new unified creep constitutive relation and a modified energy-based fatigue model have been established respectively to describe the creep flow and predict the fatigue life of Sn−Pb solders. It is found that the relation successfully elucidates the creep mechanism related to current constitutive relations. The model can be used to describe the temperature and frequency dependent low cycle fatigue behavior of the solder. The relation and the model are further employed in part II to develop the numerical simulation approach for the long-term reliability assessment of the plastic ball grid array (BGA) assembly. The project supported by the National Natural Science Foundation of China (59705008)     

Quantitation and identification of polynuclear aromatic hydrocarbons by liquid chromatography and multiwavelength absorption spectrometry

This paper describes the combined use of liquid chromatographic separation with multiwavelength absorption detection for the quantitation and identification of polynuclear aromatic hydrocarbons. Quantiative results are presented for three- and four-component mixtures with complete and partial separation. Qualitative data are presented for a twelve-component synthetic mixture and for extracts from a filter used to collect particulate emissions from a biomass-gasifier system. It is shown that multiwavelength data-processing methods commonly applied to absorption spectra can be applied with significant advantage to second-derivative spectra. Results indicate that significant improvements can be achieved by the use of different wavelength ranges for different components in mixtures. Detection limits for single-component samples varied between 3 and 11 μg l^?1 for eleven hydrocarbons and the scatter about calibration plots for mixtures was in the range of 0.05 to 0.4 μg ml^?1. The identities of all twelve components in the synthetic mixture were confirmed and nineteen components were identified in the sample from the biomass gasifier filter.     

Algorithm for error-compensated kinetic determinations without prior knowledge of reaction order or rate constant

The development and evaluation of a new algorithm for error-compensating predictive kinetic determinations are described. With the new algorithm it is possible to fit kinetic data without prior knowledge of the rate constant, reaction order or initial and final values of the detector signal. A curve-fitting method is used to obtain values of these parameters that give the best fit of the model to the data. Although intended to be used primarily to compute signal changes between t=0 and ∞, the method can also be used to determine reaction orders. Although the algorithm fails for reaction orders of zero and unity, it works well for orders between these values and orders greater than unity. Simulated data are used to evaluate the effects of reaction order, signal noise and data range on computed values of signal change and, to a lesser extent, reaction order.     

Kinetic study of competing first-order processes: simultaneous quantification of hemoglobin and methemoglobin in whole blood

The development and evaluation of a kinetic method for the simultaneous quantification of methemoglobin and hemoglobin is described. A unique feature of the reaction/monitoring system is that the two species produce signals that change in opposite directions. Attempts to optimize the reaction conditions, procedures for preparing reliable standards, a new multiwavelength method used for comparison purposes and results for synthetic standards and blood samples to which known amounts of methemoglobin are added are described. Combined effects of competing directions of signal change, large concentration differences and conditions required for pseudo-first-order behavior results in a relativity narrowly defined set of conditions that permit simultaneous determinations. Even so, results for methemoglobin were in reasonable agreement between the kinetic and spectrophotometric methods (slope 1.05, intercept 0.17 mmol l^?1); difficulties in achieving pseudo-first-order behavior yielded less reliable results for hemoglobin with a least-squares slope of 1.16 for a comparison of results by kinetic and spectrophotometric methods. This latter problem had an adverse effect on comparison of percentages of methemoglobin in samples even though concentration values were in good agreement.     

Echelle-spectrometer/image-dissector system for elemental quantitation by continuous-source atomic absorption spectrometry

The performance of an echelle-spectrometer/image-dissector system is evaluated for elemental quantitation by continuous-source atomic absorption spectrometry. Flame and graphite-furnace atomizers were used, as well as two different spectrometer configurations. Quantitative results obtained with the flame atomizer and a low-resolution spectrometer configuration are discussed briefly; results obtained with the graphite-furnace atomizer and a higher-resolution configuration are presented in detail. Absorption sensitivities for calcium (422.7 nm), chromium (425.4 and 357.9 nm), copper (324.8 nm), and manganese (403.1 and 279.5 nm) were all within a factor of 4–6 of comparable line- source absorption sensitivities, and calibration curves were linear up to absorbances of about 0.1. Further development of the system for simultaneous multi-element quantitation is discussed.     

Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part II: Reliability experiment and numerical simulation

In the present study, a facility, i.e., a mechanical deflection system (MDS), was established and applied to assess the long-term reliability of the solder joints in plastic ball grid array (BGA) assembly. It was found that the MDS not only quickly assesses the long-term reliability of solder joints within days, but can also mimic similar failure mechanisms in accelerated thermal cycling (ATC) tests. Based on the MDS and ATC reliability experiments, the acceleration factors (AF) were obtained for different reliability testing conditions. Furthermore, by using the creep constitutive relation and fatigue life model developed in part I, a numerical approach was established for the purpose of virtual life prediction of solder joints. The simulation results were found to be in good agreement with the test results from the MDS. As a result, a new reliability assessment methodology was established as an alternative to ATC for the evaluation of long-term reliability of plastic BGA assembly. The project supported by the National Natural Science Foundation of China (59705008)