Application of personal microcomputers in the analytical laboratory--I: Potentiometric analysis

A novel general-purpose interface-controller unit has been designed and applied in potentiometric analysis. The unit is operated by a personal microcomputer programmed in BASIC. The interface-controller permits direct reading of specific ion-electrodes and can activate, under program control, laboratory instruments such as motor-driven burettes. The interface-controller is expendable to 16 analogue input channels, 16 binary (logic) input lines and 16 control relays but requires only one microcomputer I/O port (a total of 9 I/O lines) to handle all operations. Analogue to digital conversion is realized by counting, with the microcomputer, the output frequency of an analogue-to-frequency converter. This inexpensive method is effective in rejecting interfering signals such as power-line interference. The system has been applied in potentiometric titration analysis for determining the apparent dissociation constants of carbonic acid in sea-water and Dead Sea brines, and for ammonia determination with a gas-sensing electrode.     

The sequential determination of arsenic,selenium, germanium and tin as their hydrides by gas—solid chromatography with an atomic absorption detector

Arsenic, germanium, selenium and tin were sequentially determined in single samples by using hydride generation followed by gas chromatography with an atomic absorption detector. Apparent detection limits varied from 3 ppb for As to 13 ppb for Ge with linear dynamic ranges of about 1.5 orders of magnitude. Relative standard deviations, evaluated in the middle of the working range, varied from 2% to 11%. Chromatographie parameters were chosen to allow for manual lamp selection and monochromator adjustment. Data handling was done by microcomputer. The analysis time was 5 min.     

Control of voltammetric experiments by means of the Commodore 64 microcomputer

An electronic interface for the Commodore 64 microcomputer suitable for generation of voltammetric waveforms and for data acquisition has been built. Used together with analogue voltammetric instruments the interface makes updating of the measurement techniques possible. Also, fast A/D-conversion and a floppy disk drive make the system useful as a universal data-acquisition unit in the laboratory. The system has been tested together with an amperometric detector in the square-wave voltammetric determination of paracetamol and iodide.     

改进单纯形法的计算机模拟及其在化学发光分析中的应用

在分析化学中常常遇到具有交互作用的多因素实验的最优化问题。它往往使一些传统的优化方法陷入困境而很难找到最优化点。而改进单纯形法(MSM)特别适合于分析化学中具有交互作用的多因素最优化实验。MSM法已经用于分析化学的各个领域。本文试图根据改进单纯形法的数学原理,用计算机模拟其优化过程。     

LiF-BaF2-LiCl熔盐体系中Li+的电化学行为

运用三电极在电化学工作站AUTOLAB以循环伏安法、计时电流法和计时电位法研究了LiF-BaF₂-LiCl熔盐体系中1203 K温度下锂在钨（W）电极上的电化学还原过程及其控制步骤. 结果表明,Li⁺在W电极上的还原过程是一步得电子的准可逆反应,析出电位在-1.0 V附近. 阴极过程受离子的扩散步骤控制,计算得出扩散系数为4.5 × 10^-6 cm²•s^-1.     

Negative temperature gradients for density programming in supercritical fluid chromatography

Summary Negative temperature programming using one to three ramps can be utilized to perform density programs in capillary and packed column supercritical fluid chromatography. This method is a less costly alternative to pressuredensity programming. A three step procedure is suggested to optimize the temperature-density program. The separation of wax and crude oil samples is shown.

---

Negative Temperaturgradienten zur Dichteprogrammierung bei der Chromatographie mit überkritischen fluiden Phasen

     

Fault propagation behavior study of CSTR in HAZOP

This paper discusses the role of process modeling in safety analysis. Process modeling is applied in the fault propagation behavior study of CSTR chemical production. For that purpose, HAZOP methodology and continuation analysis were used. The proposed hazard identification methodology involves analysis of steady-state multiplicity and safe operating conditions as well as those which can shift process units from one steady state to another. All presented case studies are also supported by system dynamic simulations, essential to detect oscillatory thermal instability. In this paper, N-oxide alkylpyridines production process was chosen to identify potential hazard and operational problems. Presented dynamic simulations represent an analysis of the system response to step changes in the key operating parameters. The effect of deviations of three key parameters on the reactor safe operation was investigated. The proposed numerical algorithms represent a mathematical engine of the simulation module within an automated model-based HAZOP analysis tool.     

Solid state thermochemical decomposition of neat 1,3,5,5-tetranitrohexahydropyrimidine (DNNC) and its DNNC-d6 perdeuterio-labeled analogue

The solid state thermochemical decomposition kinetics and activation energy of neat 1,3,5,5-tetranitrohexahydropyrimidine (DNNC) and its DNNC-d₆ deuterium labeled analogue were obtained by isothermal differential scanning calorimetry (IDSC) at 142, 145, and 148 °C. Global rate constants and kinetic deuterium isotope effect (KDIE) data from the exothermic decomposition process suggest that homolytic CH bond rupture, in one or both types of chemically non-equivalent methylene (CH₂) groups of the DNNC ring structure, constitutes the exothermic rate-controlling step. A DNNC-d₆ energy of activation equal to 115 kJ/mol was determined for this initial autocatalytic exothermic energy release from which a 106 kJ/mol activation energy was calculated for unlabeled DNNC. This exothermic autocatalytic decomposition process follows an extended endothermic induction period for DNNC which shows a higher 128 kJ/mol activation energy during which a catalytic initiating species may form by a rate-controlling step different from CH bond rupture.     

Computerized system with a hard-wired data-acquisition unit for potentiometric stripping analysis

The system comprises an electrochemical module interfaced to an controlled by an Apple-IIe microcomputer. A high data-acquisition rate (660 kHz) is achieved by equipping the electrochemical module with a separate memory which is updated in hardware during recording of the stripping step. When a preset cut-off potential is exceeded, data acquisition is automatically terminated, and potentiostatic conditions are resumed. The electrochemical module also contains facilities for instrumental control. The controlling program for the microcomputer is written in assembler code, which can be linked to BASIC routines if necessary. Examples are given to illustrate the advantages of fast data acquisition in improving detection limits and reducing deposition times.     

Mechanism and kinetics of thermal decomposition of precipitates of the zinc oxide-aluminium oxide system from non-isothermal tg curves

Kinetics of decomposition of the precipitates of the ZnO&2sbndAl₂O₃ system, prepared by coprecipitation and mechanical mixing of the individual precipitates, have been studied. The decomposition of zinc basic carbonate is a first order rate process with an activation energy of 34.5 kcal/mole (Coats and Redfern equation). The decomposition of aluminium hydroxide is also best described as a first order rate process with one break in the Coats and Redfern plot corresponding to activation energies of 29.4 and 8.3 kcal/mole respectively. The entire course of decomposition of coprecipitated as well as mechanically mixed samples cannot be described by any one of the many rate equations available. Consequently, the Coats and Redfern equation has been employed. The plots indicate one or two breaks and thus two to three values of activation energy are reported. From the results it is to be concluded that decomposition of these precipitates is a heterogeneous process. The first step is definitely the decomposition of zinc basic carbonate followed by decomposition of aluminium hydroxide and/or interaction of the two precipitates resulting in the formation of “precursor” to spinel. The results of our earlier investigation on the same system (especially the formation of precursors) are well supported by the results reported in this investigation. p]A new equation (a modified form of the Elovich equation) has been proposed for such heterogeneous decomposition processes. The proposed equation also appears to be the general form of the equations where diffusion is the rate controlling process.     

The electron dose monitoring and control system in EB radiation processing for wires and cables

This paper introduces a close-loop microcomputer control system used for EB radiation processing of wires and cables, which is based on the measurements and calculations of the absorbed dose distribution of 0.6–2.0 MeV electrons in circular compound materials. The calculation of electron energy deposition in 4-layer media is carried out by the bipartition model of electron transport.

The design ideas, system configuration and implementation of this control system governed by a 586 personal computer under windows 98 OS are described in this paper. The field operation results such as control precision and step response curves of this system are also given. The control system has been used for EB radiation processing of wires.     

Organocatalytic Trapping of Elusive Carbon Dioxide Based Heterocycles by a Kinetically Controlled Cascade Process

A conceptually novel approach is described for the synthesis of six-membered cyclic carbonates derived from carbon dioxide. The approach utilizes homoallylic precursors that are converted into five-membered cyclic carbonates having a β-positioned alcohol group in one of the ring substituents. The activation of the pendent alcohol group through an N-heterocyclic base allows equilibration towards a thermodynamically disfavored six-membered carbonate analogue that can be trapped by an acylating agent. Various control experiments and computational analysis of this manifold are in line with a process that is primarily dictated by a kinetically controlled acylation step. This cascade process delivers an ample diversity of six-membered cyclic carbonates in excellent yields and chemoselectivities under mild reaction conditions.     

Simultaneous determination of multiple components in flow-injection systems by square-wave amperometry

Two or more components can be determined in a single sample by using a flow-injection system with an electrochmical detector, a microprocessor-based potentiostat, and a microcomputer. The computer generates a repeating staircase potential program with a superimposed square wave. Square-wave amperometric measurements at each potential step are used to construct the current/time response at the potential. By appropriate selection of step potentials, the reconstructed response from each step corresponds to the flow-injection response of a particular component. The approach is evaluated by applying it to the simultaneous determination of copper, lead, cadmium and zinc. Limits of detection range from 8 to 18 μg 1^?1. Sample throughput is 80 h^?1.     

Total syntheses, fragmentation studies, and antitumor/antiproliferative activities of FR901464 and its low picomolar analogue

FR901464 is a potent anticancer natural product that lowers the mRNA levels of oncogenes and tumor suppressor genes. In this article, we report a convergent enantioselective synthesis of FR901464, which was accomplished in 13 linear steps. Central to the synthetic approach was the diene-ene cross olefin metathesis reaction to generate the C6-C7 olefin without the use of protecting groups as the final step. Additional key reactions include a Zr/Ag-promoted alkynylation to set the C4 stereocenter, a mild and chemoselective Red-Al reduction, a reagent-controlled stereoselective Mislow-Evans-type [2,3]-sigmatropic rearrangement to install the C5 stereocenter, a Carreira asymmetric alkynylation to generate the C4' stereocenter, and a highly efficient ring-closing metathesis-allylic oxidation sequence to form an unsaturated lactone. The decomposition pathways of FR901464's right fragment were studied under physiologically relevant conditions. Facile epoxide opening by beta-elimination gave two enones, one of which could undergo dehydration via its hemiketal to form a furan. To prevent this decomposition pathway, a right fragment was rationally designed and synthesized. This analogue was 12 times more stable than the right fragment of the natural product. Using this more stable right fragment analogue, an FR901464 analogue, meayamycin, was prepared in 13 linear steps. The inhibitions of human breast cancer MCF-7 cell proliferation by synthetic FR901464 and meayamycin were studied, and the GI50 values for these compounds were determined to be 1.1 nM and 10 pM, respectively. Thus, meayamycin is among the most potent anticancer small molecules that do not bind to either DNA or microtubule.     

A Bayesian method for construction of Markov models to describe dynamics on various time-scales

The dynamics of many biological processes of interest, such as the folding of a protein, are slow and complicated enough that a single molecular dynamics simulation trajectory of the entire process is difficult to obtain in any reasonable amount of time. Moreover, one such simulation may not be sufficient to develop an understanding of the mechanism of the process, and multiple simulations may be necessary. One approach to circumvent this computational barrier is the use of Markov state models. These models are useful because they can be constructed using data from a large number of shorter simulations instead of a single long simulation. This paper presents a new Bayesian method for the construction of Markov models from simulation data. A Markov model is specified by (τ,P,T), where τ is the mesoscopic time step, P is a partition of configuration space into mesostates, and T is an N(P)×N(P) transition rate matrix for transitions between the mesostates in one mesoscopic time step, where N(P) is the number of mesostates in P. The method presented here is different from previous Bayesian methods in several ways. (1) The method uses Bayesian analysis to determine the partition as well as the transition probabilities. (2) The method allows the construction of a Markov model for any chosen mesoscopic time-scale τ. (3) It constructs Markov models for which the diagonal elements of T are all equal to or greater than 0.5. Such a model will be called a "consistent mesoscopic Markov model" (CMMM). Such models have important advantages for providing an understanding of the dynamics on a mesoscopic time-scale. The Bayesian method uses simulation data to find a posterior probability distribution for (P,T) for any chosen τ. This distribution can be regarded as the Bayesian probability that the kinetics observed in the atomistic simulation data on the mesoscopic time-scale τ was generated by the CMMM specified by (P,T). An optimization algorithm is used to find the most probable CMMM for the chosen mesoscopic time step. We applied this method of Markov model construction to several toy systems (random walks in one and two dimensions) as well as the dynamics of alanine dipeptide in water. The resulting Markov state models were indeed successful in capturing the dynamics of our test systems on a variety of mesoscopic time-scales.     

Evaluation of colour changes of indicators: the supercolor program

SUPERCOLOR is a microcomputer program for the computation of chromaticity parameters from spectrophotometric data. The program is written in BASIC for the HP-200 computer series and it allows the characterization of indicator colour transitions in the standard CIE chromaticity systems. The numerical results for up to 12 indicators can be compared in the same plot for each chromatic system, so that colour changes are easily compared. The pK_a values, pH transition ranges, pH of maximum colour change, SCD values and optimum indicator concentration for visual titrations can be calculated, as well as the colour coordinates.SUPERCOLOR also provides subroutines for computation of screened indicators and simulation of the colour changes of these indicators or other indicator/inert dyes mixtures. The results for some common indicators are presented.     

Automated on-line membrane extraction liquid chromatographic determination of phenols in crude oils, gasolines and diesel fuels.

Determination of phenols in crude oils and derived fuels requires a sample pretreatment step, usually performed by liquid-liquid extraction or preparative chromatography. In this work, sample preparation is accomplished using a silicone membrane separation unit coupled on-line to a high performance liquid chromatograph with amperometric and ultraviolet detection. The contents of phenol, cresols and dimethylphenols were determined in thirty three samples including three crude oils, twenty gasolines and ten diesel fuels. The whole set-up is fully automated through a feed-back system that allows the microcomputer controlling the process to examine the signals in real time and to make decisions while the experiment is running.     

On-line cell lysis and DNA extraction on a microfluidic biochip fabricated by microelectromechanical system technology

Integrating cell lysis and DNA purification process into a micrototal analytical system (microTAS) is one critical step for the analysis of nucleic acids. On-chip cell lysis based on a chemical method is realized by sufficient blend of blood sample and the lyzing reagent. In this paper two mixing models, T-type mixing model and sandwich-type mixing model, are proposed and simulation of those models is conducted. Result of simulation shows that the sandwich-type mixing model with coiled channel performs best and this model is further used to construct the microfluidic biochip for on-line cell lysis and DNA extraction. The result of simulation is further verified by experiments. It asserts that more than 80% mixing of blood sample and lyzing reagent which guarantees that completed cell lysis can be achieved near the inlet location when the cell/buffer velocity ratio is less than 1:5. After cell lysis, DNA extraction by means of a solid-phase method is implemented by using porous silicon matrix which is integrated in the biochip. During continuous flow process in the microchip, rapid cell lysis and PCR-amplifiable genomic DNA purification can be achieved within 20 min. The potential of this microfluidic biochip is illustrated by pretreating a whole blood sample, which shows the possibility of integration of sample preparation, PCR, and separation on a single device to work as portable point-of-care medical diagnostic system.     

Kinetic method of analysis by analogue computer simulation

The simulation by an analogue computer of slow reactions used for the purpose of chemical analysis is described. Bromination of maleic and fumaric acids is used for illustration. The concentration of bromine is traced spectrophotometrically as a function of time and the trace simulated with an analogue computer by the trial and error method. The initial concentration of the substance in question and the rate constant of the reaction are determined from the values given to the computer variables to obtain the best fit. Only a single experiment is required for the analysis. The procedure can be followed easily without laborious mathematical or graphical treatment.