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50, 153 (1974). (13) K. €3. Prater and A. J. Bard, J. Electrochem Soc., 117, 207 (1970). (14) K. B. Prater in "Computers in Chemistry and Instrumentation", Vol. 2, J. S. Mattson, H. B. Mark, Jr., and H. C. MacDonald, Jr., Ed., Marcel Dekker, New York, 1972. (15) R. C. Weast, "CRC Handbook of Chemistry and Physics", The Chemical Rubber Company, Cleveland Ohlo, 1968. (16) H. R. Mahler and E. H. Cordes, "Biological Chemistry", Harper and Row, New York, 1966, Chapter 6. (17) H. H. Weetail, Anal. Chem., 46, 602A (1974). (18) G. L. Smith, M.S. Thesis, University of Arizona, Tucson, Ariz., 1975.
RECEIVEDfor review April 7,1976. Accepted June 24,1976. This investigation was supported in part by National Science Foundation Grant MPS7308683.
Fully Automated Stopped-Flow Studies with a Hierarchical Computer Controlled System Glen E. Mieling, Richard W. Taylor,' Larry G. Hargis,2 James English, and Harry L. Pardue" Department of Chemistry, Purdue University, West Lafayette, Ind. 47907
The development and evaluatlon of a fully automated, computer controlled stopped-flow spectrophotometer is described. A microcomputer controls several operations including the preparation of reagents from up to five dlfferent solutions and one diluent, the drawing of measured volumes of the reagent and sample into a sampllng unit, and stopped-flow mlxing of the reagent and sample. A mlnlcomputer controls the operatlon of the microcomputer, performs data acquisition and processing operations, and makes decisions relative to the acceptability of acquired data. Quantitative data are presented to demonstrate the performance characteristics of individual components as well as the total system. Results reported include mole ratio and continuous variation plots for complexed metal ions, and a partial simplex study of the TI(IV)-H202 complex in the presence of EDTA.
Several recent papers have described computer controlled instrumentation for equilibrium and kinetic studies (1-4). Because the computer is involved in a closed loop configuration with the reagent preparation and measurement hardware, some of these systems are applicable to both routine applications involving repetitive operations and nonroutine applications requiring predetermined or computer originated changes in experimental conditions based upon results of current experiments (I). One common feature among these systems is the fact that the minicomputer must handle all of the instrumental control functions in addition to data acquisition, storage, processing, and display and decision making operations. One objective of this work was to evaluate the capabilities of a microcomputer used in a hierarchical arrangement with a minicomputer to relieve the latter of some of the time-consuming control functions encountered with slow systems which require constant or frequent attention. This report describes the design and performance characteristics of a completely automated stopped-flow instrument system which uses a microcomputer for control and a miniPresent address, Department of Chemistry, University of Oklahoma, Norman, Okla. 73069. Present address, Department of Chemistry, University of New Orleans, New Orleans, La. 70122. 1686
computer for data acquisition and processing. Also, the paper describes a reagent preparation system which is more flexible and which is less subject to mechanical problems than syringe based systems described earlier ( I ) . Quantitative data which illustrate the reliability of the system and which demonstrate its applicability to equilibrium and kinetic studies are included in the report. Data show that the system should be particularly useful for measurement and process optimization studies which have been gaining popularity in recent years
(5). INSTRUMENTATION The automated stopped-flow instrument consists of a hierarchical computer system, a reagent preparation unit, a sampling unit, a Sturtevant-type stopped-flow mixing system and a stabilized photometer. Figure 1 represents the interactions among the minicomputer (Model 2100A, HewlettPackard Company, Palo Alto, Calif. 94304), the microcomputer (Model 8008, Intel Corporation, Santa Clara, Calif. 95051) and the other components of the stopped-flow system. Operator communication with the system is via the minicomputer which handles several other functions including scheduling and initiation of experiments, acquisition, processing, and display of data, as well as decision-making processes associated with any set of experiments. The microcomputer is dedicated to controlling the reagent preparation and stopped-flow mixing system and to monitoring the status of selected hardware components. Data transfer between the minicomputer and its several peripherals, including the microcomputer, is under priority interrupt control. Intercomputer data transfers are made via a 16-bit duplex register card in the minicomputer and a buffered 8-bit input multiplexer and a 16-bit latched output from the microcomputer. The minicomputer interface includes a 12-bit, eight channel analog-to-digital converter (ADC) (Model AN 5200 Analogic Company, Waltham, Mass. 02154) and a general purpose interface which features a programmable clock, buffered inputloutput data lines, and expandable logic. Since this interface is similar to others used routinely on many laboratory computer 'systems (6),it is not discussed further here, but details can be supplied to interested readers. The microcomputer used in this work was an Intel 8008 with 3072 words of random access memory (RAM) and 512 words
ANALYTICAL CHEMISTRY, VOL. 48, NO. 12, OCTOBER 1976
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MINI-COMPUTER (H.P 2100)
