Multiple Electrochemical Impedance Spectra Parameterization (MEISP+). Version 2.0. Kumho Petrochemical Co. Ltd., Kumho Chemical Laboratories, P.O. Box 64, Yuseong, Taejeon, 305-600, Korea. Fax: 82 42 862 5651. http://powergraphy.com. Contact Kumho for price. The purpose of this software is to fit electrochemical impedance spectra to equivalent circuit models by the nonlinear least-squares method and to deduce the values of the circuit elements that best fit the data. Competing software includes “ZSimpWin” from Perkin-Elmer and “Zplot/Zview” from Scribner Associates, but I will only compare this software with the latter (v 2.3d), since it is the one with which I have experience. The program’s Web site and documentation say nothing about hardware and operating system requirements, and I was unable to install it under Windows 2000, although it did run successfully under Windows NT4 on a 400 MHz machine. The program has hardware “dongle” copy protection, requiring the dongle always to be present. (Zplot requires the dongle to be inserted only every six months, which is a reasonable compromise between adequate copy protection and the inconvenience of moving the dongle between home and work.) I began by creating some equivalent circuits. Circuits are generated by a subprogram (CEDIT) that can also be run in stand-alone mode. It can create circuits of arbitrary connectivity, made from resistors, capacitors, inductors, and special elements, and output them in standard SPICE file format. The elements are connected by dragging wires between them in an obvious way that kept my six-year-old amused for some time. For distributed elements, I had to sort out the distinction between titles (must be X1, X2, ...), names (leave alone unless userdefined) and parameter names (must be no duplicates), but once I had done this I had no problem constructing my circuit. The special elements can be any of 26 types of distributed elements used in fitting electrochemical impedance spectra (I could not think of any missing ones), or they can be impedance functions defined by the user. User-defined functions are entered as lines of a subprogram in a text file and can use a variety of functions such as sqrt, tanh, or the predefined distributed elements. This is a nice feature for anyone with rudimentary programming knowledge. However, my first attempt to create my own constant-phase element raised several questions not answered by the documentation: Could I put a complicated expression in the return line? Should I use ** or ∧ to raise powers, or did I have to use the “pow” function, even though the exponent was not complex? As in other places in the software, the user needs to experiment a little before things will work. The user who has an impedance function so arcane that it cannot be handled by any of the above methods can write and compile his or her own .dll files and use them with MEISP+ (a feature I did not test). MEISP+ is certainly ahead of other software packages in terms of the ultimate flexibility in creating circuits. Zplot is restricted to parallel/serial combinations and preselected 1554 VOL. 124, NO. 7, 2002
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simple or distributed elements, although it might be argued that you are not practically limited unless you are a specialist who wants to make some very exotic circuits. I evaluated this software using two experimental impedance spectra. One was for thallium electrodeposition at a singlecrystal platinum electrode, which obviously fit the circuit with a parallel Rct/Cdl combination in series with the solution resistance; the second was of a small fuel cell stack. The first step was to read in the data file, which can be in Zplot, EG&G M398, BAS/Zahner, Gamry, Powergraphy, or plain ASCII format. It read the Zplot fuel cell file without difficulty. For the thallium data, I tried the ACSII format (three columns for frequency, real part, and imaginary part, separated by commas or spaces), but the program crashed. I eventually found that the format is very fussy: a single space separator worked, but a comma and a space did not. Having loaded in my thallium data set and selected my premade circuit, I hit “prefit” to automatically choose initial values of the circuit elements, then “fit” to refine the values by nonlinear least squares, and presto, I had convergence to the same values as I had obtained previously using Zplot. The agreement of the results was not so surprising, since both MEISP+ and Zplot use Macdonald’s LEVM as the underlying nonlinear least-squares engine and use similar default fitting options (the LEVM report can be output for diagnostic purposes). Not having to select initial values for the parameters is a very nice feature. Zplot and LEVM users know that poor initial guesses for the parameters can easily lead to the dreaded “singular matrix” problem. Consequently, the user may need to know a lot about circuit impedance behavior just to make good guesses for initial values. My fuel cell spectrum proved to be a more difficult test of this feature. The equivalent circuit was a difficult one, since it had two CPE elements in parallel and inductive behavior at low frequencies. This time the program’s initial guesses led to a spectrum that correctly had two loops above the axis at higher frequencies but that failed to go below the axis at lower frequencies to model the inductor. The documentation suggests the prefit algorithm is not set up for inductive behavior. In this case, the initial guesses were not helpful, and the subsequent fitting led to convergence to a wildly incorrect result. I did not further test the guessing ability of MEISP+, but even if it fails sometimes, it is a useful feature. Another competitive advantage claimed for this program is that it can fit sets of impedance spectra. Aside from the ability to plot a parameter vs the variable changing from spectrum to spectrum (e.g., potential) or to produce a 3-D plot of all the spectra, this worked identically to Zplot’s “batch” mode. (Apparently ZSimpWin also has this feature.) Another claim is for the program’s generic battery impedance function with 10 parameters, which is supposed to fit all possible battery chemistries. The model seems physically reasonable, but I am not sufficiently versed in battery impedance to support or refute this rather bold claim. No doubt this would be useful for routine 10.1021/ja015328m CCC: $22.00 © 2002 American Chemical Society
COMPUTER SOFTWARE REVIEWS
battery testing, where variation in a parameter may be a diagnostic signal for a certain failure mode. I occasionally got fits that bore no resemblance to the data, came across incomprehensible error messages, or crashed the program, so the user is certainly not shielded from all problems. There are several minor annoying points, for example, the spelling “Nuquist” for “Nyquist”, the “Bode” plot option only shows log real and log imaginary parts of impedance vs log frequency and not log magnitude and phase vs log frequency, and the main window is slightly larger than the screen (at least on my system) and has to be shifted over to see the plots in their entirety. The documentation covers all topics and is quite good on the use of the various distributed elements; however, it is still short on some details and could use some thorough editing. Most of my complaints are in the category of rough edges rather than fatal problems and will no doubt be remedied in a future release. In general, the features of this program have been well thought out. I liked the ability to force the time constant order and the ability to force several circuit elements to have the same value (useful for transmission line models). These sorts of features, and especially the ability to define arbitrary impedance functions, make it a good choice for the specialist. For most users and especially for the naive user, the automatic choice of initial parameter values is the most useful feature, which makes MEISP+ a competitive choice. David Harrington, UniVersity of Victoria JA015328M 10.1021/ja015328m
KnowItAll Analytical System. Bio-Rad Laboratories, Sadtler Division, 3316 Spring Garden St., Philadelphia, Pennsylvania 19104. www.sadtler.com. In most analytical laboratories, organizing vast amounts of data from myriad sources can be both an administrative challenge and an impediment to scientific discovery. All too often, key details remain obscured simply because of the difficulty of extracting them from the overwhelming wealth of information available. A new software package released by the Sadtler Division of Bio-Rad Laboratories, the KnowItAll Analytical System, seeks to help scientists overcome this problem by providing them with a coherent collection of tools for extracting valuable facts from data and easily forming them into appealing reports. The KnowItAll software consists of a common graphical interface containing various plug-ins, each designed to perform a specific function. With such a structure, Bio-Rad has succeeded in creating a program with nearly seamless interoperability between the different components. Practically any type of information can be transferred from one plug-in to another simply by clicking on one of the context-sensitive buttons that directs the user to typical functions. The interface also contains a pane of user-configurable menus at the left of the main window that let the user easily switch between plug-ins. By default, the menus are sorted by analysis type, grouping all of the tools relevant to IR analysis, for instance, into one panel. Overall, the interface is fairly intuitive, and anyone with experience in a windowing operating system should face only
a modest learning curve before becoming comfortable with the program’s basic features. The software was installed easily, but the product activation scheme, which requires a custom license key from Bio-Rad, could be problematic should the software need to be moved to a different computer. Although the software did not ship with a printed manual, the online help system offers thorough explanations of most topics. This help system is augmented by an online support page on the Internet that contains, among other things, a series of tutorial movies that reasonably introduce the user to the program’s various aspects. Additionally, KnowItAll also has a context-sensitive help function that offers concise but sometimes vague descriptions of the visible functions. At the core of the KnowItAll system are the basic data handling tools in the DrawIt and ReportIt plug-ins. In DrawIt, Bio-Rad presents an advanced and full-featured chemical drawing program that supports most common file types, eliminating the need for any additional chemical drawing software. Similarly, the ReportIt plug-in allows for good handling of data, text, and graphics, making feasible the complete generation of scientific reports and documents. Despite support for a large range of file formats, however, formats used by some notable instrument manufacturers are absent, potentially causing compatibility problems in some laboratories. Although KnowItAll touts its applicability to NMR, IR, MS, UV/vis, and GC data, the actual functionality seems somewhat skewed toward NMR and IR spectra. The generally excellent tools for analyzing these spectra allow for easy manipulation and processing as well as analysis based on database look-ups and comparison of multiple spectra. The AnalyzeIt plug-in for IR spectra, in particular, allowed for nearly effortless functional group analysis and can interface with Sadtler’s extensive library of IR spectra. Additionally, the PredictIt plug-in proved able to predict the locations of both 1H and 13C NMR peaks from a molecular structure on the basis of a database search for atoms similarly situated. Unfortunately, KnowItAll’s handling of data from other analytical sources was less impressive. Users dealing with data from MS, UV/vis, and GC are limited to database searches based on molecular structure, observed peaks, or a wide range of physical properties. For these types of data, KnowItAll lacks any ability to process spectra or chromatograms. By purchasing the optional MineIt Database Building plug-in, the usefulness of the software can be increased with time, however, by allowing the user to create custom, searchable databases of spectra or chromatograms of any type. Nevertheless, this shortcoming could mitigate the software’s usefulness to many laboratories. Fortunately, the modular structure of KnowItAll opens the door for the development of third-party add-ins that will allow for further customization of the software and offer the possibility of more specialized analyses. Bio-Rad currently offers several optional plug-ins of its own. In addition to the Database Building option mentioned above, the AssignIt option allows the user to build databases of NMR spectra containing a great deal of additional peak data, including factors such as intensities and coupling constants. In addition, the Socrates’ IR Power Pack offers direct links from the AnalyzeIt plug-in to an electronic version of George Socrates’ Infrared Characteristic Group Frequencies. For those interested in IUPAC naming, the IUPAC J. AM. CHEM. SOC.
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NameIt and IUPAC DrawIt offer the ability to generate a name for a chemical structure and vice versa. Beyond software plugins, Bio-Rad also offers subscriptions to its online databases of IR, NMR, and MS spectra, accessible through the same straightforward interface as its local databases. Overall, the KnowItAll Analytical System’s usefulness is easily apparent, particularly in laboratories that generate large amounts of IR and NMR data. Furthermore, its breadth offers
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potential cost and time savings by eliminating the need for multiple software packages and streamlining the data reporting process. Courtney Sherman and Jennifer Brodbelt, The UniVersity of Texas JA015371+ 10.1021/ja015371+
