Software
Simulating GC Elution lyst to provide acceptable resolution in an data are used to compute AS and AH val ues, retention times are predicted to acceptable analysis time. Pro ezGC, a program written by Analyti within 0.5-1.0% of experimental times. This agrees with my GC simulation experi cal Innovations, Inc. (Kettering, OH), is designed to aid GC temperature program ence. Even better, errors in predicted re selection by performing numerical simula tention times of similar analytes that are separated together are often correlated tions of GC elution at the user's com strongly. This means that retention time mand. It runs on PC-compatible comput Analytical Innovations, Inc. ers with an 8088 or higher CPU, though I differences are predicted far better than would recommend an 80386 or higher. one might expect. For example, two ana lytes with predicted retention times of 10.0 Pro ezGC The software runs in DOS or in a DOS and 10.5 min will probably have an exper Restek window in Windows or OS/2 software. 110 Benner Circle To set up Pro ezGC, one provides reten imental retention time difference of 0.450.55 min, even if the experimental reten Bellefonte, PA 16823-8812 tion times for the target analytes taken tion times are 10.3 and 10.8 min. 814-353-1300; 814-353-1309 (fax) from at least two isothermal or tempera It is a great pleasure to alter a tempera Version 1.59; $695 ture-programmed chromatograms on the same column, along with the flow con ture program and watch changes in the chart of predicted retention times and/or Finding efficient temperature programs ditions and column geometry under the plotted chromatogram. A motivated for multianalyte GC separations can be which the data were taken. At the user's novice gas chromatographer could bene hard work. Although today's chromatogra- command, the program computes parti phers generally enjoy stable instruments tion AS and AH values for each analyte. fit greatly by spending time with this pro gram. The real power arises when the user and reproducible selectivity, they are al These values can then be used to predict ways tempted to include more analytes retention times and thus interanalyte reso asks the program to try a large number of feasible temperature programs and to list of interest within a single chromatogram lution quality and analytical run times for to improve efficiency. Because it is easier as many temperature programs as de the programs in order of attractiveness. This process is a grid search rather than to change flow and temperature software sired. an optimization, but with a little care a user than to change selectivity by replacing Written materials provided with the can get very good results. the column, required separations are gen software indicate that when appropriate erally optimized by selecting a promis ing column, thenfindingoptimum condi tions for that column. Pro ezGC was writ ten to assist chromatographers in finding beneficial separation conditions, particu Column : Rtx-1701 15 fi, 0.25 mm, 0.50 Micron larly of the temperature program. Comment : Chlorinated Pesticides Relative retention of two analytes on a Ouen : H O C 9 8C/min to 200C 8 4C/min to 270C Carrier : Helium given column under a set of conditions de Regulation : Pressure Program pends on the difference between entropy 50.0kPa Β 4kPa/min to 90.0kPa I? 6kPa/min to values (AS) and enthalpy values (AH) of HOkPa to Constant Flou partition between the gas and liquid 42 out of 42 components > 1.00 Rs phases. There are three cases. When the It Component Name Retention Time Width Resolution AS and AH values of two analytes are too (min) (mill) similar, no temperature program can separate them; a different column is 1, Cis-Di-allate 7.8Θ8 0.060 3.96 2. Propachlor 8.044 0.060 1.55 needed. When only AS differs, the separa 4. Trifluralin 8.136 0.057 1.11 tion is easy; any temperature will do and the chromatographer is not needed. When el AH differs, however, optimization is tricky for even just two analytes. When nu merous analytes are involved in this case, Using data from an Rtx-1701 column, Pro ezGC can evaluate 7500 temperature and it can be difficult for even a talented ana pressure programs to find the optimum combination.
ezGC
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Analytical Chemistry, August 1, 1995
Unfortunately, the user has no way to express the relative valuation of analysis time and resolution other than by supply ing a minimum predicted resolution and a maximum analysis time. Instead, each satisfactory temperature program is listed with its analysis time and minimum reso lution, and the user simply selects from this list. If the user specified an appropri ate range of initial temperatures, ramp rates, and flow rates, the best chromatogram is often better than that obtained by extensive trial and error. The danger with powerful simulation software is that one may blindly apply it without experience or thought, much as GC/MS library searches are routinely mis used. Pro ezGC 's approach is strictly nu merical, so that it is easy to simulate chromatograms taken at 600 °C or at 99 °C/ min ramp rates. This danger is inherent to any simulation approach, making user judgment important. To their credit, the authors have taken pains to guide the user, especially in the well-written "Guide lines for Initial Data" section. Having done many of these simula tions years ago, I was surprised by how fast this software's advanced numerical techniques run on today's PCs. An 80486/66 MHz system can search a range of temperature programs, numerically in tegrating 12 zone migrations for each pro gram, at the rate of about 20-30 chromatograms/s. A satisfactory grid search takes less than 1 min. One need only real ize that most autosamplers take longer to complete one injection cycle to see the promise of this approach. Libraries of AS and AH values can be created by the user from input retention data, and some libraries can be purchased from the authors. The purchased librar ies I tested gave predicted Kovats reten tion indices very close to literature experi mental values taken on similar phases, as long as I used reasonable ramp rates and appropriately low initial temperatures. Pro ezGC competendy manages these librar ies through various built-in utilities. One
wishes for these libraries to be managed in a windowing environment in the same way Windows File Manager facilitates file manipulations. One may bring in ASCIIand ΑΙΑ-formatted retention data from in tegration computer reports through built-in import utilities. The least attractive part of the software by far is its installation. Unbelievably, Pro ezGC is hardware copy protected with a button and button holder that must be in serted in your printer cable. The software will not run without the button or if your printer is simply off or out of paper. If you want to leave your printer off, you must remove the button holder from your ca ble. If this button or holder breaks, you're out of luck and have to buy another copy of the program. To quote from the man ual, Pro ezGC is "protected from illegal or unauthorized use." Potential users are forewarned that it is protected as well from your own legitimate, fully paid use if, through no fault of your own, your button is lost, damaged (e.g., by lightning), sto len, or, I might add, if you are moved to hurl it at the wall in frustration. Like most DOS programs, Pro ezGC keeps a list of printers to which it can send data. Although the list contains numer ous popular printers that are compatible with a great many more, my attempt to print to a Panasonic KX-4420 laser printer had serious font scaling problems. Pro ezGC is probably already as easy to use as the DOS/text environment allows. However, the inherently interactive nature of rapid simulation simply cries out for a true graphic environment. Imagine mov ing a ramp rate slider and watching the chromatogram change. A Windows ver sion would also solve most printer compat ibility problems. Adding extensions for multidimensional GC (including valve tim ing), cryofocusing (including zone heat ing rate), and perhaps serially coupled cap illary columns would also be useful. Restek supports this product by mail, telephone, and fax. With some apprecia tion of its power and pitfalls, a competent
gas chromatographer can apply Pro ezGC to all sorts of "what if" testing, occasional temperature-program grid searching in labs that develop lots of multianalyte GC methods, and educational uses. Reviewed by Eric V. Dose, 470 Claren don Ave., Winter Park, FL
SOFTWARE RELEASED DESOC Stanford Bookstore 8424 Central Avenue Newark, CA 94560 800-533-2670; 415-322-1936 (fax) $200 commercial; $98 academic
DESOC retrieves or estimates 12 physicochemical properties using state-of-theart algorithms and temperature functions. Properties covered include octanolwater partition coefficient, vapor pressure, water solubility, Henry's Law constant, liquid density, boiling point, and enthalpy of vaporization. The software for IBM compatibles requires a 286 or higher CPU, VGA monitor, 18 MB free hard disk space, 3.5-in. floppy disk drive, 4 MB RAM, and DOS 5.0.
SigmaGel for Windows Jandel Scientific Software 2591 Kerner Blvd. San Rafael, CA 94901 415-453-6700; 415-453-7769 (fax) Version 1.0; $495
SigmaGel for Windows allows scientists to analyze electrophoretic gels on PCs us ing three different measurement modes: lane, spot, or molecular weight mode. Any TWAIN compliant scanner can be used to scan gels, or users can load images saved in standard image file formats. Mini mum system requirements include a 486/33 CPU, Windows 3.1,5 MB free hard disk space, 8 MB RAM, 256-color VGA monitor (640 χ 480 display), and Micro soft-compatible mouse. Analytical Chemistry, August 1, 1995 477 A
