Interactive Computer Models for Analytical Chemistry Instruction

Spectroscopy Instrumentation and methodology

Color Temperature of a Blackbody Source	Animated Diffraction Grating	Photomultiplier Light Measurement System	Monochromator

Comparison of Analytical Calibration Methods	Multiwavelength Spectrometry	Lock-in Amplifier	Wavelength modulation system

Molecular spectrometry

U.V.-Visible Spectrophotometer	Dual Wavelength Spectrophotometer	Instrumental Deviations from Beer's Law	Calibration Curve Fitting Methods in Absorption Spectroscopy

Signal-to-Noise Ratio of Absorption Spectrophotometry	Effect of Slit Width on Signal-to-Noise Ratio in Absorption Spectroscopy	Scanning Fluorescence Spectrometer	Fluorescence Spectroscopy Signal-to-Noise Ratio

Atomic spectrometry

Signal and Photon SNR of Atomic Emission Spectrometer	Effect of Slit Width on Emission Spectroscopy SNR	Line Wing Overlap	Spectroscopy of Atomic Absorption

Classical, electrical, and computational methods

Worksheets for Analytical Calibration Curves	Calcium Ion Selective Electrode model	Resolution of Capillary Chromatography	Discrete Equilibrium  Chromatography Model

Triprotic Titration Data Analysis	Monoprotic Titration Curve model	Introduction to Signal Processing	Interactive Simulations of Basic Electronic Circuits

This is a collection of free, downloadable, interactive computer models of common analytical instruments and techniques. Most have a point-and-click interface; you click buttons and drag sliders to control variables and the model responds dynamically, often much faster than real time. Note that these are not really simulations of particular commercial instruments and were not intended to train instrument operators. They are rather interactively manipulable mathematical models that are essentially sets of linked equations that describe various parts of or aspects of each system. The advantage of linking these equations in spreadsheet is that it gives the students and instructor an opportunity to explore how these textbook relationships interact with one another. My models give you the ability to change many of the chemical and instrumental variables that effect the outcome, including not only the variables that are conventionally adjustable in the laboratory (such as the wavelength of a spectrometer or the concentration of a chemical solution), but also the instrumental design variables that are determined by the instrument manufacturer and can not normally be adjusted by the experimenter (such as the ruling density of a grating or the focal length of a spectrometer).

Most of the spreadsheets produce graphs and charts that illustrate the internal operation of, or mimic the output generated by, these systems. Because they are just spreadsheets, it's easy for instructors and students to inspect the equations that drive these models. Unlike closed proprietary programs, the mathematical basis of these models is not hidden but rather easily accessible and can be viewed, modified, corrected, or extended by any instructor who is familiar with the basics of modern spreadsheet construction.

I originally designed these models for courses I used to teach during the 1990's at the University of Maryland at College Park: Instrumental Analysis (an upper-division undergraduate laboratory course) and Spectrochemical Methods (a graduate lecture course). The spreadsheets were based on the level of treatment in the textbooks for those courses and were designed to be used by individual students either as homework assignments, for in-class use in a computer lab environment, in the laboratory for the analysis of student-generated data, or as a supplement to laboratory experiments, to allow investigations into the fundamentals of system behavior for which time is not available in the laboratory. The spreadsheets can also be used by the instructor in lecture-demonstration environments. Student-assignment handouts and suggested experiments are included for most of them.

The mathematical basis for each model is described in PDF files, including all cell definitions and equations that relate the variables. The equations themselves are usually taken directly from the typical textbook treatment for each topic, sometimes with additions from other sources or with the addition of small amounts of random variability to make the behavior closer to real measurement systems.

Instructors are able to, and are invited to, modify these spreadsheets in any way for their students. See the unsolicited user comments below from actual users of these spreadsheets. 

OpenOffice Calc Versions
Calc is the Open Document spreadsheet format, part of the OpenOffice Suite, which students and faculty can download and use without cost, from OpenOffice.org for Windows, Macintosh, and Linux. Calc is basically the same as Excel. To run these Calc spreadsheets, you have to first download the OpenOffice installer (download from openoffice.org), then install it (by double-clicking on the installer file that you just downloaded), and then download my spreadsheets from this site.  Once OpenOffice is installed, you can run my spreadsheets just by double-clicking on them. The OpenOffice suits also includes a full-featured word processor, a presentation program, and other components. There is no need for students to buy the expensive Microsoft Office suite; the latest version of OpenOffice is always available for free download. Note: Downloading the individual spreadsheet .ods files with some versions of Interent Explorer will change the file types from ".ods" to ".zip"; you will have to edit the file names and change the extensions back to ".ods" for them to work properly. This problem does not occur in Firefox or in Chrome.

  The Calc versions of these models will also run on LibreOffice Calc, for example running on a Raspberry Pi 3.

WingZ Versions
These models were originally developed in the early 90's in WingZ (.WKZ) format, the first object-oriented spreadsheet with a built-in scripting language called HyperScript., but that program is now obsolete. This is still a useful format, because the HyperScript language has some has some unique capabilities that are useful in this sort of simulation and because the WingZ player program has a very modest memory footprint and runs very quickly even on older, smaller, or slower 32-bit computers (but not unfortunately on 64-bit Windows). I am gradually re-writing these models in the industry-standard, non-proprietary Open Document format (using OpenOffice Calc) and in Excel, but until that work is complete, some of them will be available only in the original WingZ format. To open the WKZ files you'll need the "player" application that  is included in the following file archives for both PCs and Mac:

If you have suggestions for other models like these that you would like to see developed, please email me at toh@umd.edu

What do the students have to say about these models?

Unsolicited Comments from Users at Other Institutions

"I was able to get everything working nicely and can promise you they will be helpful with my students."

"Today I had the first simulation experiment and the students were excited...."

"The [simulated] lab was much more interesting than the lecture, this is for sure!...I had very good feedback from students..."

"...thank you so much for your website!!! "

"...I have found [your worksheets] of great use whilst working on my current project."

"Wow! Nice work ... and lots of it. Your stuff is wonderful!"

"I found your website very informative."

"What I like about your grating demo is that it clearly shows how increased dispersion causes the different wavelengths to have to travel different distances to the sensor...."

"Let me congratulate you on a fine web page! I'm a technical support engineer for Wingz ... and I rarely run across such sophisticated use of our products."

"Thank you for your tremendous work. Hope I can leverage it for the benefit of students."