- June 01, 2003, Dr. Richard M. Podhajny, Ph.D., Contributing Editor
Although I didn't appreciate it at the time, as I was going to college in the 1960s, major changes were taking place in analytical instrumentation.
During those college years, the identification of chemicals was done primarily by wet chemical techniques such as the use of “chemical derivatives” rather than instrumentation techniques. This “wet chemistry” approach to analysis was time-consuming but offered some real advantages to the understanding of materials and their chemical reactions.
By the time I was studying in graduate school, wet chemistry analytical techniques were being downsized in favor of using new instrumentation. IR spectroscopy, gas chromatography, nuclear magnetic resonance, and liquid chromatography became the familiar tools of most graduate students.
Today, many of these instruments are commonplace in most laboratories and are refined further with computer enhancement to a level not foreseen 30 years ago.
Fourier Transform Infrared (FTIR) spectrophotometers introduced in the late '60s were very large and expensive instruments. FTIR is an enhanced IR spectrophotometer that makes use of Michelson's interferometer.
That is, instead of separating different wavelengths for measurement, the complete spectrum is encoded as an interferogram in a few seconds of measurement time, and the spectrum is computed by fast Fourier transform. Today, like many electronic devices, FTIR is affordable to most QC and R&D laboratories.
Having spent many years running IR spectra, I have been most impressed by the enhanced capabilities of new FTIR spectrophotometers for quality control and research applications.
I refer to this technique as a “fingerprint” analysis. Unlike other instruments, the IR spectrum allows a broad look at the chemical composition of the sample. Although the fingerprint looks very complicated, an FTIR can take the data, rapidly compare its “fingerprint file,” and provide useful analysis.
Just a few years ago, if you wanted to take an IR spectrum of a solid, you needed to make a KBr window pellet so a spectrum could be generated. Today's FTIR accessories allow the solid to be scanned using a reflective attenuated IR spectrum that provides a good spectra by reflecting the IR at shallow angles to the sample surface. The net result: You can take an IR spectrum quickly without needing to make a KR window. That means faster analysis.
The advantages of today's FTIR spectrophotometers are not only that you can get reliable fingerprints of your samples; the instruments also can be used to quantify ingredients in the sample, and you can use subtraction to eliminate fingerprints. Validation software is available for many of these FTIR instruments.
But, what I like best about the new FTIR spectrophotometers is the ATR accessories that allow the elimination of sample preparation to run solids and liquids, as well as printed samples.
If you ever had a problem where you suspected a surface contaminant, you definitely will appreciate the microscope accessory. It is well suited for printers and converters that must investigate and analyze very small areas. A very small object can be focused in the view screen and be analyzed by IR spectroscopy. Software is available that allows the analyst to “map” the surface in terms of the FTIR surface analysis and identify contaminants.
Using the FTIR as a tool for assessing quality can reduce many incoming tests on raw materials. Batch-to-batch comparisons can be made readily, and rejection standards can be set.
Improvements in instrumentation provide real cost savings compared to many “wet chemistry” testing alternatives. The technological advances in instrumentation provide opportunities to streamline your QC process in a cost-effective manner. It is an indispensable tool in troubleshooting and R&D.
Dr. Richard M. Podhajny has been in the packaging and printing industry for more than 30 years. Contact him at 215/616-6314; firstname.lastname@example.org.