Model 21 — the standard instrument for infrared analysis; a double beam recording spectrophotometer offering complete flexibility in resolution, spectral presentation and recording speeds, and a complete range of accessories, including scale expansion for trace analysis. Calibrated wavelength with standard optics covers both the near infrared and the fundamental regions of the spectrum. The Model 21 is used in more industrial and academic laboratories than any other infrared instrument.
COMPLEX KINETIC STUDY COMPLETED IN THREE HOURS BY INFRARED Kinetic chemical changes, such as polymerization, that take place in organic compounds with increasing temperature are of interest in many areas of research and quality control. Few problems tax the ingenuity of the analytical chemist more than devising procedures to study such changes. A case in point: Recently a major aircraft manufacturer was evaluating a polymeric material composed of triallyl cyanurate and a polyester. The material kept breaking down at elevated temperatures. Answers to several questions might provide clues to a reformulation that would improve the heat resistance of the material. Among these questions: Was the change a sudden one that took place at some critical temperature, or was it progressive? If the latter, what chemical evolution did the material undergo as it deteriorated? A P-E representative acquainted with the manufacturer's problem suggested that a sample be sent to P-E's Applications Laboratory for study using infrared analytical techniques. Three hours after the Applications Lab started the analysis, the spectra were ready for interpretation. A record of the complete kinetic change in the material over the entire range of application temperatures had been made (see spectra, left). Behind this accomplishment was utilization of one of the many opera-
tional modes in which the P-E Model 21 Spectrophotometer — the standard instrument for infrared analysis — can perform. The standard mode of operation reported here permits automatic continuous analysis of samples which are undergoing rapid kinetic change. In the case of the aircraft company's analysis, the procedure was as follows: At the end of this scan, while the instrument was automatically recycling, the sample temperature was stepped up 25 °C by means of a Variac temperature control on the heated sampling stage. With the chart paper left on the drum, the scan was repeated. In the absence of any chemical change at the increased temperature, the second spectrum would be identical to the first. But if the 25 °C increment of temperature had altered the composition of the sample, the second trace would diverge from the first. At the end of each scan, the procedure was repeated with a 25 °C increase in temperature each time. This resulted in four superimposed spectra recorded over a range of 100°C (See Figure 1 ) . To differentiate superimposed spectra, the pen ink color was changed during each recycling return run—from green to blue, red, and finally black. To study the total temperature range of interest, three recordings were made to provide data within each 100°C temperature increment (See Figs. 2 and 3 ) .
The spectroscopist now had a complete history of the sample taken at 25 °C increments of temperature. He was able to determine when, what and how much chemical change had occurred. With this information in hand, he was able to make a quick and intelligent evaluation of the polymers. Similar data might be obtained to predict aging brought about by other mechanisms such as ultraviolet irradiation or chemical oxidation. A P-E Model 21 Double-Beam Infrared Spectrophotometer with automatic precision recording permits kinetic studies to be made fast and accurately. Write us at 751 Main Avenue for a description of this instrument, which includes information on many other important performance features.
I N S T R U M E N T
Other applications of IR to Kinetic Studies • • • • • • • • • • • •
Ultraviolet irradiation studies High energy particles interaction Oxidation susceptibility Solubility rates versus temperature Polymerization rates Crystallization studies Pressure fluctuation Pyrolysis Evaporation rates Dissociation studies Catalysis Contamination
D I V I S I O N
Perkin-Elmer Corporation N O R W A L K ,
C O N N E C T I C U T
W e ' l l be glad to send you more information on any of these ifems or to put you on the mailing list for INSTRUMENT NEWS, a quarterly published by P-E fn further research, material anaiysis and production through electro-optical instrumentation. Write us at 751 Main Avenue, Norwalk, Conn. For further information, circle number 37 A on Readers' Service Card, page 89 A VOL. 3 0 , N O . 6, JUNE 1 9 5 8
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