mercury vapor spectra 1 st Order Spectrum Grating: 118Qg/mm 4000 A Blaze Slits: lOO^im χ 12 7mm
1st Order Spectrum Grating 1180 g/mm 4000 A Blaze Slits 10um χ 5mm
Time (min)
3021 5 A 3023 5 A 3025 6 A 3027 5 A (Left to Right)
Hg 3021 3027 Quadruplet
3650 1 A 3654 8 A 3663 3 A (Lett to Right)
Hg 3650 3663 Triplet
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CZERNY-TURNER MODEL MP-1018B MONOCHROMATOR For UV, Visible, and NearInfrared. 1180 grooves/mm standard. Wavelength readout directly in angstroms. Variable slit width readout in microns. Six switch-selectable scanning speeds; bidirec tional. Computer compatible. 24-page catalog of photo metric instruments available.
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Time (min)
Figure 3. Chromatopyrogram of silicone rubber Β
jector barrel and the space inside the injector liner where the sample is lo cated is in a static condition without back-flush. As soon as the pyrolysis probe is sealed, the normal carrier gas flow is resumed and gas chromato graphic analysis begins. All volatile in gredients of the sample are thus subjected to CPG analysis. Another factor is that the dynamic percolating conditions in the heated injection port substantially lower the boiling tem peratures of the monomeric ingredi ents to such an extent that practically all volatile ingredients are vaporized instantaneously at 270 °C while the high polymers are not affected (11). The requirement of only a minute sample size in the range of sub-milli grams to micrograms also favors a rapid and complete vaporization of the volatile ingredients. And the fast vaporization results in sharp peaks and a stable recorder baseline during sample insertion. Meeting all of these conditions means CPG can also be used for the direct introduction of heterogeneous viscous liquid samples for GC analysis (9), simplified headspace-type analy sis, and splitless sample injection for capillary GC (9). CPG Applications
CPG has modernized industrial quality control test procedures, and it also has problem-solving applications. Many real-world analyses involving rubberlike polymeric materials, which in the past required long research ef forts, can now be completed by CPG
CIRCLE 187 ON READER SERVICE CARD
316 A • ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
within an hour. It is CPG that solved the urgent identification problem we described earlier concerning the unstamped mis sile part. We knew the part should have been fabricated from an ap proved Boeing proprietary formula tion that was based on a specific siloxane polymer. Figure 2 is the chromato pyrogram of the sample, which was re moved from the missiles by a pseudonondestructive technique. It is identi cal to that of the specified Boeing pro prietary material (silicone rubber A). The unmarked missile part had been unambiguously identified within the time limit and the missiles could be delivered on schedule! Figure 3 shows the chromatopyrogram of a different silicone rubber (silicone rubber B) for comparison purposes. A second case that required a CPG solution occurred in the Boeing AWACS project. The AWACS (Air borne Warning and Control System) is the aircraft with a flying-saucerlike radome mounted on top of a Boeing 707 air frame. During a routine inspection of the prototype AWACS aircraft it was discovered that some rubber sheaths covering high voltage electric cables showed signs of crazing while other similar sheaths didn't show such failure signs. Failure of electric insula tion might result in serious difficulties in operating the AWACS system, so the problem was immediately investi gated. The approach was to first find out what materials were involved by chemical analysis and then to deduce the cause of failure. The sample of the failed sheath was
