Isoprene detector

Isoprene, the most abundant hydrocarbon emitted to the atmosphere by plants, can also be measured using ozone chemiluminescence. As discussed above, al-kenes react with ozone to produce formaldehyde in its A2 electronic state, in addition to several other chemiluminescent products. In a fast isoprene detector manufactured by Hills Scientific (Boulder, CO), the chemiluminescence is detected using a blue-sensitive PMT to maximize the sensitivity for isoprene detec-... 

The reaction between olefins and ozone produces light that can be measured and related to the concentration of the reactants. One of the preferred methods for measuring ambient ozone concentrations utilizes the chemiluminescence generated in the ozone-ethylene reaction for detection. Recently, Hills and Zimmerman (16) described the use of this detection principle for determining hydrocarbon concentrations. They utilized the chemiluminescence created when ozone reacts with isoprene for development of a continuous, fast-response isoprene analyzer. This real-time isoprene system is reported to be linear over three orders of magnitude and to have a detection limit of about 1 ppbv. Because the system doesn t include a preseparation of hydrocarbons, interferences from other olefins (ethylene, propylene, and so forth) could occur. Thus far the chemiluminescent detector has been used to monitor isoprene emissions under conditions in which the concentrations of olefins that could interfere are negligible compared to those of the biogenic hydrocarbon. 

The RGD has been used to measure selected OxHCs like acetaldehyde and acetone and also olefinic compounds like isoprene. Analytes in the He effluent of the analytic column reduce HgO solid to Hg vapor emitting UV radiation that is detected. The temperature of the detector must be kept to 200°C. The detector is concentration sensitive, with MDQs for acetaldehyde and acetone in the sub-pmofe range. 

Fig. 6a-c. Diffraction envelopes for hydrogenous diblock copolymers of styrene and isoprene. (Ref. a Cylindrical isoprene domains b Lamellar domains c Spherical styrene domains a illustrates the decrease in resolution on moving the detector... 

FIGURE 11.36 Gas chromatogram showing pyrolysis of isoprene-butadiene rubber [1 = butadiene, 2 = isoprene, 3 = butadiene dimmer, 4 = Umonene (isoprene dimmer)]. Conditions pyrolyzer—CDS Analytical Model 2500, 750°C, 20 s interface oven 300°C, GC—6890 (Agilent), colunrn HP-5, 30 m x 0.25 nun. Carrier gas helium, 5.9 psi, split ratio 75-1, temperature program 40°C, 2 min, 6°C/min to 295°C. Detector mass selective detector. [Reprinted with permission from T. P. Wampler, J. Chromatogr. A 842, 207-220 (1999), Figure 7.]. 

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