Temperature programming ramp profiles

In modem gas chromatographs the temperature controller of a column oven is a microprocessor incorporated into a feedback loop, allowing both temperature programming ramp profiles and isothermal heating to be accomplished accurately and reproducibly. Under microprocessor control, a flap or door movement permits the blending of the proper amount of ambient lab air with oven air in the control of oven temperature. In addition, a cryogenic valve can be opened by a microprocessor for delivery of carbon dioxide or liquid nitrogen in the column oven. 

The NOx profiles (chemiluminescence) and CO2 signal (m/e 44) during a temperature programmed ramp are displayed in Fig. 2. NO2 was released in a single, almost symmetrical peak at 481 K while NO was released in three stages a sharp peak at 486 K and two smaller peaks at 527 and 596 K. The tail of the latter corresponded with the temperature at which an abrupt increase in CO2 was observed, reaching a 50% conversion level at 613 K. Beyond this, a much more gradual increase in CO2 production was... 

The temperature-programmed reduction profiles were obtained by passing 5% H2/Ar gas mixture through the catalyst while increasing the temperature at a linear rate. The amount of samples for all experiments was about 50 mg. The gas flow velocity was 30 ml/min, and the rate of temperature ramping was 3 °C /min... 

Temperature-programmed reduction (TPR) profiles of fresh catalyst samples were obtained using a Zeton Altamira AMI-200 unit. Calcined fresh samples were first heated and purged in flowing argon to remove traces of water. TPR was performed using 30 cc/min 10% H2/Ar mixture referenced to argon. The ramp was 5°C/min from 50 to 1,100°C, and the sample was held at 1,100°C for 30 min. 

Metabolite profiling should be performed on a capillary column 30 m X 0.25 mm x 0.25 pm (DB-5 from J W or equivalent) with the following temperature program in the GC oven isothermal for 2 min at 70°C, followed by a 15°C/min ramp to 330°C the final temperature should be held for 6 min. Cooling of the GC system should be as rapid as the instrument specifications allow. The transfer line temperature should be adjusted to 250°C and matched by the ion source conditions. 

The rate of temperature programming or ramp rate can influence the bleed profile from a column. As the rate of temperature programming increases, column bleed also increases. Finally, the more sensitive element-specific detectors (e.g., an BCD or NPD) will generate a more pronounced bleed profile if the stationary phase contains a heteroatom or functional group (-CN or -F) to which a detector responds in a sensitive fashion. 

After ramping the temperature to 150 °C, the sample was held isothermally at 150 "C for 20 minutes, cooled to -100 °C, and then exposed to a second 5 °C/min heating up to 150 °C. The dielectric profiles of the retested sample are identified as 2nd Temperature Scan . All of the curves in Figures 15.12(a) and (b) were generated in a single experiment, which had been programmed by customising the temperature profile. 

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