Temperature programme

All subsequent green coke operations were made in a second coker, which was fashioned from steel pipe approximately 18 cm in diameter and 25 cm in length. A metal plate was welded to one end and a metal collar was welded to the other end such that a steel lid could be bolted to the system. Typically, about 250 to 500 g of pitch were sealed imder nitrogen in the coker reactor and the system placed in a large temperature-programmable furnace. The heat treatment process was as follows. The temperature was raised 5°C/min to 350 °C and then l°C/min to 425°C and the temperature held at 425°C for 90 minutes. Finally the temperature was raised further at 3°C/min to between 500 and 600°C, and held there for 3 hours. The coker was cooled to room temperature and the material recovered to determine green coke yield. 

Temperature programming was introduced in the early days of GC and is now a commonly practiced elution technique. It follows that the temperature programmer is an essential accessory to all contemporary gas chromatographs and also to many liquid chromatographs. The technique is used for the same reasons as flow programming, that is, to accelerate the elution rate of the late peaks that would otherwise take an inordinately long time to elute. The distribution coefficient of a solute is exponentially related to the reciprocal of the absolute temperature, and as the retention volume is directly related to the distribution coefficient, temperature will govern the elution rate of the solute. 

Figure 7.4 Microcomputer programming of a hatch cooling crystallizer. A, crystallization vessel, B, control heater, C, control cooler. surrounding the draft-tube), D, contact thermometer, E, discharge plug and conical baffle), F, recorder, G, relay, H, temperature programmer, I, cooling water pump, J, cooling water reservoir, K, water inflow L, water outflow after Jones and Mullin, 1974)...

Figure 7.6. Experimental set up for temperature-programmed desorption in ultrahigh vacuum. The heat dissipated in the tantalum wires resistively heats the crystal the temperature is measured by a thermocouple spot-welded to the back of the crystal. A temperature programmer heats the crystal at a rate of typically 1-5 K s b Desorption of gases...

The TPD unit was constructed at the Signal UOP Research Laboratory. It Includes a Carle 111 H gas chromatograph with Pd/Ag hydrogen separator, Leeds Northrup temperature programmer, Bascom-Turner 8000 series recorder with data processing and storage capabilities and a custom designed quartz reactor. 

Figure 3.8 Alternative designs for cold on-column injectors, h, Injector with a duck bill valve (Hewlett-Packard), B, an injector with provision for secondary cooling of the column inlet (Carlo-Erba), and C, a temperature- programmable on-column injector with its own oven isolated from the column oven (Varian Associates).

As indicated in Section 6.2.2, DI-CIMS suffers from poor reproducibility. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible. The method depends on polymer formulation standards that are reliably mixed. Wilcken and Geissler [264] described rapid quality control of l- xg paint samples by means of temperature-programmable DI-EIMS with PCA evaluation. 

The use of stable, narrow-bore columns and fast oven temperature programmes result in analysis times of 5-15min, while maintaining the final resolution obtained with conventional GC approaches. Fast GC-MS (5-200 s) requires the matching of several technologies ... 

Figure 7.27 Constructed Gram-Schmidt chromatogram of a temperature-programmed packed-capillary LC separation of 4.8 ig Irgafos P-EPQ dissolved in DMF temperature programme 50°C for 8min, 4°Cmin-1 up to 140°C. Legend 1, mono-P-EPQ 2, Irgafos 168 3, 4,3 -P-EPQ 4, oxidised 4,4 -P-EPQ 5, 4,4 -P-EPQ. After Bruheim et al. [511]. From I. Bruheim et al., Journal of High Resolution Chromatography, 23, 525-530 (2000). Wiley-VCH, 2000. Reproduced by permission of Wiley-VCH.

Rheological measurements. Routine viscosity measurements were made with a Wells-Brookfield micro-cone and plate viscometer, or a Brookfield LVT(D) viscometer with UL adapter. Viscosity-temperature profiles were obtained using the latter coupled via an insulated heating jacket to a Haake F3C circulator and PG100 temperature programmer or microcomputer and suitable interface. Signals from the viscometer and a suitably placed thermocouple were recorded on an X-Y recorder, or captured directly by an HP laboratory data system. 

In DI-MS, solid or liquid samples are introduced into a small glass cup and then the cup is inserted into a spring-loaded holder (probe tip). This is heated by a coiled heater up to a maximum of 450 °C thus allowing the sample to be volatilised. The probe can be heated in two different ways ballistic mode or temperature-programme mode. In ballistic mode the probe heats at the maximum rate (150 °C min J) up to the final temperature desired. In the temperature-programme mode the probe heats at a specified rate (from 10 to 100 °C min 1) up to the final set up temperature. 

FIGURE 9.2 Gas chromatograms of an FT product, original and precolumn hydrogenated. Ampoule samples taken from the gaseous product flow at ca. 200°C. GC conditions Capillary, 100 m dr 0.25 mm df, 0.5 pm methyl silicone cross-linked temperature programm -80 to 270°C carrier gas H2 introducing gas N2 FID. 

The final stage is to control the temperature programme in order to promote the growth of the silver droplets to the size required to produce the yellow colour, in the same way as the production of ruby red glasses. 

All gas chromatography parameters, including temperature programme rates and hold times, are controlled by the microprocessor and set through the CRT keyboard. Up to five sets of parameters can be stored on the computer disk for instant recall. 

Glass column, 1.8m long, 6mm dia., packed with 3% OV-1 on Chromosorb W 80-100 mesh carrier gas, 70ml nitrogen min-1 injection port temperature, 150-C temperature programme, initial 50°C for 2min, programmed at 15°C min-1, until 150°C sample trap temperature, 80-100°C... 

All gas chromatography was carried out with pressure regulated helium carrier gas and the following temperature programme 15°C for 2 mins and then 5°C to 250°C. 

Kankare, J.J. Simple Temperature Programmer for a Mass Spectrometer Direct Insertion Probe. Anal. Chem. 1974, 46, 966-967. 

Several examples illustrate the use of GC/MS for analysis of explosives Trace analysis of explosives in water by GC/MS was carried out using a cooled temperature-programmable injector and a 15 mx 0.255 (Xm ID, 0.25 (Xm film thickness, DB-1 column [7]. 

These liner exchange systems make feasible yet another analysis mode direct thermal desorption (DTD). Here the liner or an insert is packed with the solid sample. The liner exchange system can then be used in place of a conventional autosampler. The liner is automatically inserted into the PTV and the volatiles thermally desorbed onto the column. Some analysts may feel uneasy about such desorption from the solid phase how does one know that all of the volatile analytes have been released from the sample crystal lattice However, where applicable, this approach may not be as difficult to validate as one might imagine. For instance, the PTV can be cooled after the analyte transfer, and then, at the end of the chromatographic temperature programme, reheated to repeat the process. Ideally all of the analyte should transfer in the first cycle and none in the second, demonstrating that complete desorption occurs in the method. 

TG is a method associated with mass change in which the mass of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme. On the other hand, DTA is a method associated with temperature change in which the temperature difference between a substance and a reference material is measured as a function of temperature whilst the substances are subjected to a controlled temperature programme. 

First, optimize the temperature programme. In the first instance, only the dry temperature need be optimized, and so aliquots of water can be dispensed into the tube. A temperature range of 100-140°C can be tried, and the temperature that gives complete drying without frothing or spitting selected. 

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