Volatile temperature programme

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. 

Purge and trap injectors are equipped with a sparging device by which volatile compounds in solution are carried into a low-temperature trap. When sparging is complete, trapped compounds are thermally desorbed into the carrier gas by rapid heating of the temperature-programmable trap. 

Two principal advantages of the probe atomization are (i) Improved control of the vapour temperature the atoms experience (ii) Rapid heating of the atomization surface to the volatilization temperature of the analyte and matrix. A comparison of typical furnace programmes for wall/platform atomization and probe atomization is given in Table 8. The probe is not in... 

The ICTAC definition of EGA a technique in which the nature and/or amount of a volatile products released by a substance are measured as a function of temperature as the substance is subjected to a controlled temperature programme is unsatisfactory in describing the current practice of EGA as a TA technique. In many ways it is too broad, since it includes other techniques such as pyrolysis-GC, and in other ways too narrow, as it would exclude studying the changing nature of the gas stream as it is passed over the sample, as in catalytic studies. The definition does not require an evolved gas analyser to be coupled to another technique, but in practice this is nearly always the case. This section will deal with EGA as it is usually carried out, which is simultaneously, combined with another technique. The commonest combinations are those with TG and TG-DTA/DSC, where EGA assists in interpreting the chemistry of the events leading to weight losses. 

In order to effect complete separation of tetramethyltin and the large quantities of diethyl ether present, it was necessary to start the temperature programme at 50 0. At a programme rate of 10°C/min. all sample components were well resolved with the least volatile, tetrabutyltin, eluting at 270°C. Excellent reproducibility... 

GLC uses a column packed with a solid support coated with a viscous liquid. The volatile sample is injected through a septum into an inert gas stream that evaporated the sample and carries it onto the column. Separation is achieved by differential partition of the sample components between the liquid coating and the continuously replaced gas stream. Eventually, each compound flushes off the column and into the detector in reverse order to their affinity for the column. The column is placed in a programmable oven and separation can be modified using temperature gradients. 

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