Modulated temperature programmed

Note 1 As an example a DSC experiment carried out with a modulated temperature program would be Modulated Temperature Differential Scanning Calorimetry (MT-DSC)... 

Knowledge of vapor pressure helps in estimating the volatility of the plasticizer. It is therefore important to find a method of determination which is precise, easy to handle, and uses commonly available equipment, for example, thermobalance. A quick and simple method was developed to determine vapor pressure at different temperatures using thermobalance.Figure 15.2 shows the data measured by the method and data from other studies. It is evident that the results are obtained with high precision. Details of method and the use of modulated temperature programs is described. ... 

Apart from combined TA techniques (on-line or not) the actual trends in thermal analysis are the introduction of modulated and high-resolution techniques, hyphenated thermal analysis methods e.g. TG-FTIR, TG-MS, DSC-XRD, etc.), alternative heating modes, microthermal analysis methods, industrial standardisation and quality control. Modulation means a periodic perturbation of a temperature program. Temperature modulation finds application in DSC, TG, DETA, TMA and uTA. Temperature-modulated techniques, such as Modulated DSC (MDSC ) and Modulated TGA (MTGATM), broaden the insight into the material properties. The use of modulated temperature programs in thermal methods has been reviewed [37,37a]. 

The ability of a GC column to theoretically separate a multitude of components is normally defined by the capacity of the column. Component boiling point will be an initial property that determines relative component retention. Superimposed on this primary consideration is then the phase selectivity, which allows solutes of similar boiling point or volatility to be differentiated. In GC X GC, capacity is now defined in terms of the separation space available (11). As shown below, this space is an area determined by (a) the time of the modulation period (defined further below), which corresponds to an elution property on the second column, and (b) the elution time on the first column. In the normal experiment, the fast elution on the second column is conducted almost instantaneously, so will be essentially carried out under isothermal conditions, although the oven is temperature programmed. Thus, compounds will have an approximately constant peak width in the first dimension, but their widths in the second dimension will depend on how long they take to elute on the second column (isothermal conditions mean that later-eluting peaks on 2D are broader). In addition, peaks will have a variance (distribution) in each dimension depending on... 

Hence, in the simplest terms, tmDSC is a description of the heat flow into the sample resulting from the sinusoidal modulation of the temperature program. Two properties of the sample can be investigated by tmDSC, the heat capacity which is directly related to the reversing component and a kinetically hindered thermal event which is related to the nonreversing component. Conventional DSC provides only a measure of the total heat flux into a sample as a function of temperature whereas tmDSC allows the heat capacity and kinetic components to be separated. However,... 

Such a differential heating program leads to increased sensitivity and resolution in TGA but also to a much increased time-frame for the analysis. Dynamic rate TG appears to have addressed both of these features and hence has much potential as a high resolution/ rapid thermal analysis system, which, unlike SCTA, can be applied for rapid and reproducible thermal analysis of a wide range of complex materials. Finally, modulated temperature thermogravimetrie analysis has enhanced potential for the kinetic analysis of thermal decomposition reactions over conventional TGA because of its greater resolution of thermal events. 

An advantage of the advanced isoconversional method is that it can be applied to study the kinetics under arbitrary temperature programs such as distorted linear (e.g., self-heating/cooling) or purposely nonlinear heating e.g, temperature modulation). To more adequately account for a strong variation of... 

Other thermal zones, which should be thermostatted separately from the column oven, include the injector and detector modules. These are generally insulted metal blocks fitted with cartridge heaters and controlled by sensors located in a feedback loop with the power supply. Detector blocks are usually maintained at a temperature selected to minimize detector contamination and to optimize the detector response to different sample types. The requirements for injectors may be different depending on their design, and may include provision for temperature programmed operation. 

Potential applications of thermal analysis and calorimetry to quality control is not limited in any way to those discussed in this chapter. Once some physical or chemical characteristic of a material or process is known and can be examined and/or characterized by these techniques, it is only the imagination that limits the possibilities for quality control applications. Both traditional techniques (DSC, TG, DMA, isothermal calorimetry, etc.) and non-traditional techniques (temperature modeling, etc.) have been shown to have potential uses for quality control. With the introduction of many new techniques (fast scanning DSC, sample controlled thermal analysis (SCTA), modulated and other temperature programmed techniques, etc.), many more new opportunities will arise for providing quality control tools. 

The starting point adopted by Reading and co-workers is a description of the heat flow into the sample which occurs as a result of the sinusoidal modulation of the temperature program,... 

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