Experimental procedure thermal analysis

As field desorption (FD) refers to an experimental procedure in which a solution of the sample is deposited on the emitter wire situated at the tip of the FD insertion probe, it is suited for handling lubricants as well as polymer/additive dissolutions (without precipitation of the polymer or separation of the additive components). Field desorption is especially appropriate for analysis of thermally labile and high-MW samples. Considering that FD has a reputation of being difficult to operate and time consuming, and in view of recent competition with laser desorption methods, this is probably the reason that FD applications of polymer/additive dissolutions are not frequently being considered by experimentalists. 

Conventional electron impact or chemical ionization mass spectrometry requires that volatilization precede ionization and this is clearly a limiting factor in the analysis of many biochemically significant compounds. A newer ionization technique, field desorption (FD) (1, 2 ) removes this requirement and makes it possible to obtain mass spectrometric information on thermally unstable or non-volatile organic compounds such as glycoconjugates and salts. This development is particularly significant for those concerned with the analysis of glycolipids and we have therefore explored the suitability of field desorption mass spectrometry (FDMS) for this class of compounds. We have evaluated experimental procedures in order to enhance the efficiency of the ionization process and to maximize the information content of spectra obtained by this technique. 

Accurate temperature calibration using the ASTM temperature standards [131, 132] is common practice for DSC and DTA. Calibration of thermobalances is more cumbersome. The key to proper use of TGA is to recognise that the decomposition temperatures measured are procedural and dependent on both sample and instrument related parameters [30]. Considerable experimental control must be exercised at all stages of the technique to ensure adequate reproducibility on a comparative basis. For (intralaboratory) standardisation purposes it is absolutely required to respect and report a number of measurement variables. ICTA recommendations should be followed [133-135] and should accompany the TG record. During the course of experiments the optimum conditions should be standardised and maintained within a given series of samples. Affolter and coworkers [136] have described interlaboratory tests on thermal analysis of polymers. 

Determination of the optimal heat treatment temperature in the reactor is done by differential thermal analysis (DTA) and thermogravimetric analysis (TG) it appears (Fig. 2) that in our experimental procedure, for all the studied granulometries (<25 to 250 gm), a specimen fired at 398 K for 3 h contains no mote gypsum, and a specimen fired at 423 K still contains almost only hemihydrate. Above this temperature anhydrite III appears. The very small amount of anhydrite 111 contained in a specimen fired at 423 K is different from a gypsum variety, but quite stable and characteristic for a variety of gypsum (Fig. 6) fZ]. 

In many of the methods of quantitative differential thermal analysis, the calibration coefficient can be mathematically deiermined and no experimental procedures are necessary. For example, Kronig and Snoodjik ((04) calculated K for a cylindrical sample holder as... 

Saffron, production, 66 Saffron flavor characterization using aroma extract dilution analysis aroma-active components, 74-78 detection of aroma-active component using OC-olfactometry, 67 experimental procedure, 67-68 volatile components, 68-74 Safranal, role in flavor, 66-78 Scmivolatile components in powdered turmeric, characterization using direct thermal extraction GC-MS, 80-96 Shallot, contribution of nonvolatile sulfur-containing flavor precursors to flavor, 53-63... 

The process of temperature calibration and measurement has been considered in considerable detail in connection with a program of work by GEFTA (German Thermal Analysis Society). The authors raise the fundamental issue that whereas the temperatures of the fixed points are defined for the substances in phase equilibrium the experimental results are measured under dynamic conditions. The authors recommend a procedure based on extrapolation of results to zero heating rate. The details are contained in a series of publications. The authorshave also considered the problem of temperature calibration under conditions of decreasing temperatures. 

This handbook is designed to provide general information on the basic principles of TA and a variety of its applications. It is composed of two 1915 parts. Part I deals with information on the transition, reaction and characteristic parameters of substances. It introduces general principles, data 1919 treatment, experimental procedures and data analysis. Part II presents about 1000 typical 1945 thermal analysis curves, with brief explanations, for a wide variety of materials, such as polymers, 1960s foods, woods, minerals, explosives, inorganic compounds, and their coupled simultaneous 1964 curves. TA charts have been contributed by Institutes and Universities in China. Part III cites 1965 various data tables relating to thermal analysis. 

The study of crystallization kinetics in glass-forming liquids has often been limited by the elaborate nature of the experimental procedures which are employed. The increasing use of thermoanalytical techniques such as differential thermal analysis (DTA) or differential scanning caloiimetiy (DSC) has, however, offered the promise of obtaining useful data with simple methods (Yinnon Uhlmann, 1983). 

Temperature-composition phase diagrams such as this are often mapped out experimentally by observing the cooling curve (temperature as a function of time) along isopleths of various compositions. This procedure is thermal analysis. A break in the slope of a cooling curve at a particular temperature indicates the system point has moved from a one-phase liquid area to a two-phase area of liquid and solid. A temperature halt indicates the temperature is either the freezing point of the liquid to form a solid of the same composition, or else a eutectic temperature. 

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