Sample controlled TA

This can only ever be a superficial view of TA in the foods area. We have concentrated mainly on calorimetry but hopefully have given an indication of the type of work which has been carried out and the areas which may see activity in the near future. 

Wu H-CH, Sarko A. Packing analysis of carbohydrates and polysaccharides. VIII the double-heUcal molecular structure of crystalline B-amylose. Carbohydr Res 1978 61 7-25. 

Waigh TA, lenkins PI, Donald AM. Quantification ofwater in carbohydrate lamellae using SANS. Faraday Discuss 1996 103 325-337. 

Donovan IW. Phase transitions ofthe starch-water system. Biopolymers 1979 18(2) 263-275. 

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Note the generic term for all TA techniques making use of such a feedback is Sample-Controlled TA (SCTA), whereas specific names will be of the form Sample-Controlled TGA (SC-TGA) etc. 

Minerals of great variety have been studied using TA techniques - particularly clay minerals and coal, lignite, and wood. Traditionally, the simultaneous methods have been applied in these cases, but increasingly, new methods such as sample controlled TA are becoming more prominent, particularly for studies of pyrolysis and combustion of coals. The rationale for using SCTA over conventional TA for the study of coal is simply related to overcoming the... 

Over the last decade, it has been internationally accepted that the generic title for TA techniques whereby the heating rate is controlled using a feedback loop as some function of the rate of reaction or the chemical or physical process under study should be sample controlled thermal analysis (SCTA) and this title now embraces Q-TG, CRTA, SIA, and dynamic rate thermal analysis. 

For mashed potato texture, profile analysis (TPA) and cone penetration tests are performed with a TA HDi Texture Analyser (Stable Micro Systems Ltd, Godaiming, UK). During the tests, the mashed potatoes are kept at 55° C by means of a temperature-controlled Peltier cabinet (XT/PC) coupled to a separate heat exchanger and PID control unit. For the cone penetration tests, a spreadability rig is used, consisting of a 45° conical perspex probe (P/45°C) that penetrates a conical sample holder containing 7 0.1 g of mashed potatoes (Alvarez et al., 2005 Canet et al., 2005b Fernandez et al, 2006). 

In a DSC experiment the difference in energy input to a sample and a reference material is measured while the sample and reference are subjected to a controlled temperature program. DSC requires two cells equipped with thermocouples in addition to a programmable furnace, recorder, and gas controller. Automation is even more extensive than in TA due to the more complicated nature of the instrumentation and calculations. 

Wils et al. (25,26) previously reported an entirely different approach to TDG analysis. TDG in urine was converted back to sulfur mustard by treatment with concentrated HC1. The sample treatment is less straightforward than the methods described above, but analysis as sulfur mustard is facile. Urine, plus 2H8-TDG as internal standard, was cleaned up by elution through two C18 cartridges. Concentrated HC1 was added and the sample stirred and heated at 120 °C. Nitrogen was blown over the solution and sulfur mustard isolated from the headspace by adsorption onto Tenax-TA. The method was used to detect TDG in urine from casualties of CW attacks (see below). A disadvantage of this method is that it may convert metabolites other than TDG to sulfur mustard. This is supported by the detection of relatively high levels of analytes in urine from control subjects. Vycudilik (27) used a similar procedure, but recovered the mustard by steam distillation and extraction. 

Scanning electron micrographs were taken with an ISIDS-130 microscope. Thermogravimetric analysis (TGA) was performed with an SDT Q600 (TA Instruments). A Seiko DMS 210 dynamic-mechanical analyzer was used for DMA measurements. For water content determination samples were allowed to equilibrate over saturated salt solutions in sealed jars at controlled relative... 

Before use, all the polymer pellets were dried at Ta +20 K for at least 48 h. Then, sheets of controlled thickness B were firstly compression molded under vacuum at Ta + 50 K and then cooled down slowly through the glass transition region. Next, samples of dimensions suitable for the SENB tests were cut from the sheets with a diamond saw, machined to produce the notch, and annealed once more at Ta +20 K for 72 h. The purpose of this thermal treatment is double first, it allows the elimination of the residual stresses induced by sample pressing and machining and secondly, it permits removal of eventual moisture which is known to affect dramatically the SAPA mechanical properties [12]. The pre-crack was produced in the samples just before testing. 

The thermogravimetric analyser is a SDT-DTA from TA Instruments, supported by an HP PC and software for control and data handling. The system consists of a dual beam horizontal balance. Each arm holds one cup and there is one thermocouple under and in contact with each cup. One cup contains the char sample and the other cup is empty, used as a reference for temperature effects. Detailed description of the instrument can be found somewhere else. Ceramic cups were used for most of the experiments. The apparatus has been recently upgraded and it was possible to operate in a TGA-DSC mode. Therefore, not only the temperature and the weight have been registered but also the heat demand of the process. Table 2 and Table 3 show the experimental matrix for this work. 

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