Methods with Pulsed Heating

With voltammetry at permanently heated electrodes, the long term period in the temperature-time diagram is utilised (see Fig. 5.1, left hand part, period following 

In Fig. 6.10, instantaneous variations of electrolysis current are given for a coarse potential staircase with overlaid heat pulses. Diagrams of this type are useful to understand how TPV curves are coming about. The diagrams contain pieces of information according to the variables potential, current, temperature and time. They are more descriptive than three-dimensional pictures would be, with the variables current, voltage and temperamre. Presentations like that one sketched in Fig. 6.10 have some characteristics of spectra, thereby sometimes they have been 

The thermoelectric spectra mentioned above have been recorded in a more extended way for different species. They played an important role in the early time when hot-wire electrochemistry has been established. Extended pictures like that in Fig. 6.11 allow to understand that TPV curves may assume different shapes dependent on the length of heating-up and cooling-down periods. For heat pulses of very long duration, when actual current rise has ceased, the resulting TPV 

In comparison to voltammetry, with heated potentiometric sensors, advantages are not obvious at first glance. Anyhow, there are chances to tune such sensors in order to achieve higher sensitivity, faster response and better selectivity. Of course, experiments are restricted to all-solid ISEs which can be heated indirectly. An interesting example was presented [19], where a heated copper disc had been modified by an ionophore layer. The slope of the sensor was strongly increased by heating, and the detection Unfit was decreased by half an order of magnitude. 

Some characteristics of the methods TPP and TPA have been outlined in a review on electrically heated electrodes [24]. 

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Several techniques are available for thermal conductivity measurements, in the steady state technique a steady state thermal gradient is established with a known heat source and efficient heat sink. Since heat losses accompany this non-equilibrium measurement the thermal gradient is kept small and thus carefully calibrated thermometers and heat source must be used. A differential thermocouple technique and ac methods have been used. Wire connections to the sample can represent a perturbation to the measurement. Techniques with pulsed heat sources (including laser pulses) have been used in these cases the dynamic response interpretation is more complicated. 

T-Jumps can also be produced by microwave heating and by laser pulse absorption. These methods remove the restriction to low-resistance solvents any solvent capable of absorbing energy of the applied frequency may be used. The heating time can be extremely short with laser heating. ... 

Cataldi, T. R., Angelotti, M., and Bufo, S.A., Method development for the quantitative determination of lactulose in heat-treated milks by HPAEC with pulsed amperometric detection, Anal. Chem., 71, 4919, 1999. 

Photolysis in Matrices Prepared by the PMI Method. In the PMI run, the matrix is annealed by heat release of each pulse and then cools down until the next pulse arrives. By controlling the interval between pulses a slower deposition rate can be obtained in the PMI method than in the SSO method (20). The time interval between pulses in the PMI method was found to influence the yields of photolysis products in the same way as did the deposition rate in the SSO method. The (1 300) Fe(C0) -N2 matrix samples prepared by the PMI method with varying time intervals between pulses were irradiated with the 250-400 nm light (20). 

This method is not only limited to halide-based ionic liquids. Synthesis of ionic liquids containing a tetrafluoroborate anion and imidazolium cation has been performed successfully [16] by use of a modified domestic microwave oven with pulsed irradiation (5 x 30 s). Approximately 90% yields of the desired ionic liquids were usually obtained compared with 36% after the same reaction time using conventional heating. Microwave irradiation has been used in the synthesis of l-ethyl-3-methylimidazolium benzoate and dialkyl imidazolium tetrachloroaluminate ionic liquids [17, 18]. These reactions were again performed in a domestic microwave oven using pulsed irradiation. 

Matrix assisted laser desorption/ionisation (MALDI) For laser desorption methods a pulsed laser is used to desorb species from a target surface. Therefore, a mass analyser compatible with pulsed ionisation methods has to be used. Typically, time-offlight (TOF) analysers are employed, but several hybrid systems (Q-TOF) and, recently, high resolution Fourier transform ion cyclotron resonance (FT-ICR) analysers have been successfully adapted (see Section 10.2.4). Direct laser desorption rehes on the very rapid heating of the sample or sample substrate to vapourise molecules without decomposition. The more recent development of MALDI relies on the absorption of laser energy by a solid, microcrystalline matrix compound such as a-cyano-4-hydroxy ciimamic acid or sinapinic acid [8, 34]. MALDI has become an extremely popular method for the rapid and sensitive analysis of high-molecular-weight compounds [4]. 

The temperature pulse decay technique has been used to measure both the in vivo and in vitro thermal conductivity and blood flow rate in various tissues (Xu et al., 1991 1998). The specimen does not need to be cut from the body, and this method minimizes the trauma by sensing the temperature with a very small thermistor bead. For the in vitro experimental measurement, the measurement of thermal conductivity is simple and relatively accurate. The infinitively large tissue area surrounding the probe implies that the area affected by the pulse heating is very small in comparison with the tissue region. This technique also requires that the temperature distribution before the pulse heating should reach steady state in the surrounding area of the probe. 

Another known method of preparing disordered aluminium hydroxide is pulse thermal heating of aluminium hydroxide at relatively low temperatures [46]. Pulse heating can be carried out by different means in the flow of hot gas, with electron beam. Pulse heating in the flow of hot gas leads to a partial dehydration of the initial gibbsite. The degree of dehydration depends on the conditions of thermal treatment. In particular, under certain conditions the formation of completely X-ray amorphous product is possible, its composition being close to that of boehmite (AlOOH). 

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