Thermometric detection

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

Twenty weakly acidic drugs, including niclosamide, were determined by a nonaqueous catalytic thermometric titration method. Catalysis of the anionic polymerization of acetonitrile was used for endpoint indication. The solvent used was a mixture of acetonitrile and dimethylformamide or pyridine, and the titrant was sodium methoxide, potassium hydroxide, tertiary butanol, or tertiary butanol-sodium nitrite. Recoveries, limits of detection and relative standard deviations were tabulated [31]. 

There is, however, a temperature range in which the y emission is a function of temperature. In this range, the anisotropy of y emission can be used as thermometric property. The advantage of using y emitters is that the detection can be done from outside the cryostat (no wiring necessary inside the cryostat). 

Z. Y. Zhang, K. T. V. Grattan, and A. W. Palmer, Phase-locked detection of fluorescence lifetime and its thermometric applications, in Int. Conf. Biomedical Optics 93, Los Angeles, January 1993. SPIE Proc. 1885, 228-239 (1993). 

TITRATION (Thermometric). This technique consists of the detection and measurement of the change in temperature of a solution as the titrant is added to it, under as near adiabatic conditions as possible. Experimentally, the titrant is added from a constant-delivery burette into die titrate (solution to be titrated) which is contained in an insulated container such as a Dewar flask. The resultant temperature-volume (or time) curve thus obtained is similar to odier titration curves, e.g., acid-base, in that the end point of the reaction can be readily ascertained. Since all reactions involve a detectable... 

S. Pirvutoiu, I. Surugiu, E.S. Dey, A. Ciucu, V. Magearu and B. Daniels-son, Flow injection analysis of mercury (II) based on enzyme inhibition and thermometric detection, Analyst, 126 (2001) 1612-1616. 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

Thermometric sensors are based on the measurement of the heat effects of a specific chemical reaction or an adsorption process that involves the analyte. In this group of sensors the heat effects may be measured in various ways, for example in catalytic sensors the heat of a combustion reaction or an enzymatic reaction is measured by use of a thermistor. Calorimetric biosensors detect variations of heat during a biological reaction. 

Fig. 8. a Schematic of the set-up for simultaneous electrochemical and thermometric determination of analytes (for a detailed explanation, see text), b Optimization of catechol detection using hybrid (electrochemical and thermometric sensing) for oxygen concentration and its effect on sensitivity of thermal detection [30]... 

Fig. 9. The linear range for urea detection using a miniaturized thermometric system...

More recently, it was demonstrated that the thermistor approach could be used to monitor specific interactions of fluoride ions with silica-packed columns in the flow injection mode. A thermometric method for detection of fluoride [56] was developed that relies on the specific interaction of fluoride with hydroxyapatite. The detection principle is based on the measurement of the enthalpy change upon adsorption of fluoride onto ceramic hydroxyapatite, by temperature monitoring with a thermistor-based flow injection calorimeter. The detection limit for fluoride was 0.1 ppm, which is in the same range as that of a commercial ion-selective electrode. The method could be applied to fluoride in aqueous solution as well as in cosmetic preparations. The system yielded highly reproducible results over at least 6 months, without the need of replacing or regenerating the ceramic hydroxyapatite column. The ease of operation of thermal sensing and the ability to couple the system to flow injection analysis provided a versatile, low-cost, and rapid detection method for fluoride. 

Based on the plethora of applications of thermistor/thermopile based devices, it can be concluded that the field of thermometric sensing offers several avenues of progress in materials science, process monitoring, process control, molecular level detection, characterization of biocatalysts, hybrid sensing and multisensing devices, as well as in telemedicine and other areas of biomedical analysis. 

On the basis of an enzyme thermistor, Mattiasson et al. (1977) developed one of the first immunosensors. Immobilized antibodies against albumin are placed in a column and set into an ET. After injection of an albumin-sample and a known amount of enzyme-labeled albumin, both are separated from the sample matrix by antibody-antigen-interaction. After injection of a substrate, the change in heat is a measure of analyte concentration. The less heat produced means that more albumin has been bound. An elution step regenerates the ELISA. Due to its thermal detection principle, the procedure is called TELISA (thermometric enzyme-linked immunosorbent assay). Figure 3 shows the principle of the TELISA procedure in its sandwich configuration. 

Capillary zone electrophoresis (CZE), with direct or indirect photometry and conductivity has become popular in wine analysis. Very little, or sometimes no sample preparation is needed and short analysis times are also apparent advantages of CE and CZE in the analysis of wine. Capillary isotachophoresis (ITP), with conductivity, thermometric, and UV absorption detection, is suitable for the separation of various anionic constituents (organic acids and inorganic anions), currently occurring in wines (Masar et al., 2001). 

The sensitive part of an electrode is covered with a membrane on which the enzyme is immobilized in immunocomplexes. The enzyme-catalyzed reaction takes place near the sensor (Mattiasson and Nilsson, 1977). The method is as fast as the thermometric assay but less sensitive. Electrode-based EIA using urease conjugates have been reviewed by Meyerhoff and Rechnitz (1980). This method has reasonably low detection limits. These promising potentiometric EIA are discussed by Boiteux et al. (1981) and Gabauer and Rechnitz (1982). 

W.R. McLean, G.E. Penketh, Automatic analysis with thermometric detection, Talanta 15 (1968) 1185. 

ThermoMetric AB Organic acids, urea. Detection of changes in tern-... 

To review some of the applicative problems related to the use of coherent methods for the detection of chemical species, we concentrate on two specific examples belonging to the realm of third-order dielectric nonlinearities. One is the so-called CARS and the other is the degenerate four-wave mixing (DFWM). This choice is also suggested by the thermometric uses of these two techniques (see the corresponding section below). 

Electrochemical biosensors may be expected to maintain their leading position up to the end of the century. In this respect, the availability of transducers, eg, ion-selective field-effect transistors prepared by mass-production technology, will result in widespread application. In addition to one-shot use, multifunctional sensing in minute volumes will be realized. In addition to electrodes, optical, thermometric, and piezoelectric transducers are likely to become exploited in the next generation of sensor. Inexpensive equipment to be used in all areas where material has to be detected and quantified will be produced by integrating the Hxation of the biocomponent with the micromechanical fabrication of the analyzers. 

ThermoMetric AB (TA Instruments-Waters LLC) Detection of changes in temperature due to immobilized enzyme-analyte reactions... 

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