Colorimetric sensing

The above system of directly sensing a process stream without more is often not sufficiently accurate for process control so, robot titration is preferred in that case by means of for instance the microcomputerized (64K) Titro-Analyzer ADI 2015 (see Fig. 5.28) or its more flexible type ADI 2020 (handling even four sample streams) recently developed by Applikon Dependable Instruments20. These analyzers take a sample directly from process line(s), size it, run the complete analysis and transmit the calculated result(s) to process operation (or control) they allow for a wide range of analyses (potentiometric, amperometric and colorimetric) by means of titrations to a fixed end-point or to a full curve with either single or multiple equivalent points direct measurements with or without (standard) addition of auxiliary reagents can be presented in any units (pH, mV, temperature, etc.) required. 

Jelinek R, Kolusheva S (2007) Biomolecular Sensing with Colorimetric Vesicles. 277 155-180 Jones W, see Trask AV (2005) 254 41-70... 

We have shown a new concept for selective chemical sensing based on composite core/shell polymer/silica colloidal crystal films. The vapor response selectivity is provided via the multivariate spectral analysis of the fundamental diffraction peak from the colloidal crystal film. Of course, as with any other analytical device, care should be taken not to irreversibly poison this sensor. For example, a prolonged exposure to high concentrations of nonpolar vapors will likely to irreversibly destroy the composite colloidal crystal film. Nevertheless, sensor materials based on the colloidal crystal films promise to have an improved long-term stability over the sensor materials based on organic colorimetric reagents incorporated into polymer films due to the elimination of photobleaching effects. In the experiments... 

COLORIMETRIC SENSING AND BIOSENSING USING FUNCTIONALIZED CONJUGATED POLYMERS... 

Tn 1950 Weitz et al. (23) developed a sensitive colorimetric method to measure small amounts of oligomeric silicic acid in the presence of polymeric forms. Oligomeric acid in this sense comprises molecules up to hexameric chains of hydrated SiC>4 tetrahedrons, which react readily with ammonium molybdate. Hence, this fraction of a sol is frequently referred to as molybdate-active silicic acid. 

It is safe to say that any conventional spectrophotometric and colorimetric analysis can be performed in an optical sensing format. That makes the optical sensors probably the most universal type of chemical sensors. Miniaturization of optical components and rapid advances in the development of new optical materials and hardware support this fast-growing area of chemical sensing. 

In this section, a visual and colorimetric NH4+ sensing film was described. The observed color gradation was suitable for human visual perception over a wide dynamic range. This NH4+ sensing film is useful for routine semiquantification of NH4+. 

Figure 3.97 Fe (III) specific colorimetric sensing by squarine-based siderophore 3.148. (Reproduced by permission of The Royal Society of Chemistry).

In the same way as the molecular or supra molecular juxtaposition of a binding site and a chromophore can result in luminescent or colorimetric sensing of target substrates, so incorporation of a redox-active centre may allow electrochemical detection of binding. In Section 4.7.2, we examined a range of hosts for anions based on the Co(III)/Co(II) redox couple in cobaltocinium based podands, corands... 

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