Home-made instruments

There is a wealth of literature on this type of Instrument dealing with various aspects of direct potentiometrlc measurements. 

Home-made computer-controlled pH-stats developed so far can be classified Into two categories (a) those where the pH Is kept by means of a delivery system Into which the acidic or baelc solution Is Introduced and (b) those using a programmable coulostat to generate the protons of hydroxyl lone required for stable pH control. 

Lemke and Hleftje [4] developed a computer-controlled pH-etat (Fig. 11.1) In which the reagent delivery system le based on a droplet generator, also computer-controlled, capable of selectively adding 0.06- L aliquots. This precise 

Schwlng at al. [7] developed a potentlometric-voltammetrlc system with digital data acquisition and treatment for the kinetic determination of mixtures of metal Ions based on ligand-exchange reactions. The resulte obtained from potentlometrlc measurements are more precise than those found with ampero-metrlc measurements (the typical relative errors are 5% and 5-10, respectively). 

The computer-controlled direct potentlometrlc analysis system devised by 

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Adiabatic calorimeters are complex home-made instruments, and the measurements are time-consuming. Less accurate but easy to use commercial differential scanning calorimeters (DSCs) [18, 19] are a frequently used alternative. The method involves measurement of the temperature of both a sample and a reference sample and the differential emphasizes the difference between the sample and the reference. The two main types of DSC are heat flux and power-compensated instruments. In a heat flux DSC, as in the older differential thermal analyzers (DTA), the... 

Electrophoretic systems for CEC which allow the pressurization of the separation capillary from both sides (see 9.2.1) up to 12 bar are commercially available. Hewlett Packard (HP) (now Agilent, Waldbronn, Germany) provides an option for pressurization up to 12 bar and Beckmann/Coulter (Fullerton CA, USA) up to 8 bar. Also some home-made instruments are described in the literature. 

The technique turned out to be extremely useful for kinetic determinations and the early home-made instruments were soon replaced by commercial products. 

The pHo obtained by means of electrokinetic measurements is reported as iep in the Method columns in the tables in Chapter 3. The trade names of commercial instruments or short descriptions of home-made instruments used for electrokinetic measurements are given when possible. The present approach is different from that in [2], in which the type of instrument was not specified. Moreover, the present book does not consider pHg values obtained by means of an electroacoustic method as a separate category, and they are also reported as iep. ... 

Both SRET and SVET perform potentiometric measurements with micrometer-sized quasi-reference electrodes (typically platinum micro-cones electrochemically coated with platinum black) held precisely above the sample surface. So far these commercial instruments have not been designed to accommodate ion-selective microelectrodes. However, some groups have reported the use of home-made instruments to probe the concentration of specific ions (see Sec. V.B). 

In dealing with the automation of potentlometric measurements a distinction Is made below between commercially available and home-made Instruments. 

A home-made Instrument of this type for use In chemically hazardous, radiation or clean laboratories was recently reported by Bond et al. [89]. Its... 

The versatile nature of calorimeters, commercial and home-made, instruments allows direct access to the thermodynamic properties of materials being studied. Calorimetry is unintrusive in the way information is extracted during a study and highly versatile, measuring from nW to MW, from near absolute zero to several thousand kelvin. The sample studied can be in any phase or mixtures of phases and calorimetry can, in principle, be used to obtain all the thermodynamic and kinetic parameters relating to a reaction, and is limited only by the sensitivity of the instrument to detect a change. 

As we see, these procedures are quite difficult, and thus it is not surprising that few commercial instruments are available to measure extensional viscosity. The present choice is quite small, being limited to Rheometric Scientific s RME extensional viscometer for polymer melts. Anyone interested in measuring extensional viscosity of other systems will have to resort to home-made instruments. 

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