Automatic titrators microprocessor

In this era of automatic titrators, microprocessor-controlled thermal analysis, and definitive spectral techniques, one of the most powerful techniques, that is, optical microscopy, is frequently overlooked. The value of direct sample observation, preferably while it is exposed to different relative humidities, cannot be overstated. In the author s laboratory, a plexiglass chamber was constructed that can be placed on the stage of the microscope, through which air of known humidity can be circulated. This simple technique has been very useful in examining the swelling (or lack) of disintegrants and the influence of very hydrophilic excipients in combination with a moisture sensitive drug. ... 

The use of "fixed" automation, automation designed to perform a specific task, is already widespread ia the analytical laboratory as exemplified by autosamplers and microprocessors for sample processiag and instmment control (see also Automated instrumentation) (1). The laboratory robot origiaated ia devices coastmcted to perform specific and generally repetitive mechanical tasks ia the laboratory. Examples of automatioa employing robotics iaclude automatic titrators, sample preparatioa devices, and autoanalyzers. These devices have a place within the quality control (qv) laboratory, because they can be optimized for a specific repetitive task. AppHcation of fixed automation within the analytical research function, however, is limited. These devices can only perform the specific tasks for which they were designed (2). 

The microprocessor control also enables the instrument to be set to calculate pA"a values directly from the pH profile it obtains by titration of a sample. A sample changer can be incorporated so that several samples can be automatically titrated. 

With this simplified procedure it is much easier to protect the system from atmospheric moisture, which must obviously be excluded. Modem K-F Titrators are equipped with special titration vessels which are designed to prevent the ingress of atmospheric moisture. Many also have microprocessors attached which will carry out the requisite operations automatically and will often provide a print-out of the results including the percentage moisture content. 

Although the DL 40 was capable of performing Karl Fischer water titrations and Mettler developed a separate microprocessor-controlled push-button operated DL 18 KF titrator, they also introduced as an all-purpose apparatus the improved DL 40 RC (see Fig. 5.11) with a dual titration head and with a modified software program to handle the new two-component titrants for Karl Fischer titration (see pp. 204-205). The instrument can also be expanded into an automatic series titrator by connecting the RT 40 sample transport for 16 samples and storage of 50 sample weights from a connected balance this series routine can be interrupted at any time after completion of the titration in progress. 

Commercially available Modem KF-Titrators are usually equipped with specifically designed titration vessels that are exclusively meant to check and prevent the contact with atmospheric moisture. Quite a few such devices are armed with microprocessors that will perform the requisite operations sequentially in a programmed manner automatically and may also dish out a print-out of the desired results including the percentage moisture content. In fact, these Modem KF-Titrators not only afford greater accuracy and precision in results but also offer much ease and convenience in routine analysis as compared to the classical techniques based on either caulometry or controlled current potentiometiy using two indicator electrodes. 

Titrations can be automated and controlled by a microprocessor. The titrant is delivered via an automatic burette and the end-point is detected potentiometrically... 

Potentiometric titrations are readily automated by using a motor-driven syringe or an automatic burette coupled to a chart recorder or digital printout system. This is described in more detail in chapter 12. A microprocessor-controlled titrator is discussed in chapter 13. 

The use of modern temperature detection methods in thermal titration has increased considerably in recent years, with several commercial instruments now available. Marini and Martin have recently reviewed this field (Marini and Martin, 1979) extensively so that only a brief discussion will be given here. We have developed a combined pH—thermal differential titration apparatus that is modelled after our earlier single-cell system (Berger et al., 1974 Marini et al., 1980). Figure 14 shows the essentials of the instrument. The unique part of this device is that it is under microprocessor control. The computer starts the titration, records the data, and speeds up or slows down the titration automatically if the curve is changing too rapidly. Data-correction programs adjust for response time and... 

Fig. 1.11 Automation of the first and third stages of the analytical process (Type 8 analyser). Scheme of microprocessor-controlled automatic potentiometric or photometric titrator.

According to the classification established by Pungor et al. [56], there are three levels of automatic tltrators defining as many degrees of automation, namely (a) hardware-controlled tltrators, (b) microprocessor-controlled titrators and (c) computer-controlled tltrators. 

Metrohm markets microprocessor-controlled Instruments for routine coulo-metric (KF 652 Processor) and amperometrlc-voltammetrlc (EP/KF 678 Processor) analyses. These Instruments are frequently used for research purposes. Thus, the Mettler Memotltrator and the Metrohm Tltroprocessor 636/Rod Stirrer 622 were used by Johansson et al. [62] to demonstrate that potentiometric two-phase titrations can be carried out in an automatic fashion. The typical background noise from the electrodes can be reduced by Introducing hydrophobic anions or cations in the aqueous phase. These ions also affect the acid-base equilibrium by extracting the sample ions as ion-pairs into the organic phase, which allows the conditional acidity constant (apparent K ) to be manipulated to make selective titrations possible. 

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