Titrators, robotic station

Most frequently, using a robotic station to develop an entire analytical process is unwarranted. In the mid-1980s, when robotic technology first reached the analytical laboratory, robots were more of a novelty than a useful tool. At that time, conventional manual titrations and similarly easy tasks were entrusted to robotic stations. At present, however, well-established criteria exist to ensure correct use of the potential of robotic technology. 

Fig. 9.9 Robot station for titration of an acid solution with solid basic standard. (A) Block diagram of the station. (B) Top view of the situation of the different elements of the station. (C) Pipette/bur-ette assembly. (D) Solvent dispenser system. (Reproduced from [16] with permission of the American Chemical Society).

The performance of the titration can be controlled In a variety of ways (see Table 13.1) by use of empirical equations for the calculation of AV from preceding titration data points by use of microprocessors to control volumetric equipment (e.g. in photometric, potentlometrlc, coulometrlc titrations) or expand the scope of a given technique by use of robot stations In Implementing laborious manual methods or In handling toxic or hazardous substances etc. End-point detection Is usually based on E/A.V maxima and on first or second derivatives In the case of microprocessor- and microcomputer-controlled processes, respectively. Table 13.2 lists a chronological selection of calculation methods applied to titration curves [46]. 

Other example is the determination of fuel parameters including the diene value and mercaptan sulfur. First, the robot weighs the sample, refluxes it in the presence of maleic anhydride, and extracts the analytes into an aqueous phase, which is poured into the titration vessel, where the robot inserts the photometric or potentiometric probe. For the determination of mercaptan sulfur, the robot also weighs the sample and removes sulfide by precipitation with a CdS04 solution and liquid-liquid extraction. Once the fuel is sulfide free, which is checked by using a photometric probe, it is poured into the titration vessel by the robot arm, which also plunges an Ag electrode prior to addition of the titrant (an AgNOs solution). In both cases, the automated titrator acts as a module of the robotic station and is operated by the robotic arm. 

---