Development of gravimetric titrator

• Grant number: 03/07873-8
• Support Opportunities: Research Grants - Innovative Research in Small Business - PIPE
• Start date: April 01, 2004
• End date: March 31, 2006
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Analytical Chemistry
• Principal Investigator: Kenneth Elmer Collins
• Grantee: Kenneth Elmer Collins
• Company: Tech Chrom Instrumentos Analíticos Ltda. - ME
• City: Campinas

Abstract

The titrator employs a gravimetric burette, which holds some beakers with different titration solutions attached to the weighing chamber of an electronic balance at the base of the chamber. The addition of solutions is controlled by electromechanical valves. The titrator carries out potentiometric, biamperometric, spectrophotometric analyses, standard addition and preparation of standardized solution. The main advantages of the gravimetric titrator are the absence of error caused by differences of viscosity in the solutions, as well as volumetric variation due to thermal dilation, when dispensing calibration from glassware. The use of the electronic balance provides fast, automated results, controlled by a microcomputer, in addition to offering reproducibility and precision unobtainable by volumetric methods. The prototype tested consists of a metal support structure, with a capacitive sensor installed in the upper part and it operates with a load capacity of 100 grams and sensitivity of one milligram. A mechanical arm links the sensor to a suspended platform with the beakers of solution, made of teflon. The beakers have in their base, an air admission orifice to compensate for the entry or exit of solution via capillary tubes connected to three-way valves. The normally open exit position of the valves is joined by capillaries to two-way valves connected to the external reservoirs. When one of the two-way valves is switched on, the corresponding solution flows from the reservoir into the suspended beaker, filling it. When one of the three-way valves is switched on, the solution contained in the respective suspended beaker is released, by gravity, into the reaction beaker by means of capillary tubes. The transferred mass is monitored by the gravimetric sensor and the entire operation is controlled by software. The internal beakers have the lower level of solution monitored by optical sensors, and they fill up automatically. The upper level is controlled by means of the mass of solution admitted. The communication of the titrator with the microcomputer is performed via an RS232 serial interface. The automated gravimetric analysis, proposed in this project, faces competition from volumetric analysis, automated or manual. The gravimetric technique has the advantage of not being subject to the thermic effects of volume dilation, alterations in the concentration and the viscosity, nor from lengthy calibration procedures. The digital analytical balance, connected to the microcomputer, allows the replacement of volumetric techniques by gravimetric ones, without the disadvantages mentioned. The drastic reduction in time and consumption of reagents afforded by the use of the gravimetric titrator and the operational rationalization of the automated analysis offered contribute to the swift off-setting of its cost. The popularization of automated gravimetry depends merely on the commercial availability of the equipment. (AU)