Abstract :
A spectrometric microtitrator was developed from a spectrometer with a microreaction chamber and a tri-colour lightemitting diode (LED) as the light source. A novel, vertical, optical geometry of the spectrometric microtitration chamber was introduced and tested. This novel geometry also required a new method for mixing the titrated solution. A laboratory-made 50 (mu)l syringe pump was used for the addition of the titration reagent. The 10-channel module for light effects, which makes possible a low-cost hardware approach to changing the titration protocols, was used for coordinating the operation of the microtitration set up. The system, with 10 channels and a regulated speed of operation, is flexible enough to allow an operator to generate different titration protocols. The performance test showed that the speed of titration-reagent addition can be regulated in the range from 0.87 to 21.8 (mu)l min-1. The smallest achievable volume addition is equal to 35 nl. The mixing rate can be continuously regulated by an electrical pulse that initiates the mixing cycle. The quickest rate is every 1.6 s, and the slowest rate is every 4.8 s. The spectrometric microtitration set up was successfully tested for several different reallife spectrometric titrations, including an iodometric titration, a determination of CO2 in deionised water, and EDTA titrations of copper(II) ions with no indicator. The volume of the examined solution can be as small as 220 (mu)l. The titration-reagent consumption is usually between 10 and 35 (mu)l. Coefficients of variation of the end point volume determination (n = 5) at different experimental conditions and different average volumes of consumed reagents (7.06, 12.17 and 22.88 (mu)l) were 2.4, 1.3 and 1.2%, respectively. The novel geometry of the spectrometric microtitration chamber proved to be useful for real-life applications.
