A New Instrument for Automatic Colorimetric and Fluorimetric Titrations

Abstract

A new instrument for automatic colorimetric and fluorimetric titrations is described. Titrant delivery is automatically stopped at the end point by the use of a microammeter with a built-in relay which stops a motor-driven buret equipped with digital read-out or a gravity driven buret equipped with solenoid control. Monochromatic light is used to excite fluorescence, which is received at 90° by a photomultiplier tube with the micro-ammeter in its anode circuit. Light transmitted through the titration vessel is detected by a barrier-layer photocell, the output of which is fed to the microammeter.

Results are given for

• (1) automatic acid-base (HCl-NH₄OH) titration using a mixed colorimetric indicator (brom cresol green-methyl red),

• (2) automatic determination of zinc or standardization of EDTA (ethylenediaminetetraacetic acid) using Superchrome Black TS as the colorimetric indicator, and

• (3) automatic determination of calcium based on complexometric titration using EDTA with Calcein as the indicator of fluorescence end point.

Automatic data presentation is achieved by printing equivalence volume in microliters or by recording complete titration curves on an X—Y recorder.

Precision, accuracy, and range of the method are discussed.

Parts of this paper were presented at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pennsylvania, February 27, 1961.