Calcium Determination by Complexometric Titration with Calcein Indicator Using Webcam for Endpoint Detection

Precise and convenient analytical methods are needed for the quantitative determination of calcium in water and food. Complexometric titration remains a reliable technique to determine calcium in milligram amounts. The titrations have been performed automatically by detecting color transitions with a webcam. Classical complexometric indicator calcein provided a sharp color transition. In diffuse reflection mode, the color appearance parameter (Hue) provides better precision and is more resistant to ambient light fluctuations compared to RGB primaries. In fluorescence mode with LED illumination, the fluorescence brightness of calcein is independent of ambient light, and the primary green color provides the sharpest endpoints. The color change during titration is better in the upper part of the acquired images due to the internal filter effect in calcein solutions. The automatic titration with a digital burette provides a standard deviation as low as 0.1 μmol. An example of its application is in the determination of calcium in commercial mineral waters. Based on the AGREE and ComplexMoGAPI rating scales, the semi-automatic titration showed better environmental assessment compared to the standard ASA method.