A liquid drop: A windowless optical cell and a reactor without walls for flow injection analysis

The design and characteristics of a dynamically growing and falling liquid drop based optical detection system are described for use with flow injection analysis (FIA). Several aspects of the analytical potential of a liquid drop as an optical cell are demonstrated by the detection of sulfate through the precipitation reaction between barium ion and sulfate ion in an FIA system. Deposition of precipitate on the windows of a conventional flow cell usually constitutes a vexing problem; this is avoided due to the windowless nature of the drop based cell. Gradient dilution techniques are conveniently implemented without precise external timing: with small drops, a single FIA peak is spread over a multitude of drops. Each individual drop represents a different dilution ratio and the dynamic range of measurement can be greatly increased based on the choice of the specific drop used for quantitation. Both absorbance/turbidimetric detection and nephelometric detection can be made on a single drop using a single optical fiber for light collection. Different configurations for mixing and reaction of the sample and reagents in a drop based system has been studied.