Permanent length of a stain detector with nonimmobilized reagent

A length of stain detector for reproducibly performing a variety of colorimetric analysis was designed and constructed. Hydrochloric acid and sodium hydroxide solutions containing methyl red were exploited as representative reagent and analyte for evaluating the performance of the detector. Injection of a known volume of basic solution into the acidic reagent flow generates a yellow stain at the display part of the detector. The behavior of the stain area (or length) was studied during its passage through the detector for quantitative estimation of the analyte concentration. As the area of the stain strongly depends on the sample volume rather than on analyte concentration, a mathematical method for comparing the analyte concentrations at different sample volumes is suggested. The operational principles and mechanism of the detector are simple, and anyone can easily extract analytical information from the resulting stain shape and length. The system is amenable to extension to a variety of colored chemical reactions based on the lack of a need for reagent immobilization. Up to one sample per 5 min can be analyzed with an RSD of about 4%. As low as 1 × 10⁴ M of NaOH can be detected and measured. The text was submitted by the author in English.