title: Chelate titrations of Ca(2+) and Mg(2+) using microfluidic paper-based analytical devices.
abstract: We developed microfluidic paper-based analytical devices (μPADs) for the chelate titrations of Ca(2+) and Mg(2+) in natural water. The μPAD consisted of ten reaction zones and ten detection zones connected through narrow channels to a sample zone located at the center. Buffer solutions with a pH of 10 or 13 were applied to all surfaces of the channels and zones. Different amounts of ethylenediaminetetraacetic acid (EDTA) were added to the reaction zones and a consistent amount of a metal indicator (Eriochrome Black T or Calcon) was added to the detection zones. The total concentrations of Ca(2+) and Mg(2+) (total hardness) in the water were measured using a μPAD containing a buffer solution with a pH of 10, whereas only Ca(2+) was titrated using a μPAD prepared with a potassium hydroxide solution with a pH of 13. The μPADs permitted the determination of Ca(2+) and Mg(2+) in mineral water, river water, and seawater samples within only a few minutes using only the naked eye-no need of instruments.
authors.affiliation: Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Karita
authors.affiliation: Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan. Electronic address: kaneta@okayama-u.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kaneta
keywords: Calcium; Chelate titration; Hardness; Magnesium; Microfluidic paper-based analytical device; Natural water