start-ver=1.4 cd-journal=joma no-vol=924 cd-vols= no-issue= article-no= start-page=60 end-page=67 dt-received= dt-revised= dt-accepted= dt-pub-year=2016 dt-pub=20160614 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Chelate titrations of Ca2+ and Mg2+ using microfluidic paper-based analytical devices en-subtitle= kn-subtitle= en-abstract= kn-abstract=We developed microfluidic paper-based analytical devices (μPADs) for the chelate titrations of Ca2+ and Mg2+ 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 Ca2+ and Mg2+ (total hardness) in the water were measured using a μPAD containing a buffer solution with a pH of 10, whereas only Ca2+ was titrated using a μPAD prepared with a potassium hydroxide solution with a pH of 13. The μPADs permitted the determination of Ca2+ and Mg2+ in mineral water, river water, and seawater samples within only a few minutes using only the naked eye—no need of instruments. en-copyright= kn-copyright= en-aut-name=KaritaShingo en-aut-sei=Karita en-aut-mei=Shingo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=KanetaTakashi en-aut-sei=Kaneta en-aut-mei=Takashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= affil-num=1 en-affil=Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University kn-affil=岡山大学大学院自然科学研究科 affil-num=2 en-affil=Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University kn-affil=岡山大学大学院自然科学研究科 en-keyword=Chelate titration kn-keyword=Chelate titration en-keyword=Microfluidic paper-based analytical device kn-keyword=Microfluidic paper-based analytical device en-keyword=Hardness kn-keyword=Hardness en-keyword=Calcium kn-keyword=Calcium en-keyword=Magnesium kn-keyword=Magnesium en-keyword=Natural water kn-keyword=Natural water END