title: Colorimetric pH measurement for seawater samples using a three light-emitting diodes detector and a calibration method for temperature dependence.
abstract: A colorimetric pH measurement of seawater samples using a light source comprising a three light-emitting diodes (TLED) detector and meta-cresol purple (mCP) as an indicator was investigated. The molar absorption ratios (e1, e2, and e3/e2) for mCP using the TLED detector at 25°C were determined to be 0, 1.9994, and 0.1010, respectively. Next, the pH values of 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) and 2-aminopyride (AMP) seawater buffers were determined. Notably, the raw pH of TRIS buffer (∼8.1) agreed with the reference value, while that for the AMP buffer (∼6.8) had an error of +0.004 due to the small absorption ratio (R) and being out of the lower adequate pH range (> 7.2) for mCP. pHT measurements obtained for seawater samples using the present colorimetric method agreed with those obtained using a glass electrode. These results demonstrate that this low-cost TLED detection system with a short cell length, 5 cm, can be used for seawater pHT analysis.
authors.affiliation: Center for Advanced Marine Core Research, Kochi University.
authors.forename: Kei
authors.initials: K
authors.lastname: Okamura
authors.forename: Hideshi
authors.initials: H
authors.lastname: Kimoto
authors.forename: Takuroh
authors.initials: T
authors.lastname: Noguchi
authors.forename: Mayumi
authors.initials: M
authors.lastname: Hatta
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kawakami
authors.forename: Takahiko
authors.initials: T
authors.lastname: Suzue
mesh_terms: D002138:Calibration; D003124:Colorimetry; D006863:Hydrogen-Ion Concentration; D008027:Light; D012623:Seawater / Q000032:analysis* / Q000737:chemistry; D013696:Temperature