Analytical Sciences
Online ISSN : 1348-2246
Print ISSN : 0910-6340
ISSN-L : 0910-6340
Original Papers
Colorimetric pH Measurement for Seawater Samples Using a Three Light-Emitting Diodes Detector and a Calibration Method for Temperature Dependence
Kei OKAMURAHideshi KIMOTOTakuroh NOGUCHIMayumi HATTAHiroaki KAWAKAMITakahiko SUZUE
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2014 Volume 30 Issue 12 Pages 1135-1141

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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.
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© 2014 by The Japan Society for Analytical Chemistry
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