In:
Scientific Reports, Springer Science and Business Media LLC, Vol. 7, No. 1 ( 2017-05-30)
Abstract:
Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple ( m CP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified m CP and a novel thermostated spectrophotometric device, the pH on the total scale (pH T ) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples as $${\boldsymbol{p}}{{\boldsymbol{H}}}_{{\boldsymbol{T}}}{\boldsymbol{=}}{\boldsymbol{-}}{\bf{log}}({{\boldsymbol{k}}}_{{\bf{2}}}^{{\boldsymbol{T}}}{{\boldsymbol{e}}}_{{\bf{2}}}){\boldsymbol{+}}\,{\bf{log}}(\frac{{\boldsymbol{R}}{\boldsymbol{-}}{{\boldsymbol{e}}}_{{\bf{1}}}}{{\bf{1}}{\boldsymbol{-}}{\boldsymbol{R}}\frac{{{\boldsymbol{e}}}_{{\bf{3}}}}{{{\boldsymbol{e}}}_{{\bf{2}}}}})$$ p H T = − log ( k 2 T e 2 ) + log ( R − e 1 1 − R e 3 e 2 ) Based on the m CP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and − $${\bf{log}}({{\boldsymbol{k}}}_{{\bf{2}}}^{{\boldsymbol{T}}}{{\boldsymbol{e}}}_{{\bf{2}}})$$ log ( k 2 T e 2 ) of purified m CP is described by the following functions: e 1 = −0.004363 + 3.598 × 10 −5 T , e 3 / e 2 = −0.016224 + 2.42851 × 10 −4 T + 5.05663 × 10 −5 ( S − 35), and − $${\bf{log}}({{\boldsymbol{k}}}_{{\bf{2}}}^{{\boldsymbol{T}}}{{\boldsymbol{e}}}_{{\bf{2}}})$$ log ( k 2 T e 2 ) = −319.8369 + 0.688159 S −0.00018374 S 2 + (10508.724 − 32.9599 S + 0.059082 S 2 ) T −1 + (55.54253 − 0.101639 S ) ln T −0.08112151 T . This work takes the characterisation of m CP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pH T measurements in polar systems.
Type of Medium:
Online Resource
ISSN:
2045-2322
DOI:
10.1038/s41598-017-02624-0
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
2017
detail.hit.zdb_id:
2615211-3
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