In-situ Spectrophotometric PH Measurements: the Effect of Pressure on Thymol Blue Protonation and Absorbance Characteristics

Amanda E Hopkins; Karen S Sell; Alan L Soli; Robert H Byrne

doi:10.1016/S0304-4203(00)00043-8

In-situ Spectrophotometric PH Measurements: the Effect of Pressure on Thymol Blue Protonation and Absorbance Characteristics

Amanda E Hopkins, Karen S Sell, Alan L Soli, Robert H Byrne

College of Marine Science

Research output: Contribution to journal › Article › peer-review

Abstract

Previous studies of the indicator thymol blue in seawater have characterized the temperature and salinity dependence of thymol blue protonation and molar absorbance. In this work, observations of thymol blue absorbance in synthetic solutions and natural seawater between 0- and 900-bar gauge pressure have been used to calculate the influence of pressure on absorbance ratios and the p K 2 for the equilibrium HI − &rlhar;H + +I 2− (where I denotes thymol blue). The influence of pressure on indicator absorbance ratios is small but significant. The molar volume change and compressibility for the thymol blue dissociation reaction at 25°C in seawater are: Δ V i =−17.2 8 ±0.1 cm 3 mol −1 and Δ κ =(−38±4)×10 −4 cm 3 mol −1 bar −1 . The pressure dependence of p K 2 at 25°C is given aslogK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2,">logK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2, where K 2 P and K 2 0 are the dissociation constants for HI − at a gauge pressure P (bars) and atmospheric pressure, respectively. The influence of pressure on thymol blue absorbance ratios ( e i ) in the expression pH= p K 2 +log( R − e 1 )/( e 2 − Re 3 ) are given as e 1 =0.0035, e 2 =2.386−(2.7×10 −6 )× P , and e 3 =0.139+(6.6×10 −6 )× P . This indicator calibration in conjunction with previous studies of thymol blue equilibria at atmospheric pressure allows in-situ spectrophotometric measurements of seawater pH throughout the oceanic water column.

Original language	American English
Journal	Marine Chemistry
Volume	71
DOIs	https://doi.org/10.1016/S0304-4203(00)00043-8
State	Published - Jan 1 2000

Keywords

Seawater pH
Spectrophotometric
Thymol blue
High pressure
Partial molar volume
Carbon dioxide system

Disciplines

Life Sciences

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https://doi.org/10.1016/S0304-4203(00)00043-8

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@article{7585f25c1017498d9cdfa724ba2f1026,

title = "In-situ Spectrophotometric PH Measurements: the Effect of Pressure on Thymol Blue Protonation and Absorbance Characteristics",

abstract = " Previous studies of the indicator thymol blue in seawater have characterized the temperature and salinity dependence of thymol blue protonation and molar absorbance. In this work, observations of thymol blue absorbance in synthetic solutions and natural seawater between 0- and 900-bar gauge pressure have been used to calculate the influence of pressure on absorbance ratios and the p K 2 for the equilibrium HI − &rlhar;H + +I 2− (where I denotes thymol blue). The influence of pressure on indicator absorbance ratios is small but significant. The molar volume change and compressibility for the thymol blue dissociation reaction at 25°C in seawater are: Δ V i =−17.2 8 ±0.1 cm 3 mol −1 and Δ κ =(−38±4)×10 −4 cm 3 mol −1 bar −1 . The pressure dependence of p K 2 at 25°C is given aslogK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2,{"}>logK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2, where K 2 P and K 2 0 are the dissociation constants for HI − at a gauge pressure P (bars) and atmospheric pressure, respectively. The influence of pressure on thymol blue absorbance ratios ( e i ) in the expression pH= p K 2 +log( R − e 1 )/( e 2 − Re 3 ) are given as e 1 =0.0035, e 2 =2.386−(2.7×10 −6 )× P , and e 3 =0.139+(6.6×10 −6 )× P . This indicator calibration in conjunction with previous studies of thymol blue equilibria at atmospheric pressure allows in-situ spectrophotometric measurements of seawater pH throughout the oceanic water column.",

keywords = "Seawater pH, Spectrophotometric, Thymol blue, High pressure, Partial molar volume, Carbon dioxide system",

author = "Hopkins, {Amanda E} and Sell, {Karen S} and Soli, {Alan L} and Byrne, {Robert H}",

year = "2000",

month = jan,

day = "1",

doi = "10.1016/S0304-4203(00)00043-8",

language = "American English",

volume = "71",

journal = "Marine Chemistry",

}

TY - JOUR

T1 - In-situ Spectrophotometric PH Measurements: the Effect of Pressure on Thymol Blue Protonation and Absorbance Characteristics

AU - Hopkins, Amanda E

AU - Sell, Karen S

AU - Soli, Alan L

AU - Byrne, Robert H

PY - 2000/1/1

Y1 - 2000/1/1

N2 - Previous studies of the indicator thymol blue in seawater have characterized the temperature and salinity dependence of thymol blue protonation and molar absorbance. In this work, observations of thymol blue absorbance in synthetic solutions and natural seawater between 0- and 900-bar gauge pressure have been used to calculate the influence of pressure on absorbance ratios and the p K 2 for the equilibrium HI − &rlhar;H + +I 2− (where I denotes thymol blue). The influence of pressure on indicator absorbance ratios is small but significant. The molar volume change and compressibility for the thymol blue dissociation reaction at 25°C in seawater are: Δ V i =−17.2 8 ±0.1 cm 3 mol −1 and Δ κ =(−38±4)×10 −4 cm 3 mol −1 bar −1 . The pressure dependence of p K 2 at 25°C is given aslogK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2,">logK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2, where K 2 P and K 2 0 are the dissociation constants for HI − at a gauge pressure P (bars) and atmospheric pressure, respectively. The influence of pressure on thymol blue absorbance ratios ( e i ) in the expression pH= p K 2 +log( R − e 1 )/( e 2 − Re 3 ) are given as e 1 =0.0035, e 2 =2.386−(2.7×10 −6 )× P , and e 3 =0.139+(6.6×10 −6 )× P . This indicator calibration in conjunction with previous studies of thymol blue equilibria at atmospheric pressure allows in-situ spectrophotometric measurements of seawater pH throughout the oceanic water column.

AB - Previous studies of the indicator thymol blue in seawater have characterized the temperature and salinity dependence of thymol blue protonation and molar absorbance. In this work, observations of thymol blue absorbance in synthetic solutions and natural seawater between 0- and 900-bar gauge pressure have been used to calculate the influence of pressure on absorbance ratios and the p K 2 for the equilibrium HI − &rlhar;H + +I 2− (where I denotes thymol blue). The influence of pressure on indicator absorbance ratios is small but significant. The molar volume change and compressibility for the thymol blue dissociation reaction at 25°C in seawater are: Δ V i =−17.2 8 ±0.1 cm 3 mol −1 and Δ κ =(−38±4)×10 −4 cm 3 mol −1 bar −1 . The pressure dependence of p K 2 at 25°C is given aslogK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2,">logK2PK20=+[2.99(±0.02)×10−4]×P−[3.3(±0.3)×10−8]×P2, where K 2 P and K 2 0 are the dissociation constants for HI − at a gauge pressure P (bars) and atmospheric pressure, respectively. The influence of pressure on thymol blue absorbance ratios ( e i ) in the expression pH= p K 2 +log( R − e 1 )/( e 2 − Re 3 ) are given as e 1 =0.0035, e 2 =2.386−(2.7×10 −6 )× P , and e 3 =0.139+(6.6×10 −6 )× P . This indicator calibration in conjunction with previous studies of thymol blue equilibria at atmospheric pressure allows in-situ spectrophotometric measurements of seawater pH throughout the oceanic water column.

KW - Seawater pH

KW - Spectrophotometric

KW - Thymol blue

KW - High pressure

KW - Partial molar volume

KW - Carbon dioxide system

UR - https://digitalcommons.usf.edu/msc_facpub/1724

UR - https://doi.org/10.1016/S0304-4203(00)00043-8

U2 - 10.1016/S0304-4203(00)00043-8

DO - 10.1016/S0304-4203(00)00043-8

M3 - Article

VL - 71

JO - Marine Chemistry

JF - Marine Chemistry

ER -

In-situ Spectrophotometric PH Measurements: the Effect of Pressure on Thymol Blue Protonation and Absorbance Characteristics

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