Marine Science Faculty Publications
Purification and Characterization of meta-Cresol Purple for Spectrophotometric Seawater pH Measurements
Document Type
Article
Publication Date
2011
Keywords
Impurities, Seawater, High-performance liquid chromatography, Absorption, Quantum mechanics
Digital Object Identifier (DOI)
https://doi.org/10.1021/es200665d
Abstract
Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances, λ1A and λ2A, used to calculate R are measured at wavelengths (λ) of 434 and 578 nm. This characterization is appropriate for 278.15 ≤ T ≤ 308.15 and 20 ≤ S ≤ 40.
Was this content written or created while at USF?
Yes
Citation / Publisher Attribution
Environmental Science & Technology, v. 45, issue 11, p. 4862-4868
Scholar Commons Citation
Liu, Xuewu; Patsavas, Mark C.; and Byrne, Robert H., "Purification and Characterization of meta-Cresol Purple for Spectrophotometric Seawater pH Measurements" (2011). Marine Science Faculty Publications. 1646.
https://digitalcommons.usf.edu/msc_facpub/1646
