College of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, Florida 33701, USA.
Environ Sci Technol. 2011 Jun 1;45(11):4862-8. doi: 10.1021/es200665d. Epub 2011 May 12.
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/(λ1)A) as follows: [formula in text] where -log(K(2)Te2) = a + (b/T) + c ln T – dT; a = -246.64209 + 0.315971S + 2.8855 × 10(-4)S2; 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(-5)T and e3/e2 = -0.020813 + 2.60262 × 10(-4)T + 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.
分光光度法程序允许快速和精确测量天然水的 pH 值。然而，这些分析中使用的酸碱指示剂中的杂质会显著影响测量精度。本工作描述了用于纯化一种指示剂间甲酚紫（mCP）的 HPLC 程序，并报告了 mCP 在一定温度（T）和盐度（S）范围内的物理化学特性（热力学平衡常数和可见光吸收率）。使用纯 mCP，可以根据测量的 mCP 吸光度比（R = λ2A/（λ1）A）来表示海水在总氢离子浓度标度（pHT）上的 pH 值，如下所示：[文本中的公式]其中-log（K（2）Te2）= a +（b/T）+ c ln T – dT；a = -246.64209 + 0.315971S + 2.8855 × 10(-4)S2；b = 7229.23864 – 7.098137S – 0.057034S2；c = 44.493382 – 0.052711S；d = 0.0781344；mCP 摩尔吸光率比（ei）表示为 e1 = -0.007762 + 4.5174 × 10(-5)T 和 e3/e2 = -0.020813 + 2.60262 × 10(-4)T + 1.0436 × 10(-4)（S – 35）。用于计算 R 的 mCP 吸光度 λ1A 和 λ2A 是在 434nm 和 578nm 波长下测量的。该特性适用于 278.15 ≤ T ≤ 308.15 和 20 ≤ S ≤ 40。
