HPLC-DAD Purification and Characterization of Meta-Cresol-Purple for Spectrophotometric Seawater pH Measurements

Davide Vivado,Pierpaolo Falco,Carmela Ianni,Paola Rivaro

doi:10.3390/w13213030

Davide Vivado, Pierpaolo Falco + Show 2 more

Open Access

https://doi.org/10.3390/w13213030

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Journal: Water	Publication Date: Oct 28, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: University of Genoa, Marche Polytechnic University

Abstract

High-quality pH measurements are essential for observing ocean acidification and interpreting its chemical and ecological effects. Spectrophotometric measure is the preferred method for pH analysis of seawater because of its high reproducibility and excellent precision. Meta-cresol purple (mCP) is one of the most used indicator dyes for spectrophotometric pH determination. Impurities in indicator salts can significantly bias spectrophotometric pH determinations, and therefore the use of purified mCP is recommended. This work describes the use of a fast, simple, and green-friendly High-Performance-Liquid Chromatography (HPLC) procedure for purification of mCP dye solution. A C18 reversed phase column was used, and different compositions of the mobile phase were considered. The selected mobile phase was 85% Milli-Q water and 15% CH3CN pH 8.0 that allowed reasonable run time and a suitable purified mCP retention time (4.65 ± 0.005 min). Aliquots of purified mCP were mixed and evaporated by rotary evaporator that resulted in the fastest preconcentration procedure among those considered in this study. Purified mCP was used for measuring the pH in seawater samples collected in the Ross Sea (Antarctica) and the values ranged between 8.202 and 7.983, with the highest values at the surface.

Highlights

High-quality pH measurements are essential for observing ocean acidification and interpreting its chemical and ecological effects [1].pH is used to evaluate effects produced by the increase of atmospheric carbon dioxide (CO2 ) on the seawater carbonate buffer system and to evaluate the consequences that a variation in the concentration of H3 O+ ions would have on the biological processes in the marine ecosystem [2]
PH is used to evaluate effects produced by the increase of atmospheric carbon dioxide (CO2 ) on the seawater carbonate buffer system and to evaluate the consequences that a variation in the concentration of H3 O+ ions would have on the biological processes in the marine ecosystem [2]
This paper reports the development of a High-Performance Liquid ChromatographyDiode Array Detector (HPLC-DAD) method for quantitatively removing the impurities contained in a commercial Meta-cresol purple (mCP) batch to obtain a refined solid

Summary

Introduction

High-quality pH measurements are essential for observing ocean acidification and interpreting its chemical and ecological effects [1].pH is used to evaluate effects produced by the increase of atmospheric carbon dioxide (CO2 ) on the seawater carbonate buffer system and to evaluate the consequences that a variation in the concentration of H3 O+ ions would have on the biological processes in the marine ecosystem [2]. In addition to the decrease in pH, the reactions caused by the increase of CO2 in the oceans led to a decrease in the availability of carbonate ions (CO3 2− ) and to a decrease both in the compensation depth and in the saturation grade (Ω) of calcite and aragonite. This phenomenon makes calcification by marine organisms increasingly difficult [4]. Biological, and ecological consequences of oceanic acidification are observed in the Southern

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