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Mass spectra of sulfonephthalein pH indicator dyes and their impurities

Authors: Regina A. Easley and Benjamin J. Place

Data Description Article: Easley RA, Place BJ (2017) Mass spectra of sulfonephthalein pH indicator dyes and their impurities. J Res Natl Inst Stan 122 (26 Apr 17).

Key words: mass spectrometry; pH indicators; seawater pH.


Sulfonephthalein pH indicator dyes have historically been noted for impurities originating from the synthesis process, which lead to batch to batch differences in pH measurements [1]. Uncertainties up to 0.1 pH units have been attributed to impurities in these reagents [2]. In an effort to understand the extent of impurities in these dyes and the potential impact on the expanded uncertainty of spectrophotometric pH measurements, we have examined seven commercially available sulfonephthalein pH indicators using liquid chromatography-mass spectrometry (LC-MS): bromocresol green (BCG), bromocresol purple (BCP), bromothymol blue (BTB), cresol red (CR), meta-cresol purple (MCP), phenol red (PR), and thymol blue (TB). Peaks eluting from the LC were subjected to fragmentation by mass spectrometry. The resulting dataset will aid in efforts to improve the synthesis or purification of these dyes [3].

Data Specifications


Proprietary Thermo Scientific MS datafiles (*.raw) have been converted into ANDI-MS (ASTM E1947) NetCDF format (*.cdf)


Thermo Scientific Q-Exactive Quadrupole-Orbitrap Mass Spectrometer

Spatial or Temporal Elements

Data collection date 2015-11-25

Data Dictionary


All datasets submitted to Journal of Research of NIST are publicly available.


Data Download

Created March 22, 2017, Updated November 15, 2019