Optical sensing of HCl with phenol red doped sol-gels

Enju Wang, Kwok Fan Chow, Wenqun Wang, Crystal Wong, Cynthia Yee, Alvin Persad, Jonathan Mann, Andrew Bruce Bocarsly

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


A dye doped sol-gel for the sensing of hydrochloric acid in solution and/or gaseous phase is described. The sol-gel is obtained by acidic hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (Ph-TriEOS) in the presence of phenol red (PR) and further spin-coating onto glass slides. The sensitive response is based on an increase of the absorption band at 510 nm of phenol red entrapped in the sol-gel casting when exposed to HCl solution or gas, due to protonation of the dye. The detection limit of the sol-gel response to moisturized gaseous HCl is below 12 ppm, and its response to HCl in solution falls in the range of 0.01-6 M. The sol-gel coating has a response time of less than 40 s in steady-state, and life-time of more than a year. Weak acids such as acetic acid, benzoic acid, salicylate acid, citrate acid, and carbonic acid do not interfere the response. The responses in acid solutions are completely reversible. In the gaseous phase, response of HCl appears to be moisture sensitive.

Original languageEnglish (US)
Pages (from-to)301-306
Number of pages6
JournalAnalytica Chimica Acta
Issue number2
StatePublished - Apr 8 2005

All Science Journal Classification (ASJC) codes

  • Analytical Chemistry
  • Biochemistry
  • Environmental Chemistry
  • Spectroscopy


  • HCl
  • Optical sensing
  • Phenol red
  • Sol-gel


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