Piezoelectric cryptand-coated quartz crystal liquid chromatographic detector for cations/anions and polar organic molecules in solutions Original Research Article

A reusable and sensitive multifunctional piezoelectric quartz crystal liquid chromatographic detector was developed for the detection of cations, anions and organic molecules in solutions. The quartz crystal coated with dioctadecanoyl-cryptand-22 could adsorb cations or anions depending on whether the cryptand was protonated or not. The cryptand molecule which can be protonated in an acid solution with pH <6.0 can absorb the anion in the solution. The adsorption of catons such as alkali, alkali earth, Cu2+, Cd2+, Zn2+, Pb2+ and Cr3+ metal ions or anions such as halides, NO3−, SO42− and CrO42−, resulted in a decrease of the oscillating frequency of the cryptand-coated quartz crystal. The cryptand-coated crystal detector can also be applied to detect organic molecules, e.g., benzoic acid, in solutions. The cryptand-coated crystal detector behaved like a commercial conductivity detector in detecting cations or anions and with a UV-Visible spectrometric detector in detecting organic molecules. The detection limits of the cryptand-coated piezoelectric detector for ions and organic molecules were estimated at about 10−5 M and 10−4 M, respectively.