Determination of Ethephon in Pesticide Formulations by Ion Exchange Chromatography with Indirect Spectrophotometric Detection

Abstract

Ethephon is approved in the European Union as a plant growth regulator and used in plant protection products. The available methods for the assay of ethephon in pesticide formulations demand decomposition of ethephon to ethene under alkaline conditions, and subsequently either titration by acidimetry or gas chromatography with flame ionization detection. The present work proposes two novel anion exchange high-performance liquid chromatographic methods with indirect spectrophotometric detection for the assay of ethephon in plant protection formulations, with a quick and simple sample preparation, involving only weighing and diluting the sample with water before injection. The study involved optimization of the pH, the concentration of a chromophore compound as the mobile phase modifier and the optimization of the mobile phase flow rate. The first method used a strong anion exchange column (250 mm × 4 mm, 10 µm, 300 Å) with isocratic elution with an aqueous mobile phase consisted of 1 mM potassium hydrogen phthalate at pH 7 by the addition of 0.6 M aqueous KOH using a 1.4 mL/min flow rate. The second approach also used a strong anion exchange column (250 mm × 4.6 mm, 5 µm, 80 Å) with isocratic elution with an aqueous mobile phase composed of 1.2 mM phthalic acid, 6 mM monopotassium phosphate and 4% (v/v) methanol at pH 2 by the addition of H₃PO₄ and 2 mL/min flow rate. The two methods were validated, applied in commercial samples and were shown to be equivalent after statistical comparison. They are considered applicable for the quality control of ethephon content in soluble concentrate formulations and surpass the existing laborious and time-consuming methods which demand decomposition of ethephon to ethene.

Keywords:

• Alkylphosphonic acids
• high-performance liquid chromatography
• indirect ultraviolet detection
• polar pesticides
• ultraviolet-transparent compounds

Acknowledgments

The technical support of Mrs Marina Kapsalou is acknowledged. This work was presented at the Eleventh Aegean Analytical Chemistry Days (AACD2018), Chania, Crete, Greece, 25–29 September 2018.