Determination of phenylenediamine isomers in hair dyes by coal cinders micro-column extraction and MEKC

Abstract

A new micellar electrokinetic chromatography (MEKC) method using beta-cyclodextrins (β-CDs) and 1-butyl-3-methylimidazolium hexafluorophosphates (ionic liquids) as additives was successfully developed for determination of para-, meta-, and ortho-phenylenediamines isomers (p-P, m-P, and o-P) in hair dyes. To improve the sensitivity of the MEKC-UV, a simple and cheap flow injection (FI) technique using a micro-column packed with coal cinders (the by-products from combustion in a boiler) as solid-phase extractant was also investigated. In the presence of 20 mmol L⁻¹ phosphates at pH 5.5, addition of 12 mmol L⁻¹ ionic liquids and 8 mmol L⁻¹ β-CDs greatly improved the separation efficiency. The three analytes could be quantitatively adsorbed by coal cinders, and desorbed readily with 0.15 mL of 0.01 mol L⁻¹ NaOH. Under the optimum conditions, an enrichment factor (EF) of 33.3 was obtained, and determination limits of p-P, m-P, and o-P were 1.97 × 10⁻⁷, 0.99 × 10⁻⁷, and 0.61 × 10⁻⁷ mol L⁻¹, respectively. The adsorption capacities of the coal cinders micro-column for p-P, m-P, and o-P were all 1.20 mg g⁻¹. The presented procedure was successfully applied to the determination of p-P, m-P, and o-P in hair dyes with satisfactory results.