Stable tetramethyl-1,10-phenanthroline osmium(iii) complex in neutral pH as a photoluminescence-following electron-transfer reagent for the detection of acetaminophen in urine and pharmaceutical formulations

Abstract

A stable [Os(tmphen)₃]³⁺ (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) reagent was prepared in neutral aqueous solution by oxidation of [Os(tmphen)₃]²⁺ with lead(IV) oxide. [Os(tmphen)₃]²⁺ and [Os(tmphen)₃]³⁺ is characterized by absorption spectroscopy. [Os(tmphen)₃]³⁺ stability is compared with [Ru(tmphen)₃]³⁺ in the same pH 7 environment. The properties of Os(III) and Ru(III) complex were investigated for use as the oxidant in a photoluminescence-following electron-transfer (PFET) system. Studies of photophysical and electrochemical properties, the stability of the Os(III) and Ru(III) complexes state in oxidizing environments, and analytical application in PFET detection of oxidizable pharmaceutical: acetaminophen (paracetamol) is presented. The limit of quantification (LOQ) was 30.2 μg L⁻¹ and 1.5 μg L⁻¹ was the limit of detection (LOD). 2x-1-Dimensional Solid Phase Extraction (2x-1D SPE) method was developed for determination of acetaminophen in urine. This method uses both the methanol concentration and the pH advantageously to preferentially isolate acetaminophen from complex sample matrix. Acetaminophen was detected in urine samples in a concentration range between 40.41 μg L⁻¹ and 360.0 μg L⁻¹. Recoveries of greater than 90% were obtained with this selective method. The method was successfully applied to the determination of acetaminophen in commercial pharmaceutical formulations.