A simple and rapid method for determination of petroleum oils in sewage sludge samples with ultrasonic solvent extraction by infrared spectrophotometry under optimized analytical conditions

Abstract

This study presents an analytical method for the determination of petroleum oils in sewage sludge samples using infrared spectrophotometry. The proposed method is based on the use of ultrasonic solvent extraction for sample preparation. Analytical conditions were studied and optimized through uniform experimental design of U₉*(9⁵). The optimized experimental conditions were obtained as follows: the extraction temperature was 50 °C, the extraction time was 45 min, the volume of extractant was 30 mL, and the ultrasonic power was at 250 W. The moisture content of the sewage sludge samples was below 10%. Similar extraction effects could be achieved through both ultrasonic solvent extraction and Soxhlet extraction methods. The detection limit was 0.9 mg kg⁻¹ (k = 3, N = 8) with 91.6–102.0% recovery. The relative standard deviation (RSD, n = 5) for the measurements of the sewage sludge samples was in the range of 1.6% and 3.5%. The proposed method was validated by the analysis of simulation soil samples and successfully applied to the determination of petroleum oils in real samples of sewage sludge with satisfactory results.