Determination of pharmaceuticals in freshwater sediments using ultrasonic-assisted extraction with SPE clean-up and HPLC-DAD or LC-ESI-MS/MS detection

Abstract

A robust and sensitive analytical method is presented for the extraction and determination of six pharmaceuticals in freshwater sediments. The pharmaceuticals were extracted from sediment using ultrasonic extraction with 2% NH₄OH in methanol (MeOH), followed by extraction into 2% formic acid in MeOH and then MeOH only. The resulting extracts were then analysed, after clean-up on HLB solid phase extraction cartridges, using a single gradient run using a Zorbax Eclipse XDB-C18 (150 × 4.6 mm, 5 μm) column and a mobile phase consisting of 10 mM ammonium acetate and MeOH (pH = 4.8). Analytes were detected and quantified using either Diode Array Detector (DAD) or tandem mass spectrometry (MS/MS) with electrospray ionization in positive mode. Validation studies were carried out using ten sediments sampled from the UK and Iraq with a wide range of characteristics. The mean calculated recoveries for fortified samples in all studied sediments ranged from 74.5 to 114.6% for atenolol, 72.3 to 124.9% for amitriptyline, 76.5 to 105% for mefenamic acid and 70.1 to 102% for diltiazem. Cimetidine and ranitidine showed lower recoveries which ranged from 40.2 to 68.4% and 30.4 to 55.2% respectively. Relative standard deviations (RSD) of recoveries for all sediment–pharmaceutical combinations ranged from 1.6 to 15.8%. The detection limits in sediments for the six analytes ranged from 15 to 58.5 ng g⁻¹ and 0.03 to 3.5 ng g⁻¹, dry weight, for HPLC-UV and LC-ESI-MS/MS respectively. Overall the results indicate that the developed method is effective for use in monitoring the concentrations of pharmaceuticals in aquatic sediments in different regions.