Determination of Nonylphenol and Nonylphenol Ethoxylates in Powdered Milk Infant Formula by HPLC-FL

Abstract

Linear nonylphenol (4-n-NP), nonylphenol isomers (NP), and NP short chain ethoxylated derivates (NPEO 1 and NPEO 2 ) show a well-reported endocrine disrupting activity due to their ability to mimic natural estrogens of living organisms. In this work, two methodologies were developed for the simultaneous extraction and determination of NP, 4-n-NP, long and short chain nonylphenol ethoxylates in commercial powdered milk infant formula using high performance liquid chromatography with fluorescence detection (HPLC-FL). Separation was performed on an Eclipse XDB-C 8 column (3 μm and 4.6 x 150 mm) in isocratic mode at 1 mL/min using a mixture of ACN―H 2 O (65:35). In the first approach, milk powder was reconstituted according to the indications of the manufacturer. A saponification step was carried out to remove triacylglycerols and, subsequently, the obtained solution was solid-phase extracted. Following this procedure, quantitative recovery and high selectivity were achieved for 4-n-NP, whereas several interferences appeared at the retention times of NPEO x , thus increasing limits of detection for these compounds. The second approach consisted of a simple ultrasonic-assisted extraction of the milk powder (non-reconstituted sample) and subsequent determination by HPLC-FL. Different organic solvents were tested for the extraction, and among them acetonitrile (ACN) provided the best results. Quantitative recoveries were obtained for all the analytes in a single extraction step of 15 min using only 1 mL of ACN. Additionally, this approach was more selective than the reconstituted milk-based procedure. The limits of detection achieved ranged from 0.010 μg/g to 0.085 μg/g depending upon the analyte.