## 1 Introduction  
Over the last few years, the exposure levels and the associated effects of endocrine disrupting chemicals (EDCs) on the environment, wildlife and humans has received increased awareness [1, 2]. The long overdue list of EDCs includes estrogen mimic compounds such as bisphenol A (BPA), 4-tert-octylphenol (OP) and nonylphenol isomers, known widely as industrial chemicals. They present multiple modes of endocrine disruption activity, with the most emphasized being the binding to the estrogen receptors (estrogen receptors \(\alpha\) and \(\beta\)) and acting competitively towards regular hormones (e.g., 17 \(\beta\)-estradiol). The alkylphenols (APs) [3, 4, 5], including NP isomers and OP as well as BPA, have shown to mimic the actions of the natural estrogen estradiol, with their biological effects being regulated by interactions with the cellular estrogen receptor. 4-t-OP and NP isomers are both degradation products of alkyl phenol ethoxylates (APEOs, non-ionic detergents) and intermediates in APEOs and phenolic resins production processes. Since 2000, they have been included in the list of priority hazardous substances by Directive 2000/60/EC [6], while since 2003 a reduction policy has been implemented in the E.U. for NP [7]. Nevertheless, 4-t-OP and NP isomers are still widespread and broadly detected in environmental compartments, such as wastewaters, potable water, rivers, biota and consequently also in food commodities [8, 9, 10, 11]. Concerning BPA, it is a high-production volume chemical mainly used as an important precursor for the production of several resins and polymers also used in food packing materials. As a result, BPA can migrate into foodstuffs and beverages from packing of products, including dairy ones [12; 13; 14; 15], while oral intake has been considered as the main route of exposure for BPA [16]. In addition, one of the main sources of exposure to BPA and APs for newborns and infants derive from migration from the lining of cans into infant formulas (IF) and from the polycarbonate baby bottles [9]. Bearing in mind that dairy food products are essential to the human diet and since their consumption is increasing worldwide, it is important to assure the safety of them in terms of the presence and levels of toxic compounds such as EDCs. Thus, the development of analytical methodologies that combine short time of analysis, simple operation steps, low consumption of reagents and possibility of multi-sample preparation that can be combined to selective and sensitive instrumentation such as chromatography-mass spectrometry instruments, is of primary interest. In this sense, a QuECHERS-based analytical methodology has been investigated in several food commodities and environmental matrices. It has been employed in the analysis of the target EDCs in a wide variety of substrates as well [17; 18; 19]. However, it has not been tested for the simultaneous extraction of these EDCs from dairy products in combination with high resolution and accurate mass detection using an LC-LTQ/Orbitrap MS system. LC-MS/MS, applying electron spray ionization ESI techniques, provides clear advantages in terms of achieving high sensitivity and low detection limits without tedious derivatization steps for the separation, identification and quantification of BPA and APs than other common methods of analysis such as GC-MS or HPLC-UV/FLD [20; 21]. Recent efforts have also been made to employ tandem-MS systems as triple quadrupole [22; 23]. However, the Orbitrap technology is proven to enable fast, sensitive and reliable detection and identification of these contaminants since high resolution and accurate mass measurements have become the reference technique for obtaining information on complex mixtures' composition, such as food samples [24].