## 1 Introduction  
Polymyxins have large molecular masses (>1000 Da) and unique structures of a cyclic heptapeptide and a linear tripeptide linked to a fatty acid chain through an amido bond. The two main compounds of the polymyxin family, polymyxin B (PMB) and polymyxin E (known as colistin (CS)) have strong activity against gram-negative as well as multidrug-resistant microorganisms (MDR), or the so-called \"last resort\" drugs [1, 2]. They have a very long application history in veterinary medicine for treating and preventing bacterial infections such as bovine mastitis [3] and diarrhea [4]. Due to easy access, they are extensively used as animal feed additives in intensive husbandry systems [5]. It has been reported that the use of polymyxins (mainly CS) accounted for one-third of antibiotics in pigs and a higher ratio in poultry [6]. However, recent evidence suggested that the increasingly wide spread of CS resistance gene (MCR-1) was attributed to the excessive consumption of polymyxins by food producing animals [7]. Once most contact is made with drug resistant bacteria through the consumption of contaminated crops, infection treatment will be more difficult because of the escape of these bacteria from antibiotics [8]. Astonishingly, polymyxin resistance genes have been frequently detected in bacteria isolated from wastewater [9], surface water [10] and ground water [11]. At this regard, the Ministry of Agriculture (MOA) of China announced prohibition of CS as animal growth promoter in 2016 [12] and European Medicines Agency launched the assessment of their guidance on CS application in Europe [13]. Since pharmaceutical concentration in water is very low, efficient enrichment strategies are essential to determine trace analytes [14; 15]. Solid-phase extraction (SPE) technique has been deemed as the most suitable alternative for the analysis of water samples. To date, SPE has not been used to concentrate polymyxins from water, yet, several reports introduced HLB, WCX and C\({}_{18}\) sorbents to extract polymyxins from animal foodstuff [16; 17], feed [18; 19] and plasma [20]. Unfortunately, traditional SPE sorbents are not selective and thus result in strong matrix effects [2; 17; 21]. To address these problems, the use of molecularly imprinted polymers (MIPs) as sorbent material appears as an optimum alternative. As tailor-made materials, MIPs have binding sites which can well match the template, allowing to capture target analytes selectively. Thanks to its high selectivity and mechanical robustness, molecularly imprinted SPE (MISPE) has been used in enriching trace analytes from water [22; 23]. Traditionally Imprinted polymers demonstrated that hydrophobic solvents could greatly contribute to molecular recognition due to the electrostatic interactions, whereas polar solvents could generate negative effect [24]. Currently, significant attempts have been made to improve binding capacity of MIPs towards some antibiotics which are large molecular mass and high water-solubility. A typical example is the synthesis of MIPs for aminoglycoside drugs using the mixture of water and methanol (MeOH) as a porogen agent [25]. Another approach is to improve the recognition of kanamycin-MIPs in aqueous phase based on sol-gel polymer matrix which was produced by hydrolyzing silicon derivatives [26]. Up to now, only one work described a molecularly imprinted membrane as the support material to selectively absorb teicoplanin (one member of polypeptide antibiotics family) [27]. The resulting MIPs reflected high recovery of teicoplanin in serum, while the specificity and purification ability between MIPs and non-imprinted polymers (NIPs) have not been verified yet. The present study, for the first time, describes the synthesis of selective MIPs with colistin as the template by precipitation polymerization. The MIPs were utilized as the SPE sorbent for the extraction and cleanup of polymyxins from environmental water.