Mapping milk samples based on the doses of selected antibiotic residues: Application of pipette tip microextraction using graphene oxide–starch–based nanocomposite

Milk is considered as one of the essential nutrients consumed daily. This important food source is easily contaminated via various ways one of which is chemical contamination [1]. β-lactam antibiotics are modern medicines which have been used often for prevention and treatment of animal husbandry infections as well as growth promotion [2]. Because of the low octanol–water partition coefficient (KO/W) values of penicillin antibiotics, the use of polar extractive phase is presumably more logical [3]. Lately, biopolymers have grabbed considerable attentions of the scientific and industrial communities, being an alternative to conventional petroleum-based plastics [4]. In this study, a method is described for the extraction and mapping of three antibiotic residues from cow milk samples using a graphene oxide–starch–based nanocomposite. The prepared nanocomposite was employed as an extractive phase for pipette tip microextraction of antibiotics from cow milk samples. The extracted antibiotics, i.e. amoxicillin, ampicillin and cloxacillin, were subsequently analyzed by HPLC–UV. Important variables associated with the extraction and desorption efficiency were optimized. The implementation of the starch–based nanocomposite in the pipette tip, led to high extraction efficiencies for the selected antibiotics. The penicillin group was validated based on the characteristic performance of the European Commission Decision 2002/657/EC by spiking the selected antibiotics to the blank milk samples. The limits of quantitation for amoxicillin, ampicillin and cloxacillin were 2.7, 3.0 and 5.0 μg kg-1 which were lower than the maximum residue limits in the European legislation. The overall obtained results indicate the superiority of the starch nanocomposite performance toward the selected antibiotics. The relative standard deviations of intra and inter–day analysis are less than 3.3 and 6.1%, respectively. Moreover, the mean recoveries of the target penicillin in the real milk samples were in the range of 83.3–105.0%. Statistical and chemometric methods revealed that the clustering of milk samples based on the doses of antibiotic residues was indeed possible.