Selective microextraction of mononucleotides from milk using alumina and stannia hollow fibers prior to their determination by hydrophilic interaction liquid chromatography-diode array detection

Alumina- and stannia-based hollow fibers were synthesized via simple sol-gel procedures and characterized with respect to morphology, crystalline phase and specific surface area. Then, an optimization study was undertaken for the preconcentration of five 5′-mononucleotides using the hollow fibers. The separation and quantification of the analytes were carried out by HILIC with diode array detection, after proper optimization of the chromatographic conditions. The method demonstrated satisfactory linearities over a concentration range of 0.09-50 μg mL−1 with regression coefficients to range from 0.9993 to 0.9997. A range of commercially available 5′-mononucleotide supplemented infant formulas and three human breast milk samples were used to apply alumina hollow fibers, as a proof of concept. Recoveries ranged from 84% to 104%, while the calculated RSDs were from 3.6% to 4.3%. The proposed preconcentration-clean-up method is environmentally friendly and convenient, indicating that alumina and stannia are suitable for the applications by immersing them into milk samples, after removal of proteins.