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Liposomes containing magnetic gold nanoparticles (AuNPs) and an enzymatic substrate (4-methylumbelliferyl-phosphate) have been used as on-flow microcontainers for reagent preconcentration in a flow injection method for the determination of alkaline phosphatase (ALP) activity. The dynamic range of the calibration graph was 6.4 × 10(-3)-0.25 U L(-1) ALP, and the detection limit was 1.9 × 10(-3) U L(-1). The precision, expressed as relative standard deviation (RSD%), was in the range of 0.7-2.4%. The overall method showed a sampling frequency of 10 h(-1). The method was applied to the determination of ALP in milk samples with recovery values ranging between 87.5 and 104.6%. The residual ALP activity in milk samples subjected to temperature treatments was also determined. The results obtained in the analysis of all milk samples were compared with those obtained by applying a previously described flow injection method.

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