Desenvolvimento de um sistema de análise em fluxo-batelada empregando detecção espectrofotométrica para a determinação de ácido siálico em leite

Abstract

In this work, it is proposed a batch-flow analysis system with heating and spectrophotometric detection coupled in the reaction cell for the determination of sialic acid in milk samples. The analytical procedure proposed for the determination of sialic acid was based on the acid ninhydrin acid reaction monitored at 470 nm. The determination of the concentration of sialic acid in milk samples allowed to evaluate the occurrence of frauds of addition of cheese whey, not allowed by current legislation. The composition of the proposed system consists of a peristaltic pump, three solenoid three-way valves, three pinch solenoid valves, a reaction/detection cell and a multichannel (UV/VIS) spectrophotometer. The control of the system was performed using the LabVIEW® program, interfaced by an electronic system based on the integrated circuit (IC) ULN2803A connected to a USB6009 interface. The proposed system made it possible to obtain linear responses between 1.0 and 10.0 mg L-1 sialic acid (R = 0.99, n = 7) with relative standard deviation less than 2% (n = 10) and limits of detection and quantification estimated at 0.239 mg L-1 and 0.726 mg L-1, respectively. The system presented analytical frequency of 7 determinations per hour, consumption of reagent solution and sample of 200 μL and 466.66 μL respectively. Compared to the official method of determination of sialic acid in milk, the proposed system showed a significant decrease of 90% in solution consumption and, consequently, decrease of the generated effluents. Studies of potential interferents demonstrated the selectivity of the proposed method. The procedure was applied to samples of UHT milk, milk powder and milk compound purchased in the local markets of the metropolitan region of Recife. Addition and recovery tests were performed to validate the procedure, obtaining a variation between 92.5 and 104%, demonstrating the efficiency of the proposed method in the detection of adulteration in milk samples with cheese serum.