A Micro-Flow-Batch Analyzer Using an In-line Cadmium Sponge Microcolumn for the Photometric Determination of Nitrate and Nitrite in Dairy Samples

In this study, a micro-flow-batch analyzer (μFBA) using an in-line cadmium reduction microcolumn for the photometric determination of nitrate and nitrite in dairy samples is described. The method is based on the Griess-Llosvay reaction and measuring of the absorbance at 540 nm using a green LED integrated into the μFBA built in the urethane-acrylate resin. Initially, the nitrite content of the dairy sample is analyzed in the mixing chamber, while the nitrate is reduced to nitrite in cadmium sponge microcolumn coupled to the microsystem. Nitrate content was calculated from the difference between nitrate plus nitrite (expressed as nitrite) and nitrite content. The analytical curve for nitrate and nitrite was linear in the work range of 10.0–100.0 μg L −1 with a correlation coefficient of 0.992 and 0.998, respectively. The limit of detection and relative standard deviation were estimated at 0.39 μg L −1 and <1.7 % ( n = 5) for nitrite and 0.41 μg L −1 and <1.3 % ( n = 5) for nitrate. Comparing with the reference methods, no statistically significant differences were observed when applying the paired t test at a 95 % confidence level. The accuracy was assessed through recovery test (97.7 to 102.9 %). The proposed microsystem-employed in-line cadmium sponge microcolumn presented satisfactory portability, robustness, flexibility, low-cost device, and reduced chemicals consumption compared to recent methods. Thus, μFBA is potentially useful as an alternative for other automatic determinations using in-line pretreatment steps.