title: A compact miniaturized continuous flow system for the determination of urea content in milk.
abstract: A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the urea concentration range from 1.0 x 10(-4) to 5.0 x 10(-3) mol L(-1) with a limit of detection of 8.0 x 10(-6) mol L(-1). The relative standard deviation (RSD) for a 2.0 x 10(-3) mol L(-1) urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h(-1). To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the data are in close agreement, at a 95% confidence level.
authors.affiliation: Embrapa Pecuária Sudeste, Caixa Postal 339, 13560-970, São Carlos, SP, Brazil. williants@hotmail.com
authors.forename: Willian Toito
authors.initials: WT
authors.lastname: Suarez
authors.forename: Osmundo Dantas
authors.initials: OD
authors.lastname: Pessoa-Neto
authors.forename: Vagner Bezerra
authors.initials: VB
authors.lastname: Dos Santos
authors.forename: Ana Rita
authors.initials: AR
authors.lastname: de Araujo Nogueira
authors.forename: Ronaldo Censi
authors.initials: RC
authors.lastname: Faria
authors.forename: Orlando
authors.initials: O
authors.lastname: Fatibello-Filho
authors.forename: Mar
authors.initials: M
authors.lastname: Puyol
authors.forename: Julián
authors.initials: J
authors.lastname: Alonso
mesh_terms: D000818:Animals; D057230:Limit of Detection; D008892:Milk / Q000737:chemistry*; D008904:Miniaturization; D015203:Reproducibility of Results; D014508:Urea / Q000032:analysis*
chemical_list: D014508:Urea