title: Determination of chromium by GFAAS in slurries of fish feces to estimate the apparent digestibility of nutrients in feed used in pisciculture.
abstract: This paper presents a simple, fast and sensitive method to determine chromic oxide (used as a biological marker of fish feed) in samples of fish feces by GFAAS through the direct introduction of slurries of the samples into the spectrometer's graphite tube. The standard samples of feces and of fish feed containing 0.10-1.00mgkg(-1) of Cr(2)O(3) were pre-frozen for 1min in liquid nitrogen and then ground a cryogenic mill for 2min, which reduced the samples' grain size to less than 60mum. The standard slurries were prepared by mixing 20mg of standard samples of fish feed or feces with 1mL of a solution containing 0.05% (v/v) of Triton X-100 and 0.50% (v/v) of suprapure HNO(3) directly in the spectrometer's automatic sampling glass. The final concentrations of Cr(2)O(3) present in the standard slurries were 2, 4, 8, 16 and 20mugL(-1). After sonicating the mixture for 20s, 10muL of standard slurries were injected into the graphite tube, whose internal wall was lined with a metallic palladium film that acted as a permanent chemical modifier. The limits of detection (LOD) and quantification (LOQ) calculated for 20 readings of the blank of the standard slurries (2%, m/v of feces or feed devoid of minerals) were 0.81 and 2.70mugL(-1) of Cr(2)O(3) for the standard feces slurries, 0.84 and 2.83mugL(-1) of Cr(2)O(3) for the standard feed slurries. The proposed method was applied in studies of nutrient digestibility of different fish feeds and its results proved compatible with the results obtained from samples pre-mineralized by acid digestion.
authors.affiliation: Faculdade de Medicina Veterinária e Zootecnia, Programa de Pós-Graduação em Zootecnia, Bolsista CAPES, Departamento de Melhoramento e Nutrição Animal, UNESP, Caixa Postal 560, 18618-000 Botucatu, SP, Brazil.
authors.forename: Fabio Arlindo
authors.initials: FA
authors.lastname: Silva
authors.forename: Cilene C Federici
authors.initials: CC
authors.lastname: Padilha
authors.forename: Luis Edvaldo
authors.initials: LE
authors.lastname: Pezzato
authors.forename: Margarida Maria
authors.initials: MM
authors.lastname: Barros
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Padilha