Nickel chemical enrichment on nylon membranes previously treated with eosin (eo) is proposed for subsequent quantification by spectrofluorimetry (lambda(em)=547 nm, lambda(exc)=515 nm). Operational variables which have influence on quantitative metal retention have been studied. At optimal experimental conditions, quantitative recovery was reached (superior to 99%), with a detection limit of 0.13 ng L(-1) and quantification limit of 0.44 ng L(-1). The calibration sensitivity was of 6x10(13) ng L(-1) for the new methodology with a linear range of 0.44-410 ng L(-1) Ni(II). The tolerance levels, respect to cations and anions as potential interferents, were studied, with good results. The methodology was validated by standard addition method and satisfactorily applied to urinary nickel determination of 50 subjects including smokers, second hand smokers and non-smokers' samples without previous treatment. Stability of biological samples was daily studied for a period of 1 month. Within-day precision was better than 0.02 CV. The reproducibility (between-day precision) was also evaluated over 3 days by performing six determinations each day with a CV of 0.052. The different groups were evaluated using one-way analysis of variance (ANOVA) followed by Tukey-Kramer multiple comparison test with satisfactory results.
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