Preparation of human and rat urine for trace metal analysis

Abstract

Human urine and particularly rat urine tend to precipitate following collection and/or storage. This precipitation was found to be a function of temperature, was not easily redissolved by dilution, and significantly reduced the concentration of certain cations in solution. We have therefore established methods for contamination-free preparations of rat and human urine samples that maintain all cations fully soluble for accurate analysis. Human urine is diluted (1 + 1) with 0.22 mol dm^–3 nitric acid, warmed to 40 °C and then equilibrated to room temperature. Rat urine samples are diluted (1 + 1 + 1) with 30% m/v hydrogen peroxide and 10 mol dm^–3 nitric acid, incubated at 40 °C (72 h), further diluted with half the original quantities of peroxide and acid, and again incubated at 40 °C (72 h) before dilution.