Relative density of urine

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By relative density of urine we mean the ratio of the density of urine to the density of water. The density of water is practically equal to 1 kg/l, so the difference between the density of water (in kg/l) and the relative density of urine is negligible. In the SI system, density has the dimension kg·m-3. The density of the sample in relation to the density of water is a relative quantity and is therefore given by a dimensionless number.

Determination of density of urine[edit | edit source]

The density of urine is estimated indirectly by the concentration of cations using diagnostic strips. The indicator zone of the strip contains a suitable polyelectrolyte as an ion exchanger and the acid-base indicator bromothymol blue. The principle of diagnostic strips is based on the exchange of cations from urine, especially Na+, K+, NH4+, for the H+ ions of the polyelectrolyte in the indication zone. The released H+ acidifies the weakly buffered acid-base indicator, which is in alkaline form. Acidification is accompanied by a change in color to bromothymol blue. The disadvantage is that examination with diagnostic strips does not take into account substances of a non-electrolyte nature such as glucose, proteins, urea, creatinine and some others.

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