[Humidity as a necessary condition for latent fingerprint detection with ninhydrin--a practice-oriented and inexpensive method using potassium citrate].

Ninhydrin is a common reagent for latent fingerprint detection on porous surfaces, and water in the form of humidity is an essential factor in the developing process. Beside climatic chambers running on electricity, the required humidity can also be reached by using saturated salt solution. The influence of different climatic conditions on the developing process is shown by using test strips (as analytical standards). For the developing process, a saturated solution of tripotassium citrate at room temperature proved to be particularly suitable. Tripotassium citrate is a non-hazardous compound, which is also used as a food additive without quantitative limitation, is environmentally safe and produced from renewable resources. In a closed box, a saturated tripotassium citrate solution generates a relative humidity of about 64% in a temperature range of 15 to 35 degrees C.