An apparatus for the collection of samples of exhaled air during normal respiration, comprising a flow generator, an orally insertable exhalation air receiver, and a device for isolating the nasal airways, wherein the apparatus further comprises: a sensor for detecting a change in a parameter representing the change from inhalation to exhalation and to transmit said change as a signal; a control unit adapted to receive said signal and to control said device for isolating the nasal airways; wherein the flow generator is connected to or integrated with the exhalation air receiver. A method of collecting samples of exhaled air during normal respiration conditions, comprising the steps of: detecting a change in a parameter representing the change from inhalation to exhalation and transmitting said change as a signal; receiving said signal in a control unit; activating a device for isolating the nasal airways; activating a flow generator connected to an exhalation air receiver; and collecting a sample of exhaled air during exhalation when the nasal airways are isolated.