Analysis system, comprising: - a confinement device for confining a liquid sample that is to be analysed, comprising a measurement chamber capable of receiving said liquid sample and delimited at least in part by a first and a second surface (13A, 13B), called the measurement surfaces, said measurement surfaces (13A, 13B) being transparent to a light radiation called the measurement radiation, and being positioned facing one another so that a distance between said measurement surfaces (13A, 13B) defines a thickness of the measurement chamber, at least a first measurement surface being movable relative to the second measurement surface, so as to permit a variation of the thickness of the measurement chamber; and also comprising at least one collecting conduit (2.1, 2.2) fluidically communicating with the measurement chamber and intended to be connected in a sealed way to a container so that it can collect the liquid sample from said container; - an optical measurement device capable of emitting measurement light radiation towards the measurement chamber, and of detecting light radiation transmitted through the measurement chamber, the latter having a thickness equal to a minimum value (e mes) called the measurement value; - a flow device capable of causing at least the flow of liquid in the collecting conduit (2.1) from the container as far as the measurement chamber; - an actuation device capable of bringing about a relative movement of the measurement surfaces (13A, 13B) relative to one another, resulting in a variation in the thickness of the measurement chamber, and thus a separation of the two measurement surfaces (13A, 13B) from one another so as to permit renewal of the liquid present in the measurement chamber, the thickness of the measurement chamber being equal to a maximum value (e 2) called the renewal value, this being greater than the minimum measurement value (e mes): characterized in that: • the measurement chamber is also delimited laterally by a flexible membrane fixed in a sealed way to the measurement surfaces (13A, 13B), allowing the thickness of the measurement chamber to be varied; • the flow device comprises the confinement device associated with the actuation device, so that increasing the thickness of the measurement chamber causes liquid to flow in the collecting conduit (2.1) from the container as far as the measurement chamber. - a confinement device for confining a liquid sample that is to be analysed, comprising a measurement chamber capable of receiving said liquid sample and delimited at least in part by a first and a second surface (13A, 13B), called the measurement surfaces, said measurement surfaces (13A, 13B) being transparent to a light radiation called the measurement radiation, and being positioned facing one another so that a distance between said measurement surfaces (13A, 13B) defines a thickness of the measurement chamber, at least a first measurement surface being movable relative to the second measurement surface, so as to permit a variation of the thickness of the measurement chamber; and also comprising at least one collecting conduit (2.1, 2.2) fluidically communicating with the measurement chamber and intended to be connected in a sealed way to a container so that it can collect the liquid sample from said container; - an optical measurement device capable of emitting measurement light radiation towards the measurement chamber, and of detecting light radiation transmitted through the measurement chamber, the latter having a thickness equal to a minimum value (e mes) called the measurement value; - a flow device capable of causing at least the flow of liquid in the collecting conduit (2.1) from the container as far as the measurement chamber; - an actuation device capable of bringing about a relative movement of the measurement surfaces (13A, 13B) relative to one another, resulting in a variation in the thickness of the measurement chamber, and thus a separation of the two measurement surfaces (13A, 13B) from one another so as to permit renewal of the liquid present in the measurement chamber, the thickness of the measurement chamber being equal to a maximum value (e 2) called the renewal value, this being greater than the minimum measurement value (e mes): characterized in that: • the measurement chamber is also delimited laterally by a flexible membrane fixed in a sealed way to the measurement surfaces (13A, 13B), allowing the thickness of the measurement chamber to be varied; • the flow device comprises the confinement device associated with the actuation device, so that increasing the thickness of the measurement chamber causes liquid to flow in the collecting conduit (2.1) from the container as far as the measurement chamber. • the measurement chamber is also delimited laterally by a flexible membrane fixed in a sealed way to the measurement surfaces (13A, 13B), allowing the thickness of the measurement chamber to be varied; • the flow device comprises the confinement device associated with the actuation device, so that increasing the thickness of the measurement chamber causes liquid to flow in the collecting conduit (2.1) from the container as far as the measurement chamber.