A flow cell (110, 310) for use with an analytical device (150, 350) having a measurement surface (155a, 355a) onto which a multiphase fluid to be measured can be received, the flow cell (110, 310) comprising: a housing (115, 315) comprising an interface for connecting to an analytical device (150, 350); a fluid chamber (120, 320) provided in the housing (115, 315), the fluid chamber (120, 320) comprising sidewalls (116, 316) at least partly defining an internal volume (120a, 320a) for receiving a multiphase fluid and an opening (125, 325) arranged so as to provide a multiphase fluid received in the internal volume (120a, 320a) to a measurement surface (155a, 355a) of an analytical device (150, 350) when the interface of the housing (115, 315) is connected to an analytical device (150, 350); and an agitation device (130, 330) comprising an ultrasonic sound-wave generator (137, 337) adapted to agitate a multiphase fluid within the internal volume (120a, 320a) of the fluid chamber (120, 320) and cause flow of the fluid within or around the fluid chamber (120, 320) and through or within the opening (125, 325), thereby providing a fluid to a measurement surface (155a, 355a) of an analytical device (150, 350) and thereby mixing the fluid within the fluid chamber (120, 320) so as to provide a homogeneous or well-mixed fluid to the measurement surface, wherein the ultrasonic sound-wave generator is separated from the internal volume (120a, 320a) by a barrier wall (133, 316, 333); and wherein the fluid chamber (120, 320) is a swirl chamber having a central axis; and wherein the agitation device (130, 330) is adapted to cause a multiphase fluid to flow around the central axis of the swirl chamber. a housing (115, 315) comprising an interface for connecting to an analytical device (150, 350); a fluid chamber (120, 320) provided in the housing (115, 315), the fluid chamber (120, 320) comprising sidewalls (116, 316) at least partly defining an internal volume (120a, 320a) for receiving a multiphase fluid and an opening (125, 325) arranged so as to provide a multiphase fluid received in the internal volume (120a, 320a) to a measurement surface (155a, 355a) of an analytical device (150, 350) when the interface of the housing (115, 315) is connected to an analytical device (150, 350); and an agitation device (130, 330) comprising an ultrasonic sound-wave generator (137, 337) adapted to agitate a multiphase fluid within the internal volume (120a, 320a) of the fluid chamber (120, 320) and cause flow of the fluid within or around the fluid chamber (120, 320) and through or within the opening (125, 325), thereby providing a fluid to a measurement surface (155a, 355a) of an analytical device (150, 350) and thereby mixing the fluid within the fluid chamber (120, 320) so as to provide a homogeneous or well-mixed fluid to the measurement surface, wherein the ultrasonic sound-wave generator is separated from the internal volume (120a, 320a) by a barrier wall (133, 316, 333); and wherein the fluid chamber (120, 320) is a swirl chamber having a central axis; and wherein the agitation device (130, 330) is adapted to cause a multiphase fluid to flow around the central axis of the swirl chamber.