A device for separating a fluid sample within a collection container, comprising: a separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) having a through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) defined therethrough along a through-axis, the separator comprising: a float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542), having a first density; and a ballast (44, 44B, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), having a second density greater than the first density, wherein a portion of the float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is connected to a portion of the ballast (44, 44B, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), characterized in that the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) has a center of mass and a center of volume and the center of mass is offset from the through-axis, the float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is adapted for deformation upon applied rotational force to the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540), the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) comprises a first opening (78, 248, 56C, 549) and a second opening (50, 250, 60C, 551), and is adapted to allow fluid to pass through the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540), the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) is adapted to transition from a first initial position in which the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) is oriented in an open position for allowing fluid to pass therethrough, to a second sealing position for preventing fluid from being received therethrough, upon applied rotational force which causes deformation of the float, and transition of the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) from the open position to the closed position coincides with rotation of the mechanical separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) from the first initial position to the second sealing position. a separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) having a through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) defined therethrough along a through-axis, the separator comprising: a float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542), having a first density; and a ballast (44, 44B, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), having a second density greater than the first density, wherein a portion of the float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is connected to a portion of the ballast (44, 44B, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), a float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542), having a first density; and a ballast (44, 44B, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), having a second density greater than the first density, wherein a portion of the float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is connected to a portion of the ballast (44, 44B, 44C, 44D, 144, 144A, 244, 244A, 344, 444, 544), characterized in that the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) has a center of mass and a center of volume and the center of mass is offset from the through-axis, the float (42, 42B, 42C, 42D, 142, 142A, 242, 242A, 342, 442, 542) is adapted for deformation upon applied rotational force to the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540), the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) comprises a first opening (78, 248, 56C, 549) and a second opening (50, 250, 60C, 551), and is adapted to allow fluid to pass through the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540), the separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) is adapted to transition from a first initial position in which the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) is oriented in an open position for allowing fluid to pass therethrough, to a second sealing position for preventing fluid from being received therethrough, upon applied rotational force which causes deformation of the float, and transition of the through-hole (46, 46C, 46D, 146, 146A, 246, 246A, 346, 446, 546) from the open position to the closed position coincides with rotation of the mechanical separator (40, 40B, 40C, 40D, 140, 140A, 240, 240A, 340, 440, 540) from the first initial position to the second sealing position.