Retention and transfer of liquids

A method for holding and transferring liquid using a fluidics module which comprises a first liquid receiving region, a second liquid receiving region, a downstream fluidics structure, a siphon channel with an apex and a connecting channel, wherein a portion of the first liquid receiving region which is radially outward with respect to a center of rotation is connected to the downstream fluidics structure via the siphon channel, and the radially outward portion of the first liquid receiving region is fluidically connected to an outlet of the second liquid receiving region via the connecting channel, wherein the first liquid receiving region and the second liquid receiving region are vented, wherein the connecting channel comprises a first end which is fluidically connected to the first liquid receiving region, and a second end which opens into a radially outward portion of the second liquid receiving region, wherein the first end of the connecting channel is radially further outward than the second end of the connecting channel, wherein an outlet end of the siphon channel is arranged radially further outward than a radially outward end of the first liquid receiving region and than a radially outward end of the second liquid receiving region, the method comprising:

• a) rotating the fluidics module about the center of rotation in order to drive parts of a first liquid introduced into the first liquid receiving region from the first liquid receiving region into the siphon channel and the connecting channel in order to effect liquid menisci of the first liquid in the first liquid receiving region, the siphon channel and the connecting channel without the first liquid passing into the downstream fluidics structure via an apex of the siphon channel and without the first liquid passing from the first liquid receiving region into the second liquid receiving region via the connecting channel,
• b) introducing a second liquid into the second liquid receiving region and rotating the fluidics module in order to drive parts of the second liquid from the second liquid receiving region into the connecting channel in order to thereby enclose a gas volume between the first liquid and the second liquid in the connecting channel and to generate a counter-pressure in the gas volume by which the second liquid is held in the second liquid receiving region and the connecting channel, and
• c) introducing additional liquid into the first liquid receiving region in order to move the liquid meniscus of the first liquid over the apex of the siphon channel in order to thereby empty the first liquid from the first liquid receiving region into the downstream fluidics structure via the siphon channel, thereby reducing the counter-pressure in the gas volume and transferring the second liquid from the second liquid receiving region into the downstream fluidics structure via the connecting channel and the siphon channel.