Abstract: A mass transfer device, such as a desorption device has fluid channels, to transfer a component one fluid to the other. A microsieve is provided separating the channels. The microsieve comprising a sieve layer with a thickness of less than two micrometer deposited on a substrate with openings to expose areas of the sieve layer with holes straight through the sieve layer. The remaining portions of the substrate form a support web to support the sieve layer. In an embodiment the liquid channel is provided on the side of the microsieve opposite the substrate portions. An efficient very low height (e.g. 25 micrometer) liquid channel may be realized in this way. Preferably the liquid is supplied using a channel plate facing the microsieve, with grooves opposite wider portions of the substrate, the liquid flowing out sideways from the grooves into areas where the low height liquid channel is formed.