A device for the dialysis of a sample includes a hermetically sealed sample chamber formed by a gasket with dialysis membranes affixed to each side in facing relationship. The gasket is impermeable to the sample being dialyzed, but is penetrable and reusable such that a sample introduction mechanism can be inserted through the gasket into the chamber, and then withdrawn without sample being permitted to leak. The device is fitted into a rigid housing containing windows and at least one port parallel to the dialysis membranes for directing the sample introduction mechanism into the gasket. The housing includes at least one pressure ridge for assisting in hermetically sealing the sample chamber and air chamber at one end for causing the device to float in an upright position when immersed in a dialysate.