FIELD: proportioning liquid by means of suction unit provided with proposed end-piece; chemical industry; motion, dilution, titration and mixing of liquids. SUBSTANCE: proposed end-piece is provided with membrane unit closing passage of gas and liquid ensuring gas and liquid tightness from first end of end-piece to suction unit when end-piece is secured to suction unit. Membrane unit includes membrane made from deformable gas-tight and liquid-tight flexible material; its shape may be restored for change of volume of space separated by membrane from space for placing liquid sample. Membrane is brought in contact with unit performing reciprocating motion in cylindrical space of suction unit for drawing sample and/or removing it. Invention proposes method for proportioning liquid by means of said unit. Construction of end-piece and method of proportioning liquid by means of this end-piece exclude choking of suction unit. EFFECT: improved quality. 16 cl, 9 dwg
