Abstract: An apparatus and method for the sampling and quantitative, IR-spectroscopic determination of impurities in hygroscopic liquids. The apparatus includes a stainless steel tube having a straight bore, a first end, and a second end. A first flange attachment is located at the first end of the stainless steel tube, and a second flange attachment is located at the second end of the stainless steel tube. First and second calcium fluoride plates are also located at the first and second ends of the steel tube, respectively. The first and second plates are oriented parallel to each other and perpendicular to the axis of the stainless steel tube. First and second outer flanges hold respective of the first and second plates in place at the first and second ends of the tube, respectively, and the first and second outer flanges are mechanically fixed to the first and second flange attachments, respectively. At least one seal separates the first plate from the first flange attachment and the first outer flange.