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. Similarly, at least one seal separates the second plate from the second flange attachment and the second outer flange. First and second three-way taps are coupled by a first stainless steel line. A second stainless steel line couples the first three-way tap to the stainless steel tube, and a third stainless steel line couples the second three-way tap to the stainless steel tube. The method includes the steps of purging the first line with nitrogen gas and purging a cell space defined by the tube at least five times.