Patent ID: 7176464

Claim:
A method of determining the concentration of impurity mixed in gas, comprising the steps of: (a) removing impurity from gas, introducing the gas into a first cell, and measuring the intensity of light transmitted through the first cell; (b) introducing gas containing impurity of which concentration is known, into the first cell or a second cell having an optical path length equal to that of the first cell, and measuring the intensity of light transmitted through the first cell or the second cell with the temperature and pressure maintained at those used at the measurement (a) above-mentioned; (c) dividing the light intensity obtained at the measurement (b) above-mentioned by the light intensity obtained at the measurement (a) above-mentioned, thereby to obtain the absorbance of the impurity, and storing this impurity absorbance in terms of a function of an impurity concentration; (d) introducing gas containing impurity of which concentration is unknown, into the first cell, the second cell or a third cell having an optical path length equal to that of the first cell, and measuring the intensity of light transmitted through the first cell, the second cell or the third cell with the temperature and pressure maintained at those used at the measurement (a) above-mentioned; and (e) dividing the light intensity obtained at the measurement (d) above-mentioned by the light intensity obtained at the measurement (a) above-mentioned, thereby to obtain the absorbance of the impurity, and applying the absorbance thus obtained to the function, thereby to obtain the impurity concentration.