Method for measuring concentration of trace amount of OH-groups contained in quartz glass

A method for measuring the concentration of OH groups that are contained in trace quantity in quartz glass, which comprises preparing a set of test pieces comprising a reference test piece from a blank of a quartz glass body whose OH group content is known and a sample test piece from a quartz glass body whose OH group content is to be measured, whereby the test pieces each have two planar planes faced to each other;

• setting the sample test piece and the reference test piece in an infrared spectrophotometer;
• successively irradiating perpendicular to one of the two planar planes an incident infrared radiation in a wavelength region of approximately 2500 nm to approximately 2950 nm, while simultaneously detecting the outgoing radiation spectrum from the other plane;
• obtaining the difference of the outgoing radiation spectrum of each of the test pieces;
• selecting the absorbance peak assigned to OH groups at a wavelength of 2720 nm to obtain the peak height thereof;
• and calculating the concentration of OH groups from the peak height in the sample test piece.