A spectroscopic measuring device for minimizing spurious absorption due to undesired gases. The device includes a probe body, or a transmission cell formed from a central measurement cell and first and second probe bodies. Each probe body is subject to leakage of undesired gas, especially over time in the presence of high pressure gas. Each probe body includes a bore located between a primary window disposed at or near a distal end and a secondary window located at or near the proximal end. It being observed that the absorbance is proportional to the pathlength and inversely proportional to the volume as long as the pressure in the probe body remains low compared to that in the measurement cell, a glass filler rod is located in the bore and a is void located adjacent to the filler glass rod, thereby minimizing spurious absorption even in the presence of leakage.