The Remspec liquid transmission head screws onto the end of the probe shaft and is readily interchangeable with the ATR head. The overall probe diameter of 6 mm (approximately 1/4 inch) is maintained for good access to very small reactors. The mid-IR signal travels from the probe through a ZnSe window and is reflected back into the probe from a mirror surface after traveling across a short space filled with the sample in which the probe is immersed. The total path length is adjustable from about 0.1 mm to about 6 mm. The tranmission probe is recommended for use in low-absorbing solvents with analytes in concentrations down to 0.1 mM.