Typically, lignins are characterized by IR spectroscopy in the solid state. The examination of lignins in solution has long been a domain of UV and NMR spectroscopy. However, with the advent of the FTIR technique, the IR spectra of liquid samples now can be readily obtained. The need to measure IR spectra in solution exists when there is not enough time to isolate lignin from solution as, for example, is the case when spent pulping liquors have to be analyzed rapidly during a pulping process for process control. This section describes briefly the common liquid sampling accessories and applications of solution state FTIR spectroscopy to lignins. For more details on FTIR spectroscopy, the reader is referred to Chapter 4.1.