Rapid determination of total dissolved solids in black liquors by ATR-UV/Vis spectroscopy

A new attenuated total reflection (ATR) ultraviolet/visible spectroscopic technique is presented for rapid determination of total dissolved solids (TDS) content in black liquors. The amount of nonabsorbing species, such as inorganic salts and carbohydrate degradation products, can affect the refractive index of the black liquor thus changing the effective optical path length in the ATR measurement. Accordingly, the ATR absorption intensity for dissolved lignin also includes information about the other dissolved solids in the liquor For the liquor samples tested, the square root of ATR response was linear with TDS from 7 to 23% solids content, and the relationship between ATR response and TDS was nearly linear from 58 to 72% solids content. This ATR technique is simple to use and can be implemented easily for online liquor TDS monitoring.