ACS spectrophotometric grade = a reagent/solvent that meets ACS Reagent Chemicals purity specifications and is specially qualified for optical transparency (very low UV–Vis absorbance/fluorescence) so it won’t distort spectrophotometric measurements. In other words, it’s “ACS grade” plus ...
ACS Spectrophotometric Grade reagents are specially manufactured to meet both the American Chemical Society (ACS) specifications and stringent optical transparency standards required for UV-Visible spectrophotometry and other high-precision spectroscopic applications.