title: The effect of ionic strength on the UV-vis spectrum of congo red in aqueous solution.
abstract: The major peak near 498 nm in the ultraviolet-visible spectrum of congo red in aqueous solution shifts toward the blue while the molar absorptivity of this peak decreases predictably with increasing ionic strength. The shift was observed for solutions in which ionic strength was varied from 0.0 to 1.8M using the uni-univalent ionic compounds, NaCl, NaClO(4), KNO(3) and KBr separately. A plot of the log of the absorbance at the peak versus ionic strength was linear as well as a plot of the log of the wavelength of the major peak (shifted from 498 nm) versus the ionic strength. The slopes of each of these plots were somewhat different depending on the ionic compound.
authors.affiliation: Department of Chemistry, State University of New York-Plattsburgh, 101 Broad Street, Plattsburgh, NY 12901, United States.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Sladewski
authors.forename: Alesha M
authors.initials: AM
authors.lastname: Shafer
authors.forename: Craig M
authors.initials: CM
authors.lastname: Hoag
mesh_terms: D001965:Bromides / Q000737:chemistry; D004396:Coloring Agents / Q000737:chemistry*; D003224:Congo Red / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D009994:Osmolar Concentration; D010472:Perchlorates / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D017670:Sodium Compounds / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*
chemical_list: D001965:Bromides; D004396:Coloring Agents; D009566:Nitrates; D010472:Perchlorates; D017680:Potassium Compounds; D017670:Sodium Compounds; D012996:Solutions; D014867:Water; D003224:Congo Red; D012965:Sodium Chloride; C031068:sodium perchlorate; C039004:potassium bromide; C023844:potassium nitrate