Specific refractive index increments of polymer systems at four wavelengths

To ascertain whether a low-angle laser scattering photometer under development (76) would give absolute molecular weights for biological macromolecules, it was necessary to obtain specific refractive index increments for light of wavelength 632.8 nm (He-Ne laser). Such data were unavailable for polymers although calibration data have been reported (27) for 589.3 and 632.8 nm for a series of electrolytic solutions. Anderson ( 7 ) also calibrated a commercial differential refractometer resembling that of Brice and Halwer ( 5 ) using the data obtained on salt solutions interferometrically by Kruis (20), and more recently Block ( 4 ) described a technique for using 632.8-nm radiation from a secondary source in differential refractometry. None of these investigators determined specific refractive index increments of polymer systems. We report refractive index increments for a number of polymers determined with the commercially available Brice-Phoenix differential refractometer at four wavelengths from 632.8 to 435.8 nm. Calibration measurements were made at 24.2 f 0.1"C by use of potassium chloride and sucrose, followed by studies of polystyrene, bovine serum albumin, D-glyceraldehyde phosphate dehydrogenase, polydimethylsiloxane, amylopectin, and deoxyribonucleic acid (DNA).