Evaluation of methods for determining the refraction correction for light‐scattering photometers

Abstract

Recent literature reports from three laboratories have treated the refraction correction for the Sofica and a noncommercial light scattering photometer. Our re‐evaluation of the data contained in these reports, as well as our experiments, indicate that the usually cited n2 refraction correction has not been unquestionably established for these instruments. In some cases, imprecise experimental techniques have been used to support this particular form of the correction. In addition, we find the optical system of the Sofica instrument results in the detector seeing vertically past the horizontal edge of the illuminated volume in violation of a basic assumption in the deduction of the n2 correction. Our experiments, as well as our interpretation of recent literature data, support an exponent of less than 2.0 for the Sofica apparatus, which is consistent with an instrument whose detector views outside the illuminated volume. However, the experimental methods available to evaluate the exponent lack the desired precision.

Molecular weight of single-stranded fd bacteriophage DNA. High speed equilibrium sedimentation and light scattering measurements

“…6 In addition to the statistical uncertainty in the weighted mean of Mw, contributions from systematic uncertainties common to both wavelengths have been included. These arise from the uncertainty in the extinction coefficient, which leads to an uncertainty in the molecular weight of 1.4%, and from uncertainty in the exponent in (Ro/«b)2, which, from the recent work of Wallace et al (1972), contributes at most a 3 % error in the molecular weight.…”

Photon correlation spectroscopy, total intensity light scattering with laser radiation, and hydrodynamic studies of a well fractionated DNA sample

“…58 We compared the Ludox calibration with a calibration using a very pure, clean benzene sample prepared in this laboratory by J. Godfrey. This had unit dissymmetry; the ratio of the intensity of scattering of unpolarized light of the benzene to the glass standard was less than 0.5% different from that specified by the Fica manufacturers and the depolarization ratio pv at 546.1 nm was 0.42 as in the l i t e r a t~r e .~~,~~ Use of values of R,(90) = 22.05 X at X = 546.1 nm and 63.7 X at 435.8 nm59960 for the Rayleigh factors for vertically polarized incident and unpolarized scattered light, and the (ne/nd2 correction gives a calibration constant, with respect to the glass stan-dard, which is the same as from the Ludox calibration to within 3%.…”