Nephelometric determination of micro amounts of nucleic acids with protamine sulfate

Nucleic acids can form large particle complexes with protamine sulfate by e lectrostatic forces, which results in strong light scattering. Based on thi s, a nephelometric method is described for sensitive and convenient determi nation of nucleic acids with protamine sulfate by using a common spectroflu orimeter. Maximum light scattering is produced in the range of pH 2.2-4.4 w ith the same excitation and emission wavelengths at 365 nm. Under optimal c onditions, the calibration curves are linear in the range 0.05-60.0 mu g cm (-3) for nucleic acids. The corresponding detection limits are 12.5 ng cm(- 3) for calf thymus DNA, 9.0 ng cm(-3) for fish sperm DNA, and 18.0 ng cm(-3 ) for yeast RNA, respectively. Six synthetic samples are determined with sa tisfactory results. The relative standard deviation of five replicate measu rements is 3.2% for 2.0 mu g cm(-3) calf thymus DNA.