1. Dilute 1 Ál of the sample 1:100 in 0.2 M EDTA (pH 8.0).
2. Spot 3 Ál of the diluted sample on a glass fiber (Whatman GF/C glass-fiber disc) or nitrocellulose filter
for determination of total cpm in the sample.
3. Transfer 3 Ál of the same dilution to a tube. Add 100 Ál of Salmon sperm DNA (50 mg/ml). Mix well.
4. Add 1.0 ml of 10% TCA (ice-cold). Leave on ice for 15 minutes.
5. Collect the precipitated DNA by vacuum filtration onto a glass fiber or nitrocellulose filter.
6. Wash the filter 6 times with 5 ml of cold 10%TCA and once with 5 ml of 95% ethanol.
7. Dry both filters in the air or under a lamp.
8. Add an appropriate amount of scintillation fluid to each filter and count using a scintillation counter.