A common radiotracer technique is to precipitate macromolecules (protein & DNA) with TCA or some other strong denaturant, collect the precipitate on a filter and count it. Often such procedures give variable results, depending upon the degree to which the sample disperses from the filter into the cocktail. A typical artifact is counts which rise over time as more material dissolves off of the filter. It is possible to avoid these artifacts by using a cocktail that dissolves the filter, reproducibly releasing all of the sample for counting.

The well-dispersed sample on the right achieves 4π counting geometry, while half of the counts with the sample on the right are lost due to absorption and attenuation of emissions by the filter paper.

Counting Samples on Cellulose-Ester Filters: The Procedure

Do not dry the filters because this will slow the dispersion process. If a filter has dried, dampen it with 1-2 drops of distilled water.

1. Place the damp filter with sample into 10ml of National Diagnostics’ Filtron X.
2. Allow to stand at room temperature for 15 minutes. Shake well and count.

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