The XAD purification method used by Stafford and colleagues at Arlington Springs addressed this problem more thoroughly than earlier methods.

The basic approach involves dissolving the mineral portion of the bone (demineralization), isolating the protein fraction (which includes collagen), and then running the protein solution through columns packed with XAD resin.

The XAD resin preferentially binds humic acids and other contaminants that would affect the radiocarbon age, while the purified collagen passes through.

The purified collagen was then characterized chemically — its amino acid composition was checked to verify that it represented genuine ancient collagen rather than a diagenetically altered product that might not reliably date the original bone.

The amino acid profile of the Arlington Springs collagen was consistent with ancient collagen that had been preserved but not extensively altered.