It is also used in radiocarbon dating to calibrate radiocarbon ages.New growth in trees occurs in a layer of cells near the bark.Charcoal is less likely than wood to have exchanged carbon with its environment, but a charcoal sample is likely to have absorbed humic acid and/or carbonates, which must be removed with alkali and acid washes. The constituents of bone include proteins, which contain carbon; bone's structural strength comes from calcium hydroxyapatite, which is easily contaminated with carbonates from ground water.Removing the carbonates also destroys the calcium hydroxyapatite, and so it is usual to date bone using the remaining protein fraction after washing away the calcium hydroxyapatite and contaminating carbonates. Collagen is sometimes degraded, in which case it may be necessary to separate the proteins into individual amino acids and measure their respective ratios and activity.However, the open lattice structure of the hydroxyapatite makes it highly contaminated with carbonates from ground water.Removal of carbonate contaminants through dilute acid washing is also not applicable because hydroxyapatite is acid soluble.
In cases when the protein portion of the bone sample is not well preserved and have already degraded due to warm conditions and fungal or bacterial attack, AMS dating labs carbon date individual amino acids to check if several of them give the same radiocarbon age.
Samples for dating need to be converted into a form suitable for measuring the content; this can mean conversion to gaseous, liquid, or solid form, depending on the measurement technique to be used.
Before this can be done, however, the sample must be treated to remove any contamination and any unwanted constituents.
When the C14 method was originally developed, Libby and his research team had to assume that the ratios of the carbon isotopes they were measuring had been altered only by 14C decay (Taylor, 1987:3) and that the sample material accurately represented the event to be dated.
Sample materials deposited in archaeological or geological contexts seldom remain in pristine condition, of course, they are often degraded and altered chemically.