|Minimum sample size: 500 mg|
|Chemical cleaning by Acid-Base-Acid procedure|
|Combustion by MnO2 sealed tube method|
Bone, teeth and ivory are very complex materials of which organic fractions are routinely used in 14C dating. Nevertheless, 14C dating of bone collagen is challenging because its preservation is influenced by several environmental factors and, moreover, the contaminants can cause false dates that are either too young or too old. Therefore, the main focus of the bone pre-treatment method at HEKAL is on the removal of such contaminants. First, the sample is washed in distilled (DI) water and dried in oven for an overnight. Then, the entire exterior of the bone is removed and after crushing the 0.5 – 1.0 mm fraction of the sample is sieved out. Generally 500-1000 mg of this fraction is used in the chemical cleaning step. Regarding the chemical cleaning, the well known ABA (acid-base-acid) process is applied at HEKAL. For this purpose a semi-automatic, continuous flow bone preparation line has been constructed where 3 types of reagents are selectively pumped into the reaction cells containing the bone samples, with a sequence of distilled water, 0.5 M HCl and 0.1 M NaOH solution. After this step and setting of the pH, the cleaned sample transferred into a test tube is placed into a heating block. The dissolved collagen/gelatine is filtered via a 2 mm glass fibre filter and freeze-dried at a vacuum of 10-1 mbar which takes about for 2 days. The dried gelatine is then placed in glass tubes along with MnO2 reagent and is combusted at 550°C in a muffle oven for a day. The revealed CO2 gas is finally purified from other by-product gases and graphite targets are prepared. The 14C measurements are performed by our Environ MICADAS AMS while data evaluation is accomplished using the BATS program package. 14C dating has played an increasing role in archaeology so, since the early 80’s, researchers of HEKAL have been aiming to yield as reliable age results as possible.