Bones are potentially the best age indicators in a stratigraphic study, because 
they are closely related to the layer in which they are found. Collagen is the 
most suitable fraction and is the material normally used in radiocarbon dating. 
Bone contaminants can strongly alter the carbon isotopic fraction values of the 
samples, so chemical pretreatment for (14)C dating by accelerator mass 
spectrometry (AMS) is essential. The most widespread method for collagen 
extraction is based on the Longin procedure, which consists in HCl 
demineralization to dissolve the inorganic phase of the samples, followed by 
dissolution of collagen in a weak acid solution. In this work the possible side 
effects of this procedure on a modern bone are presented; the extracted collagen 
was analyzed by ATR-IR spectroscopy. An alternative procedure, based on use of 
HF instead of HCl, to minimize unwanted degradation of the organic fraction, is 
also given. A study by ATR-IR spectroscopic analysis of collagen collected after 
different demineralization times and with different acid volumes, and a study of 
an archaeological sample, are also presented.