Any strong acid will dissolve hydroxyapatite given enough time. The easiest thing to try is concentrated nitric acid microwave digestion, or nitric-perchloric acid mixtures with microwave digestion.

There are so many solvents are available to dissolve the metal ions but based on the sample, the selection of the solvents will be varying. In general, a combination of concentrated inorganic acids gives better result, especially Nitric acid and Hydrochloric acid. If the sample have higher lipid contented use a minor quantity of H2O2.

After ionization of sample at 540 C for 6 h, you can use diluted (3:1) acids (Nitric acid+Hydrochloric acid) at the ratio of 4:1 to dissolve.

Hydrochloric acid is the best. I don't think nitric acid is necessary - there is nothing to oxidize, also hydrochloric acid usually is more pure and dissolves better (because of chloride complexes forming).

thank you for all, I have tried concentrated Hcl but result was not so good then add minor amount of water into it and found complete dissolution of metal ion co-doped HAp then diluted solution was used for ICP-OES analysis.