Thank you very much for your answers. Today I'm going to my supervisor and we will see what happen...
By the way it was my first forum activity ;) and I'm happy that I found this site!!!

I've just started my PhD.(field of interst analytical chemistry)My question is: if you had to proposed subject of your thesis or you got it from your supervisor? I have to choose it by myself and it is a little difficult...Now I have an impression that everything is made...or maybe it's a sign that I am not able to do the PhD?