Neeran:An HPLC-mass is simply a continued mass spectrometric analysis of eluent from the HPLC column directly. Typical method involves electrospray MS or MALDI-TOF.
In case of HPLC, you will got information about number of compounds present in your sample and also the percentage of different components. In case of HPLC-MS, there is additional information about the Molecular mass of the components along with there qualitative and quantitative profile.