You can use techniques such as inductively coupled plasma mass spectrometry (ICP-MS) to determine the quantities of various metals in samples. It is a destructive technique, but highly quantitative.
Well, one simpler way, for silver, which often works well is using the UV-VIS spectroscopy for determining the plasmon resonance peak. I often give this task while teaching nanotechnology, where I ask the students to make a calibration curve and then measure the plasmon resonance peak intensity and then cross-check the data with XRF results....... it works in many of the samples that we tested