For ppm levels of several thousands, a gravimetric assay should be sensitive enough a method. Just take gross and tare weights before and after evaporation of the water from the microdyn. The evaporation can be done without heating. Just let the microdyn sample sit at room temperature in an open beaker, but covered with a filter paper, for as many days as it takes to dry out. Incidentally, I used this method to get a solid sample of tetrasilver tetroxide, ag4o4, from a pint of silspa. Solid ag4o4 is a beautiful charcoal-grey compound with an earthy, clay-like smell and distinctive taste.
Best regards, Matthew
