There are various chemical and physical methods. The one easy way is, for example, gravimetry: You weigh the powder and heat it therefore to air in the oven. Rest of metal be oxidized and the powder be heavy. With this weight gain can be calculated metal content.

Try XRF analysis

I guess you can use SEM/EDS analysis, we recently used it to determine the alloy composition of metallic alloy nanoparticles

http://pubs.acs.org/doi/abs/10.1021/acsnano.5b08057

XRD with quantitative Phase analysis (eg by Rietveld Method) of your powders is also an option. taking under consideration that your Material is fully crystalline ( no amorphous amount). Take care for sample preparation by grinding to adequate particle size of your powders befördert you do powder diffraction and analysis.

X-ray diffraction

(XRD) is routinely employed to characterize the phase

composition and percent crystallinity

If you know the densities of the metal and the oxide separately, you could measure the density of your mixture.