Method for quantitatively analyzing substances containing elements other than carbon, hydrogen and oxygen by (1) adsorbing such substances on a particulate, substantially dust and contaminant free carbonized product prepared by (A) first partially dehydrochlorinating a normally crystalline vinylidene chloride polymer at temperatures below the melting point of such polymer to an extent of at least about 5 percent of theoretical HCl loss, then (B) completing the dehydrochlorination of such material, in the substantial absence of oxygen, by heating the material to carbonizing temperatures of from about 600.degree.C to about 1200.degree.C; then (2) analyzing the substance adsorbed on such carbonized product.