The coincident measurement of both nuclear products at their complementary angles was used to determine6Li by the reactions6Li(d, α)4He and6Li(p, α)3He, and7Li by the reaction7Li(p, α)4He. Elemental lithium was determined in natural samples or samples of known isotopic composition. Isotopic analyses could be carried out over the entire range from 0 to 100 atom% with a relative standard deviation of about 4%. The CMCP technique is highly specific and effectively eliminates interference and background.