FIELD: oil analysis. SUBSTANCE: content of metallic porphyrins in oil and products of oil refining is found by optical density of characteristic bands in absorption spectra of analytical concentrates with due account of background absorption of accompanying non-porphyrin components. In this case background absorption of metallic porphyrin on characteristic length of wave is determined either graphically or by calculation by intensity of absorption in three reference points of background curve by means of conversion of system of coordinates to its semi-logarithmic form in which curve of background absorption is converted to straight line and by inverse conversion of system. EFFECT: decreased determination error. 3 cl, 2 dwg
