MASS SPECTROMETRIC IDENTIFICATION OF METALLOPORPHYRINS IN SEDIMENTS AND ITS SIGNIFICANCE IN PETROLEUM GEOCHEMISTRY

This paper describes a process including: extraction of metalloporphyrins from sediments with 9:1(v/v)benzene and methanol mieture，separation using column chromatography,and purification using Thin Layer chromatography. The metallopor-phyrins were identified by- means of h1S, computer sy-stem.The results of this study-indicate the presence of two series of metalloporphv-tins, i. e. Ni-ETIO(or vo-ETIO)and Ni-DPEP(or vo一OPEP)in geologic samples. Average molecular weight and ranges of the two series of metalloporphytins, homologous compound ratios,skewness and band width of MS spectrum peaks for each of the serieswere calculated.The significance of these parameters in petroleum geochemistry is also discussed in detail.This paper also presents a useful method for mass spectrometric identi-fication of metalloporphytins.The authors believe that the geochemical significance of these parameters is as follows:(1)The significance of nickel and vanady-1 porphyrins on sedimentary facies:According to the analytical result，the porphyrins from the marine carbonate source rocks of southern China are mainly- composed of vanadyl porphyrin,and no nickel porphyrin is detected.While the samples recognized geologically as continental facies are mainly composed of nickel porphy-rin, and no vanady-1 porphyrin is detected.In addition, vanady1 porphyrin has a much broader range of molecular weight than nickel porphyrin.Thus，different porphyrins can be used as indicators of sedimentary facies.(2)The maturity- and evolution of organic matter:In geological body，the degree of transformation of the porphyrins from deoxophylloerythroetioporphyrin( DPEP) to etioporphyrin(ETIO)is proportiuual to heat history，temprcture, pressure and time.Therefore，We can use series ratio, i.e.ΣIDPEP, ΣIETIO ratio, to reflect the mat:rity of organic matter.hor example, the series ratio for sample 1 is 1.24,that for sample 2 is 3.09.Sample 3 comes from the depth interval of 1615一1686m with immature hydrocarbons, while Sample 4 comes from the depth of 2200m with mature hydrocarbons.Their series ratios are 9.06 and 3.96 respectively.Furthermore.the molecular weight of the porphyrin and the relative content of low carbon numberporphyin also show a tendency relating to the heat evolution regularity of organicmatter.(3)Skewness of metalloporphyrins: fable 3 shows that sample 3 is an imma-Lure source rock, its skewness of ETIO series is negative, other samples are all positive for the ETIO series，and the skewness of DPEP series is all negative.Therefore，the polarity and value of skewness can be used as evolution and maturity-indicators to point out the evolutional tendency.(4)bass spectrometry of metalloporphyrin shows that the peak on the mass spectrogram is carbon number C₃₂ and that the chlorophylla being converted into DPEP is also carbon C₃₂.It is suggested that chlorophylla may be postulated as petro-porphyrin precursor.(5)Quantitative mass spectrometric analysis of metalloporphyrins can precisely provide the average molecular weight of porphyrins.Thus when porphyrins is quantified with UV一VIS spectrophotometer, the content of porphyrin can be calculated more correctly，if the data obtained from mass spectrometry are used。