The present invention relates to a complex comprising a transition metal cation (i); a ligand (ii) comprising at least one chelating group, preferably from 1 to 4 chelating groups, more preferred 2 or 3 chelating groups, wherein the chelating group(s) is/are selected from hydroxamate group —N(O″)—C(═O)—R, catechol ate group, carboxyl ate group, partly or totally protonated forms of these chelating groups and mixtures of these chelating groups and/or their partly or totally protonated forms, wherein R is hydrogen or a C1 to C5 alkyl group; and a magnetic bead (iii); wherein the magnetic bead (iii) and the ligand (ii) are covalently bonded. The invention also relates to the use of the complex for reduction of the content of at least one phosphor-oxy-substance, which preferably comprises a structural element —O—P(O″)(═O)—O— within its structure, in a fluid sample, as well as to a method for decreasing the content of at least one phosphor-oxy-substance, preferably a phospholipid, in a fluid sample, comprising a step of adding the complex. The invention further relates to a supernatant obtained or obtainable from this method and to the use of a supernatant obtained or obtainable from the method for qualitative and/or quantitative determination of at least one analyte in said supernatant. Furthermore, the invention relates to a method for qualitative and/or quantitative determination of at least one analyte in a fluid sample and to a method for determining the kind and/or amount of at least one phosphor-oxy-substance in a fluid sample.

The present invention relates to a complex comprising a transition metal cation (i); a ligand (ii) comprising at least one chelating group, preferably from 1 to 4 chelating groups, more preferred 2 or 3 chelating groups, wherein the chelating group(s) is/are selected from hydroxamate group N(O)C(O)R, catechol ate group, carboxyl ate group, partly or totally protonated forms of these chelating groups and mixtures of these chelating groups and/or their partly or totally protonated forms, wherein R is hydrogen or a C1 to C5 alkyl group; and a magnetic bead (iii); wherein the magnetic bead (iii) and the ligand (ii) are covalently bonded. The invention also relates to the use of the complex for reduction of the content of at least one phosphor-oxy-substance, which preferably comprises a structural element OP(O)(O)O within its structure, in a fluid sample, as well as to a method for decreasing the content of at least one phosphor-oxy-substance, preferably a phospholipid, in a fluid sample, comprising a step of adding the complex. The invention further relates to a supernatant obtained or obtainable from this method and to the use of a supernatant obtained or obtainable from the method for qualitative and/or quantitative determination of at least one analyte in said supernatant. Furthermore, the invention relates to a method for qualitative and/or quantitative determination of at least one analyte in a fluid sample and to a method for determining the kind and/or amount of at least one phosphor-oxy-substance in a fluid sample.