Method for analyzing an API, medical food, a reagent, a food additive, a pharmaceutical composition or nutraceutical, wherein the API, the medical food, the reagent, the food additive, the pharmaceutical composition or nutraceutical comprise at least one compound with a molecular weight of at least 200, wherein the compound is a chemically complex molecule, wherein said chemically complex molecule is an inositol polyphosphate selected from the group containing from 2 to 6 phosphate groups including ions or salts thereof, wherein this compound can also be quantified together with its related impurities, wherein the method for analyzing comprises at least the following steps: i) preparing at least one standard sample, preferably of a known concentration or from a known concentration of the chemically complex molecule to be detected and/or quantified; ii) introducing the standard sample into the stream of a solvent system; wherein the solvent system comprises potassium hydroxide or sodium hydroxide, said sodium hydroxide optionally additivated with isopropanol; wherein the pH of at least one solvent which forms the solvent system has been buffered; iii) passing the sample and the solvent system through at least one ion-exchange chromatographic column of divinylbenzene polymer, while maintaining the pressure of the system between 5 and 1500 atm; iv) identifying the retention time and/or quantifying the intensity of the signal of when the chemically complex molecule is eluted, by means of a detector capable to detect the elution of the chemically complex molecule; v) preparing a sample of the chemically complex molecule from the API, a medical food, a reagent, a food additive, a pharmaceutical composition or nutraceutical comprising the chemically complex molecule to be detected and/or quantified, wherein the process to prepare the sample comprises at least dissolving totally or partially the API, a pharmaceutical composition or nutraceutical to form a solution or a slurry, and, if necessary, treating the solution or the slurry to remove particles in suspension; vi) repeating the steps (ii) and (iii) with the sample prepared in the step (v); together or sequentially with the standard; vii) detecting and/or quantifying the presence of the chemically complex molecule by comparison of retention time and/or intensity of signal of the standard sample or the standard samples. i) preparing at least one standard sample, preferably of a known concentration or from a known concentration of the chemically complex molecule to be detected and/or quantified; ii) introducing the standard sample into the stream of a solvent system; wherein the solvent system comprises potassium hydroxide or sodium hydroxide, said sodium hydroxide optionally additivated with isopropanol; wherein the pH of at least one solvent which forms the solvent system has been buffered; iii) passing the sample and the solvent system through at least one ion-exchange chromatographic column of divinylbenzene polymer, while maintaining the pressure of the system between 5 and 1500 atm; iv) identifying the retention time and/or quantifying the intensity of the signal of when the chemically complex molecule is eluted, by means of a detector capable to detect the elution of the chemically complex molecule; v) preparing a sample of the chemically complex molecule from the API, a medical food, a reagent, a food additive, a pharmaceutical composition or nutraceutical comprising the chemically complex molecule to be detected and/or quantified, wherein the process to prepare the sample comprises at least dissolving totally or partially the API, a pharmaceutical composition or nutraceutical to form a solution or a slurry, and, if necessary, treating the solution or the slurry to remove particles in suspension; vi) repeating the steps (ii) and (iii) with the sample prepared in the step (v); together or sequentially with the standard; vii) detecting and/or quantifying the presence of the chemically complex molecule by comparison of retention time and/or intensity of signal of the standard sample or the standard samples.