The signal response linearity in phthalates determination using ESI-MS method with the Loop injection technique

The possibility of using ESI-MS technique for the quantitative determination of six most commonly used phthalates (DMP, DnBP, BzBP, DEHP, DiNP, DiDP) was tested. The test was performed by using Loop technique for recording chromatogram obtained after the injection of different phthalates concentrations. The investigation was performed by determining the linear relationship between the concentration of phthalates and the peak areas in the chromatogram of mass range which corresponds to the molecular ion and ion adduct with sodium. The obtained results showed that there is linearity between the concentration of phthalates and peak areas in the chromatogram of monitoring molecular and adduct ions with sodium in case of DiNP (r > 0.999) and DMP (r > 0.999 for the molecular ion; r > 0.989 for the ion adduct with sodium). The results obtained for the molecular ion in DiDP case showed a better linear relationship than the ion adduct with sodium, while the results obtained for BzBP showed opposite values. The same correlation coefficients for both monitoring ions, molecular ion and ion adduct with sodium were obtained for DEHP (r = 0.98371 and 0.98962, respectively). The correlation coefficients DnBP showed lower values than other linear coefficients (r = 0.96034 and 0.94669, respectively). Although the signals of adduct ions with sodium are steady and intense, they are not reliable for quantification since the source of sodium ions is not defined and therefore, the actual amount of sodium in the sample may vary.