Analytical method for predicting interference in ion mobility spectrometric detection of drug compounds with phthalates

In ion mobility spectrometry (IMS), ions are distinguished by their mobility through a gas, which depends on their size, shape, and charge. Ions with very similar reduced ion mobility ( K o ) values are not separated. This technique is widely used for the onsite detection of drug compounds. However, the presence of phthalates can interfere with IMS-based detection of drug compounds because some of them may have K o values similar to those of drug compounds. In this study, the interference of phthalates in the IMS detection of drug compounds was investigated using drug compounds and phthalates in the molecular weight range of 134–335 g mol −1 . The relationships between K o and the m / z value, collision cross section ( CCS ), maximum cross section ( CS max ), and minimum cross section ( CS min ) of the product ions were examined. The CS max and CS min values were calculated from the energy-minimized structures of the ions. It was found that the m / z , CCS , and CS max values were not closely related to the K o value. However, the CS min values showed a strong correlation with the K o values, exhibiting excellent linear relationships with R 2 values of 0.997 for the drug compounds and 0.990 for the phthalates. By comparing the CS min values of drug compounds and phthalates, the probability of their peaks overlapping in the IMS spectra can be determined. For chemicals that are difficult to identify, the overlap of the peaks with the target chemicals can be determined using their CS min values.