Analysis of liquid samples by Low-Temperature Plasma Ionization Source-ion mobility spectrometry

Abstract

In this study, liquid pharmaceutical samples are analyzed using an ion mobility spectrometer (IMS) with the Low-Temperature Plasma Ionization Source (LTPI) for the first time, overcoming limitations for this system due to intense interaction with IMS cell without sample pre-preparation. The direct sample introduction or newer methods that were presented in recent years in the LTP-MS are useful in mass spectroscopy, but these methods are incompetent in IMS. In new LTP-IMS, first, the sample is vaporized, then transferred to the ionization source by the carrier gas, and finally ionized. The new method has several salient characteristics as follows in comparison to the other similar devices. A new efficient way for sample entering which needs less amount of sample, does not waste it and ionizes liquid samples without any preparation or pre-extraction because the ionization source can vaporize, desorb, and ionize the samples simultaneously. In this work, the IMS cell, LTP, and sample introduction system must sync together, so they were redesigned to eliminate incompatibilities. Afterward, to achieve the best response, before evaluating the device, all parameters consist of gas flow, voltage, frequency, exhaust diameter of source, and IMS cell parameters were optimized. Then several pharmaceutical samples, including Papaverine, Codeine, Caffeine, and Diethylamine were analyzed to evaluate the qualitative and quantitative characteristics of the device. The samples were dissolved in methanol and detected in a few seconds, with a low detection limit of 41.75 ng for Codeine, 7.50 ng, and 8.25 ng for Caffeine and Papaverine, respectively.