Quantitative Measurement And Comparison Of Ion Suppression In Ambient Ionization Mass Spectrometry

Mass spectrometry could analyze a variety of molecules by transfering them into gas phase ions for detection.Due to its high sensitivity,high specificity,and high throughput,MS has been widely used in biomedicine,environmental investigation,food science,and pharmaceutical.Many researchers put their attentions on the development of new ionization sources.Many new ionization sources have been designed and applied on analyzing multiple components and complex matrix,such as urine,serum,blood and so on.But for those conventional ionization sources,such as ESI and MALDI,the ion suppression in analyzing complex sample limits their further applications in complex matrix.In order to decrease the ion suppression,GC-MS,LC-MS and CE are developed,and they have greatly promoted the analysis in complex matrix.,and by separating the different components,these techniques could significantly reduce the ion suppression.But the problem of time-consuming and still complicated sample pretreatments still needs to be solved.Ambient ionization is a kind of ionization source that has the advantages of in-situ,real-time,few sample pretreatment procedures.Since DESI,a typical and first ambient ionization,was invented by Cook's group,ambient ionization sources have caught people's increasing attention.So far,many in-situ,real-time,high-throughput and non-destruction ambient ionization technique have been developed for complex multiple-components analysis.Herein,DESI and PS were investigated.Desorption electrospray ionization(DESI)has the similar mechanism with ESI,after a sample extraction process before MS analyzing.Paper spray(PS),is another spray-based ambient ionization,which use solvent to extract sample molecules placed on paper substrate,and ionize sample under high voltage,similar to ESI.DESI and PS have been used to analyze varied compounds in different kinds of matrix,like urine and serum.It has been declared these two ionization sources function better than ESI in multiple compounds,especially in biomatrix.This conclusion is speculated to be based on that DESI and PS has a lower ion suppression when the amount of interference is much more than analyte,due to the special extraction process.So far all works about ion suppression are focusing on how to reduce the ion suppression.Few work is trying to quantify the ion suppression or give out a method to measure the ion suppression for comparison or for optimizing.In this study,a quantified study using constant tioconazole and varied atenolol is performed to quantify the ion suppression for ESI,PS and DESI-MS by the signal loss of constant tioconazole with increasing concentration of atenolol.First we quantified and compared the ion suppression for PS and ESI in order to prove this method functions well.Second we quantified and compared the ion suppression for DESI and ESI to prove DESI is better than ESI in ion suppression.We also studied the ion suppression for DESI and ESI with varying parameters(flow rate,solvent components,capillary inner diameter,DESI substrates).A CTVA mixture was used in this work to measure the ion suppression of DESI,PS,ESI,and prove that DESI and PS have a better ion suppression effect than ESI.This quantificational method could evaluate the ion suppression of any ionization source,theoretically.And we believe that this method would help other researchers to choose appropriate ionization technique for sample analysis in complex matrix.