Integrated sample desalting, enrichment, and ionization on an omniphobic glass slide for direct mass spectrometry...

Direct and rapid mass spectrometry (MS) analysis is desired for many applications including environmental monitoring, forensic analysis, chemical and biological defense, and point-of-care testing. However, sample pretreatment is often necessary for analyzing targets from complex matrices using MS due to ion suppression. To achieve rapid MS analysis calls for simple and efficient solutions for sample processing and ionization. Here, a simple sample pretreatment and ionization workflow is reported, which achieves sample desalting, enrichment, and ionization on a single glass slide.

Desalting is achieved based on crystallization and re-dissolution-induced spontaneous separation of analytes and salt. Efficient sample enrichment is achieved during the crystallization process by modifying the glass surface with an omniphobic coating. Finally, vibrating sharp-edge spray ionization is employed to ionize the target molecules directly on the glass slide. Thus, all the necessary sample operations prior to MS analysis are completed on the sample glass slide.

Efficient sample enrichment on the omniphobic glass slide is first visualized using food dyes. The benefits of the desalting and enrichment steps for detecting macrolide antibiotics in 1× phosphate buffered saline (PBS) solutions are demonstrated by comparing samples with different treatment procedures. Finally, quantification of macrolide antibiotics from PBS and serum samples is demonstrated. A linear range between 2 nM and 10 μM has been achieved for the serum sample with a limit of detection of 1 nM.

A simple, flexible, low-cost, and highly integrated workflow for detecting target molecules from complex matrices using MS is demonstrated. This method will be valuable to many applications that require rapid and efficient MS analysis of complex samples.