Abstract
A major problem limiting reproducible use of liquid extraction surface analysis (LESA) array sampling of dried surface-deposited liquid samples is the unwanted spread of extraction solvent beyond the dried sample limits, resulting in unreliable data. Here, we explore the use of the Droplet Microarray (DMA), which consists of an array of superhydrophilic spots bordered by a superhydrophobic material giving the potential to confine both the sample spot and the LESA extraction solvent in a defined area. We investigated the DMA method in comparison with a standard glass substrate using LESA analysis of a mixture of biologically relevant compounds with a wide mass range and different physicochemical properties. The optimized DMA method was subsequently applied to urine samples from a human intervention study. Relative standard deviations for the signal intensities were all reduced at least 3-fold when performing LESA-MS on the DMA surface compared with a standard glass surface. Principal component analysis revealed more tight clusters indicating improved spectral reproducibility for a human urine sample extracted from the DMA compared to glass. Lastly, in urine samples from an intervention study, more significant ions (145) were identified when using LESA-MS spectra of control and test urine extracted from the DMA. We demonstrate that DMA provides a surface-assisted LESA-MS method delivering significant improvement of the surface extraction repeatability leading to the acquisition of more robust and higher quality data. The DMA shows potential to be used for LESA-MS for controlled and reproducible surface extraction and for acquisition of high quality, qualitative data in a high-throughput manner.
Highlights
Liquid extraction surface analysis−mass spectrometry (LESA-MS) is an ambient mass spectrometry technique in which analytes are extracted from a surface by the formation of a liquid microjunction between the extraction solvent and the surface.[1]
All Relative standard deviations (RSD) were below 8% when extracted from the Droplet Microarray (DMA) while extraction from glass resulted in RSDs above 20% which is higher than the limit of the acceptable precision (15%) for an analytical method.[30]
Analytical replicates of a human urine control sample (n = 5) were dispensed at five locations on glass as well as on five DMA spots, and the dried urine spots were analyzed with liquid extraction surface analysis (LESA)-MS (Supplementary File 3)
Summary
Liquid extraction surface analysis−mass spectrometry (LESA-MS) is an ambient mass spectrometry technique in which analytes are extracted from a surface by the formation of a liquid microjunction between the extraction solvent and the surface.[1]. Repeatable probe solvent recovery as well as extraction efficiency could be optimized by designing a substrate surface, which confines both the liquid sample and the LESA extraction solvent within a consistent area We propose that these requirements can be met by using a platform for high-throughput cell screening called the Droplet Microarray (DMA; http://www.aquarray.com/). We compare the DMA high-throughput array to a standard glass microscope slide, which is often used as a substrate for LESA-MS,[3,4,7,12−22] to test the hypothesis that confining the sample as well as the extraction solvent in a defined area assists in obtaining repeatable solvent recovery leading to improved spectral reproducibility and multivariate modeling
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