MALDI MS and ICP MS Detection of a Single CE Separation Record: A Tool for Metalloproteomics

Abstract

In this work, a novel approach based on off-line coupling of a single run of capillary electrophoresis (CE) separation to both matrix-assisted laser desorption/ionization (MALDI) and substrate-assisted laser desorption inductively coupled plasma (SALD ICP) mass spectrometry (MS) is presented. Using a liquid junction and subatmospheric deposition chamber, CE fractions were extracted from a separation capillary and collected as 20-nL droplets on a custom-built polyethylene terephthalate glycol (PETG) target plate coated with a 10-nm gold layer which guaranteed compatibility with both MALDI and SALD ICP techniques. The MALDI matrix solution was then added to the produced spots. After it was dried, the separation record was consecutively analyzed in MALDI MS and ICP MS instruments. Thus, both proteomic and metallomic information was obtained off-line from a single CE run. The concept was demonstrated by the analysis of a mixture of rabbit liver metallothionein isoforms. In an additional study, the droplets representing the archived separation record were alternately mixed with two different MALDI matrices to obtain complementary information on both the apoproteins and their complexes with metals from a single separation run. The presented technique is a viable alternative to online coupling of column separation to electrospray MS and nebulizer ICP MS.

LC coupled to ESI, MALDI and ICP MS – A multiple hyphenation for metalloproteomic studies

“…In our previous design, polyethylene terephthalate glycol (PETG) coated with~10 nm gold layer was used to ensure compatibility with both SALD ICP MS and MALDI MS processes [29]. Here, we tested the feasibility of a commercial MALDI target made of a conductive plastic.…”

“…A high concentration of methanol or acetonitrile enhances the ESI process, but, in the case of ICP MS, adversely increases instability of plasma and leads to carbon deposition on the sampling cone and torch [28]. The presence of a buffer is necessary for LC separation of biomolecule-metal complexes to maintain the metal-protein integrity and stability [28,29]; at the same time, additives and buffers have a significant effect on both ICP and ESI processes.…”

“…The off-line hyphenation of a single CE separation run to MALDI and SALD ICP MS has already been presented in our previous work [29]. Due to an inability to split the effluent in capillary electrophoresis, the off-line coupling was performed using a liquid junction and a subatmospheric deposition chamber.…”

“…Due to an inability to split the effluent in capillary electrophoresis, the off-line coupling was performed using a liquid junction and a subatmospheric deposition chamber. The flow from the liquid junction was deposited on a target inside the chamber, preserving a high separation efficiency of CE [29,30]. The off-line arrangement overcame the major practical difficulties arising from multiple hyphenation, compatibility of the separation eluent with both detection techniques and the necessity of having both spectrometers side by side.…”

Atomic Spectrometry Update: review of advances in elemental speciation

“…Tomolova et al 215,216 have developed an off-line coupling interface for CE separations which utilized a liquid junction and sub-atmospheric deposition chamber to collect fractions of CE effluent on to disposable PETG targets plated with a thin gold lm, making them usable for both MALDI and SALD ICP MS analyses aer covering with a solution of MALDI matrix. Certainly the coupling of LA sample introduction to both elemental and molecular MS has numerous applications in the area of bioimaging.…”