Sample preconcentration in open microchannels combined with MALDI‐MS

Abstract

In this work, a method for preconcentrating samples in 1 cm long, 50-150 μm wide open microchannels is presented. Platinum electrodes were positioned at the channel ends, voltage was applied, and charged analyte was preconcentrated at the oppositely charged side during continuous supply of sample. The preconcentration was initially studied in a closed system, where an influence on the analyte position from a pH gradient, generated by water electrolysis, was observed. In the open channel, the analyte distribution after preconcentration was evaluated using MALDI-MS with the channel as MALDI target. MALDI matrix was applied with an airbrush or by electrospray matrix deposition and by using the latter technique higher degrees of crystallization in the channels were obtained. After preconcentrating a 1 nM cytochrome c solution for 5 min, corresponding to a supplied amount of 1.25 fmol, a signal on the cathodic channel end could be detected. When a solution of cytochrome c trypsin digest was supplied, the peptides were preconcentrated at different positions along the channel depending on their charge.

Computer simulations of sample preconcentration in carrier‐free systems and isoelectric focusing in microchannels using simple ampholytes

“…Fractionation of the peptides into two groups as predicted by computer simulation (Fig. 3C) was also observed in prefractionation experiments with a CytC trypsin digest [18]. The 1495 and 964 mass peptides (which have pI values around 4, see Table 2) were concentrated on the anodic side of the channel, whereas the 633, 778 and 1168 mass peptides (pI values around 10, Table 2) were concentrated on the cathodic side.…”

“…In order to compare experimental results from carrier‐free systems with simulation data, both the ideal case of CytC (model protein in experimental work ) dissolved in pure water (Fig. B) and CytC dissolved in water fortified with carbonic acid and/or salt were simulated (Fig.…”

“…Impurities originating from improperly cleaned labware and through leaking from disposable plasticware commonly used in the laboratory [27], were not considered. In order to compare experimental results from carrierfree systems with simulation data, both the ideal case of CytC (model protein in experimental work [18]) dissolved in pure water ( Fig. 2B) and CytC dissolved in water fortified with carbonic acid and/or salt were simulated (Fig.…”

Interface solution isoelectric focusing with in situ MALDI‐TOF mass spectrometry

“…However, to conjugate sIEF with MALDI‐TOF MS, it usually requires mobilization of focused bands to the outlet of the channel , which causes band broadening and loss of resolution . To avoid this problem, several recent research efforts have been carried out to promote in situ MALDI detection without mobilization, using microfabricated grooves with or without removable top cover layer as the separation channel . sIEF bands were dried or frozen‐dried on chips, and subjected to direct MALDI‐TOF MS analysis in the grooves.…”

Sample preconcentration from dilute solutions on micro/nanofluidic platforms: A review

“…The literature contains many proposals for sample preconcentration in micro/nanofluidic devices, including field amplified sample stacking (FASS) [11][12][13][14][15], isotachophoresis [16][17][18][19][20][21], electrokinetic trapping [22][23][24][25], micellar electrokinetic sweeping [26], chromatographic preconcentration [27,28], electrowetting [29], and membrane preconcentration [30,31]. Of these various techniques, electrokinetic trapping based on nanoporous charge-selective membranes [32][33][34][35][36][37][38][39] or nanofluidic channels [40][41][42][43][44] is one of the most commonly used for the detection of charged biomolecules. Electrokinetic trapping has several important advantages for the preconcentration of charged biological samples.…”