Settlement of the Sweet-spot Problem of MALDI Crystals Using Cyclodextrin-supported Matrix

Abstract

One of the problems of matrix-assisted laser desorption/ ionization (MALDI), the inhomogeneity of analytematrix mixed crystals, can be settled moderately by the clathration of organic matrices into a cyclodextrin cavity. The homogeneous distribution of matrix and analyte was confirmed by scanning electron microscopy (SEM) and position-dependent mass spectrometry.Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization method, which does not decompose analyte molecules during ionization. MALDI combined with mass spectrometry (MALDI-MS) has been widely used as a valuable tool for analysis in many research fields.1,2 Despite the widespread application, MALDI-MS has several drawbacks at the same time; inhomogeneity of the spatial distribution of matrix analyte crystals is one disadvantage. It requires searching for "sweet spots" to measure intense mass peaks. This sweet-spot problem has been discussed, and it was suggested that inhomogeneous incorporation of analyte in matrix crystals is one of the reasons.3 By using imaging methods, inhomogeneity of the spatial distribution of analyte has been discussed. 47 Nishikaze et al. reported that the sweet spot for measuring glycopeptides was related to crystal polymorphs of a matrix molecule (2,5-dihydroxybenzoic acid; DHBA), which was confirmed by Raman spectra of the matrix. 8 It was reported that making a comatrix with glycerol efficiently improves spatial distribution of matrixanalyte crystals. Fluorescent-labeled analytes have been also used.9 Recently, we have reported that the clathration of matrices into cyclodextrins (CD-supported matrix) leads to observation of only the peak of protonated analyte. 10 We also found that CD-supported matrix made lowmolecular-weight mass regions almost transparent by preventing the dissociation of matrix molecules.11 In this paper, we report that the above sweet-spot problem in MALDI can be also settled moderately by using CD-supported matrices.Matrices, DHBA, 2,4,6-trihydroxyacetophenone (THAP), and 2,4-dihydroxyacetophenone (DHAP), were purchased. ¢-Cyclodextrin (¢CD) was dissolved in distilled water to a concentration of 10 mM. The matrix was dissolved in a mixture of acetonitrile and water (7:3 in volume) containing trifluoroacetic acid (TFA, 0.1% in volume), and a 75 mM solution was obtained. The solutions (150¯L of ¢CD and 20¯L of THAP (DHAP)) were pipetted into a vial, and the mixture was sonicated to form a CD-supported matrix. A 0.1 mg mL ¹1 of analyte solution was also prepared. One microliter each of the CD-supported matrix and the analyte solution was pipetted onto a stainless steel plate, left in air for few minutes to evaporate the solvent, and then analyzed by a homemade mass spectrometer 10 with the fourth harmonics generation of a Nd:YAG laser (266 nm, 10 Hz, 5 ns, and 10¯J). Each mass spectrum was obtained by averaging 64 continuous scans. The morphology of the matrixanalyte mixture was monitored by SEM (JSM-6100, JEOL). Figure 1a shows a SEM image of mixed crystals of an analyte (substance P; Su...

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2013–2014

“…Experiments were performed with DHB and THAP. With DHB, in particular, strong signals from the ring of crystals around the periphery of the sample spot were replaced by high quality spectra from all areas of the target (Fujita & Fujino, ). As an example of the use of this method, a mixture of CD and THAP has been used for analysis of low molecular weight drugs as [M + H] + ions with complete suppression of the [M + Na] + and [M + K] + ions (Yonezawa et al, ).…”

Amorphous Conjugated Polymers as Efficient Dual‐Mode MALDI Matrices for Low‐Molecular‐Weight Analytes

“…in the low mass range (m/z≤1000 Da), often complicating or preventing LMWC analytics. A number of approaches were explored to avoid intense matrix signal generation by SOMs, e. g. matrix suppression effects, cyclodextrin‐supported 2,5‐DHB matrix, improved reactive functional groups, and chemical derivatization . Also, new classes of matrix systems were developed and successfully established, e. g. nanoparticles, ionic liquids, graphene, doped graphene, graphene oxides, graphite (GALDI‐MS), metal oxides, mostly targeting polar and non‐polar, biochemical LMWCs (e. g. amino acids, nucleosides, steroids, etc.…”

Analyses of functional polymer-modified nanoparticles for protein sensing by surface-assisted laser desorption/ionization mass spectrometry coupled with HgTe nanomatrices

“…Accordingly, polydispersity is relatively easier to interpret from the MALDI-MS spectra of polymers [8,9]. The use of organic matrices in MALDI-MS can, however, result in an inhomogeneous distribution of analyte crystals, leading to poor reproducibility [10,11]. In addition, polymers subjected to highpower UV-laser irradiation in MALDI-MS can undergo undesirable fragmentation [12][13][14].…”