Search

In this note, we report that high quality ganglioside profiles with minimal loss of sialic acid residues can be obtained in the positive ion mode by using a 5-methoxysalicylic acid (MSA) matrix for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Our results showed that MSA produced much less sialic acid losses from gangliosides than DHB, although MSA and DHB are differ only by their functional groups at their 5-positions (-OH for DHB and -OCH for MSA). Furthermore, our data also demonstrated that addition of an alkali metal additive was effective for simplifying ganglioside profiles, but not necessary for stabilizing glycosidic bonds of gangliosides if MSA was used as a matrix. This suggests that MALDI MS with MSA has a potential to gain additional benefits from the positive-ion mode analyses without losing performance in ganglioside profiling. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

RATIONALE: Quantifying polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) with a conventional crystalline matrix generally suffers from poor sample-to-sample or shot-toshot reproducibility. An ionic-liquid matrix has been demonstrated to mitigate these reproducibility issues by providing a homogeneous sample surface, which is useful for quantifying polymers. In the present study, we evaluated the use of an ionic liquid matrix, i.e., 1-methylimidazolium α-cyano-4-hydroxycinnamate (1-MeIm-CHCA), to quantify polyhexamethylene guanidine (PHMG) samples that impose a critical health hazard when inhaled in the form of droplets. METHODS: MALDI-TOF mass spectra were acquired for PHMG oligomers using a variety of ionic-liquid matrices including 1-MeIm-CHCA. Calibration curves were constructed by plotting the sum of the PHMG oligomer peak areas versus PHMG sample concentration with a variety of peptide internal standards. RESULTS: Compared with the conventional crystalline matrix, the 1-MeIm-CHCA ionic-liquid matrix had much better reproducibility (lower standard deviations). Furthermore, by using an internal peptide standard, good linear calibration plots could be obtained over a range of PMHG concentrations of at least 4 orders of magnitude. CONCLUSIONS: This study successfully demonstrated that PHMG samples can be quantitatively characterized by MALDI-TOFMS with an ionic-liquid matrix and an internal standard. [ABSTRACT FROM AUTHOR]

This paper reviews the application of ambient desorption/ionization (ADI) mass spectrometry (MS) to the direct analysis of solid materials. First, ADI methods are introduced according to the sampling and desorption processes, including liquid extraction, plasma desorption, thermal desorption, and laser ablation/desorption, along with their practical features and limitations in the direct analysis of solid objects. Various cases of real-world analysis are also summarized: analysis of active compounds in pharmaceuticals and herbal medicines; analysis of food products for quality control and origin tracking; forensic analysis for sexual assault crimes, explosives, and illicit drug abuse; and surface contaminant analysis for food and environmental safety control. An overview of relevant discussions shows that ADI-MS techniques allow the direct desorption and ionization of analytes from untreated samples under ambient conditions, resulting in tremendous improvements in efficiency in speed and procedural simplicity. • Ambient desorption/ionization (ADI) methods enable fast direct MS analysis of solid materials with minimal sample preparation. • Features and limitations of each ionization technique in direct solid material analysis are discussed. • Applications in pharmaceutical, food, herbal, forensic, and environmental analyses are presented. [ABSTRACT FROM AUTHOR]

Arginine residues in a protein can be enzymatically deiminated to citrulline residues, and this post-translational modification of proteins, called citrullination, has been known to be associated with autoimmune diseases such as rheumatoid arthritis. Since citrullination of an arginine residue causes a mass shift of only 1 Da, isotopic distribution patterns of citrullinated and its control (non-citrullinated) peptides overlap each other, and the resulting isotopic pattern is skewed with respect to that of the control peptide. Recently, Deforce and coworkers utilized the citrullination-induced skewed isotopic patterns for estimating the extent of citrullination ( J. Proteome Res. 2012, 11, 5245). However, electrospray ionization ( ESI), which Deforce and coworkers employed, is not fully suitable for this type of quantification because the number of potential charge sites on a citrullinated peptide is less than that on its control peptide and this leads to different ion abundances for a given charge state. In this study, we employed matrix-assisted laser desorption/ionization ( MALDI) instead of ESI for quantification of citrullination because the preference for singly charged ion formation by MALDI may overcome the aforementioned issue. Our results show that the isotopic patterns generated by MALDI time-of-flight ( TOF) mass spectrometry ( MS) reflect the citrullination contents better than those generated by ESI linear ion trap ( LIT) MS. [ABSTRACT FROM AUTHOR]

Abstract: Enzymatic conversion of arginine to citrulline by peptidyl arginine deiminase is associated with peptide presentation and development of autoimmunity in rheumatoid arthritis. In order to facilitate identification of the citrullination site, citrulline residue was modified using 4-bromophenyl glyoxal, and 194Da mass increase and incorporation of the Br signature were confirmed by MALDI-TOF MS. Using this approach, we identified four and five citrullination sites of bovine serum albumin and bovine fibrinogen, respectively. MALDI-TOF/TOF MS was used to unambiguously identify two citrullination sites from bovine fibrinogen. [Copyright &y& Elsevier]