3D-Printed Paper Spray Ionization Cartridge with Fast Wetting and Continuous Solvent Supply Features

We report the development of a 3D-printed cartridge for paper spray ionization (PSI) that can be used almost immediately after solvent introduction in a dedicated reservoir and allows prolonged spray generation from a paper tip. The fast wetting feature described in this work is based on capillary action through paper and movement of fluid between paper and the cartridge material (polylactic acid, PLA). The influence of solvent composition, PLA conditioning of the cartridge with isopropanol, and solvent volume introduced into the reservoir have been investigated with relation to wetting time and the amount of solvent consumed for wetting. Spray has been demonstrated with this cartridge for tens of minutes, without any external pumping. It is shown that fast wetting and spray generation can easily be achieved using a number of solvent mixtures commonly used for PSI. The PSI cartridge was applied to the analysis of lidocaine from a paper tip using different solvent mixtures, and to the analysis of lidocaine from a serum sample. Finally, a demonstration of online paper chromatography–mass spectrometry is given

Boron-Doped Diamond Electrodes for the Electrochemical Oxidation and Cleavage of Peptides

Electrochemical oxidation of peptides and proteins is traditionally performed on carbon-based electrodes. Adsorption caused by the affinity of hydrophobic and aromatic amino acids toward these surfaces leads to electrode fouling. We compared the performance of boron-doped diamond (BDD) and glassy carbon (GC) electrodes for the electrochemical oxidation and cleavage of peptides. An optimal working potential of 2000 mV was chosen to ensure oxidation of peptides on BDD by electron transfer processes only. Oxidation by electrogenerated OH radicals took place above 2500 mV on BDD, which is undesirable if cleavage of a peptide is to be achieved. BDD showed improved cleavage yield and reduced adsorption for a set of small peptides, some of which had been previously shown to undergo electrochemical cleavage C-terminal to tyrosine (Tyr) and tryptophan (Trp) on porous carbon electrodes. Repeated oxidation with BDD electrodes resulted in progressively lower conversion yields due to a change in surface termination. Cathodic pretreatment of BDD at a negative potential in an acidic environment successfully regenerated the electrode surface and allowed for repeatable reactions over extended periods of time. BDD electrodes are a promising alternative to GC electrodes in terms of reduced adsorption and fouling and the possibility to regenerate them for consistent high-yield electrochemical cleavage of peptides. The fact that OH-radicals can be produced by anodic oxidation of water at elevated positive potentials is an additional advantage as they allow another set of oxidative reactions in analogy to the Fenton reaction, thus widening the scope of electrochemistry in protein and peptide chemistry and analytics

Effect of iTRAQ Labeling on the Relative Abundance of Peptide Fragment Ions Produced by MALDI-MS/MS

The identification of proteins in proteomics experiments is usually based on mass information derived from tandem mass spectrometry data. To improve the performance of the identification algorithms, additional information available in the fragment peak intensity patterns has been shown to be useful. In this study, we consider the effect of iTRAQ labeling on the fragment peak intensity patterns of singly charged peptides from MALDI tandem MS data. The presence of an iTRAQ-modified basic group on the N-terminus leads to a more pronounced set of <i>b</i>-ion peaks and distinct changes in the abundance of specific peptide types. We performed a simple intensity prediction by using a decision-tree machine learning approach and were able to show that the relative ion abundance in a spectrum can be correctly predicted and distinguished from closely related sequences. This information will be useful for the development of improved method-specific intensity-based protein identification algorithms

A New Strategy To Stabilize Oxytocin in Aqueous Solutions: II. Suppression of Cysteine-Mediated Intermolecular Reactions by a Combination of Divalent Metal Ions and Citrate

A series of studies have been conducted to develop a heat-stable liquid oxytocin formulation. Oxytocin degradation products have been identified including citrate adducts formed in a formulation with citrate buffer. In a more recent study we have found that divalent metal salts in combination with citrate buffer strongly stabilize oxytocin in aqueous solutions (Avanti, C.; et al. <i>AAPS J.</i> <b>2011</b>, <i>13</i>, 284–290). The aim of the present investigation was to identify various degradation products of oxytocin in citrate-buffered solution after thermal stress at a temperature of 70 °C for 5 days and the changes in degradation pattern in the presence of divalent metal ions. Degradation products of oxytocin in the citrate buffer formulation with and without divalent metal ions were analyzed using liquid chromatography–mass spectrometry/mass spectrometry (LC–MS/MS). In the presence of divalent metal ions, almost all degradation products, in particular citrate adduct, tri- and tetrasulfides, and dimers, were greatly reduced in intensity. No significant difference in the stabilizing effect was found among the divalent metal ions Ca²⁺, Mg²⁺, and Zn²⁺. The suppressed degradation products all involve the cysteine residues. We therefore postulate that cysteine-mediated intermolecular reactions are suppressed by complex formation of the divalent metal ion and citrate with oxytocin, thereby inhibiting the formation of citrate adducts and reactions of the cysteine thiol group in oxytocin