Without any sample pretreatment, trace amounts of melamine in various milk products were rapidly detected noting the characteristic fragments (i.e., m/z 110, 85, and 60) in the MS/MS spectrum of protonated melamine molecules (m/z 127) recorded by using surface desorption atmospheric pressure chemical ionization mass spectrometry. Signal responses of the most abundant ionic fragment (m/z 85) of protonated melamine were well correlated with the amounts of melaime in milk products, showing a dynamic range about 5 orders of magnitude. The limit of detection (LOD) was found to be 3.4 x 10(-15) g/mm(2) (S/N = 3) for the detection of pure melamine deposited on the paper surface, which was much lower than that for detection of melamine in powdered milk (1.6 x 10(-11) g/mm(2), S/N = 3) or liquid milk (1.3 x 10(-12) g/mm(2), S/N = 3). The significant difference in LOD was ascribed to the relatively strong molecular interactions between melamine and the matrix such as proteins in the milk products. As demonstrated using desorption electrospray ionization (DESI) for melamine detection, weakening the molecular interaction between analytes and proteins is proposed as a general strategy to improve the sensitivity of ambient mass spectrometry for direct detection of analytes bound in protein matrixes. The relative standard deviation (RSD) and the recovery of this method were found to be 5.2 approximately 11.9% and 87 approximately 113%, respectively, for the detection of melamine in milk products. A single sample analysis was completed within a few seconds, providing a particularly convenient way to rapidly screen melamine presence in milk products.

Electrospray ionization (ESI) is a mass spectrometric technique widely used in various fields including chemistry, biology, medicine, pharmaceutical industry, clinical assessment, and forensic science. In this study, we report a simple and economical ESI-mass spectrometry (MS) technique, which makes use of disposable wooden tips (wooden toothpicks) for loading and ionization of samples. Samples could be loaded by normal pipetting onto the tip or simply dipping the tip into sample solutions. The hydrophilic and porous nature of wood allows effective adhesion of the sample solution for durable ion signals. The tip can be directly connected to nano-ESI ion sources of various mass spectrometers. Upon application of high voltage to the tip, desirable mass spectra could be obtained. We demostrated that this new technique is applicable for analysis of various samples, including organic compounds, organometallic compounds, peptides, proteins, and samples that cannot be directly analyzed by conventional ESI techniques, e.g., slurry samples and powder samples. The slim and hard properties of the wooden tip enable sampling from specific locations such as corners and small openings, indicating potential applications of the new technique in forensic investigations. The observation of electrospray ionization from wooden materials also allows us to get new insights into the materials that can be directly ionized for mass spectrometric analysis.

The adsorption of methylene blue (MB) from aqueous solution on a HKUST-1/GO (MOFs : HKUST-1) composite was studied in view of the adsorption isotherm, kinetics and regeneration of the sorbent.The adsorption isotherms of methylene blue (MB) on the HKUST-1/GO composite followed both the Freundlich isotherm and the Langmuir isotherm. Adsorption kinetics and thermodynamic parameters were determined from the experimental data. The used HKUST-1/GO could be regenerated by acetone, so it can be recycled for reuse. The high adsorption capacity and excellent reusability make HKUST-1/GO attractive for the removal of MB from aqueous solution.

Extractive electrospray ionization (EESI) is a powerful ambient ionization technique that can provide comprehensive mass spectrometric (MS) information on aerosols, complex liquids, or suspensions without any sample pretreatment. An understanding of the EESI mechanism is critical for defining its range of application, the advantages, and limitations of EESI, and for improving its repeatability, sensitivity, and selectivity. However, no systematic study of EESI mechanisms has been conducted so far. In this work, fluorescence studies in the EESI plume using rhodamine 6G and H-acid sodium salt directly demonstrate that liquid-phase interactions occur between charged ESI droplets and neutral sample droplets. Moreover, the effect of the composition of the primary ESI spray and sample spray on signals of the analyte in EESI-MS was investigated systematically. The results show that the analyte signals strongly depend on its solubility in the solvents involved, indicating that selective extraction is the dominant mechanism involved in the EESI process. This mechanistic study provides valuable insights for optimizing the performance of EESI in future applications.