Quantification of a mixture of peptides in solution was achieved by disposable patterned hydrophilic chip based matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI MSI). Compared with other quantitative methods for peptides in solution, this method is label-free and does not require separation of the multiple components of the solution before analysis. Uniform hydrophilic spots and high mass accuracy measurements provided confident identification and quantitative analysis of imaged compounds. The linear correlation between concentration and grayscale of image in the range of 5 fmol/μL to 1 pmol/μL was obtained for all four peptides. Good sensitivity and excellent reproducibility were also achieved. The method expands the application of MALDI MSI from tissues to solutions.Label-free quantification of a peptide mixture in solution was achieved by disposable patterned hydrophilic chip based matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI MSI).

Primary aromatic amines (PAAs) are substances with toxicity and suspected human carcinogenicity. A facile method for highly sensitive detection of PAAs using surface-enhanced Raman spectroscopy (SERS) is reported. The immobilization of Au nanoparticles (AuNPs) on the glycidyl methacrylate–ethylene dimethacrylate (GMA-EDMA) materials makes the substrate a closely packed but not aggregated Au NP arrays which provides a prominent SERS enhancement. Four PAAs with different substituent groups, namely, p-toluidine, p-nitroaniline, benzidine and 4,4-methylene-bis-(2-chloroaniline) have been successfully identified and quantified. High sensitivity and good linear relationship between SERS signals and concentrations of PAAs are obtained for all four PAAs.The immobilization of Au nanoparticles (AuNPs) on the glycidyl methacrylate–ethylene dimethacrylate (GMA–EDMA) materials provides a prominent SERS enhancement. It has been successfully applied for the detection of four primary aromatic amines (PAAs).

•Matrix selection for polymer guanidine biocides characterization by MALDI–TOF MS was reported.•Different matrices were suitable for single polymer guanidines and oxygen-containing polymer guanidines.•Structural information of three polymer guanidine was analyzed from their best spectra.•Quantum chemical calculations were carried out to deduce the importance of PA in matrix selection.Due to the diversity of polymer materials, there is no universal approach in matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) to characterize a particular polymeric system. Three commercially available polymer guanidine biocides, Poly(hexamethylene guanidine) chloride (PHMG), Polyhexamethylene biguanide (PHMB), Poly-[2-(2-ethoxy)-ethoxyethyl]-guanidinium-chloride] (PEEG) were chosen for the investigation of matrix selection using MALDI–TOF MS. No unique matrix was found to satisfy all three guanidines because of the extra C-O bonds in PEEG. Sinapic acid (SA), α-Cyano-4-hydroxycinnamic acid (CHCA) seemed to be ideal for PHMG and PHMB, but 2-(4-Hydroxybenzeneazo)benzoic acid (HABA), 2,5-dihydroxybenzoic acid (DHB) were for PEEG. Proton affinities (PA) of the matrix and analyte were combined to explain this phenomenon. Matrices with lower PA were more sensitive for the polymer guanidine with lower PA.

We report on a microfluidic platform that integrates a winding microdroplet chip and a surface-enhanced Raman scattering (SERS) detection system for trace determination of crystal violet (CV). Colloidal silver was applied to generate SERS. Compared to the continuous flow microfluidic system, the microdroplet based detection described here effectively eliminates any memory effects. Effects of flow pattern, droplet size, surfactant, and position of detection were optimized. Under optimal conditions, there is a linear correlation between signal and the concentration of CV in the 10 nM to 800 nM range, with a correlation coefficient (R2) of 0.9967. The limit of detection in water is 3.6 nM.