Laser-Induced Microplasma as an Ambient Ionization Approach for the Mass-Spectrometric Analysis of Liquid Samples

Influence of ZnO morphology on the capability of portable paper-based electrospray ionization mass spectrometry to determine therapeutic drugs in complex matrices

Adsorbents play a significant role in enhancing the analytical sensitivity of target analytes in complex samples by mitigating matrix effects. In our recent report, ZnO stood out among various adsorbents to determine target therapeutic drugs in complex biological matrices when applied for portable paper-based electrospray ionization mass spectrometry (PPESI-MS). However, the influence of the morphology of ZnO on the performance of PPESI-MS is elusive. Herein, different morphologies of ZnO particles were prepared via co-precipitation or ultrasonic methods, and their capability to determine different therapeutic drugs in serum were systemically investigated. The results demonstrated that flower-shaped ZnO gave a superior capacity, and its analysis sensitivity was 2.9-12.8-fold higher than those achieved with other ZnO morphologies. Further characterization revealed that the unique performance of flower-shaped ZnO was closely associated with its favorable desorption behavior to drugs, small spray plume, and few spray emitters at the tip of coated paper substrate. To illustrate the potential of flower-shaped ZnO, its coated paper was used as a substrate for the determination of various drugs in complex matrices such as serum, and a limit of detection as low as 2 pg mL-1 was achieved. The corresponding recoveries ranged from 93.2% to 107.2%. The developed protocol is promising in high-sensitivity analysis of target drugs in complex sample matrices.

Nanospray Laser-Induced Plasma Ionization Mass Spectrometry for Rapid and Sensitive Analysis of Polycyclic Aromatic Hydrocarbons and Halogenated Derivatives

Polycyclic aromatic hydrocarbons (PAHs) and halogenated derivatives are a series of environmental pollutants with potential toxicity and health risks on biosystems and the ecosystem. Rapid and sensitive analysis of trace PAHs and halogenated PAHs in complex environmental samples is a challenging topic for analytical science. Here we report the development of a nanospray laser-induced plasma ionization MS method for rapid and sensitive analysis of trace PAHs and halogenated PAHs under ambient and open-air conditions. A nanospray tip was applied for loading samples and placed pointing to the MS inlet, being a nanospray emitter with the application of a high voltage. A beam of laser was focused to induce energetic plasma between the nanospray emitter and the MS inlet for ionization of PAHs and halogenated PAHs for mass spectrometric analysis. Meanwhile, an inner-wall naphthyl-coated nanospray emitter was developed and applied as a solid-phase microextraction (SPME) probe for highly selective enrichment of trace PAHs and halogenated PAHs in complex environmental samples, and some organic solvent was applied to desorb the analytes for nanospray laser-induced plasma ionization MS analysis. Satisfactory linearity for each target PAH and halogenated PAH was obtained, with correlation coefficient values (r) no less than 0.9917. The method showed extremely high sensitivity for analysis of trace PAHs and halogenated PAHs in water, with limits of detection (LODs) and quantification (LOQs) of 0.0001-0.02 and 0.0003-0.08 μg/L, respectively. By using the inner-wall naphthyl-coated nanospray laser-induced plasma ionization MS method, sensitive detection of trace PAHs and halogenated PAHs in real sewage and wastewater samples was successfully achieved.

Unsupervised Reconstruction of Analyte-Specific Mass Spectra Based on Time-Domain Morphology with a Modified Cross-Correlation Approach

Concomitant species that appear at the same or very similar times in a mass-spectral analysis can clutter a spectrum because of the coexistence of many analyte-related ions (e.g., molecular ions, adducts, fragments). One method to extract ions stemming from the same origin is to exploit the chemical information encoded in the time domain, where the individual temporal appearances inside the complex structures of chronograms or chromatograms differ with respect to analytes. By grouping ions with very similar or identical time-domain structures, single-component mass spectra can be reconstructed, which are much easier to interpret and are library-searchable. While many other approaches address similar objectives through the Pearson's correlation coefficient, we explore an alternative method based on a modified cross-correlation algorithm to compute a metric that describes the degree of similarity between features inside any two ion chronograms. Furthermore, an automatic workflow was devised to be capable of categorizing thousands of mass-spectral peaks into different groups within a few seconds. This approach was tested with direct mass-spectrometric analyses as well as with a simple, fast, and poorly resolved LC-MS analysis. Single-component mass spectra were extracted in both cases and were identified based on accurate mass and a mass-spectral library search.

Determination of monosaccharides hydrolyzed from polysaccharides in activated sludge by ion chromatography-mass spectrometry with online pretreatment of column switching technique

The simultaneous determination of monosaccharides present in the activated sludge would be crucial to understand the water treatment mechanism. Herein, an ion chromatography-mass spectrometry (IC-MS) with online pretreatment of column switching technique was proposed to analyze monosaccharides hydrolyzed from extracellular polysaccharides in the activated sludge. When the matrix was eliminated in the first dimension, monosaccharides were immediately identified by IC-MS. The improved ionization efficiency was achieved with the addition of T-joint prior to MS. During the performance test, our established method showed excellent detection limits ranging from 0.34 to 2.15 μg/L for all sugar targets. Great linearity (R ≥ 0.9955) was also achieved using this method in the range from 0.01 to 5 mg/L. Furthermore, the average recoveries were obtained between 84.82 and 113.46%. RSDs for peak areas and retention times were determined as 3.76% and 0.27%, respectively. Finally, this approach provided a rapid, convenient, and practical determination of monosaccharides in the activated sludge, which would be helpful for the analysis of monosaccharides derived from other biological samples.