Aflatoxin B1 (AFB1) is a common mycotoxin present in agricultural and food products. Therefore, rapid screening methods must be developed for AFB1 detection with high sensitivity and good selectivity. In this study, we developed an analytical method based on the combination of solid-phase microextraction (SPME) with carbon fiber ionization (CFI)-mass spectrometry (MS) to detect the presence of trace AFB1 from complex samples. A pencil lead (type 2B, length: ~2.5 cm) with a sharp end (diameter: ~150 μm) was used as the SPME fiber and the ionization emitter in CFI-MS analysis. Owing to the graphite structure of the pencil lead, AFB1 can be trapped on the pencil lead through π–π interactions. After adsorbing AFB1, the pencil lead was directly introduced in a pipette tip (length: ~0.7 cm; tip inner diameter: ~0.6 mm), placed close (~1 mm) to the inlet of the mass spectrometer, and applied with a high voltage (−4.5 kV) for in situ AFB1 elution and CFI-MS analysis. A direct electric contact on the SPME-CFI setup was not required. Followed by the introduction of an elution solvent (10 μL) (acetonitrile/ethanol/deionized water, 2:2:1 (v/v/v)) to the pipette tip, electrospray ionization was generated from the elution solvent containing AFB1 for CFI-MS analysis. A reactive SPME-CFI-MS strategy was employed to further identify AFB1 and improve elution capacity using our approach. Butylamine was added to the elution solvent, which was then introduced to the pipette tip inserted with the SPME fiber. Butylamine-derivatized AFB1 was readily generated and appeared in the resultant SPME-CFI mass spectrum. The lowest detectable concentration against AFB1 using our approach was ~1.25 nM. Our method can distinguish AFB1 from AFG1 in a mixture and can be used for the detection of trace AFB1 in complex peanut extract samples.

The purpose of this study was to evaluate the total phenolic and flavonoid contents in acid methanol extracts of 19 plant species grown and used in Taiwan. The antioxidant activity of leafy plant extracts was determined by measuring the trolox equivalent antioxidant capacity (TEAC), oxygen radical absorption capacity (ORAC), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. Polyphenol, flavonol, and flavonoid levels were high in Sonchus oleraceus (SO), Ohwia caudate Thunb. Ohashi (OC), Foeniculum vulgare Mill. (FV), and Artemisia princeps Pamp. var. orientalis (Pamp.) Hars. (ArP, fresh) as compared to the rest of tested plants. In addition, quercetin, myricetin, and morin were abundant in Dendranthe mamori folium (Ramat.) Tzvelev. (DM, dry), FV, SO, Alternanthera philoxeroides (Moq.) Griseb. (AlP), ArP (fresh) and Lonicera japonica Thunb. (LJ). Higher levels of the TEAC, ORAC, and DPPH radical scavenger were generated from extracts of OC, SO, DM (dry), and ArP (fresh). Significant and positive correlations among antioxidant activity and polyphenols and anthocyanidins were observed. ORAC values were also correlated with quercitin and morin. Therefore, these phytochemicals were some of the main components responsible for the antioxidant efficacy of tested plants.

This study demonstrated a facile ionization method with the use of real samples for the ionization of their main compositions at ambient conditions for mass spectrometric analysis. Analyte ions derived from the real samples were readily observed in the mass spectrum when placing the samples close (≤1 mm) to the inlet of the mass spectrometer applied with a high voltage. No additional accessories such as an ionization emitter, a plasma generator, or a high voltage power supply were required for this approach. Ionization of semivolatiles derived from the samples occurred between the samples and the inlet of the mass spectrometer presumably owing to the dielectric breakdown induced by the electric field provided by the mass spectrometer. Real samples including plants, medicine tablets, and gloves with contaminants were used as the model samples. The putative ionization mechanisms are also discussed in this study.

Tetracycline (TC) is an antibiotic that has been widely used in the animal husbandry. Thus, TC residues may be found in animal products. Developing simple and sensitive methods for rapid screening of TC in complex samples is of great importance. Herein, we demonstrate a fluorescence-sensing method using Zn2+ as sensing probes for the detection of TC. Although TC can emit fluorescence under the excitation of ultraviolet light, its fluorescence is weak because of dynamic intramolecular rotations, leading to the dissipation of excitation energy. With the addition of Zn2+ prepared in tris(hydroxymethyl)amino-methane (Tris), TC can coordinate with Zn2+ in the Zn2+-Tris conjugates to form Tris-Zn2+-TC complexes. Therefore, the intramolecular motions of TC are restricted to reduce nonradiative decay, resulting in the enhancement of TC fluorescence. Aggregation-induced emission effects also play a role in the enhancement of TC fluorescence. Our results show that the linear dynamic range for the detection of TC is 15–300 nM. Moreover, the limit of detection was ~7 nM. The feasibility of using the developed method for determination of the concentration of TC in a complex chicken broth sample is also demonstrated in this work.

No abstract