New urea-modified paper substrate for enhanced analytical performance of negative ion mode paper spray mass spectrometry.

Electrospray ionization mass spectrometry (ESI-MS) analysis in the negative ion mode is adversely affected by ionization suppression caused by electrical discharge and the presence of salts. Paper spray mass spectrometry (PS-MS) also suffers from the above phenomenon, being built on principles similar to those of ESI. Herein, we report the use of a paper substrate modified by 1-[3-(trimethoxysilyl)propyl]urea to improve the sensitivity of quantitative PS-MS analysis in the negative ion mode. The obtained results demonstrated that the urea modified paper substrate can effectively bind anions and highly polar compounds in the sample solution, decreasing competitive ionization in the negative ion mode of PS-MS and significantly reducing the signal intensity of Cl- adducts. In addition, the analyte responses were also significantly improved owing to the decreased electrical discharge observed for the less polar surface to decrease electrical discharge. Compared to non-modified PS-MS, urea-modified PS-MS exhibits a much higher sensitivity, showing 2-109 times improved signal-to-noise ratio (S/N). In real sample analysis, the limits of detection (LODs) of salicylic acid in urine and terpene lactones in Ginkgo biloba extract (EGb) were improved 10-fold and 2-40-fold, respectively, compared to that of non-modified PS-MS.

Rapid analysis of Callicarpa L. using direct spray ionization mass spectrometry.

Direct spray such as leaf spray and paper spray ionization mass spectrometry (MS) is a powerful type of ambient MS for phytochemical analysis. In this paper, direct spray MS methods to rapidly distinguish and analyze five species of Callicarpa L. have been developed. To distinguish species, leaf spray MS was employed to directly analyze leaves. A small triangular leaf sample was wetted with 15 µL of spray solvent and a high DC voltage was then simply applied to the wet leaf sample, which was positioned in front of the inlet of a mass spectrometer to produce electrospray ionization. The MS signals of phenylpropanoid glycosides, i.e. forsythiaside B, poliumoside, verbascoside in leaves could be sensitively detected. The content characteristics of the phenylpropanoid glycosides in five species including Callicarpae kwangtungensis Folium, Callicarpae macrophyllae Folium, Callicarpa nudiflora Folium, Callicarpae formosanae Folium, Callicarpa longissima Folium could be used to distinguish them, then the mass spectra of the Callicarpa L. samples were analyzed using principal component analysis(PCA) or partial least squares-discriminant analysis(PLS-DA). For the rapid semi-quantitative analysis, of phenylpropanoid glycosides in leaves, paper spray MS was employed to determine phenylpropanoid glycosides in the extracts of Callicarpa L. leaves. Ginsenoside Rg1 was selected as an internal standard (I.S.). The calibration curves were constructed through ratios of target ion abundance to I.S. ion abundance vs. concentration of targets. The linearity range was 8-250 µg/mL (R(2)=0.9947) for forsythiaside B, 9-280 µg/mL (R(2)=0.9939) for verbascoside, and 9-260 µg/mL (R(2)=0.9917) for poliumoside, respectively. The limit of detection (LOD) was 1 µg/mL, 0.5 µg/mL and 1 µg/mL for forsythiaside B, verbascoside, and poliumoside, respectively.