Graphene was dispersed in an aqueous solution with poly(sodium 4-styrenesulfonate) as a dispersant. The charge of the graphene came to be apparently negative by the adsorption of poly(4-styrenesulfonate) ion (PSS). Two kinds of PSS were examined: the average molecular masses of 70,000 and 1,000,000 (PSS 70,000 and PSS 1,000,000, respectively). Capillary electrophoresis was used to evaluate the dispersion of the apparently anionic graphene in an aqueous solution. A broad signal corresponding to the dispersed graphene was detected in the electropherograms. The effective electrophoretic mobility of the dispersed graphene was somewhat larger at higher concentrations of PSS 70,000, suggesting that the adsorbed amount of PSS 70,000 increased. Even when the separation buffer did not contain PSS, the broad signal of the anionic graphene was still detected. The peak height and/or the peak area, as well as the effective electrophoretic mobility of the graphene decreased little at the reduced applied voltages, i.e., at longer separation/detection time. Therefore, the adsorption of PSS is irreversible or the desorption of PSS from the graphene surface is very slow. Accordingly, the dispersed graphene with PSS would be separated from the matrix PSS by the electrophoretic separation.
Curcumin has been shown to be pharmacologically active in the prevention and treatment of various human diseases. In this study, we developed a fluorous derivatization method for selective analysis of curcumin with liquid chromatography (LC)tandem mass spectrometry (MS/MS). Curcumin was derivatized with the thiol-containing fluorous reagent (1H,1H,2H,2Hperfluoro-1-decanethiol) under mild conditions via Michael addition reaction, and the obtained derivative was introduced to a fluorous LC column (Fluofix-II 120E, 150 × 2.0 mm i.d., 5 μm, Wako). The selectively retained fluorous-derivatized curcumin on the column was also enabled highly sensitive detection with negative electrospray ionization MS/MS. Pretreatment of human serum sample was used protein precipitation with CH3CN. The linearity obtained by the present method showed good linearity (r2 = 0.9998) in the range of 7.4-442 ng/mL serum, and the limit of detection (S/N = 3) and limit of quantification (S/N = 10) were 1.8 ng/mL serum and 6.1 ng/mL serum, respectively. The present method was successfully applied to the analysis of curcumin in human serum sample.
A quality assessment method for eight commercially available optically active flavor compounds: menthol, menthyl acetate, perillaldehyde, 1,8-cineole, α-pinene, limonene, neomenthol, and neomenthyl acetate, was developed for commercial foods. The simultaneous determination of the eight flavor compounds and the optical purity test for the complete enantiomeric separation of each flavor compound were achieved by gas chromatography-mass spectrometry (GC/MS) equipped with a tandem capillary column consisting of a fused silica column (DB-17MS) coupled with a cyclodextrin chiral column (β-DEX). The extraction of the flavor compounds from the food samples was carried out by a multiple headspace (MHS) solid-phase microextraction (SPME) technique in order to improve the quantitativeness of SPME. Optimization of MHS-SPME using a mathematical technique with repeated extraction yielded the total peak area of each flavor compound and excellent recoveries from the food samples in three repeated measurements. Of the twelve commercial samples subjected to the optical purity test, some were found to have undesirable enantiomers that are not designated as flavor compounds by the Food Hygiene Law of Japan. The results show the efficiency of the developed method, and suggest a need to conduct further optical purity tests for the quality assessment of flavor compounds in commercial foods.
To construct liquid chromatography (LC)-based bioanalytical method for therapeutic monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs), twelve commercially available therapeutic mAbs and one ADC were chemically reduced, and the generated fragments were analyzed by high-temperature reversed-phase LC. For most therapeutic mAbs, single peaks of light and heavy chains were detected, indicating a possibility of homogeneous LC analysis using light chains. However, characteristic fragmentations were observed in infliximab, pembrolizumab, ramucirumab, and trastuzumab emtansine. We also performed a simple validation using the fragmented light chains for the bioanalysis of bevacizumab. The limit of detection (LOD) and limit of quantification (LOQ) of bevacizumab were 0.63 and 2.10 µg/mL, respectively, with dithiothreitol reduction, and 0.74 and 2.48 µg/mL, respectively, with tris (2-carboxyethyl) phosphine reduction. These results indicate that both the reductants confer sufficient linearity, LOQ, and LOD for the light chain analysis of bevacizumab. Thus, this method, combined with affinity purification, can be used for the bioanalysis of bevacizumab.