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An off-line two-dimensional high-speed counter-current chromatography method combined with gradient and recycling elution mode was established to isolate terpenoids and flavones from the leaves of Andrographis paniculata (Burm. f.) Nees. By using the solvent systems composed of n-hexane/ethyl acetate/methanol/water with different volume ratios, five compounds including roseooside, 5,4'-dihydroxyflavonoid-7-O-β-d-pyranglucuronatebutylester, 7,8-dimethoxy-2'-hydroxy-5-O-β-d-glucopyranosyloxyflavon, 14-deoxyandrographiside, and andrographolide were successfully isolated. Purities of these isolated compounds were all over 95% as determined by high-performance liquid chromatography. Their structures were identified by UV, mass spectrometry, and (1) H NMR spectroscopy. It has been demonstrated that the combination of off-line two-dimensional high-speed counter-current chromatography with different elution modes is an efficient technique to isolate compounds from complex natural product extracts.

A nanocomposite material consisting of a copper ion-based metal–organic gel (MOG-Cu) and multiwalled carbon nanotubes (MWCNTs) was prepared and served to construct a sensor for electrochemical detection of nitrite. The micromorphology of the MOG-Cu-MWCNT nanocomposite was characterized. The effects of MWCNT doping on the formation of a Cu-based MOG and its electrochemical property for nitrite electro-oxidation were evaluated. It shows that the optimal amount of MWCNTs does not influence the formation and nanofiber structure of the Cu-based MOG but can increase the electrochemical surface area and facilitate the interfacial charge transport. Hence, the oxidation current of nitrite at the MOG-Cu-MWCNT-coated glass carbon electrode (GCE) is considerably enhanced in contrast to the MOG-Cu/GCE. The analytical performances of the MOG-Cu-MWCNTs/GCE for electrochemical detection of nitrite were investigated. Operated in optimum conditions, the oxidation peak current at a potential of about 0.77 V versus a saturated calomel electrode shows direct proportion correlation with concentration of nitrite. The linear range is 0.3–100 μM. The sensor demonstrates fair anti-interference capacity, high sensitivity, a low detection limit (0.086 μM), satisfactory reproducibility, and storage stability, being a valuable tool for the electrochemical monitoring of nitrite in food samples.

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