Chunfeng Duan

A fluorometric paper-based sensor array for the discrimination of heavy-metal ions

A fluorometric paper-based sensor array has been developed for the sensitive and convenient determination of seven heavy-metal ions at their wastewater discharge standard concentrations. Combining with nine cross-reactive BODIPY fluorescent indicators and array technologies-based pattern-recognition, we have obtained the discrimination capability of seven different heavy-metal ions at their wastewater discharge standard concentrations. After the immobilization of indicators and the enrichment of analytes, identification of the heavy-metal ions was readily acquired using a standard chemometric approach. Clear differentiation among heavy-metal ions as a function of concentration was also achieved, even down to 10(-7)M. A semi-quantitative estimation of the heavy-metal ion concentration was obtained by comparing color changes with a set of known concentrations. The sensor array was tentatively investigated in spiked tap water and sea water, and showed possible feasibility for real sample testing.

Sorptive extraction techniques in sample preparation for organophosphorus pesticides in complex matrices.

Organophosphorus pesticides (OPPs), widely known as persistent organic pollutants, are the most popular contaminants in agriculture products in developing countries. The determination of OPPs in complex matrices, such as food, environmental and biological samples, usually requires extensive sample pretreatment. This review focuses on the sorptive extraction techniques applied as sample pretreatment for OPPs in complex matrices, including solid-phase extraction (SPE) and solid-phase microextraction (SPME). These methods are evaluated and the applications of each technique are demonstrated extensively with many practical examples.

BODIPY-based fluorometric sensor array for the highly sensitive identification of heavy-metal ions.

A BODIPY(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)-based fluorometric sensor array has been developed for the highly sensitive detection of eight heavy-metal ions at micromolar concentration. The di-2-picolyamine (DPA) derivatives combine high affinities for a variety of heavy-metal ions with the capacity to perturb the fluorescence properties of BODIPY, making them perfectly suitable for the design of fluorometric sensor arrays for heavy-metal ions. 12 cross-reactive BODIPY fluorescent indicators provide facile identification of the heavy-metal ions using a standard chemometric approach (hierarchical clustering analysis); no misclassifications were found over 45 trials. Clear differentiation among heavy-metal ions as a function of concentration was also achieved, even down to 10(-7)M. A semi-quantitative interpolation of the heavy-metal concentration is obtained by comparing the total Euclidean distance of the measurement with a set of known concentrations in the library.

Quantification of endogenous brassinosteroids in plant by on-line two-dimensional microscale solid phase extraction-on column derivatization coupled with high performance liquid chromatography–tandem mass spectrometry

An on-line two-dimensional microscale solid phase extraction (2DμSPE)-on column derivatization (OCD)-high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) method was developed for quantification of brassinosteroids (BRs) in plant tissues. Five BRs with widest distribution in plant species and high bioactivity (24-epibrassinolide, 24-epicastasterone, 6-deoxo-24-epicastasterone, teasterone and typhastero) were selected as target analytes. 2DμSPE column packed sequentially with phenyl boronic acid silica sorbent (the first dimension) and C18 silica sorbent (the second dimension) was used to selectively extract and enrich BRs by 110-146 times. OCD was carried out on the second dimension of 2DμSPE column with m-aminophenylboronic acid (m-APBA) as a derivatization reagent, enhancing the sensitivity of MS/MS to BRs by 13-8437 times. It was also found that pre-trap of derivatization reagent on the C18 section of 2DμSPE column could increase reaction efficiency by 3-10 times. The whole process time of the on-line system was less than 30min. The detection limits of the method for five BRs were between 1.4 and 6.6pg with RSDs less than 10%. Endogeneous BRs in tomato leaves were analyzed by using this method. Owing to the high selectivity of this on-line 2DμSPE system, BRs in plant extracts could be quantified using matrix-free standard calibration method with relative recoveries in the range of 80-124%.

A vacuum assisted dynamic evaporation interface for two-dimensional normal phase/reverse phase liquid chromatography.

A vacuum assisted dynamic solvent evaporation interface for coupling of two-dimensional normal phase/reverse phase liquid chromatography was developed and evaluated. A normal-phase liquid chromatographic (NPLC) column of a 250mmx4.6mm I.D. 5microm CN phase was used as the first dimension, and a reversed-phase liquid chromatographic (RPLC) column of 250mmx4.6mm I.D. 5micromC(18) phase was used as the second dimension. The eluent from the first dimension flowed into a fraction loop, and the solvent in the eluent was dynamically evaporated and removed by vacuum as it was entering the fraction loop of the interface. The non-evaporable analytes was retained and enriched in about 5-25microL solution within the loop. Up to 1mL/min of mobile phase from the first dimension can be evaporated and removed dynamically by the interface. The mobile phase from the second dimension then entered the loop, and dissolved the concentrated analytes retained inside the loop, and carried them onto the second dimension column for further separation. The operation conditions of the two dimensions were independent from each other, and both dimensions were operated at their optimal chromatographic conditions. We evaluated the interface by controlling the loop temperature in a water bath at normal temperature, and investigated the sample losses by using standard samples with different boiling points. It was found that the sample loss due to evaporation in the interface was negligible for non-volatile samples or for components with boiling point above 340 degrees C. The interface realizes fast solvent removal of mL volume of fraction and concentration of the fraction into tenth of microL volume, and injection of the concentrated fraction on the secondary column. The chromatographic performance of the two-dimensional LC system was enhanced without compromise of separation efficiency and selectivity on each dimension.

Quantification of endogenous brassinosteroids in sub-gram plant tissues by in-line matrix solid-phase dispersion-tandem solid phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry

A matrix solid-phase dispersion (MSPD)-tandem mixed mode anion exchange (MAX)-mixed mode cation exchange (MCX) solid phase extraction-high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) method was developed for quantification of six endogenous brassinosteroids (BRs) (24-epibrassinolide, 24-epicastasterone, 6-deoxo-24-epicastasterone, dolichosterone, teasterone and typhasterol) in rice plant tissues. Non-polar interferences were removed effectively by C8 dispersant used in MSPD, while the following tandem MAX-MCX process facilitated the elimination of polar and ionizable compounds. The weak reversed-phase retention feature of MAX-MCX leaded to good compatibility of the elution solvents in the in-line coupled MSPD-MAX-MCX system. This system was optimized for extraction and purification of BRs in plant samples. The effects of the type of solid phase, the elution solvent, the extraction temperature and the clean-up material were studied. Before HPLC separation, BRs purified were derivatized by m-aminophenylboronic acid to enhance the sensitivity of MS/MS to BRs. Compared with traditional liquid-liquid extraction and solid phase extraction (LLE-SPE), the proposed MSPD-MAX-MCX method showed higher extraction efficiency, lower matrix effect, and advantages of easy manipulation and time-saving. The in-line MSPD-MAX-MCX coupled with HPLC-MS/MS method provided a linear response over two orders of magnitude of BRs concentration with correlation coefficients above 0.9982, limits of detection between 0.008 and 0.04ngmL(-1), relative standard deviations (RSDs) below 29.4%, and recoveries above 77.8%. The proposed method has been successfully applied to analysis of endogenous BRs in rice plant at booting stage and maturity stage.

Colorimetric sensors with different reactivity for the quantitative determination of cysteine, homocysteine and glutathione in a mixture

We report a facile method for the quantitative detection of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) in a mixture. BODIPY-based sensors 1 and 2 are synthesized, and the diverse reactivities of 1 and 2 in the presence of a mixture of biothiols lead to distinct absorption spectra at a specified period of time. With a spectral analysis, we are capable of distinguishing three biothiols and achieving the quantitative determination of Cys, Hcy and GSH in a mixture.

Ultrasensitive quantification of endogenous brassinosteroids in milligram fresh plant with a quaternary ammonium derivatization reagent by pipette-tip solid-phase extraction coupled with ultra-high-performance liquid chromatography tandem mass spectrometry.

Determination of endogenous brassinosteroids (BRs) in limited sample amount is vital to elucidating their tissue- and even local tissue-specific signaling pathway and physiological effects on plant growth and development. In this work, an ultra-sensitive quantification method was established for endogenous BRs in milligram fresh plant by using pipette-tip solid-phase extraction coupled with ultra-performance liquid chromatography tandem mass spectrometry (PT-SPE-UPLC-MS/MS), in which a quaternary ammonium phenyl boronic acid, 4-borono-N,N,N-trimethylbenzenaminium iodide (BTBA) was first developed for chemical derivatization of BRs. Due to the cationic quaternary ammonium group of BTBA, the ionization efficiencies of the BRs chelates with BTBA (BTBA-BRs) were enhanced by 1190-448785 times, which is the highest response enhancement factor among all derivatization reagents reported for BRs. In addition, PT-SPE packed with C18 sorbent was first used for purifying BRs from plant extracts, so the required sample amount was minimized, and recoveries higher than 91% were achieved. Under the optimized conditions, the minimal detectable amounts (MDA) of five target BRs were in the range of 27-94 amol, and the correlation coefficients (R(2)) were >0.9985 over four orders of magnitude. The relative recoveries of 75.8-104.9% were obtained with the intra- and inter-day relative standard deviations (RSDs) less than 18.7% and 19.6%, respectively. Finally, three BRs were successfully quantified in only 5mg fresh rice plant samples, and 24-epiBL can even be detected in only 0.5mg FW rice leaf segments. It is the first time that the BRs content in sub-milligram fresh plant sample has been quantified.

Dispersive liquid-liquid microextraction of trace Hg2+ for visual and fluorescence test.

In this work, trace Hg(2+) in environmental water samples was first preconcentrated by dispersive liquid-liquid microextraction (DLLME), and then was colorated by one common rhodamine B thiolactone (RBT) probe for visual and fluorescence detection. In this way, a highly sensitive and selective method was developed for field monitoring of Hg(2+) in environmental waters. The color of RBT test solution could change clearly from colorless to pink around the level of 2 μg L(-1)Hg(2+), which just meets with the maximum residue level of Hg(2+) in drinking water recommended by U.S. EPA, so the water samples with Hg(2+) concentration over 2 μg L(-1) could be selected rapidly by naked eye. Moreover, the quantification of Hg(2+) could be obtained by fluorescence detection of test solution. The best extraction efficiency of Hg(2+) by DLLLME could be obtained by using 200 mL water sample (pH 5.0, 50°C), 150 μL extraction solvent (lauric acid, LA) and 3 mL dispersive solvent (methanol). Thus an enrichment factor of ≈ 407 and the limit of fluorescence detection of 0.03 μg L(-1) could be achieved. The method was also highly selective for Hg(2+) with tolerance to at least 1000-fold of the foreign metal ions. This method was successfully applied to detect Hg(2+) in deionized water, tap water and sea water.

Hollow fiber-based liquid-liquid-liquid micro-extraction with osmosis: II. Application to quantification of endogenous gibberellins in rice plant.

The phenomenon and benefits of osmosis in hollow fiber-based liquid-liquid-liquid micro-extraction (HF-LLLME) were theoretically discussed in part I of this study. In this work, HF-LLLME with osmosis was coupled with high performance liquid chromatography-triple quadrupole mass spectrometry (HPLC-triple quadrupole MS/MS) to analyze eight gibberellins (gibberellin A(1), gibberellin A(3), gibberellin A(4), gibberellin A(7), gibberellin A(8), gibberellin A(9), gibberellin A(19) and gibberellin A(20)) in rice plant samples. According to the theory of HF-LLLME with osmosis, single factor experiments, orthogonal design experiments and mass transfer simulation of extraction process were carried out to select the optimal conditions. Cyclohexanol - n-octanol (1:3, v/v) was selected as organic membrane. Donor phase of 12 mL was adjusted to pH 2 and 20% NaCl (w/v) was added. Acceptor phase with an initial volume of 20 μL was the solution of 0.12 mol L(-1) Na(2)CO(3)-NaHCO(3) buffer (pH 9). Temperature was chosen to be 30 °C and extraction time was selected to be 90 min. Under optimized conditions, this method provided good linearity (r, 0.99552-0.99991) and low limits of detection (0.0016-0.061 ng mL(-1)). Finally, this method was applied to the analysis of endogenous gibberellins from plant extract which was obtained with traditional solvent extraction of rice plant tissues, and the relative recoveries were from 62% to 166%.