Zhaoyun Cao

Simultaneous determination of triazine herbicides in rice by high-performance liquid chromatography coupled with high resolution and high mass accuracy hybrid linear ion trap-orbitrap mass spectrometry.

A method was developed for the simultaneous determination of 10 triazine herbicides (cyanazine, simazine, simetryn, metribuzin, atrazine, ametryn, terbuthylazine, prometryn, terbutryn, and dimethametryn) in rice samples by high resolution and high mass accuracy hybrid linear ion trap-Orbitrap mass spectrometer. After extraction with acetonitrile and evaporation, the herbicides were redissolved in n-hexane and purified on a Florisil solid-phase extraction column. All compounds were separated within 12 min, producing more than 11 data points for each herbicide and high mass accuracy quantified ions which the mass errors of absolute value were less than 1.9 ppm in pure solution and 2.1 ppm in the matrix-matched standards solution. The method was validated in terms of the limits of detection and the limits of quantification. The linearity was satisfactory, with a correlation coefficient of >0.9975. Precision and recovery studies were evaluated at three concentration levels for Japonica, Indica, and Glutinous rice matrix. The mean recoveries obtained for all analytes in spiked Xiushui 03, Liangyoupeijiu, and Taihunuo rice samples were 83.3-99.0%, 82.0-99.7%, and 84.2-99.4%, respectively, with relative standard deviation in range 1.7-10.6%, 1.2-10.7%, and 1.9-11.6% for spiked rice samples, respectively. The intra-day precision (n=5) for the 10 herbicides in rice samples spiked at an intermediate level was between 2.8% and 7.9%, and the inter-day precision over 10 days (n=10) was between 5.5% and 15.9%.

Direct determination of glyphosate and its major metabolite, aminomethylphosphonic acid, in fruits and vegetables by mixed-mode hydrophilic interaction/weak anion-exchange liquid chromatography coupled with electrospray tandem mass spectrometry.

A novel method was developed for the direct, sensitive, and rapid determination of glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), in fruit and vegetable samples by mixed-mode hydrophilic interaction/weak anion-exchange liquid chromatography (HILIC/WAX) coupled with electrospray tandem mass spectrometry (ESI-MS/MS). Homogenized samples were extracted with water, without derivatization or further clean-up, and the extracts were injected directly onto the Asahipak NH2P-50 4E column (250 mm × 4.6 mm i.d., 5 μm). The best results were obtained when the column was operated under mixed-mode HILIC/WAX elution conditions. An initial 10-min washing step with acetonitrile/water (10:90, v/v) in HILIC mode was used to remove potentially interfering compounds, and then the analytes were eluted in WAX mode with acetonitrile and water containing 0.1 molL(-1) ammonium hydroxide under gradient elution for the ESI analysis in negative ion mode. Limits of quantification of glyphosate and AMPA were 5 μgkg(-1) and 50 μgkg(-1), respectively, with limits of detection as low as 1.2 μgkg(-1) for glyphosate and 15 μgkg(-1) for AMPA. The linearity was satisfactory, with correlation coefficients (r)>0.9966. Recovery studies were carried out on spiked matrices (6 vegetables, 3 fruits) with glyphosate at four concentrations and AMPA at three concentrations. The mean recoveries for glyphosate and AMPA were 75.3-110% and 76.1-110%, respectively, with relative standard deviations in the range of 1.1-13.8%. The intra-day precision (n=7) for glyphosate and AMPA in vegetable and fruit samples spiked at an intermediate level between 5.9% and 7.5%, and the inter-day precision over 11 days (n=11) was between 7.0% and 13%.

Characterization of cadmium-resistant bacteria and their potential for reducing accumulation of cadmium in rice grains

Cadmium (Cd) pollution is a serious widespread environmental problem that not only destroys the microbial ecology of soil and decreases crop production, but also poses a serious risk to human health. Many methods have been used for the remediation of Cd pollution but none of these is totally satisfactory. Microbial remediation strategies have attracted increasing interest since they are environmentally friendly and cost-effective. In the present study, three Cd-resistant bacteria were isolated and evaluated for potential application in Cd bioremediation. Based on their morphological, physiological and biochemical characteristics, together with 16S rDNA gene sequence analyses, bacteria were identified as Stenotrophomonas acidaminiphila (2#), Pseudomonas aeruginosa (9#) and Delftia tsuruhatensis (12#). Pseudomonas aeruginosa showed very high tolerance to metals, especially Cd (2200mg/L), Zn (1800mg/L) and Pb (1200mg/L), and is thought to be a multi-metal-resistant bacterium. Pseudomonas aeruginosa was also sensitive to 13 different antibiotics. The effects of the bacterial strains on the growth of rice plants and their ability to reduce Cd accumulation from Cd-contaminated soils in pot experiments were also evaluated. For Oryza sativa L. A grown in contaminated soil (3mg/kg Cd), the accumulation of Cd was decreased by 31.2 and 25.5% in brown rice and polished rice, respectively, by strain 9#; Pseudomonas aeruginosa was more effective in reducing Cd accumulation in rice grains than a mixture of strains. For Oryza sativa L. B, a mixture of strains acting synergistically was more effective than a single strain in reducing Cd accumulation; treatment with mixed strains (strains+3mg/kg Cd) resulted in 41.3, 35.9, and 32.6% reductions in Cd accumulation in unhulled rice, brown rice and polished rice, respectively. Although different results were obtained for two rice varieties, it can still be concluded that Cd-resistant bacteria are suitable for reducing Cd accumulation in rice grains and show potential for bioremediation of Cd-contaminated soils.

Profiling of phytohormones and their major metabolites in rice using binary solid-phase extraction and liquid chromatography-triple quadrupole mass spectrometry

A high-throughput method was developed using liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS) for the profiling and quantification of 43 phytohormones and their major metabolites, including auxins, abscisic acid, jasmonic acid, salicylic acid, cytokinins and gibberellins in a single sample extract. Considerable matrix effects (MEs) were observed (with most ME values in the range of 29%-84%, but maximum MEs of more than 115%, even up to 206%, existed) in sample extracts for most of the compounds studied. The application of the proposed binary solid-phase extraction using polymer anion and polymer cation exchange resins, was performed to purify 25 acidic and 18 alkaline phytohormones and their major metabolites prior to the LC-MS/MS analysis, which markedly reduced the MEs to acceptable levels, with ME values in the range of ±15%. Moreover, all of the isomers of cytokinins and their metabolites were fully separated on a sub-2μm particle C18 reverse-phase column with the optimized mobile phase consisting of methanol and 5mM ammonium formate. The method showed good linearity for all 43 analytes with regression coefficients (R(2))>0.991. Limits of detection ranged from 0.19 to 7.57 fmol for auxin, gibberellins, abscisic acid and their metabolites, 29.7 fmol for jasmonic acid, 18.1 fmol for salicylic acid, and from 0.03 to 0.31 fmol for cytokinins and their metabolites. The mean recoveries for all of the analytes were from 70.7 to 118.5%, and the inter-day precisions (n=6) were less than 18.7%, with intra-day precisions (n=6) within 25.4%. Finally, 20 compounds were successfully quantified in rice sample profiles using the proposed method, which will greatly facilitate the understanding of hormone-related regulatory networks that influence rice growth and development. To our knowledge, there are limited reports that measure this level of phytohormone species in rice samples using a single analysis.

A novel method for the simultaneous analysis of seven biothiols in rice (Oryza sativa L.) using hydrophilic interaction chromatography coupled with electrospray tandem mass spectrometry.

Analysis of biothiols is still problematic, due to their high polarity, oxidation sensitivity and time-consuming sample preparation. In this paper, a direct, rapid and sensitive method was developed for simultaneous quantification of unbound cysteine (Cys), glutathione (GSH) and phytochelatins (PCs) in rice leaf, stem and root samples by hydrophilic interaction chromatography coupled with electrospray tandem mass spectrometry (HILIC-MS/MS). Homogenized samples were extracted with water containing 50mM dithiothreitol, without derivatization and further clean-up, and the extracts were injected directly onto an Xbridge Amide-HILIC column (3.5μm, 150mm×2.1mm i.d.). The best chromatographic separation and MS sensitivity was achieved using a linear gradient elution with 10mM aqueous ammonium formate and acetonitrile as the mobile phase. In MS/MS mode the detection limit (S/N≥3) of seven biothiols was 3-105nM. Good linearities were observed (r>0.995) with linear dynamic range at least over three orders of magnitude. Recoveries for most analytes were within the range of 77-128%, with relative standard deviations less than 18.2%. The intra-day precision (n=7) was 6.1-11.7%, and the inter-day precision over 15 d (n=15) was 8.5-16.3% for all biothiols. The optimized HILIC-MS/MS method was applied to study the influence of different cadmium (Cd) concentrations (0, 1 and 50μM) on contents of Cys, GSH and PC2-6 in rice tissue. With increasing Cd concentrations in nutrient solutions, contents of PC2-4 in rice roots increased but contents of Cys and GSH decreased. Contents of PC2-4 in both rice leafs and stems increased markedly at high dose Cd (50μM) treatment compared with controls, compared with low Cd concentrations (1μM). However, both PC5 and PC6 were not detected throughout the stress experiment.

Accurate determination of arsenic and selenium in plant food samples by using ICP-MS/MS

Arsenic (As) and selenium (Se) in food have caused public concern. Determination of As and Se in plant food samples encounters mass spectral interferences. The influence of polyatomic and doubly charged ions on the determination was evaluated by monitoring 75As, 77Se, 78Se, 80Se, and 82Se in four modes. The result showed that serious interferences were observed by using “no gas” mode (octopole vented, single quadrupole mode). Most but not all interferences could be removed when using He mode (He used as the collision gas, single quadrupole mode) or H2 mode (H2 used as the reaction gas, MS/MS mode), while O2 mass-shift mode (O2 used as the reaction gas, MS/MS mode) enabled the effective removal of all interferences. In the O2 mass-shift mode configuration, the ions of interest were filtered twice by using the mass-to-charge ratio, enabling the removal of all interfering species. As and Se concentrations could be determined interference-free by using mass-shift mode with O2 as reaction gas. The performance of O2 mass-shift mode was investigated for the determination of As and Se in five plant reference materials. The obtained results were consistent with the certified values, indicating that the O2 mass-shift mode was an effective method to determine As and Se in plant food samples. The detection limits of the method for 75As, 77Se, 78Se, 80Se, and 82Se were 0.5, 0.7, 1.1, 0.3 and 0.6 ng g−1, respectively.

Analysis of ustiloxins in rice using polymer cation exchange cleanup followed by liquid chromatography–tandem mass spectrometry

Ustiloxins are cyclopeptide mycotoxins produced by the pathogenic fungus Ustilaginoidea virens of rice false smut. Quantification of ustiloxins is essential to assess the food safety of rice infected by rice false smut disease. This paper describes a sensitive method for the simultaneous quantification of ustiloxins A, B, C, D and F in rice grains using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Since notable matrix enhancement effects (21%-78%) occurred for all of the target analytes (except for ustiloxin A), several solid phase extraction materials were tested for their ability to retain ustiloxins from aqueous solutions prior to the LC-MS/MS analysis, including C18 sorbents, polymer anion exchange sorbents resin (PAX), and polymer cation exchange resin (PCX). The PCX resin was adopted due to its higher extraction capability and selectivity for all targets compared to others, and in this case, almost no matrix effects (-5% to 8%) were observed for all of the ustiloxins monitored. The developed method reached limits of quantification of 0.2-2ngg-1, and linearity was statistically verified over two orders of magnitude with regression coefficients (R2)>0.991. The mean recoveries were from 85% to 109%, and the inter-day precisions (n=11) were less than 16%, with intra-day precisions (n=6) within 12%. Analysis of samples showed that ustiloxin A was the dominant species, with the content ranging from 5.5 to 273.8ngg-1, followed by ustiloxin B (≤88.7ngg-1), while concentrations of ustiloxins C, D and F were slightly lower (≤43.2ngg-1). To our knowledge, this is the first report on the determination and analysis of five ustiloxins simultaneously in a single analysis.

[Determination of six novel amide fungicides in vegetables and fruits by liquid chromatography-tandem mass spectrometry].

A method was developed for the simultaneous determination of mepanipyrim, silthiofam, boscalid, fluopicolide, mandipropamid, cyflufenamid in vegetables and fruits by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The analytes were extracted from the samples by acetonitrile and purified by Florisil SPE. The six novel amide fungicides were separated on a Poroshell 120 EC-C18 column with the mobile phases of water and acetonitrile, and finally detected by MS/MS with positive electrospray ionization (ESI+) in multiple reaction monitoring (MRM) mode, quantified by external standard method. Under the optimal analytical conditions, the correlation coefficients (r) of the six novel amide fungicides were not lower than 0. 999 0 in the concentration range from 0.5 to 100 microg/L. The limits of detection (S/N > or = 3) of the method were 0.15 microg/kg for boscalid, silthiofam, mandipropamid, cyflufenamid, 0.10 microg/kg for mepanipyrim and 0.17 microg/kg for fluopicolide. The recovery tests were performed for the 7 types of vegetables and the 3 types of fruits at the spiked levels of 0.5, 5 and 50 microg/kg, and the recoveries of the six analytes ranged from 65% to 124% with the relative standard deviations (RSDs, n = 5) of 1%-18%. The matrix effects in vegetables and fruits of the six amide fungicides were significantly reduced by the purification of Florisil SPE compared with the modified QuEChERS. The method is easy, fast, sensitive and accurate, and can meet the requirements of the determination of the six amide fungicide residues in vegetables and fruits.

[Determination of glyphosate and aminomethylphosphonic acid in rice using liquid chromatography-tandem mass spectrometry].

A method was developed for the determination of glyphosate (GLY) and aminomethylphosphonic acid (AMPA) in rice using liquid chromatography tandem mass spectrometry (LC-MS/MS). The sample was extracted with water followed by a simple cleanup with a C18 solid phase extraction (SPE) cartridge, and then GLY and AMPA were derivatized using 9-fluorenylmethoxycarbonyl (FMOC-Cl) in borate buffer. The derivatives of GLY and AMPA were separated on a C18 column with gradient elution with the mobile phase of acetonitrile and 5 mmol/L ammonium acetate (pH 9), and finally detected with negative ion electrospray ionization-mass spectrometry (ESI-MS) in multiple reaction monitoring (MRM) mode. The results showed that the linearities of GLY and AMPA were in the concentration range of 0.000 50 to 1.0 mg/L with the correlation coefficients of 0.999 7 and 0.999 9, respectively. The mean spiked recoveries of GLY and AMPA at 3 spiked levels ranged from 72.5% to 113.6% with the relative standard deviations (RSD, n = 5) of 3.8% - 16.2%. The limits of detection were 2.0 and 3.0 microg/kg for GLY and AMPA, respectively. This method is rapid, sensitive, and suitable for simultaneous determination of GLY and AMPA in rice.

Nickel in milled rice (Oryza sativa L.) from the three main rice-producing regions in China

ABSTRACT Nickel (Ni) concentrations in milled rice obtained from China and their variations among different provinces and varieties, as well as associated health risks, were investigated. Results showed that the mean Ni concentration in milled rice was 0.49 ± 0.51 mg/kg, which was much higher than reported in United Kingdom, French and Iranian cereals. There were significant variations (P < 0.05) of Ni concentrations in milled rice among different provinces and among varieties in the same province. According to the dietary risk assessment, the mean values of the target hazard quotient for chronic risk ranged from 1.24 to 1.46 for 2–4, 4–7 and 7–11-year-old children, and all values of margin of exposure for hypersensitivity risk were considerably below 10 for all age groups, indicating that the current dietary exposure to Ni in rice is of concern for 2–11-year-old children and Ni-sensitised individuals. It is essential to establish a continuous monitoring programme to control Ni contamination in rice.