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1.
Krska R Welzig E Drs E Josephs RD Schothorst RC Van Egmond HP Pettersson H Chan D MacDonald S 《Journal of AOAC International》2006,89(6):1573-1580
Thirteen European laboratories experienced in the analysis of mycotoxins participated in an intercomparison study within a European Commission-funded project. Goals of the study were to check the fitness for purpose of a small batch of gravimetrically prepared calibrants; to compare individually prepared calibrants with common calibrants; to check the feasibility of toxin mixtures as calibrant solutions; and to give recommendations on the production of future certified reference materials (CRMs) with regard to the nature of the calibrant and the means of certification. Each laboratory received ampules of each common calibrant containing single toxins [solution containing either deoxynivalenol (DON), 3-acetyl-DON (3-Ac-DON), nivalenol (NIV), or 15-acetyl-DON (15-Ac-DON)] and 3 ampules of toxin-mixture (solutions of DON + 3-Ac-DON + NIV in acetonitrile) of known concentrations (about 20 microg/mL). Ampules with single toxins (solution containing either DON, 3-Ac-DON, NIV, or 15-Ac-DON) and a toxin-mixture (solutions of DON + 3-Ac-DON + NIV in acetonitrile) of unknown concentrations were distributed to the participants for quantification. The participating laboratories used mainly high-performance liquid chromatography (HPLC)-diode array detection UV for DON, 3-Ac-DON, NIV, and 15-Ac-DON; gas chromatography-electron capture detection (GC-ECD) and GC-mass spectrometry methods were used sparingly. Linear calibration curves were achieved by >90% of the participants. Relative between-day variation (RSDr) of 26% of the laboratories was greater than the target value of 5% for HPLC, and RSDr of 32% of the laboratories was greater than the desired value of 10% for GC. Relative between-laboratory variation (RSDR) of the GC results obtained with single common calibrants was greater than the target value of 16% for all laboratories. RSDR of the HPLC results for the common unknown single toxin solutions was less than the target value of 8% except for 15-Ac-DON. Generally, better recoveries were observed from common calibrants (102% for mix calibrants and 98% for single calibrants) than from individually prepared calibrants (95%). This international comparison study clearly showed the high scattering of results in the analysis of type-B trichothecenes, particularly when GC was used. Obviously, this intercomparison study was not suited for the certification of B-trichothecenes. A certification of the proposed calibrant material was therefore recommended on the basis of its gravimetrical preparation. 相似文献
2.
Krska R Schothorst RC van Egmond HP Josephs RD Lepschy J Pettersson H Chan D Berthiller F Schuhmacher R Kandler W Parich A Welzig E 《Analytical and bioanalytical chemistry》2005,382(8):1848-1858
The lack of reliable, certified calibrant solutions for the Fusarium mycotoxins deoxynivalenol (DON), 3-acetyl-DON (3-Ac-DON), 15-acetyl-DON (15-Ac-DON) and nivalenol (NIV) is a serious drawback in the already problematic area of trichothecene analysis. For this reason, purified DON, 3-Ac-DON, 15-Ac-DON and NIV standards were processed, the conditions required for their isolation and purification were optimised, and the crystalline toxins were thoroughly characterised. Several complimentary analytical methods were used to evaluate the identities of the mycotoxins and the types and amounts of impurities; results obtained from 1 H and 13 C NMR spectra, as well as from IR-spectra, were in agreement with the literature. Elemental analysis revealed that the isolated NIV occurs as monohydrate. If this is not known it results in a weighing error of approximately 5%. Differential scanning calorimetry (DSC) was only successful for 15-Ac-DON, as the other trichothecenes decomposed during measurements. No traces of chloride, nitrate and sulphate were found by means of ion chromatography (IC). As expected UV absorption spectra for DON, NIV, 3-Ac-DON and 15-Ac-DON yielded max values of 216, 217, 217 and 219 nm, respectively. Minor peaks due to impurities were observed by high performance liquid chromatography (HPLC) with UV detection. The main impurity peak in the DON sample was identified by LC-tandem mass spectroscopy (LC-MS/MS) as 4,7-dideoxy-NIV (7-deoxy-DON), which occurs at levels of approximately 1.4%. Gas chromatography (GC) was performed, coupled with either an electron capture detector (ECD), a flame ionisation detector (FID), or a mass spectrometric detector (MS); however, derivatisation prior to GC analysis makes the estimation of impurities difficult. LC-MS/MS was found to be unsuitable for quantifying levels of impurities. It can be concluded that high-purity (>97%) B-trichothecene standards were successfully processed and fully characterised for the first time.Dedicated to the memory of Wilhelm Fresenius 相似文献
3.
Microwave digestion and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-SFMS) has been applied to the
determination of Pb in rice flour. In order to achieve highly precise determination of low concentrations of Pb, the digestion
blank for Pb was reduced to 0.21 ng g−1 after optimization of the digestion conditions, in which 20 mL analysis solution was obtained after digestion of 0.5 g rice
flour. The observed value of Pb in a non-fat milk powder certified reference material (CRM), NIST SRM 1549, was 16.8 ± 0.8 ng
g−1 (mean ± expanded uncertainty, k = 2; n = 5), which agreed with the certified value of 19 ± 3 ng g−1 and indicated the effectiveness of the method. Analytical results for Pb in three brown rice flour CRMs, NIST SRM 1568a,
NIES CRM 10-a, and NIES CRM 10-b, were 7.32 ± 0.24 ng g−1 (n = 5), 1010 ± 10 ng g−1 (n = 5), and 1250 ± 20 ng g−1 (n = 5), respectively. The concentration of Pb in a candidate white rice flour reference material (RM) sample prepared by the
National Metrology Institute of Japan (NMIJ) was observed to be 4.36 ± 0.28 ng g−1 (n = 10 bottles).
Figure Digestion blank of Pb was carefully reduced to approximately 0.2 ng g-1 which permitted the highly precise determination of Pb at low ng g-1 level in foodstuff samples by ID-SFMS 相似文献
4.
A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO2) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic
diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol)
(TX). Under static conditions phenol was quantitatively extracted onto TX-SiO2 in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO2 for phenol is 2.4 mg g−1 with distribution coefficients up to 3.4 × 104 mL g−1; corresponding data for 1-naphthol are 1.5 mg g−1 and 3 × 103 mL g−1. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than
0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol
and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A
540) and phenol concentration (C) in water was found according to the equation A
540 = (6 ± 1) × 10−2 + (0.9 ± 0.1)C (μmol L−1) with a detection range from 1 × 10−8 mol L−1 (0.9 μL g−1) to 2 × 10−7 mol L−1 (19 μL g−1), a limit of quantification of 1 μL g−1 (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric
method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical
analysis. The detection limit of 1-naphthol with this method is 6 μL g−1 while the quantification limit is 20 μL g−1. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one
to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g−1. 相似文献
5.
A fast and sensitive liquid chromatography–mass spectrometry method was developed for the determination of ursolic acid (UA)
in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed
on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate
using gradient elution. Quantification was performed by selected ion monitoring with (m/z)− 455 for UA and (m/z)− 469 for the IS. The method was validated in the concentration range of 2.5 − 1470 ng mL−1 for plasma samples and 20 − 11760 ng g−1 for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7%
to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 − 106.9% and 82.1 − 108.1%, respectively. Recoveries
in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL−1 or 4.0 ng g−1. The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The
main pharmacokinetic parameters obtained were T
max = 0.42 ± 0.11 h, C
max = 1.10 ± 0.31 μg mL−1, AUC = 1.45 ± 0.21 μg h mL−1 and K
a = 5.64 ± 1.89 h−1. The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method
is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats. 相似文献
6.
Robert Köppen Wolfram Bremser Tatjana Rasenko Matthias Koch 《Analytical and bioanalytical chemistry》2013,405(14):4755-4763
Deoxynivalenol (DON), nivalenol (NIV) and zearalenone (ZEN) are toxic secondary metabolites produced by several species of Fusarium fungi. These mycotoxins are often found together in a large variety of cereal-based foods, which are regulated by maximum content levels of DON and ZEN. To date, suitable certified reference materials (CRM) intended for quality control purposes are lacking for these Fusarium mycotoxins. In order to overcome this lack, the first CRM for the determination of DON, NIV and ZEN in naturally contaminated wheat flour (ERM®-BC600) was developed in the framework of a European Reference Materials (ERM®) project. This article describes and discusses the whole process of ERM®-BC600 development, including material preparation, homogeneity and stability studies, and an interlaboratory comparison study for certification. A total of 21 selected expert laboratories from different European countries with documented expertise in the field of mycotoxin analysis took part in the certification study using various gas and liquid chromatographic methods. The certified values and their corresponding expanded uncertainties (k?=?2) were assigned in full compliance with the requirements of ISO Guide 35 and are as follows: 102?±?11 μg?kg?1 for DON, 1000?±?130 μg?kg?1 for NIV and 90?±?8 μg?kg?1 for ZEN. 相似文献
7.
Viñas P López-García I Bravo-Bravo M Briceño M Hernández-Córdoba M 《Analytical and bioanalytical chemistry》2012,403(4):1059-1066
A miniaturized dispersive liquid–liquid microextraction (DLLME) procedure coupled to liquid chromatography (LC) with fluorimetric
detection was evaluated for the preconcentration and determination of thiamine (vitamin B1). Derivatization was carried out by chemical oxidation of thiamine with 5 × 10−5 M ferricyanide at pH 13 to form fluorescent thiochrome. For DLLME, 0.5 mL of acetonitrile (dispersing solvent) containing
90 μL of tetrachloroethane (extraction solvent) was rapidly injected into 10 mL of sample solution containing the derivatized
thiochrome and 24% (w/v) sodium chloride, thereby forming a cloudy solution. Phase separation was carried out by centrifugation, and a volume of
20 μL of the sedimented phase was submitted to LC. The mobile phase was a mixture of a 90% (v/v) 10 mM KH2PO4 (pH 7) solution and 10% (v/v) acetonitrile at 1 mL min−1. An amide-based stationary phase involving a ligand with amide groups and the endcapping of trimethylsilyl was used. Specificity,
linearity, precision, recovery, and sensitivity were satisfactory. Calibration graph was carried out by the standard additions
method and was linear between 1 and 10 ng mL−1. The detection limit was 0.09 ng mL−1. The selectivity of the method was judged from the absence of interfering peaks at the thiamine elution time for blank chromatograms
of unspiked samples. A relative standard deviation of 3.2% was obtained for a standard solution containing thiamine at 5 ng mL−1. The esters thiamine monophosphate and thiamine pyrophosphate can also be determined by submitting the sample to successive
acid and enzymatic treatments. The method was applied to the determination of thiamine in different foods such as beer, brewer’s
yeast, honey, and baby foods including infant formulas, fermented milk, cereals, and purees. For the analysis of solid samples,
a previous extraction step was applied based on an acid hydrolysis with trichloroacetic acid. The reliability of the procedure
was checked by analyzing a certified reference material, pig’s liver (CRM 487). The value obtained was 8.76 ± 0.2 μg g−1 thiamine, which is in excellent agreement with the certified value, 8.6 ± 1.1 μg g−1. 相似文献
8.
Shukor MY Rahman MF Shamaan NA Lee CH Karim MI Syed MA 《Applied biochemistry and biotechnology》2008,144(3):293-300
Molybdenum-reducing activity in the heterotrophic bacteria is a phenomenon that has been reported for more than 100 years.
In the presence of molybdenum in the growth media, bacterial colonies turn to blue. The enzyme(s) responsible for the reduction
of molybdenum to molybdenum blue in these bacteria has never been purified. In our quest to purify the molybdenum-reducing
enzyme, we have devised a better substrate for the enzyme activity using laboratory-prepared phosphomolybdate instead of the
commercial 12-phosphomolybdate we developed previously. Using laboratory-prepared phosphomolybdate, the highest activity is
given by 10:4-phosphomolybdate. The apparent Michaelis constant, K
m for the laboratory-prepared 10:4-phosphomolybdate is 2.56 ± 0.25 mM (arbitrary concentration), whereas the apparent V
max is 99.4 ± 2.85 nmol Mo-blue min−1 mg−1 protein. The apparent Michaelis constant or K
m for NADH as the electron donor is 1.38 ± 0.09 mM, whereas the apparent V
max is 102.6 ± 1.73 nmol Mo-blue min−1 mg−1 protein. The apparent K
m and V
max for another electron donor, NADPH, is 1.43 ± 0.10 mM and 57.16 ± 1.01 nmol Mo-blue min−1 mg−1 protein, respectively, using the same batch of molybdenum-reducing enzyme. The apparent V
max obtained for NADH and 10:4-phosphomolybdate is approximately 13 times better than 12-phoshomolybdate using the same batch
of enzyme, and hence, the laboratory-prepared phosphomolybdate is a much better substrate than 12-phoshomolybdate. In addition,
10:4-phosphomolybdate can be routinely prepared from phosphate and molybdate, two common chemicals in the laboratory. 相似文献
9.
Gazi E Dwyer J Lockyer NP Gardner P Shanks JH Roulson J Hart CA Clarke NW Brown MD 《Analytical and bioanalytical chemistry》2007,387(5):1621-1631
Prostate cancer (CaP) cells preferentially metastasise to the bone marrow, a microenvironment that plays a substantial role
in the sustenance and progression of the CaP tumour. Here we use a combination of FTIR microspectroscopy and histological
stains to increase molecular specificity and probe the biochemistry of metastatic CaP cells in bone marrow tissue derived
from a limited source of paraffin-embedded biopsies of different patients. This provides distinction between the following
dominant metabolic processes driving the proliferation of the metastatic cells in each of these biopsies: glycerophospholipid
synthesis from triacylglyceride, available from surrounding adipocytes, in specimen 1, through significantly high (p ≤ 0.05) carbohydrate (8.23 ± 1.44 cm−1), phosphate (6.13 ± 1.5 cm−1) and lipid hydrocarbon (24.14 ± 5.9 cm−1) signals compared with the organ-confined CaP control (OC CaP), together with vacuolation of cell cytoplasm; glycolipid synthesis
in specimen 2, through significantly high (p ≤ 0.05) carbohydrate (5.51 ± 0.04 cm−1) and high lipid hydrocarbon (17.91 ± 2.3 cm−1) compared with OC CaP, together with positive diastase-digested periodic acid Schiff staining in the majority of metastatic
CaP cells; glycolysis in specimen 3, though significantly high (p ≤ 0.05) carbohydrate (8.86 ± 1.78 cm−1) and significantly lower (p ≤ 0.05) lipid hydrocarbon (11.67 ± 0.4 cm−1) than OC CaP, together with negative diastase-digested periodic acid Schiff staining in the majority of metastatic CaP cells.
Detailed understanding of the biochemistry underpinning the proliferation of tumour cells at metastatic sites may help towards
refining chemotherapeutic treatment. 相似文献
10.
Bolade O. Agboola Sibulelo L. Vilakazi Kenneth I. Ozoemena 《Journal of Solid State Electrochemistry》2009,13(9):1367-1379
Electrochemistry of water-soluble cobalt(II) tetrasulfophthalocyanine (CoTSPc) electrodeposited on glassy carbon nanotube
pre-modified with acid-functionalized multi-walled carbon nanotubes (MWCNT) is described. Both charge transfer resistances
toward [Fe(CN)6]3−/4− redox probe and electrocatalytic responses toward epinephrine (EP) detection follow the trend: bare GCE < GCE-MWCNT < GCE-CoTSPc < GCE-MWCNT-CoTSPc.
EP analysis was then carried out in details using GCE-MWCNT-CoTSPc. The catalytic rate constant value k
ch = 2.2 × 107 (mol cm−3)−1 s−1 was obtained from rotating disk electrode experiment. Interestingly, GCE-MWCNT-CoTSPc efficiently suppressed the detection
of ascorbic acid (the natural interference of neurotransmitters in physiological conditions) showing good sensitivity (0.132 ± 0.003 A
l mol−1), limit of detection (4.517 × 10−7 mol l−1), and quantification (15.056 × 10−7 mol l−1). In addition, GCE-MWCNT-CoTSPc was conveniently used to determine EP in epinephrine hydrochloric acid injection with recovery
of 101.1 ± 2.2%. 相似文献
11.
Rodrigues TH Rocha MV de Macedo GR Gonçalves LR 《Applied biochemistry and biotechnology》2011,164(6):929-943
In this work, the potential of microwave-assisted alkali pretreatment in order to improve the rupture of the recalcitrant
structures of the cashew able bagasse (CAB), lignocellulosic by-product in Brazil with no commercial value, is obtained from
cashew apple process to juice production, was studied. First, biomass composition of CAB was determined, and the percentage
of glucan and lignin was 20.54 ± 0.70% and 33.80 ± 1.30%, respectively. CAB content in terms of cellulose, hemicelluloses,
and lignin, 19.21 ± 0.35%, 12.05 ± 0.37%, and 38.11 ± 0.08%, respectively, was also determined. Results showed that, after
enzymatic hydrolysis, alkali concentration exerted influence on glucose formation, after pretreatment with 0.2 and 1.0 mo L−1 of NaOH (372 ± 12 and 355 ± 37 mg gglucan−1) when 2% (w/v) of cashew apple bagasse pretreated by microwave-assisted alkali pretreatment (CAB-M) was used. On the other hand, pretreatment
time (15–30 min) and microwave power (600–900 W) exerted no significant effect on hydrolysis. On enzymatic hydrolysis step,
improvement on solid percentage (16% w/v) and enzyme load (30 FPU gCAB-M−1) increased glucose concentration to 15 g L−1. The fermentation of the hydrolyzate by Saccharomyces cerevesiae resulted in ethanol concentration and productivity of 5.6 g L−1 and 1.41 g L−1 h−1, respectively. 相似文献
12.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,138(10):941-949
Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
13.
The fungicide triadimenol consists of a mixture of two diastereoisomers. Diastereoisomer A (1RS,2SR) could be obtained from the mixture by fractionated crystallization from ethanol/water and toluene, successively, whereas
diastereoisomer B (1RS,2RS) could be separated by column chromatography on a silica gel column using ethylacetate as eluent. Four different crystal
forms of diastereoisomer A could be derived. The modifications were characterized by means of thermal analysis (thermomicroscopy,
DSC), FTIR-spectroscopy, FT-Raman-spectroscopy and powder X-ray diffraction, as well as pycnometry. The thermodynamic relationships
are illustrated in a semischematic energy/temperature-diagram which provides information about the relative thermodynamic
stabilities and physical properties of the four crystal forms. Mod. II (m.p. 132 °C, ΔHf 33.1±0.2 kJ mol−1, density 1.271±0.001 g cm−3) was obtained from toluene after the separation of diastereoisomer A and is enantiotropically related to mod. I (m.p. 138 °C,
ΔHf 32.0 ± 0.2 kJ mol−1, density 1.243±0.001 g cm−3). The transition point of mod. II with mod. I was determined between 30 and 40 °C, which means that mod. II is thermodynamically
stable at ambient conditions. Mod. III (m.p. 112 °C, ΔHf 25.1±0.5 kJ mol−1) and mod. IV were obtained from the melt. Furthermore, the phase diagrams of the binary systems of diastereoisomer B and
the four modifications of diastereoisomer A were calculated by means of the experimentally obtained thermodynamical data.
Received September 30, 1999. Revision July 30, 2000. 相似文献
14.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,28(4):941-949
The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
15.
Vega D Agüí L González-Cortés A Yáñez-Sedeño P Pingarrón JM 《Analytical and bioanalytical chemistry》2007,389(3):951-958
The voltammetric behaviour and amperometric detection of tetracycline (TC) antibiotics at multi-wall carbon nanotube modified
glassy carbon electrodes (MWCNT-GCE) are reported. Cyclic voltammograms of TCs showed enhanced oxidation responses at the
MWCNT-GCE with respect to the bare GCE, attributable to the increased active electrode surface area. Hydrodynamic voltammograms
obtained by flow-injection with amperometric detection at the MWCNT-GCE led us to select a potential value E
det = +1.20 V. The repeatability of the amperometric responses was much better than that achieved with bare GCE (RSD ranged from
7 to 12%), with RSD values for i
p of around 3%, thus demonstrating the antifouling capability of MWCNT modified electrodes. An HPLC method with amperometric
electrochemical detection (ED) at the MWCNT-GCE was developed for tetracycline, oxytetracycline (OTC), chlortetracycline and
doxycycline (DC). A mobile phase consisting of 18:82 acetonitrile/0.05 mol L−1 phosphate buffer of pH 2.5 was selected. The limits of detection ranged from 0.09 μmol L−1 for OTC to 0.44 μmol L−1 for DC. The possibility to carry out multiresidue analysis is demonstrated. The HPLC-ED/MWCNT-GCE method was applied to the
analysis of fish farm pool water and underground well water samples spiked with the four TCs at 2.0 × 10−7 mol L−1. Solid-phase extraction was accomplished for the preconcentration of the analytes and clean-up of the samples. Recoveries
ranged from 87 ± 6 to 99 ± 3%. Under preconcentration conditions, limits of detection in the water samples were between 0.50
and 3.10 ng mL−1. 相似文献
16.
The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated
by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton–Robinson (BR) buffer of pH 2.6–10.3, an irreversible
and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the
sweep rate (ν) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible
first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (α) involved in the rate-determining step calculated from the linear plots of E
p,a against ln (ν) in the pH range investigated were in the range 0.64 ± 0.05 confirming the irreversible nature of the oxidation peak. In
BR buffer of pH 7.6–8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against
domperidone concentration at this peak potential was linear in the range 5.20 × 10−6 to 2.40 × 10−5 mol L−1 with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 × 10−7 and 9.1 × 10−7 mol L−1, respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 × 10−6 mol L−1 of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 ± 3.1%), dosage
form (98.35 ± 2.9%), and in tap (97.0 ± 3.6%) and wastewater (95.0 ± 2.9%) samples. The method was validated by comparison
with standard titrimetric and HPLC methods. Acceptable error of less than 3.3 % was also achieved.
Figure In aqueous media at pH 7.6- 8.4, the DPV and cyclic voltammetry of the drug domperidone (I) at GCE showed an irreversible
and diffusion controlled oxidation wave. The values of the electron transfer coefficient (α) involved in the rate determining
step were found in the range 0.64± 0.05 confirming the irreversible nature of the peak. The analysis of the drug in pure form
and in wastewater samples was successfully achieved 相似文献
17.
Acetylcholinesterase-based biosensors for quantification of carbofuran, carbaryl, methylparaoxon, and dichlorvos in 5% acetonitrile 总被引:1,自引:0,他引:1
Valdés-Ramírez G Cortina M Ramírez-Silva MT Marty JL 《Analytical and bioanalytical chemistry》2008,392(4):699-707
Amperometric acetylcholinesterase biosensors have been developed for quantification of the pesticides carbofuran, carbaryl,
methylparaoxon, and dichlorvos in phosphate buffer containing 5% acetonitrile. Three different biosensors were built using
three different acetylcholinesterase (AChE) enzymes—AChE from electric eel, and genetically engineered (B394) and wild-type
(B1) AChE from Drosophila melanogaster. Enzymes were immobilized on cobalt(II) phthalocyanine-modified electrodes by entrapment in a photocrosslinkable polymer
(PVA-AWP). Each biosensor was tested against the four pesticides. Good operational stability, immobilisation reproducibility,
and storage stability were obtained for each biosensor. The best detection limits were obtained with the B394 enzyme for dichlorvos
and methylparaoxon (9.6 × 10−11 and 2.7 × 10−9 mol L−1, respectively), the B1 enzyme for carbofuran (4.5 × 10−9 mol L−1), and both the B1 enzyme and the AChE from electric eel for carbaryl (1.6 × 10−7 mol L−1). Finally, the biosensors were used for the direct detection of the pesticides in spiked apple samples. 相似文献
18.
To investigate the production of cellulases and xylanases from Penicillium echinulatum 9A02S1, solid-state fermentation (SSF) was performed by using different ratios of sugar cane bagasse (SCB) and wheat bran
(WB). The greatest filter paper activity obtained was 45.82 ± 1.88 U gdm−1 in a culture containing 6SCB/4WB on the third day. The greatest β-glucosidase activities were 40.13 ± 5.10 U gdm−1 obtained on the third day for the 0SCB/10WB culture and 29.17 ± 1.06 U gdm−1 for the 2SCB/8WB culture. For endoglucanase, the greatest activities were 290.47 ± 43.57 and 276.84 ± 15.47 U gdm−1, for the culture 6SCB/4WB on the fourth and fifth days of cultivation, respectively. The greatest xylanase activities were
found on the third day for the cultures 6SCB/4WB (36.38 ± 5.38 U gdm−1) and 4SCB/6WB (37.87 ± 2.26 U gdm−1). In conclusion, the results presented in this article showed that it was possible to obtain large amounts of cellulases
and xylanases enzymes using low-cost substrates, such as SCB and WB. 相似文献
19.
Biljana Šmit Biljana Petrović Sofija Sovilj Dragan Čanović Živadin D. Bugarčić 《Monatshefte für Chemie / Chemical Monthly》2008,139(10):1197-1202
The reactions of cisplatin with nizatidine and ranitidine were studied in D2O at pD 7.4 and 298 K by means of 1H NMR spectroscopy. The second order rate constants, k
2, for the reaction of cisplatin with nizatidine is (2.71 ± 0.11) × 10−4 M
−1 s−1, and for the reaction with ranitidine (6.72 ± 0.17) × 10−4 M
−1 s−1. The reactions of nizatidine and ranitidine were also studied with other Pd(II) and Pt(II) complexes. The set of the complexes
was selected because of their difference in reactivity, steric hindrance, and binding properties.
Correspondence: Prof. Dr. Živadin D. Bugarčić, Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac,
Serbia. 相似文献
20.
Isa Ruppen Canás Keith O’Callaghan Cian Moroney Brett Hamilton Kevin J. James Ambrose Furey 《Analytical and bioanalytical chemistry》2010,398(3):1477-1491
The azaspiracids are a family of lipophilic polyether marine biotoxins that have caused a number of human intoxication incidents
in Europe since 1995 after consumption of contaminated shellfish (Mytilus edulis). Levels of azaspiracids in shellfish for human consumption are monitored in accordance with EU guidelines: only shellfish
with less than 160 μg kg−1 are deemed safe. The limited availability of commercially available standards for azaspiracids is a serious problem, because
validated LC–MS methods are required for routine analysis of these toxins in shellfish tissues. The procedure described herein
has been used for the separation and the isolation of four azaspiracid (AZA) toxins from shellfish, for use as LC–MS–MS reference
materials. Five separation steps have been used to isolate azaspiracids 1, 2, 3, and 6. The purity of the toxins obtained
has been confirmed by multiple mass spectrometric methods using authentic azaspiracid standards. The same techniques have
been used for quantification of the toxins extracted. The isolation procedure involves several chromatographic purification
techniques: solid-phase extraction (diol sorbent, 90% mass reduction, and 95 ± 1% toxin recovery); Sephadex size-exclusion
chromatography (87% mass reduction and up to 95 ± 2% toxin recovery), Toyopearl HW size-exclusion chromatography (90% mass
reduction and up to 92.5 ± 2.5% toxin recovery), and semi-preparative LC (78 ± 3% toxin recovery). The procedure effectively
separates the toxins from the sample matrix and furnishes azaspiracid toxins (AZA1, AZA2, AZA3 and AZA6) of sufficient purity
with an average yield of 65% (n = 5). Triple-quadrupole mass spectrometry was used for qualitative and quantitative monitoring of the isolation efficiency
after each stage of the process. High-resolution mass spectrometric evaluation of the toxic isolated material in both positive
and negative modes suggests high purity. 相似文献