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Bulletin des Sociétés Chimiques Belges. 08/2010; 98(6):371 - 374.
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ABSTRACT: The spectrophotometric study of the orange 2‐oximinodimedone dithiosemicarbazone‐Ni(II) complex was made in dimethylformamide‐water solution (ϵ 440 nm=7200 l. mol−1. cm−1; stoichiometry 2:1 reagent to Ni(II) and apparent stability constant 1.0x106). A new method for the spectrophotometric determination of Ni(II) is proposed for concentrations between 0.36 and 6 μg ml−1.
Bulletin des Sociétés Chimiques Belges. 08/2010; 95(4):293 - 295.
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ABSTRACT: The fluorescence emission of the fluoroquinolones enoxacin (ENO), ciprofloxacin (CIPRO), norfloxacin (NOR) and ofloxacin (OFLO) notably increased by UV irradiation during few minutes, in ethanolic-water medium. An HPLC method has been developed, for the determination of these fluoroquinolones, based in the separation of the formed irradiation photoproducts. Optimization of the analytical wavelengths has been carried out by fast multiemission scanning fluorescence detection. The highest sensitivity has been found when measuring at emission wavelengths of 407 and 490 nm, for ENO and OFLO, respectively, and at 444 nm for both NOR and CIPRO (exciting at 277 nm). According to the criterium of Clayton, using 0.05 as false positive and false negative error assurance probabilities, detection limits of 7.3, 6.0, 6.3 and 14.5 ng/mL, for ENO, NOR, CIPRO and OFLO, respectively, have been found. Urine and serum samples have been successfully analyzed, with recovery values ranging among 99-97% and 98-103%, for urine and serum, respectively.
Journal of Chromatography B 09/2005; 822(1-2):185-93. · 2.89 Impact Factor
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ABSTRACT: Demeclocycline (DM) and methacycline (MT) have been determined by europium-sensitized fluorescence, using EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant. The methods have been developed in slightly alkaline solutions, with the formation of a new chelate where the lanthanide ion is bound to the beta-diketone group. Calibration graphs between 0.01 and 0.1 microg mL(-1) have been obtained for DM and MT determination. Both methods have been applied to the determination of these tetracyclines in serum samples with satisfactory recovery results.
Journal of Pharmaceutical and Biomedical Analysis 05/2005; 37(5):1101-4. · 2.97 Impact Factor
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ABSTRACT: Ternary mixtures of fluoroquinolones, with a 7-piperazinyl substituted group have been simultaneously determined in human urine samples by application of a multivariate calibration partial least squares (PLS) model. The calibration set was designed with 15 urine samples containing different concentrations of the three fluoroquinolones and 16 blank urine samples. The concentration range for the fluoroquinolones were up to 25ngml(-1) for norfloxacin (NOR), 80ngml(-1) for ofloxacin (OFLO) and 300ngml(-1) for enoxacin (ENO). The method is based on the native fluorescence emission of these compounds in sodium dodecyl sulfate (SDS) medium, at pH 4.0, when exciting at 277nm. A selection of the emission wavelength range used for the analysis was made for each component. Intraday and interday precision values were determined. Figures of merit as selectivity, sensitivity, limit of detection (LOD) and analytical sensitivity were also calculated. Using the standard addition methodology, five urine samples from five different persons, fortified with three concentration levels of the fluoroquinolones, were analyzed. The limits of detection in urine were 10.0, 0.5 and 0.8ngml(-1) for ENO, NOR and OFLO, respectively.
Talanta 04/2004; 62(4):853-60. · 3.79 Impact Factor
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ABSTRACT: The simultaneous polarographic determination of the ternary mixture of captan-captafol and folpet is studied. The polarographic signals of these compounds in their mixture show a high overlapping. For this reason different chemometric methods such as PLS, PCR and artificial neuronal network (ANN) have been utilized for the simultaneous determination of these compounds in mixtures. The calibration model is built from solutions containing river water of known pesticide concentrations and the signals obtained by Sampled DC and DPP (differential pulse polarography) have been used. The analysis of both synthetic and real samples (river water) has been carried out by PLS with satisfactory results in most cases. It is possible to determine 0.25 ppm of each pesticide in river water samples after a preconcentration step by extraction into diethyl ether. ANN has also been applied to improve the results obtained by the PLS tool when the sampled DC current is recorded or when liquid-solid extraction with C18 cartridges is performed.
Computers & Chemistry 10/2001; 25(5):459-73.
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ABSTRACT: An electroanalytical method has been developed for the detection and determination of the pesticide 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2ylidineamine (Imidacloprid) by square wave adsorptive stripping voltammetry on a hanging mercury drop electrode (HMDE) in aqueous solution with Britton-Robinson buffer as supporting electrolyte. The best adsorption conditions were found to be pH 7.2, an accumulation potential of -1050 mV (HMDE vs. Ag/AgCl-KCl 3M) and an accumulation time of 50 s. Effects of square wave frequency, step potential and pulse amplitude were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2 x 10(-8)-5 x 10(-7) M with a detection limit of 1.6 x 10(-8) M (Clayton et al. method). The method is applied to the direct determination of the pesticide in river water samples. For a concentration of 4.1 x 10(-8) M a recovery value of 104+/-3% is obtained. In order to determine lower concentrations, previous preconcentration and cleaning steps (liquid-liquid extraction into CH(2)Cl(2) and solid-phase extraction with Sep-Pak C(18) cartridges) are carried out. The recovery values obtained in spiked river water are 89+/-4% for 2 x 10(-8) M and 90+/-6% for 8 x 10(-9) M.
Talanta 02/2001; 53(5):943-9. · 3.79 Impact Factor
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ABSTRACT: Ultraviolet (UV) irradiation was used to obtain fluorescent photoproducts from four non-fluorescent benzoylurea (BU) insecticides (flufenoxuron (FLF), lufenuron (LUF), hexaflumuron (HF) and triflumuron (TRF)). The effect of solvent, pH (in aqueous solutions), organic solvent percentage and UV irradiation time on the excitation and emission wavelengths and fluorescence intensity were investigated. The largest fluorescence signals and the shortest UV irradiation time were obtained in methanol, ethanol and 2-propanol. Linear calibration graphs were established in the interval between 0.025 and 1.000 microg ml(-1) from FLF and TRF and between 0.050 and 1.000 microg ml(-1) from LUF and HF with regression coefficients larger than 0.99. A method based on the use of the first-derivative of the spectra of photoproducts was applied to the determination of BU insecticides in river water samples and in technical formulations. The mean recoveries ranged from 95.0% to 110.0% in river water samples and from 92.0% to 101.0% in technical formulations, according to the compound. A preconcentration step, using LLE, allowed to reach the concentration levels established by the EU directive for pesticides in drinking water.
Talanta 02/2001; 53(5):915-25. · 3.79 Impact Factor
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ABSTRACT: We have used an artificial neural network to optimize the composition of the mobile phase for an isocratic HPLC method for
the analysis of nitrophenol pesticides and related compounds, on the basic of different response functions, and have compared
the results with those obtained by application of response-surface methodology. These studies resulted in the selection the
mobile phase 10:30:15:45 methanol-acetonitrile-tetrahydrofuran-buffer solution (0.1m acetic acid and 0.1m sodium perchlorate); the flow-rate was 1 mL min−1. Under these conditions a chromatogram showing twelve well-resolved peaks was obtained in 14 min. Although the peaks corresponding
to ethylparathion and medinoterb acetate overlapped severely, it was possible, by use, of a diode-array spectrophotometer
for detection, and by combining the absorbance measured at different wavelengths as the signal, to separate the peaks corresponding
to one or other of the compounds. Calibration plots were constructed for the concentration range 2–10 ppm. Detection limits,
calculated by the method of Clayton et al., were approximately 0.32–0.69 ppm. The method has been applied to the analysis
of these compounds in fortified river water samples, after previous preliminary preconcentration by solid-liquid extraction
on a C18 cartridge.
Chromatographia 12/2000; 53(1):40-46. · 1.20 Impact Factor
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ABSTRACT: A kinetic study of the degradation of dinobuton in an alkaline medium has been undertaken by using a stopped-flow pneumatic system. A semiautomatic method for determining dinobuton is proposed for the first time. A detection limit of 0.40 microg mL(-)(1) was calculated. Simultaneous determination of dinobuton and dinoseb can be made by combination of equilibrium and kinetic measurements. The proposed method has been applied to analyze binary mixtures of dinobuton and dinoseb samples with the amount of both components simulating the composition of one undegraded and several degraded dinobuton samples. Also, the procedure has been tested in the analysis of a commercial formulation of dinobuton and the results validated with high-performance liquid chromatography (HPLC).
Journal of Agricultural and Food Chemistry 06/1999; 47(5):1976-80. · 2.82 Impact Factor
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Biomedical Chromatography 04/1999; 13(2):189 - 190. · 1.97 Impact Factor
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ABSTRACT: The voltammetric behavior of propyl gallate (PG), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) has been studied at the glassy carbon electrode (static and rotating), in an acetonitrile-water medium using LS, sampled DC, DP and cyclic voltammetry. The use of a Britton-Robinson buffer (pH 2.8) containing 20 % of acetonitrile together with the sampled DC mode allows one to analyze binary and ternary mixtures of these antioxidants by applying a PLS type 1 multivariate approach. After optimization of the parameters of the chemometric procedure, the proposed method was validated with synthetic samples and applied for the determination of these antioxidants in different spiked samples of packet soup.
Electroanalysis 12/1998; 10(7):497 - 505. · 2.87 Impact Factor
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ABSTRACT: Simple binary mixtures composed of very similar pteridines (neopterin and pterin) have been resolved by derivative spectrophotometry. Detection limits of 0.30 microgram ml-1 and 0.12 microgram ml-1 for pterin and neopterin, respectively, have been calculated. Also, different mixtures of pteridines considered as disease markers, such as pterin, neopterin, xanthopterin and isoxanthopterin, have been determined by using a partial least-squares (PLS-2) model. Calibration set containing 0-7 micrograms ml-1 for each component was used. The resolution of several mixtures and single determination was tested in artificial samples.
Journal of Pharmaceutical and Biomedical Analysis 10/1998; 17(8):1325-34. · 2.97 Impact Factor
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ABSTRACT: Multi-wavelength detectors offer improved detection capabilities for liquid chromatographic methods, but require multivariate approaches to utilise all the available information. The photodiode-array detector in high-performance liquid chromatography (HPLC) generates a three-dimensional data matrix, which is conventionally presented as an isometric projection or a contour plot. In this work, a new graphical technique is described for improving the quantitative results obtained from HPLC, using the available spectrochromatographic information in both the time and wavelength domains. The technique consists of performing cross-sections through the data matrix to obtain the maximum analytical information for each of the analytes. Hence, the resolution of overlapping peaks and the sensitivity in the determination are optimised. In order to demonstrate the validity and simplicity of the approach, the method has been applied to the resolution of synthetic mixtures of iprodione, procymidone and chlorothalonil. Also, the method has been satisfactorily applied to the simultaneous determination of the pesticides in environmental groundwater samples.
Talanta 09/1998; 46(6):1329-40. · 3.79 Impact Factor
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ABSTRACT: A sensitive and simple liquid chromatographic method to determine glyoxal, methylglyoxal, and diacetyl is reported. The method is based on the conversion to the corresponding pteridin derivatives (pterin, 6-methylpterin, and 6,7-dimethylpterin). The proposed method using fluorometric detection has been applied to the determination of the three alpha-dicarbonyl compounds in human urine. Linearity (peak area vs concentration of alpha-dicarbonyl) was observed at least up to 43 microM. Detection limits of 32 pmol for glyoxal, 11 pmol for methylglyoxal, and 99 pmol for diacetyl were calculated (20 microliters was injected). Levels of 132 microM for glyoxal and 15 microM for methylglyoxal were determined in normal urine samples, while diacetyl was not detected.
Analytical Biochemistry 02/1998; 255(2):263-73. · 3.00 Impact Factor
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ABSTRACT: A HPLC method with coulometric detection has been established to carry out the separation of the three nitrofuran derivatives, nitrofurantoin, furazolidone and furaltadone. A Nova-Pak C18 column (150 x 3.9 mm) and a Coulochem II detector from ESA have been used. After obtaining the hydrodynamic curves of the three compounds in the porous graphite electrode a potential of -600 mV was selected as the working potential. The influence of other variables such as mobile phase composition and flow-rate were studied. The mobile phase considered as an optimum was acetonitrile-0.1 M aqueous solution of sodium perchlorate (28:72), with 0.5% glacial acetic acid. The oxygen of the mobile phase was removed with a vacuum system on-line and a nitrogen stream was used to remove the oxygen of the samples. The calibration graphs and the detection limits were established. The method proposed was used, with good results, for the determination of the three compounds in milk.
Journal of Chromatography 04/1997; 764(2):243-8. · 4.53 Impact Factor
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Journal of Liquid Chromatography & Related Technologies 09/1996; 19(16):2681-2690. · 0.71 Impact Factor
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ABSTRACT: The simultaneous determination of salicylic acid and diflunisal in human serum has been accomplished by synchronous fluorimetry, in combination with partial least-squares multivariate calibration. The total luminescence information of the analytes has been used to optimize the spectral data set for the calibration, by analysis of the three-dimensional excitation-emission matrices. The synchronous spectrum, maintaining a constant difference of Deltalambda = 128 nm between the emission and excitation wavelengths, has been selected as optimum to perform the determination. The method is based on the fluorescence of these compounds in chloroform containing 1% (v/v) acetic acid. Serum samples are treated with trichloroacetic acid to remove the proteins, and both analytes are extracted into chloroform-1% (v/v) acetic acid prior to the determination. For concentrations ranging from 60-240 mug ml(-1) of each drug, analytical recoveries range from 96% to 103% for salicylic acid and from 97% to 105% for diflunisal.
Talanta 09/1996; 43(8):1349-56. · 3.79 Impact Factor
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ABSTRACT: A quaternary mixture of sulfametazine (SM), sulfaquinoxaline (SQ), sulfatiazole (ST) and sulfamerazine (SR) was resolved
by application of a partial least squares (PLS) method. A calibration set of standard samples has been designed. Squared correlation
coefficients of 0.9981 for SM, 0.9904 for SR, 0.9993 for SQ and 0.9996 for ST were obtained by using the optimized PLS-1 model.
Artificial mixtures of the four sulfonamides were satisfactorily analyzed. The possibility of a simultaneous determination
in milk is presented.
Fresenius Journal of Analytical Chemistry 04/1996; 354(2):245-249.
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ABSTRACT: A method is described for the simultaneous determination of the main urinary acetylsalicylic acid (aspirin) metabolites, salicyclic, salicyluric and gentisic acids, based on their native fluorescence. The urine was extracted into diethyl ether in acid medium, and back-extracted with glycine/sodium hydroxide buffer solution at pH 9.4. A comparative study of the results found using the excitation, the emission and the combination of the excitation plus the emission spectral data, as analytical signals, was performed. The data set, composed of the excitation plus the emission spectra, was selected as the analytical signal. The optimum wavelengths to record the excitation (lambda(em)=444 nm) and the emission spectra (lambda(ex)=323 nm) were selected to maximize the contribution from gentisic acid, which is the minor urinary metabolite. Partial least squares (PLS-1) multivariate calibration was then applied for the determination. Recovery values from urine samples spiked with salicyclic, salicyluric and gentisic acids varied from 90.1 to 97.6% (mean 93.6%), from 90.0 to 110% (mean 97.9%) and from 89.9 to 104.7% (mean 98.5%), respectively.
Analytical and Bioanalytical Chemistry 10/1995; 353(2):211-4. · 3.78 Impact Factor
