共查询到20条相似文献,搜索用时 15 毫秒
1.
Ricardo J.N Bettencourt da Silva Helena Figueiredo M.Filomena G.F.C Camões 《Analytica chimica acta》2003,477(2):169-185
A methodology for the estimation of sample processing and sub-sampling performance based on the comparison of the global method experimental dispersion of results with the uncertainty estimated from developed models for the subsequent analytical steps is presented. This approach is a valuable alternative to the evaluation of adequate experimental information using a classical ANOVA, since the significance of the sample processing and sub-sampling is evaluated with a higher number of degrees of freedom for the same number of experimental assays, due to the high number of degrees of freedom associated with the uncertainty estimated for the subsequent analytical steps from the combination of the involved sources of uncertainty.Considering the construction of a model to describe the performance of the analytical steps following sample processing and sub-sampling over a broad concentration range, the experimental assays involved at the evaluation of the sample processing and sub-sampling can be performed at any concentration meeting the previously validated range and several months after the development of that model once its adequacy has been proven over time.This approach, which also allows the construction of a detailed performance model for the global analytical method over a broad concentration range, was applied to the determination of pesticide residues in apples by gas-chromatography with electron capture detector.Considering that no information was available regarding the samples heterogeneity, sub-sampling performance was evaluated considering a sample representing the worst expectable homogeneity. This was accomplished by spiking just one out of the 10 halves of apples processed in each sample.The developed model for the performance of the analytical method was successfully and easily applied to routine analysis through an automated link between the information generated by the chromatograph software with a file containing the model. 相似文献
2.
固相萃取-气相色谱-质谱法测定果蔬中36种农药残留 总被引:1,自引:0,他引:1
采用气相色谱-质谱法测定果蔬中36种农药残留。果蔬试样经丙酮-水匀质,二氯甲烷液-液萃取,然后过石墨化炭黑固相萃取柱净化,浓缩定容后在DB-5毛细管色谱柱(30 m×0.25 mm,0.25μm)分离,质谱中选择电喷雾离子源-选择离子监测模式。36种农药残留的质量浓度在一定范围内与其峰面积呈线性关系,检出限(3S/N)均不高于15μg·kg-1。加标回收率在75.3%~115%之间,测定值的相对标准偏差(n=6)在0.6%~7.8%之间。 相似文献
3.
R. J. N. Bettencourt da Silva M. Filomena G. F. C. Camões João Seabra e Barros 《Accreditation and quality assurance》1998,3(4):155-160
Every analytical result should be expressed with some indication of its quality. The uncertainty as defined by Eurachem ("parameter
associated with the result of a measurement that characterises the dispersion of the values that could reasonably be attributed
to the, . . ., quantity subjected to measurement") is a good tool to accomplish this goal in quantitative analysis. Eurachem
has produced a guide to the estimation of the uncertainty attached to an analytical result. Indeed, the estimation of the
total uncertainty by using uncertainty propagation laws is components-dependent. The estimation of some of those components
is based on subjective criteria. The identification of the uncertainty sources and of their importance, for the same method,
can vary from analyst to analyst. It is important to develop tools which will support each choice and approximation. In this
work, the comparison of an estimated uncertainty with an experimentally assessed one, through a variance test, is performed.
This approach is applied to the determination by atomic absorption of manganese in digested samples of lettuce leaves. The
total uncertainty estimation is calculated assuming 100% digestion efficiency with negligible uncertainty. This assumption
was tested.
Received: 3 November 1997 · Accepted: 2 January 1998 相似文献
4.
Koichi Inoue Nuntawat Prayoonhan Haruhito Tsutsui Tasuku Sakamoto Maiko Nishimura Toshimasa Toyo'oka 《Journal of separation science》2013,36(8):1356-1361
Dichlorprop is available for agricultural use as a chiral pesticide. In this study, the stereoselective determination of dichlorprop enantiomers in tea samples such as green, black, jasmine, and oolong was developed by ultra performance LC with fluorescence spectrometry after covalent chiral derivatization. The separation was achieved on an Acquity BEH C18 column with the mobile phase consisting of 0.1% formic acid in acetonitrile/water at a flow rate of 0.4 mL/min. In the covalent chiral derivatization using (S)‐(+)‐4‐(N,N‐dimethylaminosulfonyl)‐7‐(3‐aminopyrrolidin‐1‐yl)‐2,1,3‐benzoxadiazole, the peak resolution between the S and R‐dichlorprop enantiomers was 2.6. LODs and LOQs values were 10 and 50 ng/mL standard solution. The linearity of the calibration curves yielded the coefficients (r2 > 0.99, ranging from 0.05 to 5 μg/mL) of determination of each of the dichlorprop enantiomers. SPE extraction was used for the sample preparation of dichlorprop in various tea samples. Recoveries were in the range of 82.4–97.6% with associated precision values (within‐day: 82.4–95.8%, n = 6, and between‐day: 83.7–97.6% for 3 days) for repeatability and reproducibility. Based on this result, our method has been proven to be highly efficient and suitable for the routine assay of dichlorprop enantiomers in various tea samples. We propose that the ultra performance LC assay after covalent chiral derivatization would be the renewed tools in the era of chiral stationary platform for chiral pesticide residues in foods. 相似文献
5.
M. Naceur Haouet M. Serena Altissimi Marisa Framboas Roberta Galarini 《Accreditation and quality assurance》2006,11(1-2):23-28
The aim of this paper is to compare the performance parameters of the Volhard method for chlorides determination obtained
applying the bottom-up approach with those experimentally achieved. The method precision, trueness, detection and quantification
limits and ruggedness are determined analysing various foods with different chloride contents. Otherwise, the measurement
uncertainty is assessed applying the bottom-up approach using only pen and paper. The comparison between the performances
established with both methods shows the validity of the metrological approach for volumetric procedures.
Presented at AOAC Europe/Eurachem Symposium March 2005, Brussels, Belgium 相似文献
6.
In this work, an analytical method for GC using direct solid sample introduction was developed to tackle the problem regarding quick detection of pesticide residue in crops and large-scale screening of samples. 10 mg of the crop solid sample without sample pre-treatment was directly introduced into a modified split/splitless injector for GC analysis. A split/splitless injector was modified to quickly remove oxygen and low boiling-point matrices of the sample. The whole sampling procedure was simple and it required less than 5 min. The experimental parameters including injector-port temperature, removal of oxygen and low boiling point matrices, size and the amount of the solid sample, oven temperature program were studied. Satisfactory recoveries of 6 pesticides (methyl parathion, fenitrothion, aldrin, dieldrin, endosulfan, o,p′-DDT) were obtained in maize and rice sample. Relative standard deviation was less than 15%. Experimental results showed that the proposed method was quick and reliable for pesticide residues analysis in crops. 相似文献
7.
Assessment of uncertainty in pesticide multiresidue analytical methods: main sources and estimation 总被引:1,自引:0,他引:1
《Analytica chimica acta》2002,454(2):297-314
The estimation of the uncertainty associated to analytical methods is necessary in order to establish the comparability of results. Multiresidue analytical methods lack very often of information about uncertainty of results with likely implications when results are compared with maximum residue levels (MRL) established by regulations. An adequate identification and estimation of each uncertainty source allows to laboratories to establish the accuracy of results and to balance with time-consuming and costs. 相似文献
8.
Cristina BlascoMónica Fernández Yolanda Picó Guillermina FontJordi Mañes 《Analytica chimica acta》2002,461(1):109-116
A liquid chromatographic (LC) atmospheric pressure chemical ionization mass spectrometric (MS) method is described for determining imidacloprid, carbendazim, methiocarb and hexythiazox in peaches and nectarines. The samples were extracted with ethyl acetate and anhydrous sodium sulfate. Recoveries yield for spiking samples were ranged from 64±9% (R.S.D) for carbendazim to 108±14% (R.S.D.) for hexythiazox at the concentration of 0.1 mg kg−1 (n=5). The correlation coefficients were greater than 0.998 over the range between 0.02 and 2 mg kg−1. The limits of quantitation (LOQ) were 0.02 mg kg−1 for all the pesticides. The applicability of the method to detect and quantify imidacloprid, carbendazim, methiocarb and hexythiazox was demonstrated successfully in 159 peach and nectarine samples obtained from an agricultural co-operative. The calculation of the estimated daily intakes (EDI) from these data showed that contribution of fruits to dietary intakes were much lower than acceptable daily intakes (ADI) proposed by international agencies. 相似文献
9.
Comparison of QuEChERS sample preparation methods for the analysis of pesticide residues in fruits and vegetables 总被引:1,自引:0,他引:1
Steven J. Lehotay Kyung Ae Son Hyeyoung Kwon Urairat Koesukwiwat Wusheng Fu Katerina Mastovska Eunha Hoh Natchanun Leepipatpiboon 《Journal of chromatography. A》2010,1217(16):2548-2560
This article describes the comparison of different versions of an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits and vegetables by concurrent use of gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) for detection. The sample preparation approach is known as QuEChERS, which stands for “quick, easy, cheap, effective, rugged and safe”. The three compared versions were based on the original unbuffered method, which was first published in 2003, and two interlaboratory validated versions: AOAC Official Method 2007.01, which uses acetate buffering, and European Committee for Standardization (CEN) Standard Method EN 15662, which calls for citrate buffering. LC–MS/MS and GC–MS analyses using each method were tested from 50 to 1000 ng/g in apple–blueberry sauce, peas and limes spiked with 32 representative pesticides. As expected, the results were excellent (overall average of 98% recoveries with 10% RSD) using all 3 versions, except the unbuffered method gave somewhat lower recoveries for the few pH-dependent pesticides. The different methods worked equally well for all matrices tested with equivalent amounts of matrix co-extractives measured, matrix effects on quantification and chemical noise from matrix in the chromatographic backgrounds. The acetate-buffered version gave higher and more consistent recoveries for pymetrozine than the other versions in all 3 matrices and for thiabendazole in limes. None of the versions consistently worked well for chlorothalonil, folpet or tolylfluanid in peas, but the acetate-buffered method gave better results for screening of those pesticides. Also, due to the recent shortage in acetonitrile (MeCN), ethyl acetate (EtOAc) was evaluated as a substitute solvent in the acetate-buffered QuEChERS version, but it generally led to less clean extracts and lower recoveries of pymetrozine, thiabendazole, acephate, methamidophos, omethoate and dimethoate. In summary, the acetate-buffered version of QuEChERS using MeCN exhibited advantages compared to the other tested methods in the study. 相似文献
10.
Zougagh M Téllez H Sánchez A Chicharro M Ríos A 《Analytical and bioanalytical chemistry》2008,391(2):709-714
A procedure for the analytical validation of a rapid supercritical fluid extraction amperometric screening method for controlling
macrocyclic lactone mycotoxins in maize flour samples has been developed. The limit established by European legislation (0.2 mg
kg−1), in reference to zearalenone (ZON) mycotoxin, was taken as the reference threshold to validate the proposed method. Natural
ZON metabolites were also included in this study to characterize the final screening method. The objective was the reliable
classification of samples as positive or negative samples. The cut-off level was fixed at a global concentration of mycotoxins
of 0.17 mg kg−1. An expanded unreliability zone between 0.16 and 0.23 mg kg−1 characterized the screening method for classifying the samples. A set of 30 samples was used for the final demonstration
of the reliability and usefulness of the method. 相似文献
11.
J. L. Martínez Vidal A. Garrido Frenich T. López López I. Martínez Salvador L. Hajjaj el Hassani M. Hassan Benajiba 《Chromatographia》2005,61(3-4):127-131
An analytical method for determining residues of twenty pesticides by liquid chromatography (LC) coupled to electrospray ionisation (ESI) tandem mass spectrometry (MS-MS) in eight commodities, cucumber, tomato, pepper, green bean, eggplant, zucchini, melon and watermelon, has been developed and validated. On one hand, calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract of each target matrix. On the other hand, calibration curves and recoveries for each commodity were compared. Cucumber was selected as potential reference matrix for the target vegetables. 相似文献
12.
A novel admicelle composing of a dialkylated anionic surfactant, di-2-ethylhexyl sodium sulfosuccinate (Aerosol-OT, AOT) and gamma-alumina was prepared by mixing them in acidic aqueous solution. The amount of the maximum sorption of AOT on 1 g of alumina at pH 2 was ca. 130 mg. By comparing the fluorescence spectra of N-phenyl-1-naphthylamine in different solvents, the solvent property of AOT-gamma-alumina admicelles was corresponding to that of toluene or diethyl ether. Thus, the AOT-gamma-alumina admicelles had greater hydrophobicity than SDS-gamma-alumina admicelles having similar hydrophobicity to 1-octanol or ethyl acetate. Hydrophobic organic compounds, chlorophenols having more than three chloro substituents, octylphenol, nonylphenol, dibutyl phthalate was almost quantitatively (98% or more) collected onto AOT admicelles composing of 1.5 g gamma-alumina and 150 mg AOT. The greater collection yields rather than those in SDS-admicellar system were ascribable to greater hydrophobicity and stability of AOT admicelles. After the 500-fold concentration, traces (nM) of organic contaminants in water samples were successfully detected with an HPLC having a photometric detector. 相似文献
13.
14.
Edmond J. Baratta 《Accreditation and quality assurance》2001,6(2):84-86
The U.S. Food and Drug Administration's (FDA) Radionuclides in Food Program was reinstituted in 1973, expanded in 1975 and
again in 1990, to its present status. The need for reference materials for radionuclides in food samples was recognized as
early as 1962. There were no available reference materials for these types of samples at that time. The materials developed
to assure that the results being obtained were acceptable were primarily milk, water and food. The radionuclides of interest
were iodine-131, cesium-137 and other short-lived radionuclides found in fission products. These were first issued through
the then Health, Education and Welfare Department's Analytical Quality Control Program and, later, in 1970 through the Environmental
Protection Agency (EPA). In November 1998, the EPA discontinued this program. The FDA is proposing to reinstitute part of
this program, as a primary laboratory, traceable to the National Institute of Technology (NIST) and included in this, the
FDA proposes to supply the States and/or their contractors with low-level standards and with milk- and water intercomparison
samples. It will also use these results where possible as collaborative studies to validate some of the more recent methods
adopted by the American Society for Testing and Materials (ASTM), American Public Health Association (APHA) and Association
of Official Analytical Chemists International (AOAC, Int'l.) The FDA will also supply low-level standards to compliment these
programs as did the EPA. It is expected that these samples will serve as performance evaluation samples for the States programs. 相似文献
15.
Summary A fast and efficient method has been developed for clean-up of fenpropathrin and fluvalinate for gas chromatographic determination
of their residues in crops, grain and soil. Charcoal (Darco-G-60) was used as adsorbent and the pyrethroids recovered by washing
the adsorbent with hexane-acetone (9∶1). The method provides a clear filtrate with no interfering peaks in the chromatogram.
Recoveries ranged 91.00–100%. 相似文献
16.
A simple method is described for the quantitative determination of organochlorine pesticides and polychlorinated biphenyls (PCB's) in water at the sub-ppb level. A micro gas-phase extractor advantageously replaces other preconcentration and purification techniques. The extract is analyzed by capillary gas chromatography without further enrichment. The recovery at the ppb level was nearly 100% for organochlorine pesticides and more than 80% for PCB's. The complete procedure including sample preparation, steam distillation-extraction, and capillary gas chromatographic analysis is carried out in less than four hours. 相似文献
17.
Analytical validation is a key requirement to asses and to prove a method's reliability and suitability for an intended use. Planar chromatographic procedures are used in different applications ranging from simple screening tests to sophisticated instrumental quantitative assays of analytes in complex matrices. This paper intends to give guidance on how to adopt international accepted formal requirements and guidelines for validation of these different TLC/HPTLC procedures. In addition, some selected parameters for robustness testing and for on going quality assurance of analytical performance based on control charts are reported. 相似文献
18.
A simple and rapid method for determining ethylenebisdithiocarbamates (EBDCs; mancozeb, maneb, and zineb) in fruits and vegetables
is described. EBDCs are transformed into dimethylethylenebisdithiocarbamate (EBDC-dimethyl) by methylation after their decomposition
with ethylenediaminetetraacetic acid (EDTA). These processes were performed simultaneously in this method. Dimethyl sulfate
was used as the methylation reagent, and acetonitrile extracts obtained from partitioning with anhydrous magnesium sulfate
and sodium chloride were subjected to dispersive solid-phase extraction with the primary secondary amine sorbent. Liquid chromatography
with tandem mass spectrometry in the positive heated-electrospray ionization mode was used for the determination of EBDC-dimethyl
produced from EBDCs. The method was validated at levels of 10, 50, and 100 ng g−1 maneb as a representative EBDC. The recoveries of the present method were between 71 and 101%. The limits of detection and
quantification were 0.24 and 0.8 ng g−1 maneb, respectively. 相似文献
19.
A method for constant-rate heating of milligram-sized samples 总被引:1,自引:0,他引:1
S. I. Stoliarov R. N. Walters R. E. Lyon 《Journal of Thermal Analysis and Calorimetry》2007,89(2):367-371
Heating a milligram-sized sample of material at a constant heating rate is usually achieved by controlling the temperature
of an electric-resistance furnace with a proportional integral derivative (PID) controller. Here we present a new method for
constant-rate heating that is based on a semi-empirical mathematical expression relating sample temperature, heating rate,
and electric power supplied to the furnace. This method uses PID control only for second-order corrections of the heating
rate. The linearity of the sample temperature vs. time curves obtained by applying this method to a simple furnace setup is the same as the linearity of the curves generated
by modern commercial thermogravimetric analyzers. 相似文献
20.
J. Sanz-Asensio A. P. Martínez-Prado M. Plaza-Medina M. T. Martínez-Soria M. Pérez-Clavijo 《Chromatographia》1999,49(3-4):155-160
Summary A study of the decay of acephate in apple samples was carried out, including penetration studies and the transformation of
acephate in to its main metabolite, methamidophos. Sample treatment involved extraction with ethyl acetate and determination
by gas chromatography with nitrogen—phosphorus detection (GC-NPD). Three different parts of the fruit were studied separately:
apple surface, peel and pulp. Recoveries were measured at three spiked levels, ranging from 0.050 to 0.504 μg g−1 for acephate and 0.049 to 0.492 μg g−1 for methamidophos. Mean acephate recoveries were 93.0 to 115.5% from peel and 99.2 to 110.2% from pulp, while methamidophos
recoveries were 77.2 to 104.2% and 77.5 to 98.6% from peel and pulp, respectively (n=6). Results showed that acephate penetrates into the fruit, where it is transformed to methamidophos. This transformation
was not seen on the external apple surface. 相似文献