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1.
Cuadros-Rodríguez L Almansa-López EM García-Campaña AM González-Casado A Egea-González FJ Garrido-Frenich A Martínez-Vidal JL 《Talanta》2005,66(4):1063-1072
The use of the recovery term has presented some confusion in Analytical Chemistry. Recent IUPAC recommendations propose to distinguish between two terms: recovery or recovery factor, ℜ, and apparent recovery, ℜ*. Apparent recovery includes recovery factor and a new recovery term proposed in this paper, named calibration recovery, ℜC, which depends of the type of systematic error due to the matrix effect (constant and/or proportional) and is related to the applied calibration methodology. This paper highlights the dependence of the calibration recovery on the sample analyte concentration and, for extension, of the apparent recovery, defines the recovery profile, and makes evident the need to determine a “fit for purpose” analyte concentration interval to comply with a regulated recovery requirements. An approach to estimate the calibration recovery and its associated uncertainty in relation to the above-mentioned dependence is presented. The usefulness of the proposed methodology has been shown in the quantification of a pesticide by GC-ECD for assessing dermal exposure. 相似文献
2.
M. Thompson 《Accreditation and quality assurance》1998,3(3):117-121
Uncertainty of sampling is the contribution from sampling errors to the combined uncertainty associated with an analytical
measurement when the measurand is the concentration of the analyte in the 'target', the total bulk of material that the sample
is meant to represent. Of the errors considered to contribute to uncertainty, random errors of sampling, characterised by
precision, are much more accessible to investigation than those due to bias. Where an approximation to random sampling can
be achieved, realistic precisions can normally be estimated. In some instances reproducibility precision is significantly
greater than repeatability precision, and the contribution of between-sampler variations to sampling uncertainty must be acknowledged.
However, the collaborative trial of a sampling method is an expensive and difficult exercise to execute. A system of internal
quality control for routine sampling can be introduced. Fitness for purpose has been defined in terms of the required combined
uncertainty of sampling and analysis.
Received: 4 November 1997 · Accepted: 26 November 1997 相似文献
3.
Polati S Roz M Angioi S Gianotti V Gosetti F Marengo E Rinaudo C Gennaro MC 《Talanta》2005,68(1):93-98
A great mean value of recovery for extraction of 3,4-dichloroaniline from a soil is calculated from individual recovery values evaluated for four different fractions of the soil. Then the uncertainty associated to this great mean recovery is calculated and used to know whether to apply or not the correction in routine analysis performed for the same kind of soil and the same analyte. The most representative fractions that, as a function of particle size, can be identified in a soil are: sand (2.000-0.063 mm), coarse silt (0.063-0.020 mm), fine silt (0.020-0.002 mm) and clay (≤0.002 mm). These fractions are here considered as sub matrices of the matrix soil.To evaluate the mean recovery and its uncertainty, as a function of the sub matrix and the analyte concentration, the four blank soil fractions were spiked with the analyte at three concentration levels (10.0, 50.0 and 100.0 mg/kg) and three replicates were performed for each experiment. The 36 samples were extracted by accelerated solvent system and the amounts of 3,4-dichloroaniline were determined by RP-HPLC analysis. From the 36 individual recovery values, the great mean and its uncertainty are calculated.Experiments performed on samples of soil of similar composition, spiked with known concentrations of the same analyte showed the goodness of the mean recovery value. 相似文献
4.
In both European legislation relating to the testing of food and the recommendations of the Codex Alimentarius Commission, there is a movement away from specifying particular analytical methods towards specifying performance criteria to which any methods used must adhere. This ‘criteria approach’ has hitherto been based on the features traditionally used to describe analytical performance. This paper proposes replacing the traditional features, namely accuracy, applicability, detection limit and limit of determination, linearity, precision, recovery, selectivity and sensitivity, with a single specification, the uncertainty function, which tells us how the uncertainty varies with concentration. The uncertainty function can be used in two ways, either as a ‘fitness function’, which describes the uncertainty that is fit for purpose, or as a ‘characteristic function’ that describes the performance of a defined method applied to a defined range of test materials. Analytical chemists reporting the outcome of method validations are encouraged to do so in future in terms of the uncertainty function. When no uncertainty function is available, existing traditional information can be used to define one that is suitable for ‘off-the-shelf’ method selection. Some illustrative examples of the use of these functions in methods selection are appended. 相似文献
5.
Edith Chow Jan Herrmann Christopher S. Barton Burkhard Raguse Lech Wieczorek 《Analytica chimica acta》2009,632(1):135-202
The influence of film morphology on the performance of inkjet-printed gold nanoparticle chemiresistors has been investigated. Nanoparticles deposited from a single-solvent system resulted in a “coffee ring”-like structure with most of the materials deposited at the edge. It was shown that the uniformity of the film could be improved if the nanoparticles were deposited from a mixture of solvents comprising N-methyl-2-pyrrolidone and water. Electrical conductivity measurements showed that both “coffee ring” and “flat” films were qualitatively similar suggesting that the films have similar nanoscale structures. To form the functional chemiresistor device, the 4-(dimethylamino)pyridine coating on the nanoparticle was exchanged with 1-hexanethiol to provide a hydrophobic sensing layer. The performance of 1-hexanethiol coated gold nanoparticle chemiresistors to small organic molecules, toluene, dichloromethane and ethanol dissolved in 1 M KCl in regard to changes in impedance and response times was unaffected by the film morphology. For larger hydrocarbons such as octane, the rate of uptake of the analyte into the film was significantly faster when the flatter nanoparticle film was used as opposed to the “coffee ring” film which has a thicker edge. Furthermore, the presence of potassium and chloride ions in the solution media does not significantly affect the impedance of the nanoparticle film at 1 Hz (<2% variation in film impedance over more than four orders of magnitude change in ionic strength). However, the ionic strength of the media affected the partitioning of the analyte into the hydrophobic nanoparticle film. The response of the sensor was found to increase with an increased salt concentration due to a salting-out of the analyte from the solution. 相似文献
6.
The ‘characteristic function’ with two empirically determined parameters α and β, is proposed as a general purpose function to describe the variation of
precision (in terms of standard deviation σ), or uncertainty, with analyte concentration c (here denoting any compositional quantity), for specific analytical methods applied to a defined type of test material. In
this study it is applied to examples of analytical data collected under ‘instrumental’ conditions for estimating precision.
The function fitted the data well, with no systematic lack of fit. The study therefore extends the range of applications of
this function. 相似文献
7.
The ‘characteristic function’ is a two-parameter function relating precision or uncertainty in analytical results to the concentration
of the analyte. In previous papers, in this series, it has been shown to provide a good model of precision measured: (a) under
reproducibility conditions and (b) under ‘instrumental’ conditions. The present study shows that it is also a valuable model
for precision estimated under repeatability conditions. The study data were large sets of duplicated results obtained for
the purposes of quality control on typical test materials in routine analysis. As the analytes exhibited concentration ranges
encompassing between one and three orders of magnitude, there was ample scope to demonstrate goodness of fit to the function
under different circumstances. 相似文献
8.
In this work, is given the Combined Standard Uncertainty (CSU) calculation procedure, which can be applied in spectrophotometric measurements. For the assessment of the computations, different approaches are discussed, such as the contribution to the Combined Standard Uncertainty of the reproducibility, the repeatability, the total bias, the calibration curve, and the type of the measurand. Results of inter-laboratory measurements confirmed the assumptions. For the minimization of the errors propagation a controlled experimental procedure was applied by this laboratory, called “errors propagation break-up” (ERBs). The uncertainty of sample concentration from a reference curve dominates the Combined Standard Uncertainty. The contribution of the method and the laboratory bias (total bias) to the CSU is insignificant under controlled conditions of a measurement. This work develops a simple methodology that can be utilized to evaluate the uncertainty and errors control on routine methods used both by academic researchers or the industrial sector. 相似文献
9.
A unique solid phase extraction (SPE) sorbent having a removable “stationary phase” is presented. This removable phase consists of alkyltrimethylammonium surfactant, which is initially immobilized onto hydrophilic strong cation exchange resin. The surfactant chain through hydrophobic interactions extracts hydrophobic analytes in the same manner as conventional bonded alkyl moieties on silica-based non-polar sorbents. For the extraction of very hydrophobic species with conventional sorbents, solvents such methylene chloride and benzene are needed to break strong hydrophobic interactions for efficient elutions. These solvents however are toxic to the analyst and present a significant environmental concern. Using a removable “stationary phase”, hydrophobic interactions need not be broken between the analyte and the sorbent. In the presented approach, the surfactant (“stationary phase”) is removed via ion exchange with exchange ions in very mild aqueous-based and instrument compatible solutions. The analyte, being associated with the surfactant, is also removed in the process. Very efficient elutions of analytes, regardless of hydrophobicity, under mild and more favorable environmental conditions are a direct benefit of having a removable “stationary phase”. Rinse solution parameters explored include exchange cation type and concentration, and alcohol type and concentration. The extraction of three test molecules of varying hydrophobicity, naphthalene, pyrene and benzo(ghi)perylene, is investigated using this sorbent material. 相似文献
10.
Luciano Farias Almeida Edvan Cirino Silva Mario Cesar Ugulino Araujo 《Analytica chimica acta》2003,486(1):143-148
A novel strategy for implementing the automatic standard addition method (SAM) is described. By using a flow-batch system that presents the intrinsic favourable characteristics of the flow and batch techniques, the proposed strategy performs fast standard additions with sufficient flexibility and versatility and employs only one standard solution per analyte. To calculate the analyte concentration, a mathematical model based on a classical SAM and flow variables of the system was developed. The proposed flow-batch SAM was applied to copper determination by flame atomic absorption spectrometry (AAS) in sugar cane-made alcoholic beverages, known as “Cachaça”, available in Brazil. A SAM has been recommended for these analyses because “Cachaças” presents a significantly different composition causing matrix effects and copper determination by calibration using matrix-matching standards can yield inaccurate results. The results show good agreement between the obtained values with the proposed flow-batch SAM and a manual SAM. The mean relative errors and overall standard deviations were always <1.0% (n=6) and 0.2 mg l−1, respectively, for 1.0-7.0 mg l−1 Cu. By using five standard addition levels, the sample throughput was 70 h−1 and the consumption of sample and standard solution were 1.5 and 0.5 ml per analysis, respectively. 相似文献
11.
《Analytica chimica acta》2004,506(1):71-80
We describe an estimation of measurement uncertainty calculated by the “bottom-up” approach for the determination of the oestrogenic compound nonylphenol in treated water samples by solid-phase extraction (SPE) and solid-phase microextraction (SPME) procedures and GC/MS detection. The results were compared and the different contributions to the uncertainty were evaluated. A study of the linear range was established and validation was performed for both methods using statistical analysis of several indicative parameters. In terms of validation data, precision (R.S.D. values <20%) and trueness (relative error <11%) were obtained for both methods under day-to-day conditions. The results of the estimation of measurement uncertainty obtained for both methods for concentrations higher than 1 μg/l have demonstrated that the time-consuming SPE method has a lower relative uncertainty (32%) than the SPME method (42.8%). The chromatographic uncertainty value was the main factor in the SPME method whereas the recovery factor (used to calculate the concentration) was the main contribution to uncertainty in the SPE method. 相似文献
12.
An approach to the assessment of the limit of detection and the limit of quantitation using uncertainty calculation is discussed.
The approach is based on the known evaluation of the limits of detection and quantitation as concentrations of the analyte
equal to three and ten standard deviations of the blank response, respectively. It is shown that these values can be calculated
as the analyte concentrations, for which relative expanded uncertainty achieves 66% and 20% of possible results of the analyte
determination, correspondingly. For example, the calculation is performed for the validation of a new method for water determination
in the presence of ene-diols or thiols, developed for analysis of chemical products, drugs or other materials which are unsuitable
for direct Karl Fischer titration. A good conformity between calculated values and experimental validation data is observed.
Received: 27 July 1998 · Accepted: 29 November 1998 相似文献
13.
14.
A methodology for the evaluation of the performance of an analytical method for incurred samples is presented. Since this methodology is based on intra-laboratory information, it is suitable for analytical fields that lack reference materials with incurred analytes and it can be used to evaluate the analytical steps prior to the analytical portion, which are usually excluded in proficiency tests or at the certification of reference materials. This methodology can be based on tests performed on routine samples allowing the collection of information on the more relevant combinations analyte/matrix; therefore, this approach is particularly useful for analytical fields that involve a high number of analyte/matrix combinations, which are difficult to cover even considering the frequent participation in expensive proficiency tests.This approach is based on the development of a model of the performance of the analytical method based on the differential approach for the quantification of measurement uncertainty and on the comparison of recovery associated with each one of the analytical steps whose performance can vary with the analyte origin, for spiked and incurred samples.This approach was applied to the determination of pesticide residues in apples. For the analytes covered, no evidence was found that the studied sample processing and extraction steps performance for this matrix varies with the analyte origins. 相似文献
15.
L. Romero 《Analytica chimica acta》2006,565(2):136-144
The ability of reverse microemulsions of the surfactant bis [2-ethylhexyl] sulphosuccinate (AOT) in heptane to extract and preconcentrate eight biogenic amines present in aqueous matrices has been explored. The “phase transfer” method, in which the surfactant solution is contacted with an aqueous salt solution containing the analytes, has been used as the analytical methodology. The extraction efficiencies have been compared with those obtained by using the “cloud point” extraction technique with Triton X-114 as surfactant, and with methylene chloride as a typical extracting solvent. In order to improve extraction and detection as compared with the underivatized amines, the fluorescent reagent dansyl chloride has been used to obtain the more hydrophobic and thus, easily extractable dansyl derivatives. Although extraction of most of the biogenic amines is high, extraction of their dansyl derivatives is practically 100%. The procedure was successfully applied to the analysis of commercial fruit juices. The analytical methodology is sensitive, fast, simple and reproducible. The LOD were in the vicinity of 1 and 2 pmol, which is similar or better than other techniques. The micellar phase is compatible with reverse phase HPLC mobile phases, which allow direct injection of the analyte after extraction. This is an advantage over solid phase extraction (SPE), where incomplete recovery can occur. Moreover, AOT showed to be better extracting surfactant for biogenic amines (and their corresponding dansyl derivatives) than Triton X-114 at the same concentration. 相似文献
16.
Solutions of Cd, Cu and Pb at concentrations of about 1000 mg/l were prepared by dissolving the pure metals in HNO3. Their concentration was verified by complexometric titration and by gravimetric analysis (Cu with salicylaldoxime, Cd with
quinaldinic acid and Pb with 8-hydroxyquinoline). The results of the two methods were very similar and the uncertainty values
were equal. However, the gravimetric determination can be regarded as more reliable, because titrimetric analysis is more
prone to error due to inaccurate end-point reading. The expanded uncertainty of the concentrations of Cd and Cu attained 1 mg/l,
which is half the value typically obtained for similar solutions from commercial manufacturers. To achieve such precise results,
the bias had to be reduced by the highest possible extent, particularly by calibrating both the balance and the volumetric
glassware. In addition to the uncertainty of the basic operations (volumetric and gravimetric), the uncertainty of the atomic
and molecular weights constituted an appreciable component in the combined standard uncertainty; this manifested itself in
the determination of Pb, where the expanded uncertainty was 2 mg/l.
Received: 24 September 1998 / Accepted: 25 January 1999 相似文献
17.
Long Yuan Li Ma Lisa Dillon R. Marcus Fancher Huadong Sun Mingshe Zhu Lois Lehman-McKeeman Anne-Françoise Aubry Qin C. Ji 《Analytica chimica acta》2016
LC-MS/MS has been widely applied to the quantitative analysis of tissue samples. However, one key remaining issue is that the extraction recovery of analyte from spiked tissue calibration standard and quality control samples (QCs) may not accurately represent the “true” recovery of analyte from incurred tissue samples. This may affect the accuracy of LC-MS/MS tissue bioanalysis. Here, we investigated whether the recovery determined using tissue QCs by LC-MS/MS can accurately represent the “true” recovery from incurred tissue samples using two model compounds: BMS-986104, a S1P1 receptor modulator drug candidate, and its phosphate metabolite, BMS-986104-P. We first developed a novel acid and surfactant assisted protein precipitation method for the extraction of BMS-986104 and BMS-986104-P from rat tissues, and determined their recoveries using tissue QCs by LC-MS/MS. We then used radioactive incurred samples from rats dosed with 3H-labeled BMS-986104 to determine the absolute total radioactivity recovery in six different tissues. The recoveries determined using tissue QCs and incurred samples matched with each other very well. The results demonstrated that, in this assay, tissue QCs accurately represented the incurred tissue samples to determine the “true” recovery, and LC-MS/MS assay was accurate for tissue bioanalysis. Another aspect we investigated is how the tissue QCs should be prepared to better represent the incurred tissue samples. We compared two different QC preparation methods (analyte spiked in tissue homogenates or in intact tissues) and demonstrated that the two methods had no significant difference when a good sample preparation was in place. The developed assay showed excellent accuracy and precision, and was successfully applied to the quantitative determination of BMS-986104 and BMS-986104-P in tissues in a rat toxicology study. 相似文献
18.
Ruud J. B. Peters Ingrid J. W. Elbers Mirjam D. Klijnstra Alida A. M. Stolker 《Accreditation and quality assurance》2011,16(11):567-574
Nowadays, a lot of time and resources are used to determine the quality of goods and services. As a consequence, the quality
of measurements themselves, e.g., the metrological traceability of the measured quantity values is essential to allow a proper
evaluation of the results with regard to specifications and regulatory limits. This requires knowledge of the measurement
uncertainties of all quantity values involved in the measurement procedure, including measurement standards. This study shows
how the uncertainties due to the preparation, as well as the chemical and compositional stability of a chemical measurement
standard, or calibrator, can be estimated. The results show that the relative standard uncertainty of the concentration value
of a typical analytical measurement standard runs up to 2.8% after 1 year. Of this, 1.9% originates from the preparation of
the measurement standard, while 2.0 and 0.53% originate from the chemical and compositional stability during storage at −20 °C.
The monthly preparation of working calibrators stored at 4 °C and used on a weekly basis, results in an additional standard
uncertainty of the analyte concentration value of 0.35% per month due to compositional stability. While the preparation procedure
is the major contributor to the total measurement uncertainty, the uncertainties introduced by the stability measurements
are another important contributor, and therefore, the measurement procedure to evaluate stability is important to minimize
the total measurement uncertainty. 相似文献
19.
Optical sensing systems for microfluidic devices: a review 总被引:1,自引:0,他引:1
This review deals with the application of optical sensing systems for microfluidic devices. In the “off-chip approach” macro-scale optical infrastructure is coupled, while the “on-chip approach” comprises the integration of micro-optical functions into microfluidic devices. The current progress of the use of both optical sensing approaches in microfluidic devices, as well as its applications is described. In all cases, sensor size and shape profoundly affect the detection limits, due to analyte transport limitation, not to signal transduction limitation. The micro- or nanoscale sensors are limited to picomolar-order detection for practical time scales. The review concludes with an assessment of future directions of optical sensing systems for integrated microfluidic devices. 相似文献
20.
S.Kamaledin SetarehdanJohn J Soraghan David LittlejohnDaran A Sadler 《Analytica chimica acta》2002,452(1):35-45
A novel strategy for building and maintaining calibration models has been developed for use when the future boundaries of the sample set are unknown or likely to change. Such a strategy could have an impact on the economics and time required to obtain and maintain a calibration model for routine analysis. The strategy is based on both principal component analysis (PCA) and partial least squares (PLS) multivariate techniques. The principal action of the strategy is to define how “similar” a new sample is to the samples currently defining the calibration dataset. This step is performed by residuals analysis, following PCA. If the new sample is considered to have a spectrum “similar” to previously available spectra, then the model is assumed able to predict the analyte concentration. Conversely, if the new sample is considered “dissimilar”, then there is new information in this sample, which is unknown to the calibration model and the new sample is added automatically to the calibration set in order to improve the model. The strategy has been applied to a real industrial dataset provided by BP Amoco Chemicals. The data consists of spectra of 102 sequential samples of a raw material. The strategy produced an accurate calibration model for both target components starting with only the first four samples, and required a further 17 reference measurements to maintain the model for the whole sampling sequence, which was over a 1-year period. 相似文献