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Feinberg M.,French National Institute for Agricultural Research | Granier G.,French Atomic Energy Commission | Mermet J.-M.,Spectroscopy Forever
Journal of AOAC International | Year: 2010

Validation is a very active field in analytical chemistry as illustrated by the numerous publications addressing this topic. According to most definitions, method validation is required to confirm the fitness-for-purpose of a particular analytical method. When considering interlaboratory validation, organization and calculation of parameters that describe method performance follow well-recognized standards. But the strategy used to verify whether the method is fit for a particular purpose is still under discussion. This paper presents a method for assessing the fitness-for-purpose of analytical methods based on results produced during interlaboratory trials. It is based on the construction of accuracy profiles, which can be used as a graphical decision support tool, and demonstrates how accuracy profiles, initially developed for in-house validations, can be extended to interlaboratory studies. These interlaboratory accuracy profiles use measurements collected under reproducibility conditions to give an interval where an expected proportion of future measurements will be located. This interval can be compared to an acceptability interval defined by the end-user to simply decide whether a method is fit-for-purpose or not. Several examples of application illustrate how data can be interpreted to draw conclusions about produced accuracy profiles and fitness-for-purpose. Hence, the accuracy profile could be used as a harmonized procedure to assess the performance of analytical methods that undergo interlaboratory validation.


Todoli J.L.,University of Alicante | Mermet J.M.,Spectroscopy Forever
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2010

The influence of the acquisition and operating parameters on time correlation between emission line intensities was investigated using axially viewed inductively coupled plasma-multichannel-based emission spectrometry and various sample introduction systems. It was found that to obtain flicker-noise limited signals, necessary to compensate for time-correlated signal fluctuations by internal standardization, the flicker-noise magnitude of the sample introduction system, the integration time and the emission line intensity had to be considered. The highest correlation between lines was observed for ultrasonic nebulization with desolvatation, the noisiest system among those considered, for which the contribution of the uncorrelated shot-noise was negligible. In contrast, for sample introduction systems characterized by lower flicker-noise levels, shot-noise led to high, non-correlated RSD values, making the internal standard method to be much less efficient. To minimize shot-noise, time correlation was improved by increasing the emission line intensities and the integration time. Improvement in repeatability did not depend only on time correlation, but also on the ratio between the relative standard deviations of the analytical and reference lines. The best signal compensation was obtained when RSD values of the reference and analytical lines were similar, which is usually obtained when the system is flicker-noise limited, while departure from similarity can lead to a degradation of repeatability when using the internal standard method. Moreover, the use of so-called robust plasma conditions, i.e. a high power (1500 W) along with a low carrier gas flow rate (0.8 L/min) improved also the compensation. Finally, high correlation and consequent improvement in repeatability by internal standardization was observed also in the presence of complex matrices (sediment and soil samples), although a matrix-induced degradation of the correlation between lines was generally observed when using ultrasonic nebulization. © 2009 Elsevier B.V. All rights reserved.


Sanchez R.,Nutrition and Food science | Todoli J.L.,Nutrition and Food science | Lienemann C.-P.,French Institute of Petroleum | Mermet J.-M.,Spectroscopy Forever
Journal of Analytical Atomic Spectrometry | Year: 2012

The benefits of using a 350 °C heated single pass spray chamber following a segmented flow injection methodology were demonstrated for the analysis of petroleum products through inductively coupled plasma atomic emission spectrometry (ICP-OES). The present work shows that a small sample volume (i.e., 5 μl or less) can be precisely injected into the system following a manual procedure. Two different sample introduction systems were employed: a Cyclonic spray chamber and a single pass spray chamber (a modified version of the Torch Integrated Sample Introduction System, TISIS) equipped with a heating brass hollow cylinder. First the effect of temperature on the peak shape and sensitivity has been studied for a set of nineteen different organic products (gasoline, superethanol, diesel and biodiesel diluted in xylene). The results have proved that the higher the chamber walls temperature, the higher the sensitivity. As a result limits of detection decreased below 7 μg l -1 for elements such as manganese, vanadium and silicon. Furthermore, memory effects were less severe as the temperature raised. Another benefit of increasing the TISIS chamber walls temperature is that matrix effects became less pronounced as compared to a Cyclonic chamber. Thus, at 350 °C non-spectral interferences are eliminated likely because the analyte transport efficiency to the plasma is close to 100% irrespective of the sample analyzed. This has two important consequences: (i) it is possible to obtain a calibration line by merely modifying the injected solution volume and (ii) a single xylene based solution can be used as a universal standard. The developed procedure was applied to the analysis of nineteen spiked petroleum derivatives with recoveries for manganese, silicon, vanadium and copper in the range 95-106%. © 2012 The Royal Society of Chemistry.


Sanchez R.,Nutrition and Food science | Todoli J.L.,Nutrition and Food science | Lienemann C.-P.,French Institute of Petroleum | Mermet J.-M.,Spectroscopy Forever
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2013

The fundamentals, applications and latter developments of petroleum products analysis through inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are revisited in the present bibliographic survey. Sample preparation procedures for the direct analysis of fuels by using liquid sample introduction systems are critically reviewed and compared. The most employed methods are sample dilution, emulsion or micro-emulsion preparation and sample decomposition. The first one is the most widely employed due to its simplicity. Once the sample has been prepared, an organic matrix is usually present. The performance of the sample introduction system (i.e., nebulizer and spray chamber) depends strongly upon the nature and properties of the solution finally obtained. Many different devices have been assayed and the obtained results are shown. Additionally, samples can be introduced into the plasma by using an electrothermal vaporization (ETV) device or a laser ablation system (LA). The recent results published in the literature showing the feasibility, advantages and drawbacks of latter alternatives are also described. Therefore, the main goal of the review is the discussion of the different approaches developed for the analysis of crude oil and its derivates by inductively coupled plasma (ICP) techniques. © 2013 Elsevier B.V. All rights reserved.


Sanchez R.,Nutrition and Food science | Todoli J.L.,Nutrition and Food science | Lienemann C.-P.,French Institute of Petroleum | Mermet J.-M.,Spectroscopy Forever
Journal of Analytical Atomic Spectrometry | Year: 2010

A method based on the use of a high temperature single pass spray chamber and the injection of a sample plug into an air carrier gas stream was developed to mitigate non spectral interferences caused by organic samples and petroleum products and to reduce plasma loading in Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The studied solvents were eleven alkanes (hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane), xylene, kerosene and tetralin. As regards to the real samples two gasolines, a kerosene and a diesel sample were taken. The evaluated sample introduction systems were a 12 cm3 inner volume single pass spray chamber (also called Torch Integrated Sample Introduction System, TISIS) with and without heating and a 40 cm3 inner volume cyclonic spray chamber that was taken as a reference device. A characterization of the matrix effect in continuous aspiration mode at a 30 μl min -1 flow rate was initially performed. Drop size distributions were measured for the aerosols generated by the nebulizer (primary aerosols) and those leaving the spray chamber (tertiary aerosols). The results proved that the median of the aerosol volume drop size distribution (D50) for primary aerosols took values from 13.2 to 15.3 μm. Meanwhile, tertiary ones changed more significantly as a function of both the solvent nature and the chamber temperature. They went from 2 to 4 μm for the TISIS at room temperature, whereas at 100 °C D50 was included within the 0.7 to 3.1 μm range. The analyte mass transported towards the plasma was also measured and it was confirmed that this parameter was directly related to the solvent volatility. Thus, at room temperature, efficiencies went from 20 to 60% for hexadecane and octane, respectively. ICP-AES sensitivities changed significantly as a function of the solvent. For real samples, heating of the chamber walls mitigated the interferences, thus, while at room temperature, gasoline samples provided more than one order of magnitude higher signals than diesel samples, at 100 °C this signal improvement factor was only of five. All these problems were mostly overcome when the segmented injection of a 5 μl sample plug was performed. It was concluded that, for all the solutions at 200 °C heating temperature the injected sample volume (c.a., 5 μl) evaporated completely before its further introduction into the plasma. Therefore, differences in analyte mass transported as a function of the solution matrix were mitigated. © 2010 The Royal Society of Chemistry.


Sanchez R.,Nutrition and Food science | Todoli J.L.,Nutrition and Food science | Lienemann C.-P.,French Institute of Petroleum | Mermet J.-M.,Spectroscopy Forever
Journal of Analytical Atomic Spectrometry | Year: 2010

The effects of the solvent dilution factor on the physical properties of the resulting organic solutions, the aerosol characteristics and the silicon sensitivity were studied in ICP-AES for four different petroleum products by using near total sample consumption systems. The four samples were two gasoline products having very different volatilities along with a kerosene and a diesel sample. Petroleum product samples were diluted with xylene using four sample dilutions; 1:2, 1:5, 1:10 and 1:50. The sample introduction systems were a single pass spray chamber associated with a micronebulizer and a demountable Direct Injection High Efficiency Nebulizer (d-DIHEN). A cyclonic spray chamber also associated with a micronebulizer was taken as the reference system. Silicon was used as the test element, because it has been previously demonstrated that the ICP-AES Si sensitivity was significantly modified according to its chemical form. Silicon was spiked in each diluted solution with the same concentration to test sensitivity. When considering the dilution factor as the key variable, it was found that for the two gasoline samples and the kerosene one, the higher this variable, the lower the sensitivity. This result was explained in terms of changes in the solution volatility and/or in the aerosol characteristics. It was also observed that the total sample consumption systems were less sensitive to changes in the properties of the resulting organic solutions than the system based on the cyclonic spray chamber. However, for the latter chamber, the properties of the resulting organic solution had a marked influence on the extent of the effect of the silicon chemical form on the sensitivity. This fact demonstrated the appearance of an undefined interaction between the analyte and the organic solution during the aerosol transport step. However, both the single pass spray chamber and the d-DIHEN mitigated this effect for all the samples. © 2010 The Royal Society of Chemistry.


Mermet J.-M.,Spectroscopy Forever
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2010

Calibration is required to obtain analyte concentrations in atomic spectrometry. To take full benefit of it, the adequacy of the coefficient of determination r 2 is discussed, and its use is compared with the uncertainty due to the prediction bands of the regression. Also discussed from a tutorial point of view are the influence of the weighting procedure and of different weighting factors, and the comparison between linear and quadratic regression to cope with curvatures. They are illustrated with examples based on the use of ICP-AES with nebulization and laser ablation, and of LIBS. Use of a calibration graph over several orders of magnitude may be problematic as well as the use of a quadratic regression to cope with possible curvatures. Instrument softwares that allow reprocessing of the calibration by selecting standards around the expected analyte concentration are convenient for optimizing the calibration procedure. © 2010 Elsevier B.V. All rights reserved.


Paredes E.,University of Alicante | Bosque J.,University of Alicante | Mermet J.M.,Spectroscopy Forever | Todoli J.L.,University of Alicante
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2010

The characteristics of the aerosols generated by pneumatic concentric nebulizers as well as sensitivities were studied in ICP-MS with a total of 26 nebulizers: 17 of the A-type, 6 of the C-type, and 3 of the K-type. Although of the same design, discrepancies in sensitivity were observed among the A1-30 type nebulizers. Free delivery rate, relation between the median of the volume drop size distribution, D50, and the capillary i.d., effect of the nebulizer gas exit cross sectional area on D50, energy transfer efficiency from the gas to the liquid stream and spatial homogeneity within the aerosol cones were studied. For a given nebulizer design, the gas exit cross-sectional area has shown to critically influence the aerosol characteristics. The aerosol generation mechanism has been explored and it has been concluded that, for A-type nebulizers the nebulization is more efficient than for C and K-type ones. The spray chamber design has also a marked effect on the results according to the particular nebulizer used. It has been observed that sample capillary was not perfectly centered with regard to the gas exit bore for several nebulizers. In order to minimize the problems associated with this bad alignment (i.e., different sensitivity depending on the nebulizer), spray chambers equipped with impact beads may be used, but to the detriment of the sensitivity. © 2010 Elsevier B.V. All rights reserved.


Mermet J.M.,Spectroscopy Forever | Granier G.,CEA Marcoule Nuclear Site
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2012

Method validation is usually performed over a range of concentrations for which analytical criteria must be verified. One important criterion in quantitative analysis is accuracy, i.e. the contribution of both trueness and precision. The study of accuracy over this range is called an accuracy profile and provides experimental tolerance intervals. Comparison with acceptability limits fixed by the end user defines a validity domain. This work describes the computation involved in the building of the tolerance intervals, particularly for the intermediate precision with within-laboratory experiments and for the reproducibility with interlaboratory studies. Computation is based on ISO 5725-4 and on previously published work. Moreover, the bias uncertainty is also computed to verify the bias contribution to accuracy. The various types of accuracy profile behavior are exemplified with results obtained by using ICP-MS and ICP-AES. This procedure allows the analyst to define unambiguously a validity domain for a given accuracy. However, because the experiments are time-consuming, the accuracy profile method is mainly dedicated to method validation. © 2012 Elsevier B.V.


Mermet J.M.,Spectroscopy Forever | Granier G.,CEA Marcoule Nuclear Site | Fichet P.,CEA Saclay Nuclear Research Center
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2012

The limit of quantitation (LOQ) is a crucial parameter in quantitative analysis. Besides the classical 10 sB approach, other concepts have been previously described based on the limitation resulting from the calibration procedure, namely from the prediction bands and the uncertainty calibration. Because of the difficulty of obtaining a reliable value of the blank standard deviation, this approach was replaced by the study of the %RSD of the net signal as a function of the concentration. Recently described, the so-called accuracy profile method, accuracy being the contribution of both the trueness and the precision, allows the analyst to define a validity domain, the lowest point acting as a limit of quantitation. The aim of this work was to determine these various limits of quantitation, including that from the accuracy profile, to compare them, and to study the parameters that can influence their values. It was concluded that the LOQ deduced from the accuracy profile is a realistic one. Its value is mainly influenced by the calibration procedure, particularly when a weighting procedure is used. A 1/y weighting factor, y being the analyte line intensity, seems to be an efficient compromise for calibration. © 2012 Elsevier B.V.

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