Standard addition

Résumé

The Standard addition method, often used in analytical chemistry, quantifies the analyte present in an unknown. This method is useful for analyzing complex samples where a matrix effect interferes with the analyte signal. In comparison to the calibration curve method, the standard addition method has the advantage of the matrices of the unknown and standards being nearly identical. This minimizes the potential bias arising from the matrix effect when determining the concentration. Variations Standard addition involves adding known amounts of analyte to an unknown sample, a process known as spiking. By increasing the number of spikes, the analyst can extrapolate for the analyte concentration in the unknown that has not been spiked. There are multiple approaches to the standard addition. The following section summarize each approach. Single standard addition used in polarography In classic polarography, the standard addition method involves creating two samples –

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https://en.wikipedia.org/wiki/Standard_addition

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The course relates on the use of electromagnetic (X-Ray) and corpuscular (electrons) radiations for physical and chemical analysis of solid materials.

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The risk of chemical mixtures to ecosystems is often assessed by applying the model of concentration addition or response addition combined with species sensitivity distribution (SSD) curves. Mixture effect predictions have been shown to be consistent only when these models are applied for a single species, however, and not with several species simultaneously aggregated to SSDs. The more stringent procedure for mixture risk assessment would hence be to apply first the concentration addition or response addition models to each species separately and, in a second step, to combine the results to construct an SSD for a mixture. Unfortunately, this methodology is not applicable in most cases because the large data sets it requires are usually unavailable. Based on theoretical data sets generated, the authors aimed to characterize the difference that can exist between these 2 methodologies. Results show that the use of concentration addition on SSD directly may lead to underestimations of the mixture concentration affecting 5% or 50% of species, especially when substances present a large standard deviation in ecotoxicity data constructing their SSD. The application of response addition can lead to over- or underestimations, depending mainly on the slope of the dose-response curves of the individual species. When assessing the risk of mixtures, one must therefore keep in mind this source of error when applying concentration addition or response addition to SSDs directly. (c) 2013 SETAC

Society of Environmental Toxicology and Chemistry Press2013

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Novel Analytical Methods for Allergy-Related Studies

Mikaël Frossard

Managing and treating diseases require a deep understanding of the pathologies coupled with accurate diagnostic procedures. The constant development and improvement of bioanalytical methods reflect the need of diagnosis ameliorations with respect to accuracy, sensitivity and efficiency. The field of allergy diagnosis is a good example. Despite affecting almost a third of the population in western countries, allergies still present complex challenges for the physicians in terms of diagnosis and allergen characterization. This thesis presents novel analytical methods developed for the fast and personalized allergy component-resolved diagnosis (CRD), the allergen identification and quantification in food matrices and the characterization of allergen modifications, notably nitration. Immunomagnetic separation (IMS) was used to perform the allergy diagnosis at the molecular level by extracting the IgE antibodies from allergic patient blood sera and probing them against individual allergens and natural allergenic extracts. The fast and highly selective IMS procedure was coupled to matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometry (MS) to identify accurately and with high sensitivity the proteins recognized as sensitizers by the patient antibodies. The developed CRD methods were successful to diagnose cowâs milk, egg, peanut and tree nuts allergies, allowing the resolution of several complex clinical cases. Additionally, precious information was collected for the cross-reactivity and cross-sensitization in peanut and tree nuts allergies using blood sera from the PronNut clinical study. Allergen nitration is one of the potential causes for the increase in allergy prevalence observed recently and requires thorough investigation. Herein, various nitrating agents were tested and compared for in vitro allergen nitration. After modifying allergens using two of the most efficient nitrating procedures, the nitration sites were identified by bottom-up proteomics (BUP) and compared to the known epitopes, bringing useful information and novel insights to the problem of correlation between protein nitration and allergenicity. The presence of a minute amount of allergens in a food product is responsible for potential life-threatening reactions in highly allergic patients and sensitive analytical methods are therefore required in food quality assessments. A proteomic-based method was used for the quality control of several food products suspected of causing severe reactions for peanut and hazelnut-allergic patients. Peptide markers were identified in a first screening of the food extracts by BUP using a high-resolution MS instrument. A standard addition method was then used to quantify peanut and hazelnut proteins by BUP using an untargeted âshotgunâ approach.

EPFL2020

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Electrochemical Detection of Free Chlorine at Inkjet Printed Silver Electrodes

Véronique Amstutz, Hongyan Bi, Fernando Cortes Salazar, Hubert Girault, Milica Jovic, Andreas Stephan Lesch

A low-cost, reliable and sensitive electrochemical method for free chlorine analysis in water using inkjet printed silver electrodes is presented. Free chlorine detection was based on linear sweep voltammetry (LSV) analysis of AgCl/Ag2O films formed over an inkjet printed silver electrode by the spontaneous reaction between silver and free chlorine species (i.e. HClO and ClO−) present in solution. The formation of AgCl/Ag2O films was studied and characterized by high resolution scanning electron microscopy (HR SEM) and X-ray photoelectron spectroscopy (XPS) techniques. LSV characterization demonstrated a quantitative linear relationship between the amount of AgCl/Ag2O formed and the concentration of free chlorine in water within a range from 1 to 100 ppm. After optimization of several parameters (e.g. scan rate, reaction time, starting potential), lowest detectable free chlorine concentration was 0.4 ppm (by standard addition method), while the limit of detection (S/N = 3) was equal to 2 ppm, with a sensitivity of 30 μC/ppm. The validation of the proposed methodology was performed by comparison with the standard N,N-diethylparaphenylenediamine (DPD) method for analyzing swimming pool water samples. Finally, it was demonstrated that reproducible and disposable silver electrodes could be easily prepared by inkjet printing in a large scale and in any required geometry to fit on-line and on-site free chlorine analyses requirements.

Elsevier Science Sa2015

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Novel Analytical Methods for Allergy-Related Studies

Mikaël Frossard

EPFL2020