Some practical considerations for linearity assessment of calibration curves as function of concentration levels according to the fitness-for-purpose approach

Jurado, José Marcos; Alcázar, Ángela; Muñiz‐Valencia, Roberto; Ceballos‐Magaña, Silvia G.; Raposo, F.

doi:10.1016/j.talanta.2017.05.049

Cited by 58 publications

(37 citation statements)

References 17 publications

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“…Further, colorimetric studies were conducted to evaluate the surfactant release under the evaluated conditions as indirect measurement. For this, a calibration curve of absorbance versus concentration was obtained for each surfactant at a fixed wavelength of 200 nm using a UV-vis spectrophotometer (Genesys 10S, Thermo Scientific, Waltham, MA, USA) [ 62 ]. The amount of released surfactant was estimated in the supernatant by absorbance measurements after 24 h of stirring.…”

Section: Methodsmentioning

confidence: 99%

Development and Evaluation of Surfactant Nanocapsules for Chemical Enhanced Oil Recovery (EOR) Applications

et al. 2018

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The primary objective of this study is the synthesis of nanocapsules (NC) that allow the reduction of the adsorption process of surfactant over the porous media in enhanced oil recovery processes. Nanocapsules were synthesized through the nanoprecipitation method by encapsulating commercial surfactants Span 20 and Petro 50, and using type II resins isolated from vacuum residue as a shell. The NC were characterized using dynamic light scattering, transmission electron microscopy, Fourier transform infrared, solvency tests, softening point measurements and entrapment efficiency. The obtained NC showed spherical geometry with sizes of 71 and 120 nm for encapsulated Span 20 (NCS20), and Petro 50 surfactant (NCP50), respectively. Also, the NCS20 is composed of 90% of surfactant and 10% of type II resins, while the NCP50 material is 94% of surfactant and 6% of the shell. Nanofluids of nanocapsules dispersed in deionized water were prepared for evaluating the nanofluid—sandstone interaction from adsorption phenomena using a batch-mode method, contact angle measurements, and FTIR analysis. The results showed that NC adsorption was null at the different conditions of temperatures evaluated of 25, 50, and 70 °C, and stirring velocities up to 10,000 rpm. IFT measurements showed a reduction from 18 to 1.62 and 0.15 mN/m for the nanofluids with 10 mg/L of NCS20, and NCP50 materials, respectively. Displacements tests were conducted using a 20 °API crude oil in a quarter five-spot pattern micromodel and showed an additional oil recovery of 23% in comparison with that of waterflooding, with fewer pore volumes injected than when using a dissolved surfactant.

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Section: Methodsmentioning

confidence: 99%

Development and Evaluation of Surfactant Nanocapsules for Chemical Enhanced Oil Recovery (EOR) Applications

et al. 2018

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“…Linearity is a requirement with OLS but it is not correct to assume that all calibration curves are linear. Different procedures for assessing linearity of a calibration, such as graphical plots, statistical tests and numerical parameters, have been proposed [7,[17][18][19]. Unfortunately, linearity assessment has been subject to different definitions and interpretations, which results in some of these procedures not being equivalent and, sometimes, contradictory results can be obtained.…”

Section: Estimation Of the Goodness-of-fitmentioning

confidence: 99%

Ordinary Least Squares with Laboratory Calibrations: A Practical Way to Show Students that This Fitting Model may Easily Yield Biased Results When Used Indiscriminately

Sánchez¹

2017

WJAC

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Analytical calibration using ordinary least squares (OLS) is the most widely applied response function for calibration in all type of laboratories. However, this calibration function is not always the most adequate and its indiscriminant use can lead to obtain biased estimates of unknowns. Students need to be taught about the practical requirements needed to obtain good results with OLS and when this fitting method is not accurate. Different experimental calibration curves were obtained in laboratory sessions using two common instrumental techniques: chromatography and atomic absorption spectrometry. After discussion seminars evaluating the data obtained by students, they were able to understand that linear fitting was not the most accurate model using atomic absorption spectrometry and a quadratic fitting provided most accurate estimates. Linearity was confirmed in chromatographic calibrations, but data presented heteroscedasticity, which is very common in calibrations done in chemical and biological analyses. A simple experiment was applied to show students how the use of the regression coefficients obtained by OLS with heteroscedastic data lead to highly biased estimates near the quantification limits of the calibration curve. The results obtained allowed to show students that, despite being widely used, OLS is not the most adequate fitting model to obtain accurate and precise results with many calibration methods routinely used in chemical and biological laboratories.

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“…Homoscedasticity of calibration data was tested at 95% confidence level. The regression was selected based on the coefficient of correlation ( r ) and in the cumulative percentage relative error (∑%RE) .…”

Section: Methodsmentioning

confidence: 99%

“…Workflow of DPS preparation and sample analysis. Blood drawn from venipuncture was used to prepare DPS and wet plasma as well as detecting hematocrit on the coefficient of correlation (r) and in the cumulative percentage relative error (Σ%RE)[31,32].…”

mentioning

confidence: 99%

Application of a micro plasma collection card for the detection of homocysteine by liquid chromatography with tandem mass spectrometry

Yuan

Chu

et al. 2018

J of Separation Science

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Generally, it is recommended that blood samples for homocysteine detection should be centrifuged immediately to separate plasma in order to avoid continuous synthesis by blood cells. The use of a micro plasma collection card may improve sample stability and result accuracy by offering automatic and instant plasma separation. We compare a micro plasma collection method with routine wet plasma to explore applications of the dried plasma spots for homocysteine determination by using liquid chromatography with tandem mass spectrometry. The method was validated for both dried plasma spots and wet plasma. The assay was linear from 0.5-45 μmol/L with good precisions and accuracies. The extraction recovery and matrix effect for dried plasma spots were >97% and 0.98 after internal standard normalization, respectively. It was reproducible for retaining homocysteine in dried plasma spots and kept stable for 30 days. The plasma conversion factor was 7.77 ± 0.7% by calculating the ratio of homocysteine concentration between dried plasma spots and wet plasma (n = 165). Neither hematocrit nor homocysteine concentration affected the plasma conversion factor as long as the hematocrit was within the normal range. The results support the clinical usefulness of the dried plasma spots as a convenient and stable biological matrix for testing homocysteine.

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Some practical considerations for linearity assessment of calibration curves as function of concentration levels according to the fitness-for-purpose approach

Cited by 58 publications

References 17 publications

Development and Evaluation of Surfactant Nanocapsules for Chemical Enhanced Oil Recovery (EOR) Applications

Development and Evaluation of Surfactant Nanocapsules for Chemical Enhanced Oil Recovery (EOR) Applications

Ordinary Least Squares with Laboratory Calibrations: A Practical Way to Show Students that This Fitting Model may Easily Yield Biased Results When Used Indiscriminately

Application of a micro plasma collection card for the detection of homocysteine by liquid chromatography with tandem mass spectrometry

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