Multi-energy Calibration Research Articles

Multi-energy calibration and induced plasma optical emission spectrometry (MEC-MIP OES) as an alternative method for the multi-elemental determination of essential elements in cocoa.

The challenge of combining MEC-MIP OES arises from the limited number of emission lines available in this analytical technique. For the MEC-MIP OES optimization, the emission line wavelengths, sample dilution, proportion sample:standard for preparing MEC solutions, and nebulizer gas flow rate were studied. Then, the use of multi-energy calibration (MEC) and microwave-induced plasma optical emission spectrometry (MIP OES) was proposed as an alternative method for the determination of essential elements (Ca, K, Mg, Mn, and Na) in cocoa. In the optimized conditions, the method presented adequate analytical performance, with recoveries of 94-104% and relative standard deviations lower than 5%, showing adequate precision. The limits of detection (mg kg-1) were 12 for Ca, 2 for K, 3 for Mg, 3 for Mn, and 6 for Na. The proposed method was applied to analyze cocoa samples cultivated in Brazil and Ecuador after acid decomposition. The results were in the range (mg kg-1) of 409-1530 for Ca, 5520-13300 for K, 1460-3210 for Mg, 16-34 for Mn, and 28-61 for Na. Samples cultivated in Ecuador presented higher metal concentrations than the Brazilian samples. The proposed procedure was an easy and reliable approach for determining metals in cocoa samples, enabling multi-elemental determination with a lower cost and simplified calibration to be applied in routine applications.

Determination of Sodium, Potassium, Calcium and Magnesium in Urine, Using Microwave Plasma - Atomic Emission Spectrometry and Multi-Energy Calibration

Microwave plasma - atomic emission spectrometry with multi-energy calibration (MP-AES-MEC) was used for the determination of four major elements in urine. In the family of atomic emission spectrometry, the distinctive features of MP-AES are: (i) nitrogen-based toroidal-shape plasma; (ii) good plasma tolerance to total solids; (iii) exceptionally low operating cost. On the other hand, due to relatively low plasma temperature, this technique is susceptible to spectral interferences and sample-to-sample fluctuating baseline is typical limitation, if previous acid digestion is not performed. MEC is a non-conventional quantification method, not requiring baseline correction and it has been selected in this work to achieve reliable determination of Na, K, Ca and Mg in simply diluted urine. The principle underlying MEC is the proportionality between signal intensity and analyte concentration, occurring at any emission line for given element. Accordingly, for each sample, only two solutions were prepared likewise in the one-point standard addition and two analytical runs were performed, yet four experimental points were generated for calibration according with the number of emission lines utilized. Based on the results obtained by analyzing urines from different subjects, the sample dilution fold was selected to adjust the analyte concentration below half of the calibration range (150 for K, 200 for Na, 50 for Ca and 25 for Mg), while the addition of standard was done roughly doubling natural concentration in the diluted sample. The evaluated instrumental limits of detection were: 0.009 ± 0.005 mg L-1 for K, 0.131 ± 0.011 mg L-1 for Na, 0.050 ± 0.014 mg L-1 for Ca and 0.059 ± 0.010 mg L-1 for Mg (five replicates in different days). Each analysis was performed in triplicate yielding percentage relative standard deviation £ 11 %. The percentage recoveries calculated taking the results obtained in acid-digested samples by external calibration as reference values were in the range: 83.3-102 % for K, 88.4-110 % for Na, 82.9-113 % for Ca and 85.8-108 % for Mg. The capability of the proposed MP-AES-MEC procedure for monitoring four elements in different clinical conditions was demonstrated by analyzing ten urines from diabetic patients and ten from non-diabetic control subjects; statistical differences between these two groups was found for Na and K. Resumen. La espectrometría de emisión atómica con excitación en plasma de microondas y con el método de calibración multi-energéa (MP-AES-MEC) fueron empleados para la determinación de cuatro elementos mayoritarios en orina. Dentro de la familia de técnicas de espectrometría de emisión atómica, las características distintivas de MP-AES son las siguientes: (i) uso de plasma de nitrógeno con geometría toroidal; (ii) buena tolerancia del plasma a sólidos totales; (iii) excepcionalmente bajo costo de operación. Por otra parte, debido a la relativamente baja temperatura del plasma, una típica limitación de esta técnica es que es susceptible a interferencias espectrales y la fluctuación de línea base entre muestras si estas no son digeridas previamente. El método MEC es un método de cuantificación no-convencional, el cual no requiere corrección de linea base y fue seleccionado en este trabajo para lograr la determinación confiable de Na, K, Ca and Mg después de una simple dilución de orina. MEC se sustenta en la proporcionalidad entre intensidad de la señal y la concentración del analito existente en cualquier linea de emisión de un elemento dado. Para cada una de las muestras, se prepararon dos soluciones, igual que en el método de un punto de adición de estándar y se realizaron dos corridas analíticas, pero se generaron cuatro puntos experimentales para la calibración, correspondientes a cuatro líneas de emisión seleccionadas por elemento. Con base en los resultados obtenidos analizando orinas de diferentes sujetos, el factor de dilución de la muestra fue seleccionado para ajustar la concentración del analito por debajo de la mitad del rango de calibración (150 para K, 200 para Na, 50 para Ca, 25 para Mg), mientras que la adición de estándar se realizó subiendo aproximadamente al doble la concentración natural en la muestra diluida. Los límites de detección instrumentales fueron: 0.009 ± 0.005 mg L-1 para K, 0.131 ± 0.011 mg L-1 para Na, 0.050 ± 0.014 mg L-1 para Ca, 0.059 ± 0.010 mg L-1 para Mg (con base en cinco réplicas realizadas en diferentes días). Cada análisis se realizó por triplicado, obteniéndose valores de desviación estándar relativa £ 11 %. Los porcentajes de recuperación calculados considerando los resultados obtenidos en muestras digeridas con ácido mediante calibración externa convencional como valores de referencia fueron los siguientes: 83.3-102 % para K, 88.4-110 % para Na, 82.9-113 % para Ca, 85.8-108 % para Mg. La capacidad del procedimiento MP-AES-MEC para monitorear cuatro elementos en diferentes condiciones clínicas se demostró analizando orinas de pacientes diabéticos y orinas de sujetos en un grupo control, encontrándose diferencias estadísticamente significativas para Na y K.

Multi-energy calibration and aerosol dilution as analytical strategies to access the in vitro bioaccessibility of essential elements and arsenic in raw and cooked shrimp by plasma-based methods

Multi-energy calibration (MEC) and aerosol dilution were evaluated as strategies for direct analysis of simulated gastrointestinal chyme to estimate the in vitro bioaccessibility of essential elements and As in shrimp by ICP OES and ICP-MS.

Multi-energy calibration for determining critical metals in nickel-metal hydride battery residues by microwave-induced plasma atomic emission spectrometry.

Nickel-metal hydride batteries (NiMH) are a secondary source of high aggregate value elements, such as nickel, manganese, cobalt, and rare earths, for which recycling typically involves acid lixiviation. Designing the recycling process requires accurate determination of the elements in the leachates, which is hindered by the high complexity of the matrix. In the present study, microwave-induced plasma atomic emission spectrometry (MIP-OES) was selected as the quantitative method for elemental analysis because of its environment friendliness and cost-effectiveness. Multi-energy calibration (MEC) was also pioneeringly evaluated to circumvent matrix effects and simplify the determination of Ce, La, Ni, Co, and Mn in sulfuric acid leachates of NiMH batteries by MIP-OES. The method's analytical performance and accuracy were critically compared with external standard calibration and the standard additions method. MEC yielded superior results, with analyte recoveries within 90-110%, precision (coefficients of variation) from 1.8% to 5.8%, and limits of detection of 10, 20, 1, 400, and 60 μg kg-1 for Ni, La, Mn, Ce, and Co, respectively. The results demonstrated the ability of MEC-MIP-OES to minimize matrix effects, as well as simplify and speed up the analysis of NiMH battery leachates, which is compatible with this high-demand analytical application.

Multienergy Calibration Applied for the Quantification of Polymer Concentration in Conjugated Polymer Nanoparticles

Multienergy Calibration Applied for the Quantification of Polymer Concentration in Conjugated Polymer Nanoparticles

Determination of fatty acids in vegetable oils by GC-MS, using multiple-ion quantification (MIQ)

Multi-energy calibration (MEC) fundamentals, developed for atomic spectrometry, were adapted in this work to determine fatty acids in vegetable oils by gas chromatography-mass spectrometry. The procedure was denoted GC-MS-MIQ, where MIQ stands for multiple-ion quantification. Transesterification reaction was accomplished and two chromatographic runs per sample were carried out, similar as in one-point standard addition. Four m/z values for each FAME were selected and linear regression was computed relating intensities of each ion in the spiked and non-spiked sample. The slope of the obtained function was used to perform quantification, based on the concentration of standard added to the sample. Results obtained for two reference materials using GC-MS-MIQ were in good agreement with those provided by external calibration and were consistent with the certified values. Eleven edible vegetable oils from Mexican market were analyzed. Based on the obtained results, GC-MS-MIQ is prompted as a feasible alternative to perform multi-component quantitative analyses avoiding external calibration and ensuring the same chemical environment for the analyte and the calibrator.

Digital-image photometry with multi-energy calibration

Simple analytical procedures that are able to circumvent matrix effects are always in high demand given the wide variety of analytical applications and the need to deal with complex-matrix samples. In this context, digital-image photometry (DIP) outstands because of its simplicity, cost-effectiveness, and portability. Typically, it involves external standard calibration (EC) based on single-channel measurements and is often prone to matrix effects. Alternatively, multi-energy calibration (MEC) has been successfully exploited as a calibration strategy to minimize matrix effects in spectrochemical analysis, as it relies on measurements at different wavelengths using a pair of calibration solutions containing the same amount of sample. Aiming at a simpler and more practical approach, the present work pioneeringly proposes multi-channel smartphone-based digital-image photometry to minimize interferences and matrix effects using the general concept of MEC. Analytical signals were based on the responses obtained at different color channels, RGB (red, green, and blue), CMY (cyano and magenta channels) and HSV (saturation values). The strategy was evaluated with model colored solutions (methyl red, brilliant blue dye, and nickel(II) sulfate) to establish boundary working conditions. For calibration solutions with a sample/standard analyte concentration ratio between 0.2 and 1.0, analyte recoveries in the 85–103 %, 92–104 %, and 87–113 % ranges were found for methyl red, brilliant blue, and nickel(II) sulfate, respectively. The method’s feasibility was then demonstrated by determination of methanol in solutions containing different amounts of glycerol, and hydrogen peroxide in milk with different fat contents. Relative errors (Er) for determination of methanol were within 2–16 % and 17–48 % using the MEC strategy and EC, respectively. For determination of hydrogen peroxide in milk, Er achieved by the proposed approach were within 6–10 %, whereas values as high as 50 % were estimated with EC. Coefficients of variation (n = 10) and limits of detection (99.7 % confidence level) for methanol and hydrogen peroxide determination were 3.5 % and 7 mg/L, and 6.6 % and 1 mg/L, respectively. These results demonstrate the proposed approach is a simple, practical, and environment friendly strategy to minimize matrix and other interfering effects.

Matrix-Matching Calibration Using Solid Standards: A Comparison between Univariate and Multivariate Strategies for the Determination of Calcium and Magnesium in Bean Seed Samples Employing Laser-Induced Breakdown Spectroscopy (LIBS)

The aim of this study was to evaluate solid calibration standards for matrix-matching comparing with multivariate calibration strategies for calcium and magnesium determination in bean seed samples employing laser-induced breakdown spectroscopy combined with direct solid analysis. Four calibration strategies, namely, (i) partial least square (PLS), (ii) principal component regression (PCR), (iii) multi-energy calibration (MEC) and (iv) one-point gravimetric standard addition (OP GSA), were assessed for fourteen bean seed samples. From all calibration strategies used in this study, univariate calibrations (MEC and OP GSA) led to better results, where for MEC, the trueness values ranged from 89 to 188% for Ca, and from 75 to 116% for Mg, and for OP GSA ranged from 76 to 112% for Ca, and 87 to 127% for Mg. Therefore, the use of solid standard combined with univariate calibration strategies has improved the accuracy by minimizing the matrix effects with appropriate blank and standard dilution.

Multi-energy calibration of a PILATUS3 CdTe detector for hard x-ray measurements of magnetically confined fusion plasmas.

A multi-energy hard x-ray pin-hole camera based on the PILATUS3 X 100K-M CdTe detector has been developed at the Princeton Plasma Physics Laboratory for installation on the Tungsten Environment in Steady State Tokamak. This camera will be employed to study thermal plasma features such as electron temperature as well as non-thermal effects such as fast electron tails produced by a lower hybrid radiofrequency current drive and the birth of runaway electrons. The innovative aspect of the system lies in the possibility of setting the threshold energy independently for each of the ∼100k pixels of the detector. This feature allows for the measurement of the x-ray emission in multiple energy ranges with adequate space and time resolution (∼1cm, 2ms) and coarse energy resolution. In this work, the energy dependence of each pixel was calibrated within the range 15 keV-100 keV using a tungsten x-ray tube and emission from a variety of fluorescence targets (from yttrium to uranium). The data corresponding to pairs of Kα emission lines are fit to the characteristic responsivity ("S-curve"), which describes the detector sensitivity across the 64 possible energy threshold values for each pixel; this novel capability is explored by fine-tuning the voltage of a six-bit digital-analog converter after the charge-sensitive amplifier for each of the ∼100k pixels. This work presents the results of the calibration including a statistical analysis. It was found that the achievable energy resolution is mainly limited by the width of the S-curve to 3 keV-10 keV for threshold energies up to 50 keV, and to ≥20 keV for energies above 60 keV.

Calibration Strategies Applied to Laser-Induced Breakdown Spectroscopy: A Critical Review of Advances and Challenges

Over the years, laser-induced breakdown spectroscopy (LIBS) has been reported in the literature as an alternative to traditional methods of analysis, becoming well established among spectroanalytical techniques. LIBS is a technique widely used for qualitative approaches; however, it is necessary considerable effort for use in quantitative analysis, mainly due to severe matrix effects. These limitations make it difficult to broaden the application of LIBS in quantitative analysis. In this sense, this review discusses recent advances in calibration strategies applied in LIBS for minimizing matrix effects and enabling determination with satisfactory accuracy and precision. Applications, advantages, and limitations of the calibration strategies, such as matrix-matching calibration (MMC), internal standardization (IS), standard addition (SA), multi-energy calibration (MEC), one-point gravimetric standard addition (OP GSA), one-point and multi-line calibration (OP MLC), slope ratio calibration (SRC), two-point calibration transfer (TP CT), single-sample calibration (SSC), multiple linear regression (MLR), principal component regression (PCR), partial least squares (PLS) and artificial neural networks (ANN) are discussed.

Multi-energy calibration: an easy strategy for fast and accurate determination of macro- and micro-nutrients in biomass waste samples by ICP OES

A promising multi-energy calibration procedure for the determination of Ca, Cu, Fe, K, Mg, Mn, Ni, and Zn by ICP OES was evaluated.

Iterative multi-energy calibration and its application in online alloy smelting process monitoring using laser-induced breakdown spectroscopy

IMEC: one standard sample, multiple rounds of self-correction, and higher performance.

Introducing multi-energy ratios as an alternative to multi-energy calibration for Br determination via high-resolution continuum source graphite furnace molecular absorption spectrometry. A case study

Two different multi-signal calibration approaches are examined and their benefits for solving matrix effects for HR CS GFMAS demonstrated.

Neodymium determination in hard drive disks magnets using different calibration approaches for wavelength dispersive X-ray fluorescence

Due to matrix effects and limitations in the calibration process for direct analysis of solids, the search for different calibration approaches is very important. This study is aimed to Nd determination in high-performance magnets from hard disk using direct solid analysis by wavelength dispersive X-ray fluorescence. Three univariate calibration methods were evaluated: multi-energy calibration, one-point gravimetric standard addition and two-point calibration transfer. These strategies employ an efficient matrix-matching method, minimizing the matrix effects related to the direct analysis of solids. The trueness values were calculated according to reference concentration by inductively coupled plasma optical emission spectrometry and the concentration obtained by univariate models. For almost all samples, the trueness values were within an acceptable range from 80 to 120%. Besides that, relative standard deviation values ranged from 3 to 27% for all cases and, the standard error ranged from 2 to 6% w w−1 Nd among the calibration methods. These parameters show the potential of these alternative calibration methods over traditional ones.

Determination of major and minor elements in Mexican red wines by microwave-induced plasma optical emission spectrometry, evaluating different calibration methods and exploring potential of the obtained data in the assessment of wine provenance

In this work, the determination of major and trace elements in Mexican wines was carried out by microwave-induced plasma optical emission spectrometry (MIP OES), setting sample dilution as the pretreatment procedure. The elements were grouped according with the required dilution fold: 1:100 for K; 1:50 for Na, Mg, Ca; 1:10 for Rb, Sr, Mn, Fe, Al and 1:4 for Cu, Cr. Due to troublesome background noise, different for each sample, matrix-matching with individual wines was necessary and three quantification methods were explored: classic standard additions (SA), standard dilution analysis (SDA) and multi-energy calibration (MEC). In order to avoid extrapolation in assessing the actual concentration of internal standard at each dilution point and to allow for longer integration time during signal acquisition, SDA was modified (nominated MSDA) and was recommended for the determination of minor elements whereas for major elements the suitable method was MEC. The results obtained by MSDA and MEC were in good agreement with those provided by SA; however, background correction was not required and both methods offer more simplicity as compared to SA. The concentration ranges found in the Mexican wines were as follows: 866–4896 mg L−1 K, 32.7–326 mg L−1 Na, 56.6–164 mg L−1 Mg, 63.9–121 mg L−1 Ca, 0.56–1.90 mg L−1 Sr, 0.35–6.31 mg L−1 Rb, 0.21–2.11 mg L−1 Fe, 0.69–1.72 mg L−1 Mn, 0.28–0.78 mg L−1 Al, 0.10–0.42 mg L−1 Cu, and Cr was not detected. Principal component analysis (PCA) allowed for separation of wines according with the winery regions: Valle de Guadalupe, Guanajuato, Aguascalientes. Furthermore, PCA revealed association of Rb, K, Ca, Sr with wines produced in Guanajuato and association of Na, Cu and Mn with those produced in Valle de Guadalupe; wines from Aguascalientes contained relatively high concentration of Fe and Al, although tight clustering of variables was not observed in this case. To establish reliable discrimination model, more samples from these and possibly from other winery regions in Mexico need to be analyzed.

Multi-energy calibration to circumvent matrix effects in the determination of biodiesel quality parameters by UV–Vis spectrophotometry

Biodiesel is a sustainable fuel, which consists of a mixture of fatty acid alkyl esters obtained by the transesterification of vegetable oils or animal fats. Due to the diversity of raw materials used in its production, the biofuel can show significant differences in its physicochemical properties, which causes severe matrix effects in biodiesel analysis. In this work, a calibration strategy recently proposed for atomic spectrometry, named multi-energy calibration (MEC), was evaluated as a tool to circumvent matrix effects in molecular spectrometry. The strategy yielded more accurate results in the spectrophotometric determination of the iodine value and free glycerol in biodiesel produced from different raw materials (root mean square error of prediction, RMSEP, values of 6.0 and 8.0, respectively), than both external standard calibration (EC, RMSEP as high as 45.6) and the standard additions method (SAM, RMSEP as high as 25.3). Moreover, results agreed with those obtained by the reference procedures at the 95% confidence level, which was not observed for EC (free glycerol determination) and SAM (iodine value determination). Coefficients of variation (n = 8) and limits of detection (99.7% confidence level) were, respectively, estimated at 1.7% and 5 g I2/100 g iodine value and 3.0% and 10 mg kg−1 free glycerol in biodiesel, which are comparable to or better than those achieved using previously proposed procedures. Thus, MEC is a viable alternative for biodiesel quality control, with outstanding minimization of matrix effects, simplicity, practicality, and environmental friendliness.

Calibration strategies for the direct determination of rare earth elements in hard disk magnets using laser-induced breakdown spectroscopy

This study is dedicated to the direct determination of base (B and Fe) and some rare earth elements (REE; Dy, Gd, Nd, Pr, Sm and Tb) in hard disk magnets. Five calibration strategies were tested and compared. Two of them are related to multivariate calibration: multiple linear regression (MLR) and partial least squares (PLS). Both presented adequate trueness values within a range of 80–120% for almost all analytes. The only exception was Tb, which was probably due to matrix effects. The use of MLR and PLS permits the testing of calibration models in the presence of interference, but matrix effects are not corrected. Because of this, three other univariate calibration methods were also tested and compared: multi-energy calibration (MEC), one-point gravimetric standard addition (OP GSA) and two-point calibration transfer (TP CT). These three calibration approaches permit matrix effects corrections, but an appropriate selection of the blank and standard is mandatory. The standard error obtained ranged from 0.01 to 6% using these univariate calibration methods.

Evaluating the applicability of multi-energy calibration as an alternative method for quantitative molecular spectroscopy analysis.

Multi-Energy Calibration (MEC) was recently proposed as an innovative analytical method to be used in efficient and accurate quantitative analysis based on atomic spectroscopy. Here, the applicability of the MEC method for quantifying molecular species using UV-Vis and fluorescence measurements was evaluated for the first time. UV-Vis and fluorescence spectra of the analytical solutions of methylene blue and eosin-methylene blue in two different solvents (distilled-deionized water and methanol) were collected. MEC showed high precision and sensitivity for determining the analyte concentration, providing similar limit of detection and quantification when compared with conventional analytical methods, such as external standard calibration and standard additions. Therefore, the present study has shown that MEC can be successfully applied for quantifying molecular species in a simple and efficient way accounting UV-Vis and fluorescence spectroscopy.

Calibration strategies to overcome matrix effects in laser-induced breakdown spectroscopy: Direct calcium and phosphorus determination in solid mineral supplements

Several calibration strategies were evaluated for Ca and P determination in mineral supplements for cattle using direct solids analysis by laser-induced breakdown spectroscopy (LIBS). Matrix-matching calibration (MMC), internal standardization (IS), multi-energy calibration (MEC) and a new calibration strategy named one-point gravimetric standard addition (OP GSA) were evaluated in order to correct for matrix effects normally observed in measurements by LIBS. The MEC and OP GSA were the calibrations strategies that led to better recoveries for Ca (86–109% MEC and 72–117% OP GSA) and for P (80–108% MEC and 82–111% OP GSA). Applying both strategies only two calibration standards were used and the presence of the sample itself in the calibration standards contributes for correcting for matrix effects. For MEC several atomic emission wavelengths with different sensitivities were used to determine the analyte concentration in the sample and also to identify spectral interferences that showed up as outliers points in the calibration curve. However, for OP GSA, only one atomic emission wavelength is used to build the calibration curve, simplifying data handling when compared to the MEC method. A statistical evaluation using student's t-test showed that there is no significant difference at 95% confidence level between the value determined and the reference value (reference material or ICP OES data) when using MEC or OP GSA calibrations. Both MEC and OP GSA can be used for direct determination of Ca and P in mineral supplements for cattle allowing proper quality control in order to support the Brazilian Regulation Normative Instruction No. 12, 2004.

Calibration strategies for determination of the In content in discarded liquid crystal displays (LCD) from mobile phones using laser-induced breakdown spectroscopy (LIBS)

Mobile phones are one of the fastest growing types of electronic waste disposed of world-wide. One of the main components in these devices is the LCD (liquid crystal display) panel that contains conductive electrodes made of indium tin oxide. A large amount of In, which is categorized as a critical raw element, has been used to manufacture indium tin oxide films. This study applies laser-induced breakdown spectroscopy (LIBS) for the analysis of LCD samples from mobile phones in order to determine the In content. Both conventional univariate calibration and non-traditional calibration using different transition energies (emission lines), named multi-energy calibration (MEC), were assessed. To evaluate the accuracy of the results, Method EPA 3052 was performed for acid digestion of the samples using microwave-assistance, and the In content was determined by ICP OES. Indium concentrations ranged from 35 to 47 mg kg−1 for all samples evaluated. The results showed the best accuracy for LIBS methods after the spectra were normalized by the carbon line at 193.09 nm. The univariate-LIBS model showed a standard error of calibration (SEC) about 10-fold lower than the samples’ concentration, LOD and LOQ of 0.3 and 1.0 mg kg−1, respectively. MEC proved to be a fast and efficient alternative for direct solid analysis, and In concentrations were determined by LIBS using only two calibration pellets. The LOD and LOQ for MEC-LIBS method were 2.1 and 7 mg kg−1, respectively.