Intensities Of Analytical Lines Research Articles

Evaluation of the use of polyvinyl alcohol in the manufacture of pressed samples for X-ray fluorescence analysis

The reliability of the results of X-ray fluorescence analysis (XRF), which is widely used in determination of the elemental composition of various materials, largely depends on the quality of sample preparation. When producing pressed tablets for X-ray fluorescence analysis of trace elements, a binder is often used in a powder form, which requires significant time for thorough homogenization. We present the results of applicating a polyvinyl alcohol solution as a binder in the manufacture of pressed samples without using a substrate in determination of microelements by XRF. The parameters for obtaining a durable tablet with a homogeneous composition that matches the condition of minimum impact on the intensity of the analytical lines of the elements being determined are presented. It is shown that the optimal sample weight for the proposed method of producing pressed tablets is 7 g with the addition of polyvinyl alcohol in a ratio of 7:1, the optimal drying time for the tablet after pressing is 1 hour. The calculated variation coefficients of the analytical signal (<2%) indicate the homogeneity of the produced tablets. The maximum values of standard deviations of pressed tablets for the selected ranges of elements are much less than acceptable, which confirms the validity of the proposed method of sample preparation. It is also shown that during long-term storage and repeated measurements, pressed tablets with the polyvinyl alcohol solution retain their original structure and intensity of analytical lines of elements. The accuracy of measurements in the subsequent determination of rock-forming elements is consistent with their certified contents. The results obtained can be used to reduce the time spent on getting a representative pressed sample when using polyvinyl alcohol, determining elements without additional support (coating films), microelement and silicate analyzes from one sample.

Pavlinsky Geliy Veniaminovich (1935–2023)

Pavlinsky Geliy Veniaminovich (1935–2023)

CALIBRATION FREE LIBS FOR THE DETERMINATION OF Mn/Fe RATIO IN FERROMANGANESE NODULES WITH PORTABLE DIODE PUMPED SOLID STATE LASER

The Mn/Fe ratio, which serves as a marker of the content of rare earth elements and the platinum group elements in ferromanganese nodules, was determined in samples taken during expeditions to the Kara Sea and the Laptev Sea, as well as in a set of certified reference materials (ОOPE 601—604). The analysis was carried out by calibration-free laser-induced breakdown spectroscopy, based on the use of plasma parameters and intensities of analytical lines of manganese and iron (Mn I 542.04 nm and Fe I 539.71 nm). Boltzmann plot was used to determine the plasma temperature and Stark broadening of Fe I line 538.34 nm was used to determine electron density. We have shown the possibility of determining the Mn/Fe ratio in range
 from 0.2 to 4.2 in ferromanganese nodules of various geographic origin. A high coefficient of linear determination (R2 = 0.938) and proportionality between the results of calibration-free laser-induced breakdown spectroscopy and inductively coupled plasma atomic emission spectrometry (1:0.99) were achieved.

A New Intensity Adjustment Technique of Emission Spectral Analysis When Measured at the Upper Limit of the Dynamic Range of Charge-Coupled Devices

The article presents a method of mathematical correction to be applied to the results of measuring the intensity of spectral lines using charge-coupled devices (CCDs) in the presence of the blooming effect. This technique is particularly applicable in atomic emission spectroscopy. It enables expansion of the dynamic range of spark emission spectrometers and significantly minimizes the result distortions of the measurements taken in the area of high element concentrations. The authors devised a mathematical model and proposed an algorithm to adjust the measured intensity of analytical lines at the photo detector upper limit, in addition to an algorithm for processing data from the spectra recording system. The proposed mathematical algorithm was integrated into the software for the SPAS-02 and SPAS-05 spark spectrometers produced in Russia, and tested in determining the chemical composition of steels. The findings show that the actual dispersion of the analytical line intensity distribution may exceed the measured dispersion by a factor of 1.5, and their intensities may differ by a factor of 2. This algorithm may be implemented in atomic emission spectrometer software and makes it possible to adjust the calibration curves for a range of high alloying element concentrations when the analytical line intensity is at the upper limit of the CCD dynamic range.

A New Technique of Eliminating the Actual Plasma Background When Calibrating Emission Spectrometers with a CCD Recording System

This research focuses on the development of a new technique of emission spectral analysis designed to accurately account for the background radiation. The technique enables the evaluation of background radiation while being unaffected by its spectral shape. This is possible through the use of standard data obtained in an analytical-line-recording process performed by light-intensity-to-electric-signal converters such as CCDs, PMTs, photodiodes, etc. This technique, when applied at a set RMS deviation of the analytical-line-radiation intensity, reduces the random error of a determined low impure-element concentration due to the optimal calibration-line slope. In areas of high concentrations, an accurate accounting of the background does little to affect the emission spectrometer’s measurement accuracy. This technique also allows the replication of calibration curves in spectrometers of the same type by a linear-intensity conversion with only two standard samples required. The technique was tested on SPAS-02 and SPAS-05 commercial spark spectrometers. The testing fully confirmed the aforementioned advantages of the developed technique. The authors also determined the applicability conditions of the conventional emission-spectrometer-recalibration method by a linear conversion of the analytical-line intensity.

Optimization of the parameters of a laser induced breakdown spectrometer (LIBS) using probabilistic-deterministic design of experiment

A method for optimizing the settings of a LIBS device aimed at achieving the maximum intensity of analytical lines of the analyte of constant composition is considered using probabilistic-deterministic design of experiments (PDDE). A mixture of Cr, Mn, Fe, Co, and Ni oxides homogenized and diluted by fusion with a lead-phosphate mixture is used as an analyte. It is shown that data of mathematical processing of 25 spectra by the PDDE method can be used to develop mathematical models which relate the line intensity with the energy of the laser pumping lamp, the lag time of the first and second Q-switches, the time delay of the exposure onset, and the total exposure time. The use of the geometric mean and mathematical model in the form of the product of the partial dependences leads to a good correlation between the calculated and experimental values of the intensity for all the considered spectral lines. The simulation results presented for 16 analytical lines of Cr, Mn, Co, and Ni illustrate the applicability of the method under consideration. The experimentally achieved maximum intensities of analytical lines in the matrix of lead-phosphate glass differ from those calculated using the obtained models by 7 – 12 %. There is a linear correlation between the experimental and calculated values of the intensity at R2 = 0.99 and an inclination angle close to 45°. The spectra recorded during the experiment can be used for optimization of other parameters, e.g., the signal-to-noise ratio. The simplicity of calculations and relatively small number of tests in the optimization experiment make the PDDE a promising method for optimizing the LIBS parameters.

X-ray fluorescence determination of small quantities of hafnium in nuclear pure zirconium materials

An important chemical impurity in the composition of zirconium materials for nuclear power engineering is hafnium, the content of which should not exceed 0.05 and 0.01% for domestic and foreign alloy grades, respectively. Hafnium, being an analogue of zirconium in its chemical properties, is difficult to be analyzed using classical methods of analytical chemistry. Among the physical methods, the X-ray fluorescence method is the most expressive, which is important in conditions of continuous production. The method of X-ray fluorescence for measuring the content of hafnium in zirconium-containing material has been tested on the example of potassium fluorozirconate, a precursor for obtaining alloys. With various combinations of crystal analyzers, detectors, and collimators of the wave-dispersive spectrometer, the ratios of the intensities of the analytical lines of Hf and Zr in the second order of reflection were refined, and the degree of decrease in the fluorescence intensity of those lines was determined. The X-ray fluorescence spectra of hafnium lines in potassium fluorozirconate at the content characteristic of nuclear-pure zirconium are studied. The possibility of recording the intensity of the Hf analytical lines and methods of eliminating the interference from the Zr lines in the second order of reflection are considered. The metrological characteristics are calculated for Hf analytical lines. It is shown that the smallest error and the lowest detection limit (0.001%) is provided when using the HfLβ1 line at certain settings of the wave-dispersive spectrometer, including the X-ray tube operation mode, a combination of a crystal analyzer, a detector and a collimator, as well as the amplitude discriminator settings. The method of accounting for the background is recommended. The proposed method of hafnium determination is applicable to the materials with a constant content of zirconium.

Comparison of matrix effects on atomic emission spectrometers with nitrogen microwave induced plasma

The creation and implementation of new sources of sample excitation and spectrometers based on them into the practice of analytical laboratories raises many questions for researchers about the obtained analytical characteristics of new equipment and analysis methods. The most important characteristics of any method include detection limits, accuracy and reproducibility of the results obtained. Matrix elements can have a significant effect on these parameters. The paper shows a comparison of the change in the intensities of analytical lines of elements in the presence of matrix elements with ionization potentials of 5.13 - 10.48 eV (Na, Cu, Pb, Cd, Zn, In, Ga, Bi) in the concentration range of 0 - 1 wt %. on commercially available atomic emission spectrometers with microwave plasma Grand-MP ("VMK-Optoelektronika") and Agilent MP-AES 4100 (Agilent Technologies). It is shown that the magnitude of the matrix effect in these excitation sources depends on the ionization potential of the matrix element and the total energy of the analyte line. A significant effect of matrix elements with a concentration of up to 1% wt. on the intensity of spectral lines of atoms and ions of the sample. Elements with medium and high ionization energies practically do not affect the intensity of atomic spectral lines of impurity elements and lead to a decrease in the intensity of ionic lines. The influence of easily ionized elements is more pronounced - both depressing and amplifying effects are observed, probably caused by both a change in the concentration of electrons in the plasma, leading to a linear change in the equilibrium between atoms and ions, and a decrease in the plasma temperature. An increase in the power supplied to the plasma on the Grand-MP spectrometer leads to a decrease in the effect of easily ionized elements on the intensity of the spectral lines of the elements. It is shown that the plasma in the Grand-MP spectrometer has better resistance to matrix influences as compared to the Agilent MP-AES 4100, which is associated with a large plasma volume and a higher input power.

Влияния связующего вещества, используемого при прессовании зол для лазерного пробоотбора, на качество аналитических сигналов определяемых элементов

This work is devoted to determining the chemical composition of coal ashes. We used the optical emission spectrometry with inductively coupled plasma and laser sampling as a research method. The aim of the work is to determine the limits of detection (LoDs) and quantitative determination (LoQs) of elements in ashes using polyvinyl alcohol (PVA) and microcrystalline cellulose (MCC) as binders. In this work, analytical signals of Al, Ba, Be, Ca, Cr, Cu, Fe, K, La, Li, Mg, Mn, Na, Ni, P, Pb, S, Sc, Sr, Ti, Y, V, Zr, and Zn were analyzed in tablets obtained from the standard samples ZUK-1, ZUK-2, SG-1A, SG-3, SGD-2A, and SO-1, compacted using PVA and MCC, as well as from binding agents themselves. To obtain compact materials based on fly ash and geological materials, both binders are suitable if their chemical purity is enough for analysis. However, when using both MCC and PVA, some drawbacks were identified. The intensities of analytical lines of the elements were determined lower during the ablation of compact ashes with MCC than with PVA. The signal-background ratio is lower when using MCC as a binder material compared with compacts based on PVA. However, the highest grade PVA according to GOST 10779-78, used in the work, contains an admixture of sodium, about 0.06 w. %, which interferes with quantitative measurements if the sodium content in the sample is comparable to this value, which can be extremely rare in the analysis of fly ashes.

Определение отношения Mn/Fe в железомарганцевых конкрециях с помощью безэталонной лазерно-искровой эмиссионной спектроскопии

AbstractThe Mn/Fe ratio in ferromanganese nodules is determined by calibration-free laser-induced breakdown spectroscopy based on the use of only the plasma temperature and electron density and the intensities of manganese and iron analytical lines (Mn I at 447.28 and 447.93 nm and Fe I at 447.65 nm). The plasma temperature was determined by the two-line method (Mn I at 447.28 and 447.93 nm), while the plasma electron density was determined by the Stark broadening of the Mg I line at 517.26 nm. The study was performed using both standard samples (OOPE series) and samples of ferromanganese nodules sampled during expeditions to the Kara and Laptev Seas. The possibility of semiquantitative determination of the Mn/Fe ratio within the range from 0.2 to 4.2, which is enough for determining this ratio in most types of nodules of different geographical origins, is demonstrated. The calibration-free analysis data correlate with the results of inductively coupled plasma atomic emission analysis.

Experience in using ALPHA-VRA-30 software for determination of iron and zinc content in organometallic compounds and polymers

X-ray fluorescence analysis (XRF)based on a technique of direct external standard with the use of one reference sample is traditionally used in the laboratory of microanalysis (INEOS RAS) for determination of metals in composition of novel organometallic compounds and polymers. Preparation of the samples-emitters consists in 150 – 200-fold dilution of the substances with emulsion polystyrene (PS), since the amount of substance for analysis is limited to 10 – 15 mg. With this dilution XRF analysis are carried out in the concentration range of metal from 0.005 to 0.5 %, where the analytical calibration curve is linear. Measurements of analytical lines are carried out on a VRA-30 spectrometer (CARL ZEISS JENA (Germany)), X-ray tube with Rh-anode, 40 kV, 20 mA. A possibility of automatic conduction of X-ray fluorescence analysis of organometallic compounds and polymers synthesized in INEOS RAS on a VRA-30 spectrometer using software ALPHA-VRA-30 is studied. Software package developed at the research and innovation center JSC «FORATEKS» (Ekaterinburg) is intended for automated control of the spectrometer functioning without an operator. The software provides the possibility of deducing analytical equations of multiple regression on the basis of measurements of the intensities of analytical lines from the reference sample, and calculates the content of chemical elements in the analyzed samples-emitters. Advantages of the developed software are demonstrated and the results of XRF obtained using both the developed software and the method of direct external standard are compared. The small difference between the results obtained by those methods (0.7 % (abs)) in determination of iron and zinc in organometallic compounds when the content of iron and zinc range within of 4 – 25 % proves the applicability of the software to studying new compounds. Software ALPHA-VRA-30 provides standardization of measurement conditions and lightens the work of the analyst when analyzing large batches of substances.

Spreading a water droplet on the laser-patterned silicon wafer substrate for surface-enhanced laser-induced breakdown spectroscopy

For effective analysis of a small amount of liquid samples such as a single-droplet, surface-enhanced laser-induced breakdown spectroscopy (LIBS) can be considered. In this method, a drop of liquid sample is placed on the solid substrate, dried, and then analyzed by LIBS. However, the dry residues are distributed inhomogeneously and moreover concentrated in a very small area on the substrate surface. This uncontrollable distribution of analytes was identified as one of the main factors deteriorating the surface-enhanced LIBS analysis performances. We demonstrated the effectiveness of a newly devised laser-patterned silicon wafer (LPSW) with 40×40 crossed 1-cm laser-produced trenches in improving the analytical performances of surface-enhanced LIBS. The LPSW substrate spreads dry residues more homogeneously in the well-defined area (1×1cm). This significantly reduces the heterogeneous saturation of the analyte and reference line intensities. In comparison with the results using bare silicon wafer substrates, linear dynamic range of the calibration curve, analysis precision, and sampling efficiency were greatly improved by the LPSW substrates. For the analysis of potassium ion dissolved in a 15-μL water droplet, the limit of detection of 0.23×10−9 mol and the analysis precision of ~4% relative standard deviation were obtained using the LPSW substrates. Consequently, the benefits from the LPSW substrates allow multiple repeatable measurements for a single aqueous solution droplet sample.

Laser-induced Breakdown spectroscopy quantitative analysis method via adaptive analytical line selection and relevance vector machine regression model

A new LIBS quantitative analysis method based on analytical line adaptive selection and Relevance Vector Machine (RVM) regression model is proposed. First, a scheme of adaptively selecting analytical line is put forward in order to overcome the drawback of high dependency on a priori knowledge. The candidate analytical lines are automatically selected based on the built-in characteristics of spectral lines, such as spectral intensity, wavelength and width at half height. The analytical lines which will be used as input variables of regression model are determined adaptively according to the samples for both training and testing. Second, an LIBS quantitative analysis method based on RVM is presented. The intensities of analytical lines and the elemental concentrations of certified standard samples are used to train the RVM regression model. The predicted elemental concentration analysis results will be given with a form of confidence interval of probabilistic distribution, which is helpful for evaluating the uncertainness contained in the measured spectra. Chromium concentration analysis experiments of 23 certified standard high-alloy steel samples have been carried out. The multiple correlation coefficient of the prediction was up to 98.85%, and the average relative error of the prediction was 4.01%. The experiment results showed that the proposed LIBS quantitative analysis method achieved better prediction accuracy and better modeling robustness compared with the methods based on partial least squares regression, artificial neural network and standard support vector machine.

The improvement of the analytical performance of direct current atmospheric pressure glow discharge generated in contact with the small-sized liquid cathode after the addition of non-ionic surfactants to electrolyte solutions

A low power direct current atmospheric glow discharge sustained in the open to air atmosphere in contact with a small-sized flowing liquid cathode was used as an excitation source in optical emission spectrometry. The composition of electrolyte solutions served as the liquid cathode was modified by the addition of non-ionic surfactants, namely Triton x-45, Triton x-100, Triton x-405 and Triton x-705. The effect of the concentration of each surfactant was thoroughly studied on the emission characteristic of molecular bands identified in spectra, atomic emission lines of 16 metals studied and the background level. It was found that the presence of both heavy surfactants results in a significant increase in the net intensity of analytical lines of metals and a notable reduction of the intensity of bands of diatomic molecules and the background. In conditions considered to be a compromise for all metals, selected figures of merit for this excitation source combined with the optical emission spectrometry detection were determined. Limits of detection for all metals were within the range of 0.0003–0.05mgL−1, the precision was better than 6%, while calibration curves were linear over 2 orders of the magnitude of the concentration or more, e.g., for K, Li, Mg, Na and Rb. The discharge system with the liquid cathode modified by the addition of the surfactant found its application in the determination of Ca, Cu, Fe, K, Mg, Mn, Na and Zn in selected environmental samples, i.e., waters, soils and spruce needles, with the quite good precision and the accuracy comparable to that for measurements with flame atomic absorption spectrometry (FAAS) and flame atomic emission spectrometry (FAES).

Подготовка легированных стеклянных литий-боратных дисков для рентгенофлуоресцентного анализа горных пород на плавильной установке VULCAN 4

A new fusion method is developed using VULCAN 4 plant to make litium-borax glass beads for XRF analysis of rocks. The sample-flux mass ratio is 1:2; the NH 4 Br, NH 4 F and LiF alloying additions are used to provide for a sustained molding process of igneous rocks. As it is established, the upper flat surface of the glass bead can be a criterion for the optimal mass of alloying substance. According to the results of electron scanning of samples, glass beads are homogeneous and do not contain any alloying substance, which could affect the distribution of other elements. According to the XRF spectrometer measurements, the principal elements of rocks and samples with different additions display some insignificant difference in their analytical line intensities. Preparation of glass beads is a well-reproduced process. Key words : rocks, XRF analysis, glass lithium-borax bead, alloying (Russian) DOI: http://dx.doi.org/10.15826/analitika.2013.17.2.002 V.Ya. Borkhodoev, S.D. Penievsky, O.T. Sotskaya North-East Interdisciplinary Science Research Institute n.a. N.A. Shilo, Far East Branch, Russian Academy of Sciences, Magadan

Estimation of applicability of scattered radiation for XRF

The applicability of coherently and incoherently scattered radiation was investigated on the example of quantifying the Nb content in wolframite. The calculated and experimental intensities of Nb K a -line for binary and multicomponent mixtures of Nb 2 O 5 with various matrices have been compared. The major oxides MgO, SiO 2 , CaO, Fe 2 O 3 , and a typical component of tungsten ore (Fe, Mn)WO 3 were used as the main matrices. Measurements were carried out using the energy dispersive X-ray spectrometer with Si(Li)-detector and radioactive isotope source 109 Cd. The analysis of data shows that when using the ratio of the intensities of coherently and incoherently scattered X-radiation of the excitation source the dependence of the analytical line intensity of niobium on the content of W in the samples is taken into account. The experimental results confirm the conclusions of the theoretical consideration. This technique was successfully used to study wolframite samples from the deposits of the Eastern andWestern Mongolia. A procedure for the determination of Cu, Mo and Fe concentrations in ores, copper and molybdenum concentrates, and enrichment waste was developed to control the process of enrichment at the mining company Erdenet,Mongolia. This procedure was based on using regression equations. The form of regression equations was chosen based on the theoretically calculated intensities. The comparison results of measurements using the newly developed technique and the standard-background method are presented. Keywords : X-ray spectral fluorescence analysis of ores and enrichment products, method of standard-background, theoretical simulation of matrix effects DOI: http://dx.doi.org/10.15826/analitika.2013.17.4.001 P.Zuzaan 1 , D.Bolortuya 1 , S.Davaa 1 , A.G.Revenko 2 1 Nuclear Research Center, National University of Mongolia , Sukhbaatar District, Ulaanbaatar, Mongolia 2 Institute of the Earth’s Crust, SB RAS , Irkutsk, Russian Federation

Optimization of conditions of the direct atomic emission analysis of oxide-silicate materials

The matrix effect of silicon on the intensity of analytical lines of admixtures has been studied in the systems silicone oxide-graphite powder and silicon oxide-carrier-graphite powder. The composition of the spectroscopic buffer and the conditions of the direct spectrochemical analysis of oxide-silicate materials (brick, concrete, refractory materials, slags, glass, ceramics, etc) have been optimized. An atomic emission procedure has been proposed and its preliminary performance characteristics have been estimated.

A logical way through the limits of quantitation in inductively coupled plasma spectrochemistry

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.

Application of nondestructive X-ray fluorescence analysis to determine the element composition of medicinal plants

A nondestructive X-ray fluorescence technique has been developed to determine Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Ba, and Pb in plants. The line element intensities were measured by an S4 Pioneer X-ray sequence spectrometer (Bruker AXS, Germany). The inversely proportional relationship was obtained between the analyte line intensity and mass of the plant, pressed on boric acid backing, for elements with an atomic number 11 < Z < 20. It was found that reduction of plant mass from 6 to 1 g leads to an increase in element determination sensitivity. The detection limits for 1 g of pressed plant were evaluated as μg/g: 5–20 (Na, Mg, Al); 1–4 (Si, P, S, Cl, K, Ca, Ti, Ba, Pb); 0.4-0.8 (Cr, Mn, Fe, Ni, Br, Cu, Zn, Rb and Sr). This technique was applied to determine the element composition of violets of Violaceae family, which are used in medicine.

Study of a new direct current atmospheric pressure glow discharge in helium

In this study a new DC-APGD operated in He was developed and characterized. The discharge is operated at 0.9 kV and about 25–35 mA and at a gas flow of 100 ml/min. The source was spectroscopically studied and parameters such as the rotational temperature (T rot), the excitation temperature (T exc), the ionization temperature (T ion) and the electron number density (n e) were determined. The current–voltage characteristic of the source was studied as well. At optimized conditions the discharge operates in the normal region of the current–voltage characteristic. Rotational and excitation temperatures determined with the use of OH band and Fe I lines as thermometric species were of the order of about 900–1200 and 4500–5500 K, respectively. This indicates that despite of the atmospheric pressure, the discharge is not in LTE. Spatially resolved temperature measurements were performed with axial as well as radial resolution and showed relatively flat profiles. Axially resolved emission intensity profiles for several species such as H, N 2, N 2 +, OH, He and Hg were determined. It also was found that H 2 introduced into the He by electrolysis of acid solutions such as in ECHG considerably increases the spectroscopically measured gas temperatures but decreases the analyte line intensities, as shown for Hg.