Accurate and rapid estimation on spectral interferences in routine analysis by ICP-AES: use of mutual interference coefficients

A practical method to estimate spectral interferences and to select optimum analytical lines in ICP-AES is suggested. Depending on the matrix composition and the amounts of the analyte, the analytical lines suffering from little interferences and the limit of determination can be determined from calculation using spectral interference coefficients. For this calculation, the spectral interference coefficients, which are defined as apparent mass of the analyte equivalent to the spectral interference from unit mass of the interferent, are obtained experimentally for 639 emission lines of 68 elements. There is a good correlation between the coefficients obtained on two spectrometers having different resolutions.     

Mutual interference coefficients obtained for 639 emission lines of 68 elements in routine analysis by ICP-AES

In our previous report [1], a practical method to obtain spectral interference coefficients and to select analytical lines in ICP-AES has been suggested.The coefficients were defined as apparent mass of the analyte corresponding to the spectral interference observed for unit mass of the interferent. In this report, data of the experimentally obtained mutual interference coefficients among 639 emission lines of 68 elements are presented. The data would be also useful for different resolution spectrometers in routine analysis, they are presented on 69 Tables as Supplementary Electronic Material. Received: 28 January 1999 / Accepted: 1 March 1999     

Mutual interference coefficients obtained for 639 emission lines of 68 elements in routine analysis by ICP-AES

In our previous report [1], a practical method to obtain spectral interference coefficients and to select analytical lines in ICP-AES has been suggested.The coefficients were defined as apparent mass of the analyte corresponding to the spectral interference observed for unit mass of the interferent. In this report, data of the experimentally obtained mutual interference coefficients among 639 emission lines of 68 elements are presented. The data would be also useful for different resolution spectrometers in routine analysis, they are presented on 69 Tables as Supplementary Electronic Material.     

X-ray fluorescence analysis of metals in ores and concentrates by Compton scattering

An X-ray fluorescence method for the analysis of ores and concentrates for one or more metals or other heavy elements is described. A tungsten-target tube is used and the spectral interference of Rayleigh and Compton scattered peaks reduced by a nickel filter. A correlation is established between the latter peak intensity and the mass absorption coefficient of the sample for the wavelength 1.6 Å. The values of mass absorption coefficients on both sides of any major element absorption edge are compared and their ratio correlated to the characteristic radiation intensity of that particular element. This permits calculation of mass absorption coefficients across major absorption edges by derivation from the measured μ 1.6 value. Spectral interferences and other difficulties advocate dilution of the samples with dipotassium disulfate. Element concentrations are calculated by comparison with a standard sample and relating mass absorption coefficients and characteristic radiation intensities of both standard and unknown. Precision and accuracy of the method are considered excellent, given the simple nature of the analytical procedure.     

ICP emission spectrometric analysis of rare earth elements in permanent magnet alloys

An analytical method for the determination of rare earth elements (REE) in a NdFeB permanent magnet alloy by ICP emission spectrometry is described. Spectral interferences, arising from overlapping, as well as matrix effects have been studied. Considering spectral interferences, sensitivities of spectral lines, background intensities and the chemical composition of the sample investigated, optimum spectral lines for each REE have been selected. Because of an unfavourable concentration ratio in samples of a NdFeB permanent magnet alloy, a preliminary separation of matrix elements from rare earth elements by ion chromatography is necessary. Different modes of elution (isocratic and gradient) with -hydroxy-isobutyric acid and different columns (NUCLEOSIL, SULFOPROPYL SI-100, DIONEX HPIC-CS3) have been tested. Optimum separation conditions have been chosen for each element and the separation efficiency at equal or different concentrations of the selected elements have been established. Although the separation of REEs resulted in partly overlapping peaks, the ratio between analyte and interferent is improved and the spectral interferences are diminished. The results obtained are in good agreement with certified values.     

A factor analysis approach to optimized line selection in inductively coupled plasma atomic-emission spectrometry

The best analytical line for determination of a specified analyte is selected from a set of lines on the basis of the least interference in a particular sample matrix, by several cycles of mathematical analysis. Unsuitable lines are rejected in the first few cycles, the best lines being retained until last. A multivariate analysis after each cycle provides an updated estimate of the analyte concentration. This process is performed without reference to spectral tables.     

Reaction chemistry and collisional processes in multiple devices for resolving isobaric interferences in ICP-MS

A low-level review of the fundamentals of ion-molecule interactions is presented. These interactions are used to predict the efficiencies of collisional fragmentation, energy damping and reaction for a variety of neutral gases as a function of pressure in a rf-driven collision/reaction cell. It is shown that the number of collisions increases dramatically when the ion energies are reduced to near-thermal (< 0.1 eV), because of the ion-induced dipole and ion-dipole interaction. These considerations suggest that chemical reaction can be orders of magnitude more efficient at improving the analyte signal/background ratio than can collisional fragmentation. Considerations that lead to an appropriate selection of type of gas, operating pressure, and ion energies for efficient operation of the cell for the alleviation of spectral interferences are discussed. High efficiency (large differences between reaction efficiencies of the analyte and interference ions, and concomitant suppression of secondary chemistry) might be required to optimize the chemical resolution (determination of an analyte in the presence of an isobaric interference) when using ion-molecule chemistry to suppress the interfering ion. In many instances atom transfer to the analyte, which shifts the analytical m/z by the mass of the atom transferred, provides high chemical resolution, even when the efficiency of reaction is relatively low. Examples are given of oxidation, hydroxylation, and chlorination of analyte ions (V+, Fe+, As+, Se+, Sr+, Y+, and Zr+) to improve the capability of determination of complex samples. Preliminary results are given showing O-atom abstraction by CO from CaO+ to enable the determination of Fe in high-Ca samples.     

Line selection and interference correction for the analysis of tungsten alloy by inductively coupled plasma atomic emission spectrometry

A method for the analysis of tungsten alloy to determine selected elements using inductively coupled plasma atomic emission spectroscopy is described, with emphasis on line selection and spectral interference. The spectral interference coefficients were calculated for the spectral lines of selected major and trace elements. These values were used to select analytical lines and to calibrate concentrtions of the analytes. The detection limits of the elements for this method were determined and compared with those obtained by flame atomic absorption spectrometry and direct current carbon are emission spectrometry. The results indicated that the detection limits for all of the elements determined by the proposed method are significantly better than those obtained by other techniques. In this study, the analytical reliability of the proposed method was estimated by comparison of the analytical data for the two types of tungsten alloys produced by the Korean Tungsten Company with those obtained by the matrix matching method and the results indicated that the accuracy of multi-element analysis is satisfactory.     

Peak purity assessment by matrix projection for spectral line selection and background correction in inductively coupled plasma optical emission spectrometry

This paper describes an improvement of the procedure, proposed previously (Spectrochim. Acta, Part B, 48 (1993) 1517), to provide information about multiplicative and spectral interferences at lines selected for the analysis of samples. The new version of the procedure only requires intensity scans across an analyte line when three solutions are aspirated: a standard solution, the sample solution and the sample spiked with the analyte standard solution. The third solution can be omitted if multiplicative interference is not of interest. Like the initial method, the present procedure does not require or assume information about the sample composition nor is the preparation of solutions of suspected interferents required. Figures of merit, namely the structured background factor, and the overall spectral interference have been devised and are used with the true detection limit at a line for line evaluation and selection. As the nonanalyte concomitant contribution to the measured spectrum is estimated, automatic background correction is possible. The proposed method not only allows selection of the spectral line, but can give a good estimate of the analyte concentration prior to a full quantitative analysis.     

Feasibility of eliminating interferences in graphite furnace atomic absorption spectrometry using analyte transfer to the permanently modified graphite tube surface

A procedure is proposed to avoid spectral and/or non-spectral interferences in graphite furnace atomic absorption spectrometry (GF AAS) by transferring the analyte during the pyrolysis stage from a solid sampling platform to the graphite tube wall that has been coated with a permanent modifier, e.g. by electrodeposition of a platinum-group metal. The direct determination of mercury in solid coal samples was chosen as a model to investigate the feasibility of this idea. The graphite tube surface was coated with palladium and the analyte was transferred from the solid sampling platform to the tube wall at a temperature of 500±50 °C. A characteristic mass of m₀=64 pg Hg was obtained for an atomization temperature of 1300 °C, proposing a quantitative transfer of the analyte to the tube wall. Calibration against aqueous mercury standards was not feasible as this element was lost in part already during the drying stage and could not be trapped quantitatively on the modified graphite tube surface. However, the results for all except one of the coal reference materials were within the 95% confidence interval of the certificate when the slope of a correlation curve between the integrated absorbance, normalized for 1 mg of sample, and the certified value for mercury was used for calibration. A detection limit of 0.025–0.05 μg g⁻¹ Hg in coal, calculated from three times the standard deviation of the investigated coal samples, could be obtained with the proposed method. The spectral interference due to excessive background absorption in the direct determination of mercury in coal could be eliminated completely. It is expected that this analyte transfer can be used in a similar way to eliminate other spectral and/or non-spectral interferences in the GF AAS determination of other volatile analytes.     

Reduction of spectral interferences in flame emission spectrometry by selective spectral-line modulation

Spectral interferences in flame emission spectrometry can be significantly reduced through the use of selective spectral-line modulation (s.l.m.). In this method, a mirrored, rotating chopper is used to direct the emission from a sample flame alternately through and around a second (modulating) flame; selective modulation is achieved when the modulating flame contains absorbing atoms identical to emitting analyte atoms in the sample flame. The effects of optical configuration and modulating conditions on working curve slope, linearity, and signal-to-noise ratio are examined. Also, the ability of s.l.m. to minimize broad-band and narrow-line spectral interferences is demonstrated. In particular, it has been shown that the interference of the 554-nm CaOH band on barium determinations can be largely overcome. Also, interference of several palladium lines on nickel in the 350-nm region can be reduced. Finally, it is shown how the interference of flame background itself can be restricted in s.l.m. procedures.     

High-resolution spectra of selected rare earth elements and spectral interferences studied by inductively coupled plasma-atomic emission spectroscopy (ICP-AES)

The rare earth elements (REEs) play very important roles in industrial manufacturing, technology development and biological processes. Due to their complex emission spectra, trace levels of REEs are difficult to analyze by conventional ICP-AES techniques. The present study investigates possible spectral interferences of matrices (rare earth oxides of Ce, Pr, Nd, Sm and Dy) on the analytical lines (± 0.1 nm) of a target REE. Detailed and well-resolved spectra for selected REEs are presented, and procedures used to rectify the problem of spectral interferences caused by REE matrices are discussed. A computer-assisted system (CAS) for spectral recognition has been developed and used to assist in the study of matrix interference. To determine directly trace rare earth elements in REE matrices without sample pre-separation, the application potential is demonstrated with a one meter sequential instrument retrofitted with a 3600 grooves/mm grating.     

Characterization of the selectivity of a phenytoin imprinted polymer

The selectivity of analytical methods based on molecularly imprinted polymers (MIPs) is due to the preferential adsorption of the analyte(s) as compared to other substances (interferences). This paper shows the theoretical and practical difficulties, which have to be considered and solved when real samples need to be analysed in a wide range of analyte and interferant concentrations. It is shown that the estimation of interference effects requires either many measurements or a realistic model of the adsorption equilibrium in mixed solutions of the analyte and the interferences. Examples are shown for positive (cooperative) interference effects, for better experimental design and interpretation of binary isotherm measurements and for establishing the chemical model of interference from selectivity measurements. The usual MIP model consisting of a cavity, which closely fits the shape of the template from all sides, appears unsuitable for this MIP, and it is replaced with a more realistic, more open model. The applicability of the results to using non-imprinted polymers as selective sorbents and to screening drug candidates is also shown.     

Investigation and quantification of spectroscopic interferences from polyatomic species in inductively coupled plasma mass spectrometry using electrothermal vaporization or pneumatic nebulization for sample introduction

A new method for quantification of spectral interferences based on analyte isotope ratio measurements in the presence of various concentrations of a specific matrix is presented. Within the method, a tolerance level is used, defined as the matrix concentration at which the ratio between analyte isotopes with and without interferences is altered by 10% compared to a pure water reference standard, normalized with respect to the analyte concentration in the solutions. This can be used to estimate the lowest analyte concentration which can be determined with a defined accuracy in the presence of a known concentration of a specific matrix. Regarding spectroscopic interference effects, comparative results for sample introduction into the ICP–MS by electrothermal vaporization, ETV, and nebulization are presented for common matrix — (Ca, Na, K, Cl, P, O) and analyte (Cr, Ni, Cu, As, Se) elements. With the exception of the spectral overlap of ³¹P₂⁺ on ⁶²Ni⁺, spectroscopic interferences were reduced by 1–2.5 orders of magnitude when using ETV for sample introduction. Reasons for the increase in the spectral interference of ³¹P₂⁺ on ⁶²Ni⁺ are discussed. For sample introduction by nebulization, it was found that spectral interferences from CaO⁺ on ⁵⁸Ni⁺ and ⁶⁰Ni⁺ were reduced in the presence of phosphate.     

Non-linear spectral interferences in an inductively coupled plasma optimized for simultaneous multi-element analysis of plant and soil samples by atomic emission spectrometry

Summary The spectral interferences by Al, Ca, Fe, K, Mg and Na in the direct simultaneous determination of As, Cd, Co, Cu, Hg, Pb and Se in plant and soil samples by ICP-AES are investigated, and a non-linear relationship between the apparent analyte concentration for As, Cd, Co, Hg and Se is observed. A correction method for non-linear spectral interferences is discussed and non-linear spectral correction coefficients are calculated.     

自模型曲线分辨法校正电感耦合等离子体原子发射光谱中严重谱线重叠干扰

对严重重叠的光谱干扰校正,采用较小间隔的光谱扫描测量,并用间隔扫描点的数据计算,可减小计算结果的误差,提高结果的准确性。本方法用于校正Nd359.259nm对Sm359.260nm和V328.939nm对Yb328.937nm谱线重叠干扰,得到了满意的结果。     

Spectral interferences in the determination of traces of scandium, yttrium and rare earth elements in “pure” rare earth matrices by inductively coupled plasma atomic emission spectrometry-I. Cerium, neodymium and lanthanum matrices

The present paper deals with spectral interferences from cerium, neodymium and lanthanum on prominent lines of scandium, yttrium and rare earth elements (REE). The “true detection limit” criterion was used for rational wavelength line selection as proposed by boumans and vrakking [Spectrochim. Acta 42B, 819 (1987); 43B, 69 (1988)]. Analysis lines selected for cerium and neodymium matrices suffered both wing and line interferences. In the case of a lanthanum matrix, it is possible to choose mostly analysis lines that are free of line interference and negligible wing interference. The high degree of spectral interferences with a cerium or neodymium matrix significantly worsens the true detection limits. This article is an electronic publication in Spearochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk with data and text files. The data files comprise in particular the tabular material of this article in electronic form.     

Reaction chemistry and collisional processes in multipole devices for resolving isobaric interferences in ICP–MS

A low-level review of the fundamentals of ion-molecule interactions is presented. These interactions are used to predict the efficiencies of collisional fragmentation, energy damping and reaction for a variety of neutral gases as a function of pressure in a rf-driven collision/reaction cell. It is shown that the number of collisions increases dramatically when the ion energies are reduced to near-thermal (< 0.1 eV), because of the ion–induced dipole and ion–dipole interaction. These considerations suggest that chemical reaction can be orders of magnitude more efficient at improving the analyte signal/background ratio than can collisional fragmentation. Considerations that lead to an appropriate selection of type of gas, operating pressure, and ion energies for efficient operation of the cell for the alleviation of spectral interferences are discussed. High efficiency (large differences between reaction efficiencies of the analyte and interference ions, and concomitant suppression of secondary chemistry) might be required to optimize the chemical resolution (determination of an analyte in the presence of an isobaric interference) when using ion-molecule chemistry to suppress the interfering ion. In many instances atom transfer to the analyte, which shifts the analytical m/z by the mass of the atom transferred, provides high chemical resolution, even when the efficiency of reaction is relatively low. Examples are given of oxidation, hydroxylation, and chlorination of analyte ions (V⁺, Fe⁺, As⁺, Se⁺, Sr⁺, Y⁺, and Zr⁺) to improve the capability of determination of complex samples. Preliminary results are given showing O-atom abstraction by CO from CaO⁺ to enable the determination of Fe in high-Ca samples.