Interelement correction

Mass absorption coefficient, measurement for interelement corrections, 174... 

Griffiths et al. [92] quantified Pt, Pd and Rh in autocatalyst digests by ICP with a CCD detector array. They compared univariate techniques (pure standards, pure standards with interelement correction factors and matrix-matched standards) and PLS, the latter being superior in general, although less effective... 

To reduce the detrimental effects of spectral interferences on element quantitation, laboratories select the spectral lines that are least affected by the background, and use the background compensation and interelement correction routines as part of the analytical procedure. The instrument software uses equations to compensate for overlapping spectral lines the effectiveness of these equations in eliminating spectral interferences must be confirmed at the time of sample analysis. That is why laboratories analyze a daily interelement correction standard (a mixture of all elements at a concentration of 100mg/l) to verify that the overlapping lines do not cause the detection of elements at concentrations above the MDLs. 

In ICP-AES analysis, the IDLs must be determined every time an instrument has been adjusted in a way that may affect its sensitivity and interelement correction. The CLP SOW requires that the IDLs be determined at a minimum on a quarterly basis. Laboratories that are not part of the CLP determine IDLs annually. Table 4.4 shows... 

Inouye, T., Harper, T., and Rasmussen, N. C., Application of Fourier transforms to the analysis of spectral data. Nucl. Instrum. Methods 76, 125-132 (1969). Jenkins, R., and Campbell-Whitelaw, A., Determination of interelement correction factors for matrix correction procedures in X-ray fluorescence spectrometry. Can. Specbrosc. 15, 32-38 (1970). 

Commercial spectrometers now come with powerful computers and software. Most of the newer ICP emission systems provide software that can assist in wavelength selection, calibration, background correction, interelement correction, spectral deconvolution, standard additions calibration, quality control charts, and report generation. 

Fly Ash and sediment CRMs A1 Cr Cu Fe Ni Ba Be Ca Co Mg Ti As B Bi Mo Se V with aqua regia/HF [WDC] [WDMCV] ICPAESr with cross flow nebulizer and torch interelement correction [ICP-AES] WDMCV-ICP-AES] (1992)... 

For this reason, the interelement, correction should be avoided by using an undisturbed emission wavelength or by using a spectrometer with a high optical resolution power. 

Figure 7.41 Direct spectral overlap of Pt and Cr emission lines. No background correction technique can solve this problem. A line with no interference must be found, an interelement correction factor must be applied or the elements must be separated chemically. [From Boss and Fredeen, courtesy of PerkinElmer Inc. (www.perkinelmer.com).]...

When quantitative analysis is needed on complex samples with peak overlaps, a method of extracting the individual intensities of each element is needed. These mathematical corrections are now performed in instrument data processing software, and may include overlap corrections, interelement corrections, matrix corrections, corrections for non-Gaussian peak shapes, and different statistical fitting routines. A combination of these corrections was used to determine the concentration of the elements in the alloy shown in Fig. 8.49. 

Interferences of types 1 and 2 can occur not only from another element in the matrix but also from an argon line or molecular species such as OH or N2. An example of a type 1 interference is the Zn(I) line at 213.856 nm overlapping with the Ni(I) line at 213.858 nm. As type 2 can be eliminated only by improved spectral resolution, mathematical algorithms are used on a routine basis to solve this type. If the interference can be identified and quantified, then interelement correction factors can be inferred in a simple manner First, a calibration for the analyte is constructed in the usual way and then different concentrations of the interfering element are studied and the apparent analyte concentration calculated at the emission line(s) of interest. 

Because many elements have several strong emission Hnes, AES can be regarded as a multivariate technique per se. Traditionally, for quantitative analysis in atomic emission spectroscopy, a single strong spectral line is chosen, based upon the criteria of Hne sensitivity and freedom of spectral interferences. Many univariate attempts have been made to compensate spectral interferences by standard addition, matrix matching, or interelement correction factors. However, all univariate methods suffer from serious limitations in a complex and Hne-rich matrix. 

Determination of calibration curves and interelement correction coefficients... 

In the extension of this least-squares procedure to cover interelement correction terms, other partial differentials must be derived for each term required, that is, of the form... 

The form of the equation after substitution is such that complete matrix solution is not necessary. Also, the interelement correction factor Oab does have some theoretical significance, and it is fairly easy to show [28] that where absorption effects predominate and the effective wavelength approximation is accurate, the constant a is equal to... 

Regression A Analysis (Inclusion of Wrong Interelement Correction)... 

This is an example of an incorrect approach that appears at first sight to give acceptable results. The approach in this case was incorrect due to a bad choice of interelement correction. The correction procedure was of the form (see Ref. 8, Chap. 9)... 

The use of mass absorption (attenuation) coefficients has been discussed throughout this text, especially with regard to the calculation of primary and secondary absorption, interelement correction coefficients, and the fimdamental parameters method of quantitative analysis. Unfortunately, at this time no single, convenient, authoritative table of mass absorption coefficients is available. Variations between the data given in published mass absorption coefficient tables may be large and often depend upon the source and manner of obtaining and refining the data (either experimental or mathematical). Table A2.1 illustrates some variations of mass absorption coefficients as a function of the data source, and this is typical of most of the published data. 

Since the composition of the sample is variable, and therefore so is its mass absorption coefficient, it is sometimes necessary to carry out interelement corrections. The values of the correction factors can either be calculated from fundamental theory using commercially available software, or by multilinear regression analysis using the calibration samples. The former is preferred since the latter can force a mathematical fit to the data which bears no relation to X-ray theory. 

Quantitative X-ray analysis in analytical electron microscopy is now a most straightforward technique. Matrix (interelement) correction procedures based upon first principles physical models provide great flexibility in examining unknown samples of arbitrary composition. According to Castaing [251,252] ... 

The sample specimen is placed in the X-ray beam and the intensities of the fluorescence lines of torium, calcium, phosphorus, sulfiir, and zinc are measured. A amilar measurement is made away from the fluorescence lines in order to obtain a bacl round correction. Concentrations of the elements of interest are determined by comparison of net signals against appropriate interelement correction factors developed fi m responses of calibration standards. 

The X-ray fluorescence spectrometer is initially calibrated with a suite of standards in order to determine by regression analysis, interelement correction fretors and instrument response factors. 

Interelement correction factors and the slope and intercept of the calibration line are obtained by the regression analysis using the program supplied with the particular instrument used (if available) or a model similar to the following form ... 

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