Matrix modification

For example, the addition of ammonium nitrate eliminates interferences due to sodium chloride according to the equation  

Sodium nitrate and ammonium chloride are formed, and these decompose or sublime at temperatures below 700 K. Excess of ammonium nitrate is also easily removed during the thermal treatment. 

Ammonium nitrate, ammonium hydrogen phosphate, and their mixtures can be used as matrix modifiers to reduce matrix effects in the determination of lead. 

The addition of lanthanum for the determination of lead eliminates the interference of sulfate and increases the sensitivity. 

Phosphoric acid can be used to avoid losses of cadmium during the 

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It is further important to note that if only solid samples are taken, the calibration curve passes through the origin as is obvious in Figure 4.4. An intercept usually caused by blank values from reagents and digestion vessels in wet analysis can be excluded except in the case of matrix modification. 

Polymer Additive Functionality" Solvent Matrix modification Minimum detection limit ... 

Lum and Callaghan [ 140 ] did not use matrix modification in the electother-mal atomic absorption spectrophotometric determination of cadmium in seawater. The undiluted seawater was analysed directly with the aid of Zeeman effect background correction. The limit of detection was 2 ng/1. 

Han et al. [142] have reported an atomic absorption spectrometric method for the determination of cadmium in seawater using sodium phosphate for matrix modification. 

Several matrix modifiers, which alter the drying or charring properties of the sample matrix, have been tested [374-378] to reduce nonspecific absorption. However, the matrix modification methods do not permit determinations of the indigenous lead in seawater because of the relatively high detection limit and poor precision, and yet gross chemical manipulations of the samples should be avoided to prevent contaminations which can be dramatic when the analyte is present at p,g/l or sub- xg/l level. 

McArthur [433] preferred to use ammonium nitrate matrix modification to determine manganese in seawater. Most of his paper discussed the charring process. He found considerable salinity dependence if charring was too rapid. There was considerable change in the salinity dependence with the age of the tubes. 

Maximum power heating, the L vov platform, gas stop, the smallest possible temperature step between thermal pretreatment and atomisation, peak area integration, and matrix modification have been applied in order to eliminate or at least reduce interferences in graphite furnace AAS. With Zeeman effect background correction, much better correction is achieved, making method development and trace metal determinations in samples containing high salt concentrations much simpler or even possible at all. 

Figure 8.25 from Brown and Dymott, The use of platform atomisation and matrix modification as methods of interference control in graphite furnace analysis, by permission of Philips Scientific and Analytical Equipment. 

In the course of dentin caries, both demineralization and reactions with the organic matrix take place. Matrix reactions include proteolysis and covalent modifications. From the introduction (Chapter 2) and the review on discoloration in caries (Chapter 3), it becomes clear that there are still few reports on the effect of matrix modifications on dentin caries. In Chapters 2, 4, and 5, the investigations were aimed at filling the information gap concerning the effect of reactions of dentin matrix on caries. To this end, degradation and modification of dentin were studied in demineralized specimens in vitro. In addition, specimens placed in dentures in situ and caries lesions in extracted teeth were analysed for modifications. 

The compounds of Group V elements are often volatile, and loss of, for example, arsenic, selenium and tellurium during ashing of the sample can be reduced by the addition of nickel, to form nickel arsenide. Such stabilization procedures are called matrix modification (see Section 3.6.4). 

Q. Explain why matrix modification may lead to more efficient matrix removal. 

Figure 21-10 Reduction of interference by using a matrix modifier, (a) Graphite furnace temperature profile for analysis of Mn in seawater, (b) Absorbance profile when 10 xL of 0.5 M reagent-grade NaCl is subjected to the temperature profile in panel a. Absorbance is monitored at the Mn wavelength of 279.5 nm with a bandwidth of 0.5 nm. (c) Reduced absorbance from 10 nl of 0.5 M NaCl plus 10 of 50 wt% NH4NO3 matrix modifier. [From M. N. Quigley and F. Vernon, "Matrix Modification Experiment lor Electrothermal Atomic Absorption Spectrophotometry." J. Chem. Ed. 1996, 73. 980.]...

OP compounds and carbamate are widely used as insecticides, pesticides, and warfare agents [20,21], Detection of pesticides is usually carried out by multiresidue methods (MRMs) of analysis, which are able to detect simultaneously more than one residue and have been developed mainly based on chromatographic techniques. Two groups of MRMs are used (i) multiclass MRMs that involve coverage of residues of various classes of pesticides, and (ii) selective MRMs, which concern multiple residues of chemically related pesticides (e.g., IV-methyl carbamate pesticides (NMCs), carboxylic acids, phenols, etc.). As foods are usually complex matrices all of the pre-analytical steps (matrix modification, extraction, and clean-up) are often necessary. 

Bettinelli M, Baroni U, Fontana F, et al. 1985. Evaluation of the L vov platform and matrix modification for the determination of aluminum in serum. Analyst 110 19-22. 

Apart from atomization in the isothermal operation mode, there is another characteristic derived from the STPF concept that is worth commenting on, namely, matrix modification. 

The second mode of action of a modifier is direct reaction with the analyte to convert it into a phase with greater thermal stability, that is, to reduce analyte volatility. In this way, the charring stage can be carried out at higher temperatures, allowing a more efficient removal of the matrix but without the loss of analyte. Examples of this type of matrix modifier include transition metal ions (mainly Pd), which form thermally stable intermetallic compounds with analytes, and magnesium nitrate, which thermally decomposes to magnesium oxide, and in the process traps analyte atoms in its crystalline matrix it is thermally stable until 1100°C. In fact, the most frequently reported mixture for matrix modification consists of Pd(N03)2 and Mg(N03)2, proposed by Schlemmer and Welz as a universal chemical modifier.17... 

Ediger, R.D. 1975. Atomic absorption analysis with the graphite furnace using matrix modification. At. Absorpt. Newsl. 14 127-130. 

With this technique, problems may arise with interference, such as background absorption—the nonspecific attenuation of radiation at the analyte wavelength caused by matrix components. To compensate for background absorption, correction techniques such as a continuous light source (D2-lamp) or the Zeeman or Smith-Hieftje method should be used. Enhanced matrix removal due to matrix modification may reduce background absorption. Nonspectral interference occurs when components of the sample matrix alter the vaporization behavior of the particles that contain the analyte. To compensate for this kind of interference, the method of standard addition can be used. Enhanced matrix removal by matrix modification or the use of a L vov platform can also reduce nonspectral interferences. Hollow cathode lamps are used for As, Cu, Cr, Ni, Pb, and Zn single-element lamps are preferred, but multielement lamps may be used if no spectral interference occurs. 

Ebdon, L. and Lechotycki, A., The determination of lead in environmental samples by slurry atomization-graphite furnace-atomic absorption spectrophotometry using matrix modification, Micmchemical J., 34, 340-348, 1986. 

Modifiers are, however, used in a rather indiscriminate way in many laboratories. If used carelessly they can contaminate the sample solution with the element that is being determined and they can actually add to the background interference which one intends to reduce. By carefully optimizing the ashing and atomization temperatures for specific food matrices, as described above, the use of matrix modifiers can be reduced to the cases when they are really necessary. An additional benefit of matrix modification is that the sample and standard matrix are made very similar, this often making the standard addition method unnecessary. How this is carried out is described in detail in most instrument manuals and in specific textbooks. Commonly used modifiers are ammonium nitrate, ammonium phosphate, Mg nitrate, Pd nitrate, and ascorbic acid. 

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