Matrix destruction

Chabaud M, Garnero P, Dayer JM, Guerne PA, Fossiez F, Miossec P Contribution of interleukin 17 to synovium matrix destruction in rheumatoid arthritis. Cytokine 2000 12 1092-1099. 

The relationship between the degradation of organic matrix and dentin lesion formation has been studied both in vitro and in situ. Several authors employed matrix destruction to assess the role of the matrix in de-and remineralization. For example, Apostolopoulos and Buonocore (1966) reported facilitated demineralization of dentin at pFl<5.5 after treatment with ethylene diamine. Inaba and coworkers (1996) found that removal of matrix from dentin lesions by hypochlorite promotes remineralization, consistent with a larger crystal surface available for mineral deposition after ashing (McCann and Fath, 1958). Flypochlorite-mediat-ed destruction also increases the permeability of mineralized dentin (Barbosa et ah, 1994). 

Widening interest in the quaHty of the environment has led to increased demand for information on a wide range of trace-metal contents of foodstuffs. Trace metals in foodstuffs are normally determined by spectroscopic techniques after complete destruction of the organic matrix. Destruction is achieved either by wet oxidation or by dry ashing additional treatment is normally required in order to obtain the metals of interest in a form suitable for analysis. Both methods of destruction are time consuming and tedious this is particularly true of the wet-oxidation procedure, which has the additional disadvantage of being potentially hazardous the methods require considerable analytical skill and experience. Both methods are prone to produce erroneous results either by the loss of an element of interest or by adventitious contamination from the component parts... 

The chemical form of the matrix in petroleum is largely unknown. Therefore, in all the procedures used, recovery had to be demonstrated by total matrix destruction (which converts the element to a common form) or by technique which is independent of form—e.g., neutron activation analysis. 

Ti Tost of the difficulties associated with ultratrace elemental analysis can be attributed, not to the detection step, but to the total process wherein the element of interest is removed from the sample matrix and presented to the detector system. Therefore, matrix destruction or separation and dissolution and/or concentration of the element(s) are extremely important in determining the total error in the analysis scheme. Tolg (1) has discussed the sources of such errors and suggested means of minimizing their effect. 

A number of methods exist for the determination of parts-per-billion (ng/g) levels of chromium in aqueous media (Table 8.1). These are repeatedly reviewed as new techniques are introduced (4,5,6). Potentially all these techniques could be applied to petroleum samples after matrix destruction, but in practice, only a few have been utilized. After wet oxidation of a large sample (> 100 g), 10 to 50 fig of chromium may be determined by a colorimetric procedure with 1,5-diphenylcarbohydrazide after iron, copper, molybdenum, and vanadium are extracted as the cup-ferrates (3). In survey analyses, Cr levels as low as 5 ng/g have been measured by optical emission spectroscopy after ashing (2,3) or directly by neutron activation with extended irradiation and counting times (1). Concentrations of chromium above 100 ng/g in used lubricating oils have been measured directly by flame atomic absorption (8) for lower concentrations, heated vaporization atomic absorption (HVAA) has been utilized (9). In the Trace Metals Project, two procedures using this latter technique were evaluated for the determination of 10 ng Cr/g in a variety of petroleum matrices. 

Except neutron activation, methods which have been used to determine mercury in organic materials involve a matrix decomposition step prior to the actual measurement. Oxidative techniques involving various combinations of acids and salts have been widely used for matrix destruction (1, 2, 3, 4, 5), as have the Schoniger, Wickbold, and other bomb and tube combustion techniques (1, 6, 7, 8, 9,10). 

Various measurement techniques have been used after matrix destruction. Small amounts of mercury are generally determined by conversion from an ionic species in aqueous solution to the elemental vapor, which is measured spectroscopically by atomic fluorescence, ultraviolet, or atomic absorption techniques (1,5, 6,9,10,11,12,13,14,15,16). Review articles covering the determination of small amounts of mercury in organic and inorganic samples (17) and the determination of mercury by nonflame atomic absorption and fluorescence spectroscopy (18) have recently appeared. In certain instances detection limits of 1 ng/g have been possible. 

Traceability is realized when an unbroken chain of calibrants links the analytical procedure to fundamental units. Very often, this chain is broken when precipitation, matrix destruction or digestion are performed. It must be proven that neither losses nor contaminations and no species alterations occur. One of the most elegant ways to achieve this aim is the incorporation of certified reference materials (CRM) into the analytical program. 

Matrix Destruction. During this step, the matrix is decomposed and removed by volatilization. Chemical reactions are often used to enable volatilization of matrix constituents or their com-... 

Thermochemistry is especially important reliable matrix destruction and removal of matrix elements without analyte loss. Thermochemical reagents such as quarternary ammonium salts (RjN Cr) mineralize organic samples at temperatures below 400 °C, and prevent losses of elements which are volatile or form volatile, perhaps organic, compounds. This may be helpful for Cd and Zn, which form volatile compounds in a number of organic matrices. Removal of NaCl, present in most biological samples, may be helpful to prevent matrix interference this must be done at low temperature to prevent analyte loss, and can be achieved by the addition of NH4NO3 ... 

Fig. 4. Proposed mechanism for zeolite and matrix destruction by vanadium showing the involvement of an Na20-V20s melt in the dealumination process.

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