Matrices digestion procedures

In the in vitro digestion method, the compound of interest is transferred from the food matrix to a bile salt micelle suspension that simulates the in vivo digestion process. This in vitro digestion procedure was first developed to estimate iron availability from meals and since then has been modified and applied to studying carotenoid bioaccessibility from various food matrices. This approach assesses the bioaccessibility of the compound from a certain meal before it is presented to and taken up by intestinal cells. 

To determine the instrumental response as a function only of the background matrix of the solution, the effect of perchloric acid on Cr, Mo, and Pd was tested independently of the digestion procedure. The variables were (1) presence of filter matrix in solution (2) presence of perchloric acid (3) presence of lanthanum flame buffer in solution and (4) concentration. The data are presented in Table XI. Slightly high recoveries (4 to 9 percent) were obtained for Cr when the filter matrix was present in solution. Recoveries of approximately 120 percent were obtained from the 1.0 ug/ml samples containing perchloric acid. This was found to be caused by Cr contamination in the perchloric acid. The corrected analytical results showed that the presence of either perchloric acid or lanthanum in solution has essentially no effect on the instrumental response for Cr in a lean air-acetylene flame. 

MS. After careful homogenization, the dried urine samples were analyzed directly by LA-ICP-MS without any time consuming digestion procedure. Matrix matched synthetic laboratory standards doped with Th (IRMM 60), uranium with natural isotope composition ( U/ U = 0.00725) and uranium isotope standard reference material (NIST U-930) at the low pgml level were prepared in order to smdy the figures of merit of the analytical methods developed. The recovery rate for thorium and uranium concentration measured on a synthetic urine laboratory standard by LA-ICP-MS varied between 91 and 104%. The precision and accuracy of the analytical methods was found to be 7 % and < 1 %, respectively, for uranium concentration, by using urine laboratory standards (at uranium concentration O.lngml. ... 

A single digestion procedure is often insufficient for the complete decomposition of a complex matrix, leading some authors to recommend a combination of two or more techniques. Two examples suffice to illustrate the principle [95,133]. The first example is pressure digestion followed by UV photolysis. It has been shown that... 

Alternatively, one can separate the proteins before breaking them into peptides and then subject them to protein breakdown to obtain the peptide. This approach involves mainly the use of gel-based procedures such as one-dimensional or two-dimensional electrophoresis (2-DE) to resolve protein mixture into protein spots based on molecular weight and charge (isoelectric point or pi). Following separation, protein spots are cut out from the gel protein is harvested from gel matrix, digested by peptides, and subjected for further mass spectrometric analysis. 

A classic example of this commonly adopted approach is the determination of a metallic trace element in a defined solid environmental matrix. This determination may involve an optimised digestion stage pertinent to a particular element and a specific matrix. Because this method may be the only validated method available, the digestion procedure is then used to determine other suites of metals in other matrices. Whether the actual procedures used are appropriate to these other metals in the suite or indeed the matrix is often not fully appreciated, or even considered, and results are generated in the hope that they will be satisfactory for the purpose. Without some form of verification, this assumption may be totally erroneous and the results generated may not be fit for purpose. 

Various sample preparation approaches, including microwave-assisted extraction and enzymatic digestion procedures, were examined to extract selenium from the defatted Brazil nut matrix among these approaches, enzymatic treatment with Proteinase K proved most effective [49]. SeMet was demonstrated to be the most abundant of these seleno-amino acids. In their study, another selenium species with m/z = 361 was also detected. By application of collision-induced dissociation (CID), there was evidence for this compound to be a dipeptide consisting of tyrosine and methionine with Se [49] as shown in Figure 9.1. It was proposed by the authors that this was a dipeptide with the structure p-HO(QH4)CH2CH(NH2)CONHCH(COOH)CH2CH2SeCH3. 

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