ACIDizing Sampled Material

Heat reagent-grade material for 1 hr at 255-265°C. Cool in an efficient desiccator. Titrate sample with acid to pH 4-5 (first green tint of bromocresol green), boil the solution to eliminate the carbon dioxide, cool, and again titrate to pH 4-5. Equivalent weight is one-half the formula weight. 

Post-column reaction is a common feature of many special types of analyses, the most well-known being the amino acid analyzer that uses ninhydrin with a post-column reactor to detect the separated amino acids. In general, derivatization and post-column reactor systems are techniques of last resort. In some applications they are unavoidable, but if possible, every effort should made to find a suitable detector for the actual sample materials before resorting to derivatization procedures. 

Weak-acid partial leach - 0.5 g of ground sample material leached for 2 hours in 5 ml of 2% HNO3 then diluted 10x with weak acid. 

Solid samples are digested with suprapure sub-boiled HN03 to avoid contamination in an acid mixture using HF, HC1 or 4 (e.g., in an open vessel directly or in a closed vessel by microwave induced digestion). The sample digestion of difficult-to-dissolve sample material in closed vessels,... 

The sample material was a hydrogel, that was made out of 11 g acrylic acid monomer (AA), 11 g acrylamide monomer (AAm), 100 g water (H20), 0.5 g cross linker MB AAm (N,N -methylenebisacrylamide) and 0.1 g of the initialisators (NH4)2S20g and K2S2O5. The solution was neutralised by 6.2 g NaOH. The constituents were put in a test tube where they react with each other as described by de Heus [3]. After the reactions between the components stopped, the material was submerged in a 0.15 molar NaCl-solution for one or two days. Then, the hydrogel was put in a cup filled with a 0.15 molar NaCl solution and was stored at room temperature. 

Trace element analysis of foods can be carried out to check for contamination by toxic elements, such as lead and cadmium, or to determine beneficial micronutrients, or as an aid to distinguishing geographical origin. In fats, small numbers of trace elements are measured after digestion of the sample in acid followed atomic absorption spectrophotometry (AAS) or by direct graphite furnace vaporization. An AAS procedure for measuring lead in edible oils and fats has been collaboratively trialed with cocoa butter as a test material (Firestone, 1994). 

The synthetic boron substituted mordenltes have alpha values similar to the aluminosilicate analogues. This Ls not surprising since boron replaces only 10% of the aluminum In these materials. For boron to affect the alpha values of these samples, the acid strength of a B-OH proton would have to be much greater than for a A1-0H proton, inihlch Ls clearly not the case. 

Table 9 summarizes procedures of blood collection for aluminum determination. Steps to avoid contamination, the analytical technique, and the aluminum levels found in the serum of healthy individuals are listed. It can be seen that, as a general procedure, plasticware was used, all materials that entered in contact with the sample were acid-washed, usually by nitric acid, and the analyses were carried out inside clean rooms. 

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