Acidity assessments, total

Moller j, Rasmussen K, Christensen L (1999) External quality assessment of methylmalonic acid and total homocystein. Clin Chem 45 1536-1542. 

For the determination of total mercury, the samples were mineralized by microwave digestion using nitric acid. The final determination was performed by CVAAS. Methylmercury was determined by CGC/ECD after extraction of 0.2 g fish powder in toluene, back extraction with a cysteine acetate solution and further extraction with toluene. Calibrations were performed by standard additions. The uncertainties of the methods of final determination were assessed by the analysis of 10 aliquots from one digest solution (nitric acid for total mercury, toluene for methylmercury). The CV of the method, therefore, does not comprise the CV introduced by the extraction procedure. 

Good linearity was achieved in both ranges of concentrations tested, with correlation coefficients higher than 0.999 in all cases. The proposed method showed a good sensitivity, with limit of detection (LOD) and limit of quantification (LOQ) of 22 and 67 ng/mL, respectively. The method also showed satisfactory precision. All relative standard deviation (RSD) values achieved for peak areas were lower than 4%. The results obtained showed that the applied method has a good reproducibility and that is stable and reliable. The recovery rate of L-ascorbic acid and total vitamin C was evaluated to assess the extraction efficiency of the proposed method and matrix effects. Satisfactory results were obtained for L-ascorbic add (96.6 4.4%) and total vitamin C (103.1 4.8%) [75]. 

In some circumstances it is possible to express protein requirements in terms of total protein alone, for example if animals are fed on a limited range of foods of known amino acid composition. This is the case for growing pigs in the USA that are fed mainly on maize and soya bean meal. Such a simplified approach cannot be sustained when a wider range of foods and by-products are used, and when diets must be formulated not only to maximise growth but also to optimise carcass composition. Feed compoimders therefore formulate pig diets to meet the requirements for at least three amino acids (lysine, methionine -I- cystine and threonine).They will also take into accoimt the availability of certain amino acids, assessed from digestibility at the terminal Ueiun (as explained in Chapter 10). 

The factors chosen for study were the concentration of the ion-pairing reagent, the solution pH ( quantitative factors) and the acid chosen for pH adjustment (formic, acetic, propionic and trifluoroacetic acids) ( quahtative factor). The effect of these factors was assessed by using responses that evaluated both the HPLC (the number of theoretical plates and the retention time) and MS performance (the total peak area and peak height) for each of the four analytes studied, i.e. 1-naphthyl phosphate (1), 1-naphthalenesulfonic acid (2), 2-naphthalenesulfonic acid (3) and (l-naphthoxy)acetic acid (4). 

The previous biomarkers relate to phenotypic assessments of microbial diversity and most will probably measure a restricted part of the total microbial pool, since not alt markers will be expressed uniformly by every cell. In contrast, methods involving the detection of nucleic acids may be directly applicable to all microorganisms provided that the complete extraction of DNA (lysis of cells) or permea-bilization of cells can be achieved. 

The effects of added C02 on mass transfer properties and solubility were assessed in some detail for the catalytic asymmetric hydrogenation of 2-(6 -meth-oxy-2 -naphthyl) acrylic acid to (Sj-naproxen using Ru-(S)-BINAP-type catalysts in methanolic solution. The catalytic studies showed that a higher reaction rate was observed under a total C02/H2 pressure of ca. 100 bar (pH2 = 50bar) than under a pressure of 50 bar H2 alone. Upon further increase of the C02 pressure, the catalyst could be precipitated and solvent and product were removed, at least partly by supercritical extraction. Unfortunately, attempts to re-use the catalyst were hampered by its deactivation during the recycling process [11]. 

Table 4. Percentage of various endpoints contribution to total environmental risk assessment of ecosystem sensitivity to acid deposition in Northern Asia (Bashkin, 1998).

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