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Bajo el nombre «control de producción» se comprende el conjunto de métodos que ayudan al fabricante del hormigón a cumplir lo especificado de la forma mas económica. Puesto que el fabricante es normalmente el responsable de la calidad de la producción, debe otorgársele también la responsabilidad de poder controlar la producción (autocontrol), dejándole la mayor libertad posible en cuanto a los métodos por medio de los cuales tratará de conseguir un hormigón de la calidad requerida en forma económica.

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid derived from dietary sources and broken down in the peroxisome to pristanic acid (2,6,10,14-tetramethylpentadecanoic acid) via α-oxidation. Pristanic acid then undergoes β-oxidation in peroxisomes. Phytanic acid naturally occurs as a mixture of (3S,7R,11R)- and (3R,7R,11R)-diastereomers. In contrast to the α-oxidation system, peroxisomal β-oxidation is stereospecific and only accepts (2S)-isomers. Therefore, a racemase called α-methylacyl-CoA racemase is required to convert (2R)-pristanic acid into its (2S)-isomer. To further investigate the stereochemistry of the peroxisomal oxidation systems and their substrates, we have developed a method using gas-liquid chromatography-mass spectrometry to analyze the isomers of phytanic, pristanic, and trimethylundecanoic acid in plasma from patients with various peroxisomal fatty acid oxidation defects. In this study, we show that in plasma of patients with a peroxisomal β-oxidation deficiency, the relative amounts of the two diastereomers of pristanic acid are almost equal, whereas in patients with a defect of α-methylacyl-CoA racemase, (2R)-pristanic acid is the predominant isomer. Furthermore, we show that in α-methylacyl-CoA racemase deficiency, not only pristanic acid accumulates, but also one of the metabolites of pristanic acid, (2,6,10)-trimethylundecanoic acid, providing direct in vivo evidence for the requirement of this racemase for the complete degradation of pristanic acid. —Ferdinandusse, S., H. Rusch, A. E. M. van Lint, G. Dacremont, R. J. A. Wanders, and P. Vreken. Stereochemistry of the peroxisomal branched-chain fatty acid α- and β-oxidation systems in patients suffering from different peroxisomal disorders.

A simple apparatus comprising basically a glass tube closed on one side, two low-pressure manometers with a range of 150 millibars, a pump with a small reservoir of compressed air as well as the necessary connections and valves allows in vitro comparisons of pressures in low-pressure cuffs whereby the introcuff-pressure can be adjusted to any value between zero and 150 milibars. One can also monitor continually the interdependence between the intracuff-pressure and the airway pressure whereby the latter can also be varied continuously.