A novel process was developed to isolate poly([R]-3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHO) and poly([R]-3-hydroxy-ω-undecenoate-co-3-hydroxy-ω-nonenoate-co-3-hydroxy-ω-heptenoate) (PHUE) from Pseudomonas putida species. Methyl tert-butyl ether (MTBE), ethyl acetate, acetone, and methylene chloride efficiently extracted PHO from freeze-dried biomass. The ratio of solvent to biomass was 15:1 (vol/wt). The nonchlorinated solvents required 18 h of extraction to achieve methylene chloride's yield of 15 wt % within 60 min. In the case of PHUE, the yield was 15-17 wt % after 60 min of extraction at room temperature, independently of the solvent used. MTBE performed best in life cycle assessment (LCA) if contamination of the environment is avoided. Filtration of the extract containing 8 wt % of raw polyhydroxyalkanoate (PHA) through activated charcoal revealed colorless polymers with less than one endotoxin unit/g. The ratio (v/v) of the solution to activated charcoal was 2:1. The loss (impurities and polymers) amounted up to 50 wt %.
In the 1990s the CCQM (Comité consultatif pour la quantité de la matière) defined the term 'primary method'. It also identified some methods that are considered to be primary. One of these methods is titrimetry. In this paper, the principle of titrimetry and two practical examples performed at the highest metrological level in the frame of key comparison CCQM-K8 are discussed. It is evident that titrimetry is a very powerful method leading to highly accurate results when performed correctly, and does not depend on whether the classical metrological approach or a new experimental design using modern laboratory technology is applied.
The homogeneity of samples intended for metrological intercomparison studies must be granted without ambiguity. This holds equally true for aqueous solutions for which the determination of betweenbottle variations requires measurement techniques with extremely high precision. Therefore measurement series were designed for automated analysis techniques such as titrimetry, optical emission spectrometry and ion chromatography which offer very high precision of results. Between-bottle relative standard deviations (RSD) of at best 0.008% were obtained with titrimetry. With optical emission spectrometry and ion chromatography, between-bottle RSD's of 0.02% and 0.05% were obtained. The contributions from these measurements were included in a conservative approach to the uncertainty budgets of the gravimetrical reference values for the analytes in the samples.
Various publications stress the importance of the repeatability (i.e. precision) of the calculation of the measurement of uncertainty. We reveal by detailing an example from production control in the pharmaceutical industry that the effect of other influence quantities should not be neglected, because their magnitude is even larger than the contribution of repeatability. We review the role of repeatability within the calculation of measurement uncertainty for several common validation and day-today measurement scenarios. They show that measurement models need to consider the measurement sequences of the various scenarios. Otherwise the size and effect of the repeatability might be overestimated. At the end Monte Carlo simulations were used to investigate the determination of the repeatability under certain restrictions. The simulation uncovered a significant bias toward the common formula for calculating the standard deviation when it is based on a duplicated measurement of a sample.
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