The stability of various biphosic systems has been determined using a High Performance Centrifugal Partition Chromatograph, and its relationship with various physical parameters has been estimated. The stability seems to be related to l, the ratio of the interfacial tension to that of the density difference between the two phases, and which is a parameter accounting for both the "Stoke's radius" of the mobiie phase, i.e. the radius of droplets of mobile phase which wiil have the same average linear velocity, 0. in the channels than the experimentally determined value, and the "fragility" of these droplets. The average linear velocity of the mobile phase is not dependent upon the acceleration field in the range studied, which means that, using the "Stoke's model" (droplets, even if they do not exist), the higher the acceleration field. the smaller the droplets. Consequently, there is a linear relationship between the efficiency and the rotational speed, provided all other parameters are kept constant.
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a laboratory comparison, CCQM-P20.f, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2007/2008. Nine national measurement institutes, four expert laboratories and the BIPM participated in the comparison. Participants were required to assign the mass fraction of digoxin present as the main component in the comparison sample (CCQM-P20.f) which consisted of digoxin material obtained from a commercial supplier stated to comply with USP requirements.In addition to assigning the mass fraction content of digoxin for the material, participants were requested, but not obliged, to provide mass fraction estimates for the minor components they identified in each sample.In contrast with the previous round of the CCQM-P20 series, in which the mass fraction content of theophylline in two comparison samples (CCQM-P20.e.1 and CCQM-P20.e.2) was determined, a wider range of results were reported for the mass fraction content of digoxin in the CCQM-P20.f comparison.A minority of participants did not appear to use conditions capable of fully resolving and/or quantifying the major related structure impurities present in the comparison sample. Among those that did achieve suitable separations, there was further variation in their reported quantifications of the individual and total related substance content which reflected in part the limited availability of reference standards for these materials and the resulting assumptions that had to be made regarding the structure and response factors relative to digoxin for each individual impurity. This was particularly relevant because of the span of molecular masses of the impurities present in the sample, which ranged from aglycones to glycones with tetrameric carbohydrate chains, relative to that of digoxin.A significant additional factor also contributed to the observed variation of results. Unlike the CCQM-P20.e samples, in which the major impurities were solely related structure organic compounds, the CCQM-P20.f study material contained significant levels of residual organic solvents (ethanol, dichloromethane and to a lesser extent toluene). The majority of participants failed to detect and allow for the presence of this class of impurity, introducing a bias towards overestimation of digoxin content in most of the individual results.However, the uncertainty budgets produced by several participants were sufficiently conservative such that their reported results were nevertheless consistent with the reference value for digoxin content assigned using a consensus mass balance approach. The results of the comparison reinforce the conclusion from previous rounds of the CCQM-P20 study that care in developing and validating the suitability of the chromatographic separation method used to resolve the main component from the related structure impurities present is essential to obtaining reliable, comparable results when using the mass balance approa...
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a laboratory comparison, CCQM-P20.e, was coordinated by the Bureau International de Poids et Mesures (BIPM) in 2006/2007. Nine national measurement institutes, two expert laboratories and the BIPM participated in the comparison. Participants were required to assign the mass fraction of theophylline present as the main component in two separate study samples (CCQM-P20.e.1 and CCQM-P20.e.2).CCQM-P20.e.1 consisted of a high-purity theophylline material obtained from a commercial supplier. CCQM-P20.e.2 consisted of theophylline to which known amounts of the related structure compounds theobromine and caffeine were added in a homogenous, gravimetrically controlled fashion. For the CCQM-P20.e.2 sample it was possible to estimate gravimetric reference values both for the main component and for the two spiked impurities.In addition to assigning the mass fraction content of theophylline for both materials, participants were requested but not obliged to provide mass fraction estimates for the minor components they identified in each sample.The results reported by the study participants for the mass fraction content of theophylline in both materials showed good levels of agreement both with each other and with the gravimetric reference value assigned to the CCQM-P20.e.2 material. There was also satisfactory agreement overall, albeit at higher levels of uncertainty, in the quantification data reported for the minor components present in both samples. In the few cases where a significant deviation was observed from the consensus values reported by the comparison participants or gravimetric reference values where these where available, they appeared to arise from the use of non-optimal chromatographic separation conditions.The results demonstrate the feasibility for laboratories to assign mass fraction content with associated absolute expanded uncertainties in the range 0.05% to 0.5% for solid organic compounds of high purity (mass fraction of main component >995 mg/g) and in the range 0.1% to 1% for compounds of lower purity (mass fraction of main component >980 mg/g).Main text. To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM Working Group on Organic Analysis.
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