PubMed · 478678
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W M Zapol. 1979. What future for ECMO?. https://pubmed.ncbi.nlm.nih.gov/478678/
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Supercritical and liquid mixtures of ethanol/H2O/CO2 are increasingly used to extract solutes from solid or semi-solid matrixes when nontoxic solvents and fast extraction kinetics are desired. Accordingly, to better understand the mass transport capabilities of these mixtures, the diffusion coefficients of benzene, anthracene, m-cresol, and p-nitrophenol in enhanced-fluidity liquid mixtures of ethanol/H2O/CO2 were studied. The effect of mixture composition and temperature variation on the measured diffusion coefficients was studied. In a mixture containing 0.61/0.39 mole ratio ethanol/H2O, the diffusion coefficients of the four solutes increased comparably either by adding 30 mol % CO2 or by changing the temperature of the mixture from 25 to 60 degrees C. The experimental data were compared to that predicted by the Stokes-Einstein and the Wilke-Chang relations. Often, the experimental diffusion coefficients were greater than those predicted by these mass transport relations. However, the Eyring relationship was useful in describing the variation of diffusion coefficients as a function of temperature change for all of the ethanol/H2O/CO2 mixtures tested.
Formation of HCO2+ from CO2 and background H2O in isotope ratio mass spectrometers has been examined in detail. The process is troublesome because its product is not resolved from 13C16O2+. The resulting, artifactual enhancement of the mass 45 ion current (and analogous enhancement of the mass 46 ion current by transfer of hydrogen to mass 45 species) can cause systematic errors in analyses of 13C based on measurement of ion current ratios in the mass spectrum of CO2. Such errors are neutralized when isotopic analyses are based on differential comparisons in which ion currents and background water levels are precisely equal during admission and ionization of both sample and standard gases. In continuous-flow systems, however, that requirement is generally not met. The resulting systematic error is proportional to the 18/44 ion current ratio. When the widely used MAT252 mass spectrometer is tuned to yield maximum sensitivity, the constant of proportionality is 26 +/- 2/1000 (i.e., the error will be 0.26/1000 if the mass 18 ion current is 100 times smaller than that at mass 44). Errors can be reduced 5-fold when the ion-source residence time of CO2+ is decreased by use of stronger ion-extraction potential gradients. Under those same conditions, sensitivity is decreased by 60%. For operation at highest sensitivity, carrier gas dew points on the order of -70 degrees C are required to obtain errors < or = 0.1/1000 for samples yielding mass 44 ion currents of 10 nA. Carrier gas dew points < or = -80 degrees C are conveniently reached by use of a Nafion dryer operated at approximately 0 degree C.
Carbon dioxide is known to be the active gas in modified atmosphere packaging. However, only the dissolved part of the CO2 will be active in the inhibition of microorganisms. When the effect of a modified atmosphere on the growth of microorganisms is modeled, the amount of dissolved CO2 should be the parameter to evaluate the effect of CO2 in modified atmospheres. Lactobacillus sake was isolated from cooked ham, identified and was chosen as a representative organism for the spoilage of modified atmosphere packed cooked meat products. In a first step a suitable liquid simulation medium for cooked meat products was selected. The growth rate of L. sake was significantly higher in modified MRS than in cooked ham, while no significant difference was observed between the growth parameters of L. sake in modified BHI and in cooked ham. Careful evaluation of the applied simulation medium was shown to be essential before application to the development of predictive models for nutrient demanding microorganisms such as lactic acid bacteria. In a second step, the influence of dissolved CO2 and the storage temperature on the growth parameters of L. sake was modeled. Temperature was shown to have a major effect on the growth rate and lag phase of L. sake. Carbon dioxide negatively influenced the growth rate of L. sake. A negative, linear relationship was observed between the growth rate and the amount of dissolved carbon dioxide. Carbon dioxide was shown, however, to have no significant effect on the lag phase of L. sake. A significant interaction term between temperature and dissolved CO2 on the growth rate of L. sake was established.