Role of membrane structure on the filtrate flux during monoclonal antibody filtration through virus retentive membranes

Virus removal filtration is a critical step in the manufacture of monoclonal antibody products, providing a robust size-based removal of both enveloped and non-enveloped viruses. Many monoclonal antibodies show very large reductions in filtrate flux during virus filtration, with the mechanisms governing this behavior and its dependence on the properties of the virus filter and antibody remaining largely unknown. Experiments were performed using the highly asymmetric Viresolve® Pro and the relatively homogeneous Pegasus™ SV4 virus filters using a highly purified monoclonal antibody. The filtrate flux for a 4 g/L antibody solution through the Viresolve® Pro decreased by about 10-fold when the filter was oriented with the skin side down but by more than 1000-fold when the asymmetric filter orientation was reversed and used with the skin side up. The very large flux decline observed with the skin side up could be eliminated by placing a large pore size prefilter directly on top of the virus filter; this improvement in filtrate flux was not seen when the prefilter was used inline or as a batch prefiltration step. The increase in flux due to the prefilter was not related to the removal of large protein aggregates or to an alteration in the extent of concentration polarization. Instead, the prefilter appears to transiently disrupt reversible associations of the antibodies caused by strong intermolecular attractions. These results provide important insights into the role of membrane morphology and antibody properties on the filtrate flux during virus filtration.     

Automatic mechanical alveolar gas sampler for multiple-sample collection in field

A mechanical alveolar gas sampler using the revolver principle capable of collecting six individual expired gas samples is described. The 0.91-kg sampler collects 19-ml samples in pre-evacuated aluminum ampoules equipped with spring-loaded valves from a sampling chamber equipped with two removable one-way valves. On depression of external handles, one of six ampoules located in a removable cartridge is aligned and advanced into the sampling chamber where its valve is opened and then closed. Releasing the handles removes the ampoule from the sampling chamber and automatically rotates the cartridge through 60 degrees to position a new ampoule in preparation for the next sampling sequence. A lock-out mechanism prevents reexposure of any of the ampoules after six samples have been taken. The performance of the sampler is described including its successful use in the field to collect alveolar gas samples on the summit of Mount Everest.     

Oscillator strengths of the 1La and 1Lb absorption bands of tryptophan and several other indoles

The intensities of the indolyl ¹L_a and ¹L_b absorption bands were investigated by using 5-methoxyindole as a model compound. With 5-methoxyindole dissolved in weakly interacting solvents, almost the entire ¹L_b electronic transition occurs at longer wavelengths than the ¹L_a transition. The resolved spectrum of 5-methoxyindole permitted estimation of its oscillator strengths and also those of other indoles dissolved in cyclohexane: indole, 0.129 (¹L_a), 0.019 (¹L_b); 5-methylindole, 0.129 (¹L_a), 0.027 (¹L_b); 5-methoxyindole, 0.138 (¹L_a), 0.045 (¹L_b); 3-methylindole and N-stearyl-L -tryptophan n-hexyl ester, 0.127 (¹L_a), 0.027 (¹L_b). Hydrogen bonding to 1-methyl-2-pyrrolidinone does not measurably affect the total near-ultraviolet oscillator strength of indoles (less than 5% change). In water and ethanol, the oscillator strength of 3-methylindole and tryptophan is 15–20% less than that of 3-methylindole dissolved in cyclohexane. The spectra of the N-stearyl n-hexyl esters of tryptophan and 1-methyltryptophan dissolved in methylcyclohexane can be generated by using ¹L_a and ¹L_b bands having shapes similar to those observed for 5-methoxyindole, if the ¹L_a and ¹L_b bands are shifted so that their O-O bands overlap (289.5 nm for tryptophan and 299.5 nm for 1-methyltryptophan).