Simple correction improving long-term reproducibility of HPLC-MS

Summary Signal intensities in long series of HPLC-MS experiments often vary, which decrease reproducibility and may cause bias in the results. It was found that the sensitivity of various components change differently; in our case variability is in the order of 20-40%; and it is most likely due to changing conditions in ESI ionization. The most often used intensity correction methods do not take this effect into account. The change in signal intensities (peak areas) can be well described by a polynomial function; we found that a 4th order polynomial is most often suitable. We suggest a simple correction algorithm based on polynomial fitting. When the experiments were inherently well reproducible, this correction improved reproducibility from 12% to 3% (on average for various components). When random errors were larger, this improvement was less significant (15% to 12% in nano-ESI), but nevertheless essential in order to avoid possible bias in the results

Simple correction improving long-term reproducibility of HPLC-MS

Chromatographic peak areas in long series of high-performance liquid chromatography-MS experiments often vary, which decrease reproducibility and may cause bias in the results. It was found that the sensitivity of various components change differently; in our case, variability is in the order of 20-40%, and it is most likely due to changing conditions in electrospray ionization (ESI). The most often used peak area correction methods do not take this effect into account. The change in peak areas can be well described by a polynomial function; we found that a fourth-order polynomial is most often suitable. We suggest a simple correction algorithm based on polynomial fitting. When the experiments were inherently well reproducible, this correction improved reproducibility from 12% to 3% (on average for various components). When random errors were larger, this improvement was less significant (15% to 12% in nano-ESI) but nevertheless essential in order to avoid possible bias in the results. Copyright © 2015 John Wiley & Sons, Ltd

Fragmentation, structure, and energetics of small sodium formate clusters : evidence for strong influence of entropic effects

The behavior of small cationic sodium formate clusters [NaOOCH]nNa+ was studied using a combination of experimental and theoretical approaches. Energy-dependent tandem mass spectra were measured using a triple quadrupole and an ion trap type instrument, while structure and energetics were obtained from density functional theory calculations. Analysis of the relative abundances and fragmentation patterns indicate the existence of certain unstable cluster sizes, like the tetramer [NaOOCH]4Na+. This observation is in contrast to alkali halides, where this species has enhanced stability. Surprisingly, this ‘anti-magic’ sodium formate cluster is shown to be compact, energetically low-lying by quantum chemical calculations. The apparent contradiction can be explained by taking into account entropy effects as calculated dissociation Gibbs free energy values show remarkably improved agreement with experimental trends. Fragmentation of these clusters is a good example of reactions that are predominantly directed by entropy and not by energy constraints

A control strategy to investigate the relationship between specific productivity and high-mannose glycoforms in CHO cells

The final publication is available at Springer via https://doi.org/10.1007/s00253-016-7380-4.The integration of physiological knowledge into process control strategies is a cornerstone for the improvement of biopharmaceutical cell culture technologies. The present contribution investigates the applicability of specific productivity as a physiological control parameter in a cell culture process producing a monoclonal antibody (mAb) in CHO cells. In order to characterize cell physiology, the on-line oxygen uptake rate (OUR) was monitored and the time-resolved specific productivity was calculated as physiological parameters. This characterization enabled to identify the tight link between the deprivation of tyrosine and the decrease in cell respiration and in specific productivity. Subsequently, this link was used to control specific productivity by applying different feeding profiles. The maintenance of specific productivity at various levels enabled to identify a correlation between the rate of product formation and the relative abundance of high-mannose glycoforms. An increase in high mannose content was assumed to be the result of high specific productivity. Furthermore, the high mannose content as a function of cultivation pH and specific productivity was investigated in a design of experiment approach. This study demonstrated how physiological parameters could be used to understand interactions between process parameters, physiological parameters, and product quality attributes