A global approach of ultrafiltration of complex biological solutions

Mitigation of Membrane Fouling Using an Electroactive Polyether Sulfone Membrane

Membrane fouling is the bottleneck limiting the wide application of membrane processes. Herein, we adopted an electroactive polyether sulfone (PES) membrane capable of mitigating fouling by various negatively charged foulants. To evaluate anti-fouling performance and the underlying mechanism of this electroactive PES membrane, three types of model foulants were selected rationally (e.g., bovine serum albumin (BSA) and sodium alginate (SA) as non-migratory foulants, yeast as a proliferative foulant and emulsified oil as a spreadable foulant). Water flux and total organic carbon (TOC) removal efficiency in the filtering process of various foulants were tested under an electric field. Results suggest that under electrochemical assistance, the electroactive PES membrane has an enhanced anti-fouling efficacy. Furthermore, a low electrical field was also effective in mitigating the membrane fouling caused by a mixture of various foulants (containing BSA, SA, yeast and emulsified oil). This result can be attributed to the presence of electrostatic repulsion, which keeps foulants away from the membrane surface. Thereby it hinders the formation of a cake layer and mitigates membrane pore blocking. This work implies that an electrochemical control might provide a promising way to mitigate membrane fouling.

Sample preparation in separation of the extracellular chitinolytic enzymes of the human intestinal bacterium Clostridium paraputrificum J4 from the culture fluids

Membrane ultrafiltration (UF) was used in sample preparation of the culture fluids of the human intestinal bacterium Clostridium paraputrificum strain J4 containing seven extracellular chitinolytic isoenzymes (38-90 kDa). The subsequent filtration of the bacteria-free supernatants was carried out through Millipore membranes with cut-off 100 and 30 kDa for separation of undigested components of the culture medium and bacterial metabolites with molecular weight higher and lower than that of the target enzymes. The chitinolytic enzymes, which were the minor components in the culture fluids, were concentrated at UF as well. The aim of the research consisted in evaluation of the effect of component composition of bacteria-free supernatants and the chemical nature of membrane active layer on partial fractionation of the chitinolytic enzymes, their recovery in retentates and purification degree. On the basis of the obtained experimental results, the sample preparation procedure of the culture fluids of C. paraputrificum J4 was established to be used further in chromatographic separations of the chitinolytic enzymes.

Investigation of commercial sorbents for the analysis of opioid peptides in human plasma by on-line SPE-CE

In this study, we investigated the performance of several commercial sorbents (Sep-pack) C18, (t)C18, C8 and (t)C2, Oasis HLB, Isolute ENV+, Strata-X and Oasis MCX) for the determination of opioid peptides by solid-phase extraction coupled on-line to capillary electrophoresis (SPE-CE). First, standard solutions were analyzed in order to achieve the lowest LOD and the best electrophoretic separations using UV detection. The best results were obtained using C18, C8 and (t)C2 sorbents, which were examined for the analysis of spiked human plasma samples. A double-step sample clean-up pretreatment, which consisted of precipitation with acetonitrile and filtration, was needed to prevent saturation of the on-line SPE microcartridge. The filtration step was critical to obtain optimum analyte recovery and to clean up the sample matrix. A range of centrifugal filters and filtration conditions were tested and the recoveries of the sample pretreatment were evaluated by CE-ESI-MS. The LODs attained through SPE-CE-UV were approximately ten-fold better with C18 than with C8 and (t)C2. The 0.1 microg/mL LODs achieved by C18-SPE-CE-UV were further improved until we could detect 1 ng/mL concentrations of opioid peptides in plasma samples by C18-SPE-CE-ESI-MS, due to the outstanding selectivity of the MS detection.

Changes in mixed liquor and organic foulant properties affect membrane fouling for non-nitrifying and nitrifying biological conditions

A submerged membrane bioreactor treated settled municipal wastewater at a non-nitrifying solids retention time (SRT) condition (2 days) and a nitrifying SRT condition (10 days), to determine the effect of nitrification on mixed liquor properties and membrane fouling. Membrane fouling rates were almost 10 times greater at the 2-day SRT compared with the 10-day SRT, and results showed increased concentrations of high-molecular-weight organic molecules at the 2-day SRT. The Fourier transform infrared spectroscopy (FTIR) results of the fouled membrane from the 2-day SRT exhibited strong peaks for carbohydrates, while the fouled membrane from the 10-day SRT did not. This is consistent with the fact that, although the total carbohydrate soluble microbial product concentration was highest at the 10-day SRT, the carbohydrate consisted of mostly low-molecular-weight (< 1 kDa) molecules, and 97% of this carbohydrate passed through the membrane at the 10-day SRT.

Sample preparation for peptides and proteins in biological matrices prior to liquid chromatography and capillary zone electrophoresis

The determination of peptides and proteins in a biological matrix normally includes a sample-preparation step to obtain a sample that can be injected into a separation system in such a way that peptides and proteins of interest can be determined qualitatively and/or quantitatively. This can be a rather challenging, labourious and/or time-consuming process. The extract obtained after sample preparation is further separated using a compatible separation system. Liquid chromatography (LC) is the generally applied technique for this purpose, but capillary zone electrophoresis (CZE) is an alternative, providing fast, versatile and efficient separations. In this review, the recent developments in the combination of sample-preparation procedures with LC and CZE, for the determination of peptides and proteins, will be discussed. Emphasis will be on purification from and determination in complex biological matrices (plasma, cell lysates, etc.) of these compounds and little attention will be paid to the proteomics area. Additional focus will be put on sample-preparation conditions, which can be 'hard' or 'soft', and on selectivity issues. Selectivity issues will be addressed in combination with the used separation technique and a comparison between LC and CZE will be made.