3D-LC-MS with 2D Multimethod Option for Fully Automated Assessment of Multiple Attributes of Monoclonal Antibodies Directly from Cell Culture Supernatants

Fully automated analysis of multiple structural attributes of monoclonal antibodies (mAbs) using three-dimensional liquid chromatography-mass spectrometry (3D-LC-MS) is described. The analyzer combines Protein A affinity chromatography in the first dimension (¹D) with a multimethod option in the second dimension (²D) (choice between size exclusion (SEC), cation exchange (CEX), and hydrophobic interaction chromatography (HIC)) and desalting SEC-MS in the third dimension (³D). This innovative 3D-LC-MS setup allows simultaneous and sequential assessment of mAb titer, size/charge/hydrophobic variants, molecular weight (MW), amino acid (AA) sequence, and post-translational modifications (PTMs) directly from cell culture supernatants. The reported methodology that finds multiple uses throughout the biopharmaceutical development trajectory was successfully challenged by the analysis of different trastuzumab and tocilizumab samples originating from biosimilar development programs.

Comprehensive two-dimensional temperature-responsive × reversed phase liquid chromatography for the analysis of wine phenolics

Phenolic compounds are an interesting class of natural products because of their proposed contribution to health benefits of foods and beverages and as a bio-source of organic (aromatic) building blocks. Phenolic extracts from natural products are often highly complex and contain compounds covering a broad range in molecular properties. While many 1D-LC and mass spectrometric approaches have been proposed for the analysis of phenolics, this complexity inevitably leads to challenging identification and purification. New insights into the composition of phenolic extracts can be obtained through online comprehensive two-dimensional liquid chromatography (LC × LC) coupled to photodiode array and mass spectrometric detection. However, several practical hurdles must be overcome to achieve high peak capacities and to obtain robust methods with this technique. In many LC × LC configurations, refocusing of analytes at the head of the ²D column is hindered by the high eluotropic strength of the solvent transferred from the ¹D to the ²D, leading to peak breakthrough or broadening. LC × LC combinations whereby a purely aqueous mobile phase is used in the ¹D and RPLC is used in the ²D are unaffected by these phenomena, leading to more robust methods. In this contribution, the combination of temperature-responsive liquid chromatography (TRLC) with RPLC is used for the first time for the analysis of phenolic extracts of natural origin to illustrate the potential of this alternative combination for natural product analyses. The possibilities of the combination are investigated through analysis of wine extracts by TRLC × RPLC-DAD and TRLC × RPLC-ESI-MS.

Investigation of the potential of mixed solvent mobile phases in temperature-responsive liquid chromatography (TRLC)

Temperature-responsive liquid chromatography (TRLC) allows for extensive retention and selectivity tuning through temperature in HPLC. This is mainly achieved through the use of a stationary phases comprising of a temperature-responsive polymer which undergoes a reversible change from hydrophilic to hydrophobic behaviour upon increasing the temperature. The approach can allow for reversed phase type separations to be achieved with purely aqueous mobile phases, whereby the retention is controlled through temperature instead of mobile phase composition. Despite the promising nature of such form of retention control under isocratic mobile phase conditions, TRLC can suffer from excessive retention of highly apolar solutes even at lower column temperatures whereby the polymer is considered hydrophilic. This is related both to a residual apolarity of the polymer chain and due to the high log P's and low water solubility of higly apolar compounds. While it was known that elution in TRLC doesn't necessarily has to be performed under purely aqueous conditions and that the use of organic co-solvents to the water is possible, the impact thereof on the temperature responsive behaviour itself had not yet been investigated in a systematic way. Therefore in this work the advantages and drawbacks of the use of the organic co-solvents methanol and acetonitrile in TRLC is assessed on two types of temperature reponsive phases: poly-N-N-propylacrylamide (PNNPAAm) and poly-N-isopropylacrylamide (PNIPAAm). The influence of organic co-solvents is investigated with two representative test mixtures (comprising 4 parabens and 5 apolar steroids).

Implementations of temperature gradients in temperature-responsive liquid chromatography

Temperature Responsive Liquid Chromatography (TRLC) offers an alternative and environmentally friendly way to perform reversed-phase like separations. Its use of temperature responsive polymers to control retention based on column temperature, instead of the fraction of organic modifier in the mobile phase mobile, eliminates the need for solvent composition gradients and allows, for example, for purely aqueous separations. In principle this temperature induced retention should allow for gradient elutions to be performed using downward temperature gradients to control retention and refocus the analyte peaks. Yet, the unavailability of dedicated commercial temperature controlling systems allowing suitable temperature control in TRLC limits implementations thereof often to isothermal or step gradient applications. In this work we study the potential of 1) a simple yet programmable water bath and of 2) a modified HPLC system allowing column temperature programming through controlled mixing of a warm and cold mobile phase streams. The performance of both systems was evaluated under both isocratic and gradient applications, resulting in a more thorough understanding of the influence of temperature gradients in TRLC. This knowledge is then applied to a sample of phenolic solutes, illustrating that, although both systems have some flaws, both are able to impose temperature gradients in TRLC resulting in significantly reduced retention and enhanced refocusing of the analyte peak.

Chemical composition of essential oils of eight Tunisian Eucalyptus species and their antibacterial activity against strains responsible for otitis

Background

The chemical composition and biological activity of Eucalyptus essential oils have been studied extensively (EOs). A few of them were tested for antibacterial effectiveness against otitis strains. The chemical composition and antibacterial activity of the EOs of eight Tunisian Eucalyptus species were assessed in the present study.

Methods

Hydrodistillation was used to extract EOs from the dried leaves of eight Eucalyptus species: Eucalyptus accedens, Eucalyptus punctata, Eucalyptus robusta, Eucalyptus bosistoana, Eucalyptus cladocalyx, Eucalyptus lesouefii, Eucalyptus melliodora and Eucalyptus wandoo. They are assessed by GC/MS and GC/FID and evaluated for antibacterial activity using agar diffusion and broth microdilution techniques against three bacterial isolates (Haemophilus influenzae, Haemophilus parainfluenzae, Klebsiella pneumoniae) and three reference bacteria strains (Pseudomonas aeruginosa, ATTC 9027; Staphylococcus aureus, ATCC 6538; and Escherichia coli, ATCC 8739). Furthermore, the selected twenty-one major compounds and all values of the inhibition zone diameters were subjected to further statistical analysis using PCA and HCA.

Results

The EO yields of the studied Eucalyptus species range from 1.4 ± 0.4% to 5.2 ± 0.3%. Among all the species studied, E. lesouefii had the greatest mean percentage of EOs. The identification of 128 components by GC (RI) and GC/MS allowed for 93.6% – 97.7% of the total oil to be identified. 1,8-cineole was the most abundant component found, followed by α-pinene, p-cymene, and globulol. The chemical components of the eight EOs, extracted from the leaves of Eucalyptus species, were clustered into seven groups using PCA and HCA analyses, with each group forming a chemotype. The PCA and HCA analyses of antibacterial activity, on the other hand, identified five groups.

Conclusion

The oils of E. melliodora, E. bosistoana, and E. robusta show promise as antibiotic alternatives in the treatment of otitis media.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03379-y.

Monoclonal antibody charge variant characterization by fully automated four-dimensional liquid chromatography-mass spectrometry

Fully automated characterization of monoclonal antibody (mAb) charge variants using four-dimensional liquid chromatography-mass spectrometry (4D-LC-MS) is reported and illustrated. Charge variants resolved by cation-exchange chromatography (CEX) using a salt- or pH-gradient are collected in loops installed on a multiple heart-cutting valve and consequently subjected to online desalting, denaturation, reduction and trypsin digestion prior to LC-MS based peptide mapping. This innovation which substantially reduces turnaround time, sample manipulation, loss and artefacts and increases information gathering, is described in great technical detail, and applied to characterize the charge heterogeneity associated with three therapeutic mAbs. Sequence coverages > 95% are obtained for major and minor charge variants (> 1.0%). Post-translational modifications (PTMs) and modification sites are readily revealed in a repeatable manner including unstable succinimide intermediates which are not maintained when performing classical in-solution overnight digestion of offline collected CEX peaks.

Middle-up characterization of monoclonal antibodies by online reduction liquid chromatography-mass spectrometry

This study describes the fully automated middle-up characterization of monoclonal antibodies (mAbs) and next-generation variants by online reduction liquid chromatography-mass spectrometry (LC-MS). Proteins were trapped on-column and subjected to online desalting, denaturation and reduction prior to reversed phase elution of the created subunits in the MS. The evaluation of more than 20 different therapeutic proteins including full length mAbs (subclasses IgG1, IgG2 and IgG4), bispecific antibodies, antibody fragments, fusion proteins and antibody-drug conjugates (ADC) revealed that the online reduction method is as powerful as the widely applied offline sample preparation with dithiothreitol (DTT) as reducing agent and guanidine hydrochloride (Gnd.HCl) as denaturant and tackles some major disadvantages associated with the latter method, i.e. corrosion of stainless steel components, adduct formation impacting spectral quality and sample stability. The value of the online reduction LC-MS method is also enforced by its ability to reveal unstable antibody variants such as succinimide intermediates of asparagine deamidation and aspartic acid isomerization which are often lost when using the offline sample preparation method. The performance of the online reduction LC-MS set-up was verified and it was revealed that the method is precise with RSD values below 0.25% and 3.0% for retention time and area, respectively. Carry-over is within acceptable limits (< 0.5%) and the reducing buffer is stable up to 24 hours.

Pharmaceutical impurity analysis by comprehensive two-dimensional temperature responsive × reversed phase liquid chromatography

In this study, the possibilities of temperature responsive × reversed phase liquid chromatography (TRLC × RPLC) are assessed in terms of pharmaceutical impurity analysis. Due to the increased peak capacity per unit time they offer, two-dimensional LC approaches are gaining relevance for the analysis of complex drug formulations. Because the latter depicts a larger predisposition for the occurrence of an increased number of impurities, current 1D-HPLC approaches often prove insufficient. Since many LC × LC methods are limited by modulation, solvent compatibility, orthogonality, and sensitivity issues, the combination of TRLC × RPLC is explored in this work for pharmaceutical impurity analysis. As this combination of a purely aqueous separation with RPLC allows for systematic and optimization-free refocusing in the second dimension, it opens possibilities for generic LC × LC requiring minimal to no method development, in this way overcoming a major perceived contemporary hurdle of LC × LC. The approach is demonstrated with a representative mixture of 17 solutes comprising 11 corticosteroids and 6 progestogens. Orthogonality and peak capacities were assessed on three RP core-shell column selectivities (Poroshell EC-C18, phenyl-hexyl and PFP). Although the TRLC × EC-C18 combination offered somewhat better orthogonality, the combination with the PFP column proved the best for the separation at hand. Depending on the composition of the mixture, the use of full, shifted, or segmented gradients allowed facile optimization of the separation. The developed platform allowed detection of the impurities at the 0.05% level compared to a selected main compound, while also opening up possibilities for analysis of formulations comprising two active ingredients.

Exploration of the Selectivity and Retention Behavior of Alternative Polyacrylamides in Temperature Responsive Liquid Chromatography

Temperature responsive liquid chromatography (TRLC) allows for separation of organic solutes in purely aqueous mobile phases whereby retention is controlled through temperature. The vast majority of the work has thus far been performed on poly[N-isopropylacrylamide] (PNIPAAm)-based columns, while the performance of other temperature responsive polymers has rarely been compared under identical conditions. Therefore, in this work, two novel TRLC phases based on poly[N-n-propylacrylamide] (PNNPAAm) and poly[N,N-diethylacrylamide] (PDEAAm) are reported and compared to the state of the art PNIPAAm based column. Optimal comparison is thereby obtained by the use of controlled radical polymerizations, identical molecular weights, and by maximizing carbon loads on the silica supporting material. Analysis of identical test mixtures of homologue series and pharmaceutical samples revealed that PNNPAAm performs in a similar way as PNIPAAm while offering enhanced retention and a shift of the useable temperature range toward lower temperatures. PDEAAm offers a range of novel possibilities as it depicts a different selectivity, allowing for enhanced resolution in TRLC in, for example, coupled column systems. Reduced plate heights of 3 could be obtained on the homemade columns, offering the promise for reasonable column efficiencies in TRLC despite the use of bulky polymers as stationary phases in HPLC.

Removal of alachlor in water by non-thermal plasma: Reactive species and pathways in batch and continuous process

Pesticides are emerging contaminants frequently detected in the aquatic environment. In this work, a novel approach combining activated carbon adsorption, oxygen plasma treatment and ozonation was studied for the removal of the persistent chlorinated pesticide alachlor. A comparison was made between the removal efficiency and energy consumption for two different reactor operation modes: batch-recirculation and single-pass mode. The kinetics study revealed that the insufficient removal of alachlor by adsorption was significantly improved in terms of degradation efficiency and energy consumption when combined with the plasma treatment. The best efficiency (ca. 80% removal with an energy cost of 19.4 kWh m^-³) was found for the single-pass operational mode of the reactor. In the batch-recirculating process, a complete elimination of alachlor by plasma treatment was observed after 30 min of treatment. Analysis of the reactive species induced by plasma in aqueous solutions showed that the decomposition of alachlor mainly occurred through a radical oxidation mechanism, with a minor contribution of long-living oxidants (O₃, H₂O₂). Investigation of the alachlor oxidation pathways revealed six different oxidation mechanisms, including the loss of aromaticity which was never before reported for plasma-assisted degradation of aromatic pesticides. It was revealed that the removal rate and energy cost could be further improved with more than 50% by additional O₃ gas bubbling in the solution reservoir.

Effects of the water-soluble fraction of a crude oil on freshwater meiofauna and nematode assemblages

Oil water-soluble fractions (WSFs) compounds have low persistence in water; evaporating in a matter of hours to days. Nonetheless, they pose high toxicity to exposed biota. Their effects may be instantaneous or delayed, affecting, respectively, mainly survival vs growth and reproduction. We investigated the effects of crude oil WSFs on freshwater meiobenthos, with a focus on nematode assemblages, in community microcosm experiments lasting 15 weeks. Treatments consisted of the application of different concentrations of oil WSFs, i.e. high (100%) medium (50%) and low (10%), and effects were assessed one, three, nine and 15 weeks after contamination, allowing us to detect both short-term and lasting effects of oil-WSF. Additionally, we compared the effects of a single contamination event with those of a so-called 'constant' oil-WSF contamination where we replenished evaporated water with water containing the medium concentration of oil WSF. Next to nematodes, the most abundant meiofaunal taxa were rotifers, gastrotrichs, oligochaetes and tardigrades. Total abundance, different diversity indices, the composition of feeding-types and the age structure were investigated in the assessment of direct oil effects on the structure of nematode assemblages. Limited immediate effects were observed, except for a significant decrease of the index of taxonomic distinctness, which already appeared in the first week. Significant impacts on total nematode abundance, diversity and species composition only became apparent after 9-15 weeks of incubation, indicating that delayed effects of a single exposure are far more pronounced than instantaneous effects. Moreover, for most response variables, the strongest impacts were not observed in the highest-concentration treatment, but in a medium-concentration treatment with regular replenishment of oil WSF, suggesting that internal exposure may be important in generating effects. Furthermore, the predictability of the sensitivity of individual species was sometimes poor, which may not only result from these species' sensitivities, but also from alterations in interspecific interactions in polluted communities. Further toxicity tests should be carried out in order to unravel the main modes of action of crude oil WSF which lead to the observed long-term sublethal effects on nematode communities.

Effects of the water-soluble fraction of a crude oil on estuarine meiofauna: A microcosm approach

Although soluble hydrocarbons persist for only hours to days in aquatic environments, they potentially pose a high toxicity to aquatic biota. Here we investigate effects of the water-soluble fraction (WSF) of crude oil on estuarine meiofauna, with special focus on nematodes. Copepods and amphipods were the most sensitive taxa, disappearing almost completely within 3 weeks after exposure. In nematodes, we observed mostly sublethal short-term effects of WSF, such as changes in feeding-type composition and age structure. In the longer term (months), total nematode density and species composition were significantly affected, whereas different diversity indices did not exhibit significant responses. Deposit-feeding and predatory nematodes were the most affected feeding types. Nevertheless, sensitivity was species-specific, with sometimes opposing responses between even congeneric species. Our results demonstrate the need to assess WSF effects on communities at the species level and over time periods well exceeding the residence time of the WSF in the environment.

Removal of alachlor, diuron and isoproturon in water in a falling film dielectric barrier discharge (DBD) reactor combined with adsorption on activated carbon textile: Reaction mechanisms and oxidation by-products

A falling film dielectric barrier discharge (DBD) plasma reactor combined with adsorption on activated carbon textile material was optimized to minimize the formation of hazardous oxidation by-products from the treatment of persistent pesticides (alachlor, diuron and isoproturon) in water. The formation of by-products and the reaction mechanism was investigated by HPLC-TOF-MS. The maximum concentration of each by-product was at least two orders of magnitude below the initial pesticide concentration, during the first 10 min of treatment. After 30 min of treatment, the individual by-product concentrations had decreased to values of at least three orders of magnitude below the initial pesticide concentration. The proposed oxidation pathways revealed five main oxidation steps: dechlorination, dealkylation, hydroxylation, addition of a double-bonded oxygen and nitrification. The latter is one of the main oxidation mechanisms of diuron and isoproturon for air plasma treatment. To our knowledge, this is the first time that the formation of nitrificated intermediates is reported for the plasma treatment of non-phenolic compounds.

Enhancing the Possibilities of Comprehensive Two-Dimensional Liquid Chromatography through Hyphenation of Purely Aqueous Temperature-Responsive and Reversed-Phase Liquid Chromatography

Comprehensive two-dimensional liquid chromatography (LC × LC) allows for substantial gains in theoretical peak capacity in the field of liquid chromatography. However, in practice, theoretical performance is rarely achieved due to a combination of undersampling, orthogonality, and refocusing issues prevalent in many LC × LC applications. This is intricately linked to the column dimensions, flow rates, and mobile-phase compositions used, where, in many cases, incompatible or strong solvents are introduced in the second-dimension (²D) column, leading to peak broadening and the need for more complex interfacing approaches. In this contribution, the combination of temperature-responsive (TR) and reversed-phase (RP) LC is demonstrated, which, due to the purely aqueous mobile phase used in TRLC, allows for complete and more generic refocusing of organic solutes prior to the second-dimension RP separation using a conventional 10-port valve interface. Thus far, this was only possible when combining other purely aqueous modes such as ion exchange or gel filtration chromatography with RPLC, techniques which are limited to the analysis of charged or high MW solutes, respectively. This novel TRLC × RPLC combination relaxes undersampling constraints and complete refocusing and therefore offers novel possibilities in the field of LC × LC including temperature modulation. The concept is illustrated through the TRLC × RPLC analysis of mixtures of neutral organic solutes.

Screening therapeutics according to their uptake across the blood-brain barrier: A high throughput method based on immobilized artificial membrane liquid chromatography-diode-array-detection coupled to electrospray-time-of-flight mass spectrometry

The Blood-Brain Barrier (BBB) plays an essential role in protecting the brain tissues against possible injurious substances. In the present work, 79 neutral, basic, acidic and amphoteric structurally unrelated analytes were considered and their chromatographic retention coefficients on immobilized artificial membrane (IAM) stationary phase were determined employing a mass spectrometry (MS)-compatible buffer based on ammonium acetate. Their BBB passage predictive strength was evaluated and the statistical models based on IAM indexes and in silico physico-chemical descriptors showed solid statistics (r² (n - 1) = 0.78). The predictive strength of the indexes achieved by the MS-compatible method was comparable to that achieved by employing the more "biomimetic" Dulbecco's phosphate buffered saline, even if some differences in the elution order were observed. The method was transferred to the MS, employing a diode-array-detection coupled to an electrospray ionization source and a time-of-flight analyzer. This setup allowed the simultaneous analysis of up to eight analytes, yielding a remarkable acceleration of the analysis time.

Numerical study and theoretical performance limit of interconnected multi-capillary gas chromatography columns with perfectly ordered pillar patterns

We present the results of a theoretical and numerical study of the chromatographic performance of a novel type of microfabricated GC column. The column consists of an array of rectangular flow diverters (pillars), creating a network of perfectly ordered, interconnected and tortuous flow-through paths. Using van Deemter and kinetic plots of simulated band broadening data, we could demonstrate that the proposed column structure performs as a bundle of parallel open-tubular capillaries with rectangular cross-section, connected by a regular pattern of channel-intermixing points that allow compensating for inevitable channel-to-channel differences in migration velocity without adding any significant dispersion themselves. The established kinetic plots also allowed to propose design rules for the optimal distance between the pillars as a function of the desired separation efficiency and the available column pressure. The simulations also allowed establishing an expression for the plate height as a function of the velocity of the carrier gas. Results are also compared to the results of a recent experimental study.

Chiral stationary phase optimized selectivity liquid chromatography: A strategy for the separation of chiral isomers

Chiral Stationary-Phase Optimized Selectivity Liquid Chromatography (SOSLC) is proposed as a tool to optimally separate mixtures of enantiomers on a set of commercially available coupled chiral columns. This approach allows for the prediction of the separation profiles on any possible combination of the chiral stationary phases based on a limited number of preliminary analyses, followed by automated selection of the optimal column combination. Both the isocratic and gradient SOSLC approach were implemented for prediction of the retention times for a mixture of 4 chiral pairs on all possible combinations of the 5 commercial chiral columns. Predictions in isocratic and gradient mode were performed with a commercially available and with an in-house developed Microsoft visual basic algorithm, respectively. Optimal predictions in the isocratic mode required the coupling of 4 columns whereby relative deviations between the predicted and experimental retention times ranged between 2 and 7%. Gradient predictions led to the coupling of 3 chiral columns allowing baseline separation of all solutes, whereby differences between predictions and experiments ranged between 0 and 12%. The methodology is a novel tool allowing optimizing the separation of mixtures of optical isomers.

Removal of several pesticides in a falling water film DBD reactor with activated carbon textile: Energy efficiency

Bio-recalcitrant micropollutants are often insufficiently removed by modern wastewater treatment plants to meet the future demands worldwide. Therefore, several advanced oxidation techniques, including cold plasma technology, are being investigated as effective complementary water treatment methods. In order to permit industrial implementation, energy demand of these techniques needs to be minimized. To this end, we have developed an electrical discharge reactor where water treatment by dielectric barrier discharge (DBD) is combined with adsorption on activated carbon textile and additional ozonation. The reactor consists of a DBD plasma chamber, including the adsorptive textile, and an ozonation chamber, where the DBD generated plasma gas is bubbled. In the present paper, this reactor is further characterized and optimized in terms of its energy efficiency for removal of the five pesticides α-HCH, pentachlorobenzene, alachlor, diuron and isoproturon, with initial concentrations ranging between 22 and 430 μg/L. Energy efficiency of the reactor is found to increase significantly when initial micropollutant concentration is decreased, when duty cycle is decreased and when oxygen is used as feed gas as compared to air and argon. Overall reactor performance is improved as well by making it work in single-pass operation, where water is flowing through the system only once. The results are explained with insights found in literature and practical implications are discussed. For the used operational conditions and settings, α-HCH is the most persistent pesticide in the reactor, with a minimal achieved electrical energy per order of 8 kWh/m³, while a most efficient removal of 3 kWh/m³ or lower was reached for the four other pesticides.

Quantitative Metabolite Profiling of an Amino Group Containing Pharmaceutical in Human Plasma via Precolumn Derivatization and High-Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry

Quantitative determination of the candidate drug molecule and its metabolites in biofluids and tissues is an inevitable step in the development of new pharmaceuticals. Because of the time-consuming and expensive nature of the current standard technique for quantitative metabolite profiling, i.e., radiolabeling followed by high-performance liquid chromatography (HPLC) with radiodetection, the development of alternative methodologies is of great interest. In this work, a simple, fast, sensitive, and accurate method for the quantitative metabolite profiling of an amino group containing drug (levothyroxine) and its metabolites in human plasma, based on precolumn derivatization followed by HPLC-inductively coupled plasma mass spectrometry (ICPMS), was developed and validated. To introduce a suitable "heteroelement" (defined here as an element that is detectable with ICPMS), an inexpensive and commercially available reagent, tetrabromophthalic anhydride (TBPA) was used for the derivatization of free NH₂-groups. The presence of a known number of I atoms in both the drug molecule and its metabolites enabled a cross-validation of the newly developed derivatization procedure and quantification based on monitoring of the introduced Br. The formation of the derivatives was quantitative, providing a 4:1 stoichiometric Br/NH₂ ratio. The derivatives were separated via reversed-phase HPLC with gradient elution. Bromine was determined via ICPMS at a mass-to-charge ratio of 79 using H₂ as a reaction gas to ensure interference-free detection, and iodine was determined at a mass-to-charge ratio of 127 for cross-validation purposes. The method developed shows a fit-for-purpose accuracy (recovery between 85% and 115%) and precision (repeatability <15% RSD). The limit of quantification (LoQ) for Br was approximately 100 μg/L.

Near-infrared luminescence and RNA cleavage ability of lanthanide Schiff base complexes derived from N,N'-bis(3-methoxysalicylidene)ethylene-1,2-diamine ligands

A complete series of lanthanide Schiff base salen-type complexes were prepared with trivalent lanthanide ions (Ln³⁺) and the N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine ligand (Ln³⁺=La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺). Three unique crystal structures of La³⁺ and Pr³⁺N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine complexes, with the La³⁺ complex prepared in two different synthetic approaches, are reported, namely a dimeric [La(H₂L)(NO₃)₃]₂ (H₂L=N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine) complex, an asymmetric two-centered [La₂(H₂L)₂(NO₃)₆] complex and a discrete mononuclear [Pr(H₂L)(NO₃)₂(H₂O)₂] complex. For Nd³⁺ and Sm³⁺, an isotypic mononuclear [Nd(H₂L)(NO₃)₃] and 1D polymeric [Sm(H₂L)(NO₃)₃(MeOH)]_n structure was obtained, respectively. The whole series of complexes was tested for their ability to cleave the 20-mer RNA oligonucleotide 5'-AGC-GAU-AAG-AUU-CAU-AUA-UC-3'. Additionally three complexes (Ln³⁺=Nd³⁺, Sm³⁺, Ho³⁺) were tested for the cleavage of the 12-mer RNA oligonucleotide 5'-GCA-CCC-UGU-CAG-3'. A detailed luminescence study was additionally carried out and revealed that the Eu³⁺ complex emitted bright red light upon excitation at both 285.8nm and 394.4nm. The Nd³⁺, Er³⁺, and Yb³⁺ complexes showed strong emission in the near-infrared region after excitation at 380nm.

Chemical profiling of the major components in natural waxes to elucidate their role in liquid oil structuring

Elucidating the composition of waxes is of utmost importance to explain their behavior in liquid oil structuring. The chemical components (hydrocarbons - HCs, free fatty acids - FFAs, free fatty alcohols - FALs and wax esters - WEs) of natural waxes were analyzed using HPLC-ELSD and GC-MS followed by evaluation of their oil structuring properties. The gel strength, including the average storage modulus and oscillation yield stress, displayed a negative correlation with FALs and a positive correlation with HCs, FFAs and WEs. The components dictating the gel strength are HCs, FFAs and WEs in a descending order of importance. The consistency of the oleogels increased with the increasing amount of FFAs and HCs and the decreasing amount of WEs and FALs. The presence of more WEs results in a strong but brittle gel with a high initial flow yield stress. We believe these results might be useful in selecting the right waxes to combine in certain fat-based food products.

Offline comprehensive liquid chromatography in combination with a Deoxyribonuclease I immobilized enzymatic reactor for selective screening of oligonucleotide mixtures

The development of a comprehensive ion-pair chromatography-immobilized enzyme reactor×ion-pair chromatography (IPC-IMER×IPC) methodology for the advanced characterization of DNA/RNA oligonucleotides (ONs) mixtures has been carried out. More in detail, a DNase I IMER has been coupled to IPC in the post column configuration, followed by the collection of the eluting fractions and reanalysis by IPC. The effect of the mobile phase over the IMER activity was qualitatively evaluated. The methodology proved to generate relevant ON degradation profiles that might be correlated with the ON stability towards nucleases. Moreover, this platform shows potential for its further implementation in selective analysis of ON mixtures and in mapping studies.

Removal of atrazine in water by combination of activated carbon and dielectric barrier discharge

Efficiency of modern wastewater treatment plants to remove or decompose persistent contaminants in low concentration is often insufficient to meet the demands imposed by governmental laws. Novel, efficient and cheap methods are required to address this global issue. We developed a new type of plasma reactor, in which atrazine decomposition by atmospheric dielectric barrier discharge (DBD) in dry air is combined with micropollutant adsorption on activated carbon textile and with extra bubbling of generated ozone. Investigation of reaction kinetics and by-product analysis shows that increasing input power with a factor 3.5 leads to deeper atrazine oxidation without significantly changing energy yield of atrazine removal. By-products of first and later generations are detected with HPLC-MS analysis in water and adsorbed on the activated carbon textile. Our reactor is compared in energy efficiency with reactors described in literature, showing that combination of plasma discharge with pollutant adsorption and ozone recycling is attractive for future applications of water treatment.

Hyphenation of a Deoxyribonuclease I immobilized enzyme reactor with liquid chromatography for the online stability evaluation of oligonucleotides

The stability of antisense oligonucleotides (ONs) toward nucleases is a key aspect for their possible implementation as therapeutic agents. Typically, ON stability studies are performed off-line, where the ONs are incubated with nucleases in solution, followed by their analysis. The problematics of off-line processing render the detailed comparison of relative ON stability quite challenging. Therefore, the development of an online platform based on an immobilized enzyme reactor (IMER) coupled to liquid chromatography (LC) was developed as an alternative for improved ON stability testing. More in detail, Deoxyribonuclease I (DNase I) was immobilized on epoxy-silica particles of different pore sizes and packed into a column for the construction of an IMER. Subsequently, the hyphenation of the IMER with ion-pair chromatography (IPC) and ion-exchange chromatography (IEC) was evaluated, leading to the successful development of two online methodologies: IMER-IPC and IMER-IEC. More specifically, natural and modified DNA and RNA oligonucleotides were used for testing the performance of the methodologies. Both methodologies proved to be simple, automatable, fast and highly reproducible for the quantitative and qualitative evaluation of ON degradation. In addition, the extended IMER life time in combination with a more straightforward control of the reaction kinetics substantiate the applicability of the IMER-LC platform for ON stability tests and its implementation in routine and research laboratories.

Model-based determination of the influence of textile fabric on bioassay analysis and the effectiveness of a textile slow-release system of DEET in mosquito control

BACKGROUND

Determining the effectiveness of a product in repelling mosquitoes or other flying insects is a difficult task. One approach is to use a bioassay with textile fabric. We investigated the role of the textile substrate in a bioassay with a numerical model, and compared the outcome with known results for DEET. The model was then used to determine the effectiveness of textile slow-release formulations based on coatings, and results were compared with those of a field study in the Cameroon. Slow-release formulations are difficult to evaluate with standard tests, as the compound needs a build-up time not present in these tests.

RESULTS

We found excellent correspondence between the model and the known DEET results without matching parameters. Slow-release approaches are deemed possible but have several drawbacks. Modelling can help in identifying optimal use conditions. The field test with a slow-release system performed better than anticipated by the model, with initially more than 90% repellency. DEET-coated textile was considered not to be marketable, however.

CONCLUSION

We advise that bioassays characterise in more detail the type of textile fabric used so as to allow conclusions to be drawn by textile modelling. As regards coated-textile slow-release systems, more research is needed. We nevertheless advise usage mainly at entry points, e.g. as scrims.

Decomposition of atrazine traces in water by combination of non-thermal electrical discharge and adsorption on nanofiber membrane

In recent decades, several types of persistent substances are detected in the aquatic environment at very low concentrations. Unfortunately, conventional water treatment processes are not able to remove these micropollutants. As such, advanced treatment methods are required to meet both current and anticipated maximally allowed concentrations. Plasma discharge in contact with water is a promising new technology, since it produces a wide spectrum of oxidizing species. In this study, a new type of reactor is tested, in which decomposition by atmospheric pulsed direct barrier discharge (pDBD) plasma is combined with micropollutant adsorption on a nanofiber polyamide membrane. Atrazine is chosen as model micropollutant with an initial concentration of 30 μg/L. While the H2O2 and O3 production in the reactor is not influenced by the presence of the membrane, there is a significant increase in atrazine decomposition when the membrane is added. With membrane, 85% atrazine removal can be obtained in comparison to only 61% removal without membrane, at the same experimental parameters. The by-products of atrazine decomposition identified by HPLC-MS are deethylatrazine and ammelide. Formation of these by-products is more pronounced when the membrane is added. These results indicate the synergetic effect of plasma discharge and pollutant adsorption, which is attractive for future applications of water treatment.

Quantification aspects of constant pressure (ultra) high pressure liquid chromatography using mass-sensitive detectors with a nebulizing interface

The present contribution investigates the quantitation aspects of mass-sensitive detectors with nebulizing interface (ESI-MSD, ELSD, CAD) in the constant pressure gradient elution mode. In this operation mode, the pressure is controlled and maintained at a set value and the liquid flow rate will vary according to the inverse mobile phase viscosity. As the pressure is continuously kept at the allowable maximum during the entire gradient run, the average liquid flow rate is higher compared to that in the conventional constant flow rate operation mode, thus shortening the analysis time. The following three mass-sensitive detectors were investigated: mass spectrometry detector (MS), evaporative light scattering detector (ELSD) and charged aerosol detector (CAD) and a wide variety of samples (phenones, polyaromatic hydrocarbons, wine, cocoa butter) has been considered. It was found that the nebulizing efficiency of the LC-interfaces of the three detectors under consideration changes with the increasing liquid flow rate. For the MS, the increasing flow rate leads to a lower peak area whereas for the ELSD the peak area increases compared to the constant flow rate mode. The peak area obtained with a CAD is rather insensitive to the liquid flow rate. The reproducibility of the peak area remains similar in both modes, although variation in system permeability compromises the 'long-term' reproducibility. This problem can however be overcome by running a flow rate program with an optimized flow rate and composition profile obtained from the constant pressure mode. In this case, the quantification remains reproducibile, despite any occuring variations of the system permeability. Furthermore, the same fragmentation pattern (MS) has been found in the constant pressure mode compared to the customary constant flow rate mode.

Performance evaluation of long monolithic silica capillary columns in gradient liquid chromatography using peptide mixtures

A systematic study is reported on the performance of long monolithic capillary columns in gradient mode. Using a commercial nano-LC system, reversed-phase peptide separations obtained through UV-detection were conducted. The chromatographic performance, in terms of conditional peak capacity and peak productivity, was investigated for different gradient times (varying between 90 and 1320min) and different column lengths (0.25, 1, 2 and 4m) all originating from a single 4m long column. Peak capacities reaching values up to n=10(3) were measured in case of the 4m long column demonstrating the high potential of these long monoliths for the analysis of complex biological mixtures, amongst others. In addition, it was found that the different column fragments displayed similar flow resistance as well as consistent chromatographic performance in accordance with chromatographic theory indicating that the chromatographic bed of the original 4m long column possessed a structural homogeneity over its entire length.