Varying pH Values Research Articles

Biodegradation Behavior Control for Shape Memory Polyester Poly(Glycerol-Dodecanoate): An In Vivo and In Vitro Study.

Poly(glycerol-dodecanoate) (PGD) has garnered increasing attention in biomedical engineering for its degradability, shape memory, and rubber-like mechanical properties. Adjustable degradation is important for biodegradable implants and is affected by various aspects, including material properties, mechanical environments, temperature, pH, and enzyme catalysis. The crosslinking and chain length characteristics of poly(lactic acid) and poly(caprolactone) have been widely used to adjust the in vivo degradation rate. The PGD degradation rate is affected by its crosslink density in in vitro hydrolysis; however, there is no difference in vivo. We believe that this phenomenon is caused by the differences in enzymatic conditions in vitro and in vivo. In this study, it is found that the degradation products of PGD with different molar ratios of hydroxyl and carboxyl (MRH/C) exhibit varied pH values, affecting the enzyme activity and thus achieving different degradation rates. The in vivo degradation of PGD is characterized by surface erosion, and its mass decreases linearly with degradation duration. The degradation duration of PGD is linearly extrapolated from 9-18 weeks when MRH/C is in the range of 2.00-0.75, providing a protocol for adjusting the degradation durations of subsequent implants made by PGD.

Actualistic Testing of the Influence of Groundwater Chemistry on Degradation of Collagen I in Bone

Recent experiments have heightened our understanding of reactions which can stabilize biomolecules during early diagenesis, yet little remains known about how groundwater chemistry can aid or hinder molecular preservation within a bone through geologic time. To elucidate this issue, we conducted actualistic experiments of bone decay employing varied fluid compositions to simulate a suite of groundwaters. Modern domestic chicken (Gallus gallus) femora were placed in a matrix of compositionally- and texturally-mature, fluvially-deposited sand. To simulate groundwater flow, deionized water or solutions enriched in calcium carbonate, phosphate, or iron were percolated through separate trials for a period of 90 days. After completion of the experiment, degradation of the bones was examined via histologic thin sectioning and two immunoassays against collagen I, the primary bone structural protein: immunofluorescence and enzyme-linked immunosorbent assay. Collagen loss was found to be greatest in the iron trial and least in the calcium carbonate trial, the latter of which experienced partial permineralization with calcite over the course of the experiment. Specifically, the iron trial was found to retain only ~35 ng of collagen I per 100 ng of protein extract, whereas the calcium carbonate trial retained ~90 ng of collagen I. Further, in the iron and calcium carbonate trials, cementation of sediment onto bone surfaces preferentially occurred over more porous regions of the epiphyses, perhaps stimulated by greater release of decay compounds from these regions of the bones. Of the two trials exhibiting intermediate results, the phosphate trial induced slightly greater decay of collagen than the deionized water control, which retained ~60 ng and ~80 ng of collagen I per 100 ng of protein extract, respectively. These results demonstrate that highly acidic conditions during early diagenesis can overwhelm any preservative effects of free radical-mediated stabilization reactions, whereas early-diagenetic permineralization can drastically slow biomolecular decay (ostensibly by hampering microbial access to the interior of a bone), thereby increasing the likelihood of a bone to retain biomolecules and/or their decay products through protracted diagenesis. Future variations of this actualistic experiment employing varied durations, solute concentrations, bacterial communities, pH values, and/or host sediments could provide further important insights into the ways in which early-diagenetic environments control the initial decay of biomolecules within bone and other tissues.

Assessing heavy-metal leaching risk in cement-industrial slag composite pastes using a mechanism-based thermodynamic approach

Various heavy metal (HM)-containing slags have been utilized to expand mineral admixture sources. However, existing evaluation methods fail to reveal the leaching details. In this study, thermodynamic modelling, combined with sorption quantification and expanded databases, was used to describe HM leaching at varied pH values. Four service conditions related to paste inner pH were set to evaluate the risks in different environments. Three types of HMs and four metallurgical slags were used as HM sources. The results show that hydroxide precipitates are the main phases controlling the leaching of precipitation-type HMs, while sorption plays an important role in controlling the leaching of amphoteric-type and anion-type HMs. When HMs exist as hard-to-dissolve phases in slags, hydration products can first act as barriers against erosion and HMs cannot leach out until the barriers disappear (pH below ∼8). The established thermodynamic method helps to evaluate HM leaching risks from concrete more scientifically.

Self-Assembled Charge-Transfer Chiral π-Materials: Stimuli-Responsive Circularly Polarized Luminescence and Chiroptical Photothermic Effects

Despite significant achievements in the field of chiroptical organic materials, the full utilization of both the excited state and ground state chiroptical properties in a single supramolecular system is still rarely disclosed. Here, we report that the rational combination of the charge-transfer (CT) interaction with the spacer effect and controlled protonation of π-histidine leads to chiroptical organic π-materials with both circularly polarized luminescence (CPL) and the supramolecular chirality-directed chiroptical photothermic effect. Three pyrene-conjugated histidine derivatives with varied acyl linkers (PyHis, PyC1His, and PyC3His) were designed to coassemble with electron-deficient 1,2,4,5-tetracyanobenzene (TCNB), leading to the formation of supramolecular CT complexes with intense orange to red CPL depending on the linker length. The linker length also affected the protonation-induced CPL responsiveness of the corresponding CT assemblies. Upon protonation of the histidine moiety, PyC3His/TCNB CT assemblies exhibited an inverted CPL signal, while PyHis/TCNB pairs gave quenched CPL due to the disassembly. The protonation-controlled PyC3His/TCNB CT assemblies at varied pH values showed different chiroptical photothermic effects (CPEs) for the same incident chiral light despite the molecular chirality of PyC3His remaining unchanged, supporting an interesting supramolecular chirality-directed photothermic effect.

Experimental investigation on microstructure and surface morphology deterioration of limestone exposed on acidic environment

Understanding evolution of microstructure and surface morphology is essential for studying the strength of building material in acidic enviorment. In this study, the microstructure of limestone samples immersed in acidic solutions of varying pH values was evaluated by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), while the joint surface morphology evolution process was determined by three-dimensional (3D) scanning experiments. Further, direct shear tests on the immersed jointed samples were conducted for shear properties analysis. It is found that the pore size distribution gradually changes from nanopore to micropore with the decrease in pH value, while the single pore area and perimeter increased and the fractal dimension decreased. Therefore, the increased pore distribution, enlarging in area, and change in the shape of the pores altered the microstructure and caused the increase in porosity. Also, with the decrease in pH value, the decrease rate of 3D relative fluctuation height, angle, and 3D area ratio increase. The 3D average fluctuation angle decreases the most, whereas the 3D area ratio decreases the least. In an acidic environment, the 3D surface morphology is significantly influenced by the 3D average fluctuation angle, which eventually changes joint roughness. Under the condition of acidic underground water, the microstructure of the joint wall and surface morphology of the joint degraded, thereby affecting the joint shear behavior. Therefore, the degradation of joint roughness coefficient and joint wall compressive strength should be considered for evaluating the joint mechanical properties in an acidic environment.

Amphiphilic Polyethylene-b-poly(L-lysine) Block Copolymer: Synthesis, Self-Assembly, and Responsivity.

Polyethylene-b-polypeptide copolymers are biologically interesting, but studies of their synthesis and properties are very few. This paper reports synthesis and characterization of well-defined amphiphilic polyethylene-block-poly(L-lysine) (PE-b-PLL) block copolymers by combining nickel-catalyzed living ethylene polymerization with controlled ring-opening polymerization (ROP) of ε-benzyloxycarbonyl-L-lysine-N-carboxyanhydride (Z-Lys-NCA) and sequential post-functionalization. Amphiphilic PE-b-PLL block copolymers self-assembled into spherical micelles with a hydrophobic PE core in aqueous solution. The pH and ionic responsivities of PE-b-PLL polymeric micelles were investigated by means of fluorescence spectroscopy, dynamic light scattering, UV-circular dichroism, and transmission electron microscopy. The variation of pH values led to the conformational alteration of PLL from α-helix to coil, thereby changing the micelle dimensions.

Influence of strontium containing fluorophosphate glass onto structural and mechanical behavior of MTA network

ObjectiveThis study aimed to evaluate the effect of incorporation of strontium based fluoro phosphate glass (SrFPG) 48P2O5–29CaO–14NaO–3CaF2–6SrO on physico chemical and biological properties of mineral trioxide aggregate (MTA). MethodsOptimized SrFPG glass powder were prepared using planetary ball mill and incorporated into MTA in varying proportion (1, 5, 10 wt%) to obtain SrMT1, SrMT5, SrMT10 bio-composite respectively. The bio-composites were characterized using XRD, FTIR and SEM-EDAX before and after soaking for 28 days in stimulated body fluid (SBF) solution. To assess the mechanical properties and biocompatibility of the prepared bio-composite, density, pH analysis, compressive strength and cytotoxicity evaluation using MTT assay were done before and after soaking for 28 days in SBF solution. ResultsA nonlinear variation in compressive strength and pH values was noted. Of the bio-composites, SrMT10 was evidenced with rich apatite formation in XRD, FTIR and SEM with EDAX analysis. MTT assay showed increased cell viability in all the samples before and after in vitro studies.

GO-Fe3O4-CeO2-CTAB nanocomposite as a high-performance adsorbent for removal of phenol from aqueous solutions

ABSTRACT This study aimed to assess GO-Fe3O4-CeO2-CTAB nanocomposite adsorption efficiency for removing the phenol molecules from the aqua solution. The researcher performed the batch investigations to estimate the percentage of phenol removal from wastewater with the variation of pH value from 3 to 10, adsorption time from 5.000 to 100.000 min, the adsorbent dose from 0.003 to 0.040 g, the phenol concentration from 20.000 to 440.000 mg L−1 and temperature from 25 to 60°C. The GO-Fe3O4-CeO2-CTAB nanocomposite produced by a Co-precipitation method was used to adsorb and remove phenol molecules from an aqueous solution. The synthesised nano-sorbent was investigated by different methods including FTIR, XRD, SEM, EDX, VSM and BET techniques. The gained data show that the best removal efficiency of phenol by GO-Fe3O4-CeO2-CTAB nanocomposite was obtained at pH = 8, the absorbent dosage of 400.000 mg L−1 (0.020 g), contact time = 60 min and temperature of 25°C. For the equilibrium study, based on the obtained coefficients correlation of definition from fitted models, the highest value is obtained for the Langmuir model, (KL = 0.048 L mg−1, qm = 492.000 mg g−1, RL = 0.509 and R2 = 0.992), so, phenol adsorption on the surfaces of GO-Fe3O4-CeO2-CTAB nanocomposite was a monomolecular adsorbed layer. Based on obtained R2 values, it can be concluded that the pseudo-second-order kinetic model seemed to be match well with the adsorption of phenol molecules at the surface of GO-Fe3O4-CeO2-CTAB nanocomposite in three concentrations of 50.000, 100.000 and 125.000 mg L−1 (qe2 = 52.080, 103.090 and 129.870 mg g−1, k2 = 0.005, 0.003 and 0.002 g mg−1 min−1, R2 = 0.999, 0.999 and 0.999 respectively).

Characterization of a novel cold-adapted intracellular serine protease from the extremophile Planococcus halocryophilus Or1.

The enzymes of microorganisms that live in cold environments must be able to function at ambient temperatures. Cold-adapted enzymes generally have less ordered structures that convey a higher catalytic rate, but at the cost of lower thermodynamic stability. In this study, we characterized P355, a novel intracellular subtilisin protease (ISP) derived from the genome of Planococcus halocryophilus Or1, which is a bacterium metabolically active down to -25°C. P355's stability and activity at varying pH values, temperatures, and salt concentrations, as well as its temperature-dependent kinetics, were determined and compared to an uncharacterized thermophilic ISP (T0099) from Parageobacillus thermoglucosidasius, a previously characterized ISP (T0034) from Planococcus sp. AW02J18, and Subtilisin Carlsberg (SC). The results showed that P355 was the most heat-labile of these enzymes, closely followed by T0034. P355 and T0034 exhibited catalytic constants (k cat ) that were much higher than those of T0099 and SC. Thus, both P355 and T0034 demonstrate the characteristics of the stability-activity trade-off that has been widely observed in cold-adapted proteases.

Effect of pH on the Electrochemical Behavior and Nitrogen Reduction Reaction Activity of Ti2N Nitride MXene

AbstractNitrogen reduction reaction (NRR) is used to convert nitrogen (N2) to ammonia (NH3) at ambient conditions. In general, acidic electrolytes are used to provide protons (H+), however, this leads to low selectivity due to H2 formation via the hydrogen evolution reaction (HER). Recently, it is shown that Ti2N MXene is active and selective for NRR in acidic electrolyte, and operates through a Mars‐van Krevelen (MvK) mechanism. However, the effect of pH on its catalytic performance is not well understood. Here, experiments are performed in varying pH values and relations are developed between pH and performance. The findings of this study indicate that the lowest NRR onset occurs within pH 2 systems exhibiting a nonlinear trend. However, as pH decreases, overpotential decreases, and kinetics increase due to H+ participation. FE values are found to increase as pH increased. These findings will be extended to other materials to design optimal electrolytic systems for NRR.

Gamma-ray irradiation and characterization of synthesized bidentate and tetradentate Schiff base ligands and their complexes with some transition metal ions

Salen ligands are essential for coordinating a diverse group of metals in their respective oxidation states. This creates significant complexes of salen metals that are used in different fields. Condensation of ehylenediamine (en) with p-methoxybenzaldehyde (L1) or o-hydroxyacetophenone (L2) with a ratio 1: 2 (en: p-methoxybenzaldehyde or o-hydroxyacetophenone) or by the interaction of o-phenylenediamine (phen) with o-hydroxybenzaldehyde (L3) or p-hydroxybenzaldehyde (L4) with a ratio 1: 2 (phen: o-hydroxybenzaldehyde or p-hydroxybenzaldehyde) has been used to prepare four symmetrical Schiff bases (L1-L4). The UV–vis spectroscopy has been used to investigate the diverse electronic transitions associated with the Schiff bases molecules as well as how these transitions are impacted by diverse polarities of solvents. Elemental analysis, FT-IR, UV–vis spectra, molar conductivity, and 1H NMR have been used to characterise all the compounds obtained in this process. The continuous variation applied alongside molar ratio spectral methods showed the formation of different complexes arising from the reaction of the ligand (L1-L4) with the metal ions Mn(II), Fe(III) and Cu(II) is 1: 1 and/ or 1: 2 (M: L). A series of universal buffer solutions (20 % ethanol v/v) with varying pH values were used in spectrophotometry to determine the acid dissociation constants of the L2 and L4 ligands. Gamma radiation was applied to examine the compounds’ irradiation stability. Additionally, the absorptions of the main functional groups were screened using FT-IR spectra before and after Gamma irradiation. The results show that all the compounds are stable after irradiation process; therefore, it could be used as enhancing agents in cancer therapy.

The wear behaviour of different metallic bond alloys tested in a modified B611-13 test in an acidic, neutral and alkaline media

The abrasive and adhesive wear behaviour of metallic bonds can be significantly affected by varying pH values of the attacking medium. However, the knowledge about the pH value influence on diamond impregnated bits used in core drilling industry is still limited. One recent publication shows the advantage of modifying a standard ASTM B611-13 test to investigate the abrasive and adhesive wear behaviour of a diamond segment bond material in a neutral regime (pH7). This study mainly focuses on the effects of a varying surrounding media on the tribological behaviour using an acidic, neutral and alkaline slurry. This emulates more aggressive conditions for the diamond segments used in mining as well as construction industry. The pH value at which such diamond segments operate can differ from pH2 up to a value of pH13. The present work studies the wear behaviour of two metallic bonds in a modified B611-13 arrangement at 4 m/s sliding speed and different pH values. The tested specimens are investigated with regard to their change in mass and microstructure at the sliding interface zone. The results reveal a significant influence of the pH value on the wear behaviour of the bond system.

Analyzing pH-dependent structural characteristics and optical transmittance of titanium dioxide

AbstractThe use of titanium dioxide (also known as titania) in solar cells, biomaterials, and photocatalytic processes has generated an ever-increasing amount of interest. Titania is widely used in a variety of applications because it is nanocrystalline, chemically stable, has a high refractive index, is mechanically hard, and transmits visible light well. In this work, titania nanoparticles were formed via sol–gel synthesis, wherein the effect of varying pH values such as 3, 5, 7, 9, and 11 has been investigated on the synthesized nanoparticles by studying their structural characteristics and analyzing their optical transmittance. Structural analysis of the synthesized TiO2shows formation of the brookite phase at all pH values under as-synthesized conditions. Moreover, structural parameters including crystallite size, dislocation density, and unit cell volume were also calculated. Cell volume was calculated at various pH levels and measured between 255.7 and 257.2 Å3. Optical analysis shows a transmission increase with a pH increase, and maximum transmission has been observed above 80% for a pH value of 11.

Study of mechanical characteristics and damage mechanism of sandstone under long-term immersion

The microscopic pore structure of sandstone gradually changes under long-term immersion, resulting in dynamic changes in the mechanical and damage properties of sandstone, which brings challenges to maintain the long-term stability of underground engineering. In this paper, the evolution of pore structure and mechanical behavior of sandstones at different immersion times (0d, 3d, 30d, 90d, 180d and 360d) is studied. A series of physico-chemical experiments and uniaxial compression tests (with simultaneous acquisition of acoustic emission (AE) signals) are conducted to explore the weakening mechanism and failure mode of sandstones during long-term immersion. The results show that long-term immersion has a significant effect on the pore structure and mechanical behavior of sandstones. Various physical parameters indicate that the change in the pore structure of a sandstone with increasing immersion time can be divided into two stages, namely the swelling stage of clay minerals (saturation process) and the corrosion stage of potassium feldspar (long-term immersion process). The variation of pH value and K+ concentration in soaking solution can provide a basis for the division of pore structure stages. From the perspective of mechanical behavior, the uniaxial compressive strength (UCS) and cumulative AE counts of a sandstone decrease by 83% and 96.8% respectively after 360 d of immersion, with enhanced plastic characteristics. The macroscopic failure mode of a sandstone changes from combination of shear and tensile crack surfaces to a single shear crack surface. Based on the results of physico-chemical experiments and mechanical tests, it can be assumed that microcracks in long-term immersion sandstones are more prone to develop along weakened cementation surfaces. Under the effect of stress, corrosion pores formed by potassium feldspar provide space for the rotation and movement of quartz grains, making it more prone to shear slip. The study results enhance our understanding of weakening mechanisms at long-term immersion and provide a basis for assessing the long-term stability of underground engineering.

Inhibitory mechanism of sodium hexametaphosphate on enzymatic browning in yellow alkaline noodles

The effect and mechanism of sodium hexametaphosphate (SHMP) on polyphenol oxidase (PPO) enzymatic browning in yellow alkaline noodles (YAN) were investigated. The browning degree and PPO activity in YAN or PPO solutions decreased with the SHMP concentrations increased. Variations in pH values (pH 7–8.5) adjusted by HCl or acetic acid slightly affected the PPO activity, but SHMP inhibited PPO activity more pronounced. The inhibition of SHMP on PPO activity was irreversible. SHMP formed coordinate covalent bonds with Cu2+ to make PPO inactive. HPLC analysis revealed that SHMP reduced the browning products and led to the color of PPO-catechol systems being lightened. Furthermore, SHMP inhibited browning by hampering the auto-oxidization of intermediate products due to the change in pH value. Besides, the HPLC chromatogram, UV–vis spectrum, and mass spectrometry revealed that SHMP could convert melanin (m/z 248.97, 723.5, and 836.58) to light-colored substances (m/z 137.11).

GPCR Signaling Measurement and Drug Profiling with an Automated Live-Cell Microscopy System.

A major limitation of time-lapse microscopy combined with fluorescent biosensors, a powerful tool for quantifying spatiotemporal dynamics of signaling in single living cells, is low-experimental throughput. To overcome this limitation, we created a highly customizable, MATLAB-based platform: flexible automated liquid-handling combined microscope (FALCOscope) that coordinates an OpenTrons liquid handler and a fluorescence microscope to automate drug treatments, fluorescence imaging, and single-cell analysis. To test the feasibility of the FALCOscope, we quantified G protein-coupled receptor (GPCR)-stimulated Protein Kinase A activity and cAMP responses to GPCR agonists and antagonists. We also characterized cAMP dynamics induced by GPR68/OGR1, a proton-sensing GPCR, in response to variable extracellular pH values. GPR68-induced cAMP responses were more transient in acidic than neutral pH values, suggesting a pH-dependence for signal attenuation. Ogerin, a GPR68 positive allosteric modulator, enhanced cAMP response most strongly at pH 7.0 and sustained cAMP response for acidic pH values, thereby demonstrating the capability of the FALCOscope to capture allosteric modulation. At a high concentration, ogerin increased cAMP signaling independent of GPR68, likely via phosphodiesterase inhibition. The FALCOscope system thus enables enhanced throughput single-cell dynamic measurements and is a versatile system for interrogating spatiotemporal regulation of signaling molecules in living cells and for drug profiling and screening.

Variation in glucosinolates and the formation of functional degradation products in two Brassica species during spontaneous fermentation

Vegetables from the Brassica species are excellent sources of glucosinolates (GLSs), the precursors of health-promoting isothiocyanates (ITCs). Fermentation enhances the biotransformation of GLSs into potential bioactive ITCs. To explore the biotransformation of GLSs during Brassica fermentation, the changes in GLSs during the fermentation of two Brassica species (i.e., cauliflower and broccoli); the formation of corresponding breakdown products; and the shifts in physicochemical parameters, bacterial communities, and myrosinase activities involved in GLSs degradation were systematically investigated. Nine aliphatic, three indolic, and two benzenic GLSs were identified in fermented cauliflower (FC) and fermented broccoli (FB). Aliphatic glucoiberin and glucoraphanin were the major forms of GLS in FC and FB, respectively; indolic glucobrassicin was also abundant in both FC and FB. The total GLS content decreased by 85.29% and 65.48% after 3 d of fermentation in FC and FB, respectively. After 2 d of fermentation, a significant increase in bioactive GLS degradation products (P < 0.05), including sulforaphane (SFN), iberin (IBN), 3,3-diindolylmethane (DIM), and ascorbigen (ARG), was observed in FC and FB compared to in fresh cauliflower and broccoli. Moreover, variations in pH value and titratable acidity in FC and FB correlated with Brassica fermentation and were accomplished by lactic acid bacteria, including Weissella, Lactobacillus-related genera, Leuconostoc, Lactococcus, and Streptococcus. These changes may enhance the biotransformation of GSLs to ITCs. Overall, our results indicate fermentation leads to the degradation of GLSs and the accumulation of functional degradation products in FC and FB.

Evaluation of Physicochemical Parameters of Biosorbents Produced from Groundnut Hull Using Microwave Assisted Irradiation Method

Samples of ground nut hull were converted to biosorbents using microwave assisted method [groundnut hull treated with hydrogen peroxide (HP-GH), groundnut hull treated with distilled water (W-GH) and raw groundnut hull (R-GH)]. The biosorbents were further characterized using physicochemical procedures (pH dependence, bulk density, surface area, ash content, and volatile matter, moisture content). The results show that HP-GH has pH = 8.9, W-GH pH = 8.4 and R-GH pH = 8.5 which is an indication that all the biosorbents have the appropriate pH values for the uptake of cationic species within aqueous systems. Surface area analysis revealed that HP-GH has the largest surface area (74.20 m2·g-1) while W-GH and R-GH have surface area values of 29.40 m2·g-1 and 21.40 m2·g-1 respectively. This suggests that modification of raw groundnut hull biomass with hydrogen peroxide possibly instigated delignification of the biomass which resulted in increased surface area for HP-GH. Results from Bulk density analysis also confirm the data obtained from surface area analysis. Accordingly, R-GH displayed the highest bulk density followed by W-GH with HP-GH showing the least bulk density. The variation in pH values among the biomass used in this study may be explained by the variation in their ash content as well because pH and ash content are positively correlated. Hence, HP-GH with a pH = 8.9 has high ash content (117.31%), W-GH with pH = 8.4 has 97.93% ash content and R-GH with pH = 8.5 has 94.26% ash content. Results from moisture content analysis show that HP-GH (99.95%), W-GH (99.97%) and R-GH (99.89%) may necessitate exposure of the biosorbents to moderate heat before use. The results obtained from this study suggest that modification of ground nut hull with either distilled water or Hydrogen peroxide by means of microwave irradiation improves physicochemical properties which may perhaps increase the adsorption capacity of the biomass.

Impact of mobile phase composition on reverse-phase separation of polar basic compounds

Method development for determination of polar basic compounds on ion-suppression reverse-phase liquid chromatography, requires appropriate selection of stationary phase and composition and pH value of the mobile phase. The addition of the organic solvent in aqueous buffers with defined pH value, results in shift of the pH value of the mobile phase, resulting in significant change in chromatographic retention and selectivity. The aim of this study was to evaluate the impact of the variation of pH value of the mobile phase and percentage of the organic solvent, on the chromatographic separation of basic compound (octenidine dihydrochloride). The design of experiment was used for the optimization of the chromatographic conditions and selection of the most suitable mobile phase composition. The optimal composition of the mobile phase, providing satisfactory chromatographic performance based on ion-suppression reverse-phase chromatography, included 0.1M citric acid/0.2M sodium dihydrogen phosphate, pH =2.5, combined with 70% v/v organic solvent-acetonitrile. The suitability of the method was confirmed by satisfactory results for the system suitability parameters, specificity, linearity and precision. Key Words: polar basic compounds, ion-suppression, pH value, composition of mobile phase

Using a batch test to derive sorption data of fluoroquinolone antibiotics in humic acids

Fluoroquinolone antibiotics (FQs) are of concern due to their disrupting effects on environmental bacterial communities. Evaluating FQ sorption by soil components is important to understand their interaction with soils and to address their environmental (bio)availability. However, data in soil organic components, especially humic acids, are scarce. Batch experiments following OECD guidelines are suitable for testing the sorption of pollutants in solid matrices. Here, we applied this methodology, with specific changes in the experimental setup, to derive sorption data and to identify the factors affecting sorption of four common FQs in seven humic acids with contrasting properties. The effect of shaking time, pH, calcium concentration in solution and dissolved organic carbon (DOC) content on the quantification of the solid-liquid distribution coefficient (Kd) of norfloxacin in three reference humic acids was evaluated. Sorption reversibility and sorption analogy of four FQs were additionally assessed in these three reference materials, whereas the effect of initial norfloxacin concentration was evaluated in the overall set of seven humic acids. Sorption was fast, strong, non-linear, irreversible and affected by changes in the pH and calcium levels in solution. The bell-shaped sorption trend at varying pH values confirmed the key role of FQ speciation in sorption and the high Kd values indicated a positive effect of soil organic matter components on FQ sorption in bulk soils at environmentally relevant pH values.•Relevant factors affecting sorption of pollutants in environmental matrices must be considered to derive Kd values with low variability and high representativeness.•In this article we modify the experimental conditions of standard batch tests to identify the factors that affect the sorption of FQs in humic acids.•The methodological approach followed can be extrapolated to the evaluation of other combinations of pollutant and environmental matrix.