Advances in ion chromatography: speciation of μ 1−1 levels of metallo-cyanides using ion-interaction chromatography

Fe(CN)^4?₆, Cu(CN)^3?₄, Co(CN)^3?₆, Fe(CN)^3?₆, Ni(CN)^2?₄ and Cr(CN)^3?₆ are determined by ion-interaction chromatography using a C₁₈ column and methanol-tetrahydrofuran-10 mM phosphate buffer (pH 7.9) (25 + 1 + 74, v/v/v) containing 5 mM tetrabutylammonium hydroxide as mobile phase, with spectrophotometric detection at 214 nm. Detection limits are in the range 0.01–0.5 mg 1^?1. In an alternative approach, an automated on-line sample preconcentration technique is used wherein a 2-ml volume of sample containing metallo-cyanides is loaded onto a C₁₈ precolumn which has been equilibrated with the above mobile phase. The bound solutes are then eluted from the precolumn to a C₁₈ analytical column where they are separated using the same mobile phase as employed to equilibrate the precolumn. Detection limits are in the rate 0.08–1.58 μg 1^?1 and calibration graphs are linear up to 200 μg 1^?1. The preconcentration step is shown to give quantitative recoveries for all species except Fe(CN)^4?₆ and (CN)^3?₄. The iron(II) complex does not bind quantitatively to the precolumn, and extensive studies with the copper complex suggested that low recoveries were due to dissociation and ligand-exchange reactions occurring during the chromatographic separation process. Negative interference effects were observed for Cl^? and SO^2?₄ when present at a level of 250 mg 1^1?, and UV-absorbing anions such as Br^?, SCN^?, NO^?₂ and NO^?₃ caused positive interference when present at concentrations as low as 1 mg 1^?1. The negative interferences could be reduced by diluting the sample and the positive interferences could be eliminated by incorporating an additional step in the preconcentration process, in which UV-absorbing anions bound to the precolumn after sample loading were eluted selectively using an eluent consisting of 10 mM NaCl in phosphate buffer (pH 6.7).     

Determination of phenyltin compounds by reversed-phase liquid chromatography

An analytical procedure for the determination of phenyltin compounds in environmental sample waters was studied. Chromatography of mono-, di- tri-phenyltin (MPT, DPT and TPT) was performed on a reversed-phase C₁₈ column with the mobile phase comprising methanol/10⁻² M H₃PO₄ (80:20 v/v) at pH 3 and UV detection at 214 nm. To enhance the sensitivity of the detection system, the post-column reaction between morin or 3-hydroxyflavone and phenyltin compounds was formed before fluorescence detection. Several parameters affecting the fluorescence intensity were studied systematically, including the optimum condition for the post-column reagent that was also compatible with the eluent. The parameters concerned in this study were the pH, the percentage of Triton X-100, the ratio of fluorigenic reagent to phenyltin compounds and the amount of methanol in the eluent. Detection limits before the preconcentration process were in the region of 1.5 ppb for TPT and 150–250 ppb for MPT and DPT, respectively. Utilizing solid-phase extraction on a C₁₈ cartridge for sample clean-up as well as preconcentration successfully reduced the detection limit of TPT to the level of ng dm⁻³ and can be applied to seawater analysis. Recovery in the range 95.0–98.0% was obtained by developing the optimum elution profile in the preconcentration step. © 1998 John Wiley & Sons, Ltd.     

Antimicrobial Peptide Modifications against Clinically Isolated Antibiotic-Resistant Salmonella

Antimicrobial peptides are promising molecules to address the global antibiotic resistance problem, however, optimization to achieve favorable potency and safety is required. Here, a peptide-template modification approach was employed to design physicochemical variants based on net charge, hydrophobicity, enantiomer, and terminal group. All variants of the scorpion venom peptide BmKn-2 with amphipathic α-helical cationic structure exhibited an increased antibacterial potency when evaluated against multidrug-resistant Salmonella isolates at a MIC range of 4–8 µM. They revealed antibiofilm activity in a dose-dependent manner. Sheep red blood cells were used to evaluate hemolytic and cell selectivity properties. Peptide Kn2-5R-NH₂, dKn2-5R-NH₂, and 2F-Kn2-5R-NH₂ (variants with +6 charges carrying amidated C-terminus) showed stronger antibacterial activity than Kn2-5R (a variant with +5 charges bearing free-carboxyl group at C-terminus). Peptide dKn2-5R-NH₂ (d-enantiomer) exhibited slightly weaker antibacterial activity with much less hemolytic activity (higher hemolytic concentration 50) than Kn2-5R-NH₂ (l-enantiomer). Furthermore, peptide Kn2-5R with the least hydrophobicity had the lowest hemolytic activity and showed the highest specificity to Salmonella (the highest selectivity index). This study also explained the relationship of peptide physicochemical properties and bioactivities that would fulfill and accelerate progress in peptide antibiotic research and development.     

Iron fractionation for corrosion products from natural gas pipelines by continuous-flow sequential extraction

The forms and quantities of iron species in corrosion product samples from natural gas pipelines were examined, using a continuous-flow sequential extraction system. Sequential extraction consists of four steps that dissolve water soluble iron (FeSO₄), acid soluble iron (FeCO₃), reducible iron (Fe-(oxyhydr)oxides) and oxidisable iron (FeS₂) fractions, respectively. Selectivity of extracting reagents for particular iron species was evaluated by determination of co-extracted anions, using ion chromatography, and evolved CO₂, using indirect flame atomic absorption spectrometer (FAAS). Iron was found predominantly in the reducible fraction (61–99%), indicating that Fe-(oxyhydr)oxides are the major constituents of the corrosion products.