Hexamethonium Hydroxide Research Articles

Properties and ionic self-assembled structures from mixture of a bola-type strong alkali dication and a branched phosphoric acid

Ionic self-assembled structures have been prepared successfully between di-(2-ethylhexyl) phosphoric acid (DEHPA) and hexamethonium hydroxide (HMO(OH)2). The DEHPA/HMO(OH)2 complexes show good surface activity at a wide mixing molar ratio of DEHPA to HMO(OH)2 (ρ), within which the critical micellar concentration (cmc) is far below that of any single component. In bulk aqueous solutions, rich phase behavior was observed by varying cDEHPA and cHMO(OH)2. When the concentration of HMO(OH)2 is in the range of 10–100mmolL−1, isotropic L1 phases, birefringent Lα phases and a phase-separated region were successively observed with increasing cDEHPA. At high cHMO(OH)2 range (>78mmolL−1), a narrow L1/Lα two-phase region with the Lα phase at the bottom was noticed between the single L1 and single Lα phase regions. The rheological properties of the samples in the single Lα phase region at 2.6⩽ρ⩽2.8 are quite similar. Cryo-TEM and freeze-fracture TEM (FF-TEM) observations revealed the presence of multilamellar vesicles with flexible and even branched bilayers. At 2.2⩽ρ⩽2.6, however, the rheological properties are highly sensitive to ρ due to the sophisticated self-assembly behavior as proved by imaging studies and 2H NMR measurements. Closely-stacked flat structures which look like foams or cellular networks have been newly discovered. Interestingly, NaCl could arouse an L1 to Lα phase transition due to the suppression of the effective area of the hydrophilic headgroups of the ionic complexes, leading to an increase of the critical packing parameter p. The viscoelasticity properties of the salt-containing Lα phases decreased with increasing salinity. We hope our research can provide new ideas for the construction of supramolecular materials by surfactant ionic self-assembly (SISA) strategy.

Direct incorporation of B, Al, and Ga into medium-pore ITH zeolite: Synthesis, acidic, and catalytic properties

Direct crystallization of B-, Al- and Ga-substituted medium-pore ITH zeolites was carried out using hexamethonium hydroxide (HMH) and N,N,N′,N′,-tetramethyl-1,6-hexanediamine (TMHDA) as structure-directing agents. The type of organic SDA was found determining the crystal size and the nature of Brønsted acid sites in isomorphously substituted ITH zeolites. The use of HMH resulted in formation of tiny (length of 0.5–3μm) needle-like ITH crystals having bridging Si(OH+)E(−) (E=B, Al, Ga) groups with acidic strength increasing in the following sequence B<Ga<Al. In contrast, ITH zeolites with bulky (length of 40–50μm) crystals prepared using TMHDA possess loosely bond framework and [(SiO)3AlOH]−H+ and (SiO)2BOH groups (absorption band at 3670cm−1) perturbing upon interaction with pyridine. B-, Al- and Ga-ITH possessing tiny crystals showed improved catalytic performance in tetrahydropyranylation of 1-hexanol in comparison with non-acidic heteroelement-free germanosilicate zeolites and isomorphously substituted ITH zeolites with bulky crystals. The yield of target ether is enhanced with increasing strength of acid sites (e.g. B-<Ga-<Al-ITH) or with growth in their concentration.

Fungal biofermentation of pine bark producing organic acids and their quantification with capillary electrophoresis

Bioprocessing of pine bark was accomplished using oyster mushroom fungi. The organic acids and inorganic anions in the extracts of fermented samples were identified by capillary electrophoresis (CE). Nine organic acids were simultaneously determined in 12min through the use of an electrolyte composed of 20mM pyrazine-2,3-dicarboxylic acid (2,3-PyDC), 1.5mM CaCl2·2H2O and 0.3mM MTAH in methanol:water (10:90, v/v) at pH 9.0. The concurrent determinations of three inorganic anions were performed in less than 10min in an electrolyte consisting of 2.25mM pyromellitic acid, 6.50mM NaOH, 0.75mM hexamethonium hydroxide, and 1.60mM triethanolamine at pH 7.70. The applied analysis methods efficiently separated and identified organic acids and inorganic anions in the extracts. Butyric, maleic and glucuronic acids were the primary organic acids formed via fermentation. Chloride, nitrate and sulphate were detected in all of the samples.

Capillary electrophoretic method for the determination of inorganic and organic anions in real samples: Strategies for improving repeatability and reproducibility

Selectivity and robustness of the pyromellitic acid (PMA) based background electrolyte was improved in order to increase its applicability for routine analysis of inorganic and organic anions in real samples. An electrolyte composed of 6.75 mM PMA, 0.5 mM hexamethonium hydroxide as electroosmotic flow (EOF) modifier, Ca 2+ 0.05 mM as complexation agent and pH adjusted to 7.6 with TEA 1 M allows for the separation of 22 inorganic and organic anions in less than 17 min. Good RSDs for within-day migration time reproducibility (0.03–0.9%) and day-to-day analyses (0.04–1.4%) were obtained by the use of two internal standards, allowing for an accurate compound identification. The detection limits ranged from 0.1 to 0.4 mg L −1 (S/N = 3) for hydrodynamic injection (1250 mbar s). The applicability of the proposed method was demonstrated by the analysis of inorganic and organic anions in diverse real samples. The recoveries obtained ranged from 93 to 106%.

Capillary electrophoresis screening of poisonous anions extracted from biological samples

A method was developed for screening human biological samples for poisonous anions using capillary electrophoresis (CE) employing indirect UV detection. The run buffer consisted of 2.25 mM pyromellitic acid, 1.6 mM triethanolamine, 0.75 mM hexamethonium hydroxide and 6.5mM NaOH at pH 7.7. Biological samples were pretreated using solid phase extraction. The method was applied to the analysis of human blood, plasma, urine, and intestinal contents. Twenty-nine different anions were detectable at aqueous concentrations of 1 part per million (ppm) with a typical analysis time less than 20 min. Intraday migration time R.S.D. and peak area R.S.D. for blood samples were less than 1.1% and 6.3%, respectively. Interday migration time R.S.D. for plasma samples ranged from 7.5% to 10.4%. The new method produced efficient separations of various target anions extracted from complex biological matrices.

Capillary electrophoresis determinations of trace concentrations of inorganic ions in large excess of chloride: soft modelling using artificial neural networks for optimisation of electrolyte composition.

In this work, using a combination of experimental design (ED) and artificial neural networks (ANN), the composition of a triethanolamine-buffered chromate electrolyte was optimised for determination of sulphate anions in the presence of high chloride excess. The optimal electrolyte, allowing a baseline-resolved separation of sulphate from chloride present in a 1500 multiple excess in less than 170 s, consists of 10 mmol/L CrO(3), 2 mmol/L hexamethonium hydroxide, 10% methanol, and triethanolamine added to adjust the pH to 8.0. The method is suitable to a wide concentration range of chloride (4-1757 mg/L) and sulphate (4-590 mg/L) with linear calibration plots (R(2) = 0.9937-0.9999). Relative standard deviations are less than 2.0% for both anions for migration times and peak areas. The detection limits (hydrodynamic injection of 1 s) were 0.6 mg/L for sulphate and 0.5 mg/L for chloride. The method was successfully applied to determination of sulphate in mineral waters containing a high chloride concentration and to determination of sulphate traces in an anticancer drug injection preparation containing a physiological level of chloride. It was shown that alpha-cyclodextrin as an electrolyte additive has a significant potential for further increasing the separation selectivity for inorganic anions.

Modification and validation of the pyromellitic acid electrolyte for the capillary electrophoretic determination of anions

For the determination of inorganic and organic anions, the pyromellitic acid (PMA) electrolyte is widely used. The pH adjustment of the self-prepared electrolyte was very challenging to satisfy the pH of specification of pH 7.8±0.1. A modification was proposed to provide a more simple electrolyte by buffering the PMA electrolyte with triethanolamine (TEA) only instead of adjusting the pH by NaOH and TEA. Thus, the proposed electrolyte consisted of 2.25 mmol l −1 PMA, 0.75 mmol l −1 hexamethonium hydroxide and 12 mmol l −1 TEA. The performance of the PMA electrolyte buffered by TEA only was compared to a commercial available PMA and statistically validated in accordance with the methodology of Taguchi. No statistically significant difference could be found for both electrolytes assessing the performance and detection limits of hydrodynamic, stacking and electrokinetic injection with transient isotachophoretic preconcentration as well as repeatability of migration times, peak resolutions and peak symmetries.

Capillary electrophoretic determination of inorganic selenium species

The performance of pyromellitic electrolyte for capillary zone electrophoresis of inorganic selenium species in the presence of selected common anions with indirect UV detection was investigated. The separation was achieved with pyromellitic electrolyte at pH 8.8 and hexamethonium hydroxide as the electroosmotic flow modifier. Obtained detection limits of 0.17 μg ml −1 for Se(VI) and 0.29 μg ml −1 for Se(IV) were improved by a factor of 5–7 in comparison with chromate electrolyte, which has been mainly employed for selenium analysis. Good resolution for nitrate–Se(VI) peaks were obtained.

Speciation of sulfur-containing anions by use of capillary electrophoresis

Optimization of a CE method with indirect UV detection for speciation of sulfur-containing anions is described. Sensitivity, selectivity, and separation using a chromate background electrolyte (the electrolyte most often used for inorganic anions) and a pyromellitate electrolyte are compared. The pyromellitate electrolyte is recommended because its use results in better sensitivity for the ions analyzed. The composition of the electrolyte was 2.25 mM pyromellitic acid, 6.5 mM NaOH, 0.75 mM hexamethonium hydroxide, and 1.6mM triethanolamine, pH 10. Separation of seven sulfur-containing anions with indirect detection at 254 nm was achieved in one run in less than 7 min.

New preconditioning strategy for the determination of inorganic anions with capillary zone electrophoresis using indirect UV detection

It is widely accepted that preconditioning procedures are indispensable in capillary electrophoresis in order to achieve reproducibility of migration times and peak areas. Several preconditioning strategies have been employed for electrophoretic determinations of inorganic anions using indirect UV detection including simple flushing with buffer or alkaline or acid pre-rinsing followed by flushing with electrolyte. We investigated the influence of various preconditioning strategies on the reproducibility of migration times and peak areas of inorganic anions. The electrolyte systems for indirect UV detection were based on pyromellitic acid and chromic acid respectively as UV absorbing probes and hexamethonium hydroxide as electroosmatic flow modifier. Preconditioning agents under investigation were electrolyte buffer, NaOH, HCl and the free acids of the UV absorbing probes. Investigations showed that reproducibility of migration times and peak areas can be significantly improved by acid pre-rinsing using the corresponding acid of the UV absorbing probes compared to preconditioning by flushing the capillary with buffer. In contrast to acid pre-rinsing using hydrochloric acid no interfering signals within the migration time window of inorganic anions under investigation can be observed. The optimized preconditioning procedure yields relative standard deviations of migration times less than 0.25% ( n=10). Relative standard deviations of corrected peak areas were below 5% applying acid preconditioning using pyromellitic acid.

Capillary electrophoretic determination of thiosulfate and its oxidation products

Capillary electrophoresis (CE) was developed for the rapid and simple determination of thiosulfate and its oxidation products such as common polythionates, sulfite and sulfate. Direct and indirect UV detection techniques were investigated. The optimized separations of UV absorbing S 2O 3 2−, S 4O 6 2−, S 5O 6 2− and S 6O 6 2− anions were carried out in 5 mmol l −1 (NH 4) 2SO 4, 5 mmol l −1 KH 2PO 4 electrolyte at pH 5.0, with direct UV detection at 214 nm. All analytes were well resolved in less than 4 min. Analysis of S 2O 3 2−, S 4O 6 2−, SO 4 2− and SO 3 2− ions can be performed in 5 mmol l −1 H 2CrO 4, 1 mmol l −1 hexamethonium hydroxide electrolyte neutralized with triethanolamine to pH 8.0, using indirect UV detection at 254 nm. However, the detection sensitivity for tetrathionate was poor. Other polythionates can not be detected at all because of their high absorbance even at 254 nm. The developed CE method was applied for the monitoring of sulfur species in spent fixing solutions during the electrolytic oxidation.

Capillary preconditioning for analysis of anions using indirect UV detection in capillary zone electrophoresis: Systematic investigation of alkaline and acid prerinsing techniques by designed experiments

It is widely accepted in capillary zone electrophoresis, that the use of alkaline prerinse procedures can improve the reproducibility of migration times and of corrected peak areas. In this study we present a systematic investigation of alkaline and acid preconditioning procedures for anion analysis using indirect UV detection by designed experiments according to the methodology of Taguchi. Four frequently used electroosmotic flow modifiers (diethylenetriamine, hexamethonium hydroxide, tetradecyltrimethylammonium hydroxide, and hexadimethrine hydroxide) were examined. The optimized procedures were evaluated with regard to the necessary preconditioning time compared to the analysis time. Furthermore, it was demonstrated that the optimized preconditioning technique could be applied to other indirect detection based CE systems. For all examined electrolyte systems, relative standard deviations below 0.5% for migration times and below 5% for corrected peak areas ( n=20) were achieved using automated peak integration without further manual reprocessing.

Capillary electrophoresis of longer-chain polyphosphates

Capillary electrophoretic separations of sodium polyphosphates with anion chain lengths from 1 to >30 are presented. A buffer containing pyromellitic acid, triethanolamine and hexamethonium hydroxide gives a high resolution separation of linear and cyclic polyphosphate species. Distinct separation patterns can be obtained in 20 min for glassy sodium phosphates with number-average chain lengths from 5 to 44. The preliminary electrophoretic separations presented here should be useful for the rapid characterization of complex polyphosphate mixtures.

Synthesis of titanium containing silica ZSM-48 (TS-48) using hexamethonium hydroxide as template

Titanium containing silica analog of ZSM-48 (TS-48) has been synthesized by a new method using hexamethonium hydroxide as a template. Titanium incorporation in the framework was evidenced from unit cell volume expansion, framework IR spectra and diffuse reflectance UV-Vis spectra.

Comparison of capillary zone electrophoresis with standard gravimetric analysis and ion chromatography for the determination of inorganic anions in detergent matrices

Low relative molecular mass inorganic anions (chloride, sulfate and nitrate) were determined on a capillary electrophoresis (CE) system (Dionex CES-1) employing a deuterium lamp for indirect detection at 254 nm. All of the anions were separated in conventional fused silica capillaries. The background electrolyte contained an ultraviolet absorbing ion, pyromellitate, and a cationic flow modifier, hexamethonium hydroxide, to reverse the electroosmotic flow in the capillary. Using this proposed method, complete resolution and quantification of three anions (Cl–, SO42– and NO3–) was achieved with calibration graphs for the individual components linear for up to 500 ppm of SO42– and 400 ppm of Cl– and NO3–, with correlation coefficients (r2) ranging from 0.994 to 0.997 and limits of detection for Cl–, NO3– at the sub-ppm level (two times the baseline noise). The upper operating range was limited to 50 ppm owing to loss of baseline resolution in higher concentrations of mixtures of analyte anions. The method was applied to the determination of sulfate in a range of different granular detergents. The instrumental and analytical precisions of the method were tested and calculated as: instrumental precision 1.5% RSD (relative standard deviation), analytical precision 1.7% RSD and an RSD of the migration times as 0.3%. The accuracy of this method was tested by comparison with standard gravimetric analysis and conventional ion chromatography. Statistical analysis of the results indicated that there was no evidence for systematic differences between the three methods. In addition, a number of potential advantages of CE are discussed.