Malcolm J. McCormick

Spectroscopic analysis of heterogeneous photocatalysis products of nonylphenol- and primary alcohol ethoxylate nonionic surfactants

Nonylphenol ethoxylate (NPE) and primary alcohol ethoxylate (PAE(9-6)) were degraded using heterogeneous photocatalysis. An aqueous surfactant solution (2L, 2000 mg/L) containing TiO2 catalyst (0.1 % w/v) was irradiated with a 400W Blacklight lamp. Analyses of the starting material and degradation intermediates were performed using gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), electrospray mass spectrometry (ESMS) and nuclear magnetic resonance spectroscopy (NMR). Identified intermediates suggested that the ethylene oxide chain was more susceptible to degradation than aliphatic or aromatic moieties. Competitive degradation was also observed. NPE was degraded more rapidly than PAE(9-6).

Crystal and molecular structure of bis-µ-(bisdiphenylphosphinomethane)-dibromodipalladium(Pd–Pd), a compound containing palladium(I)

The crystal structure of [Pd(dppm)Br]2(dppm = Ph2PCH2PPh2) shows that the palladium(I) atoms are directly metal–metal bonded and adopt an idealised square-planar stereochemistry.

X-Ray crystal and molecular structure of µ-carbonylbis-µ-(bisdiphenylarsinomethane)-dichlorodipalladium(I); a binuclear compound of palladium(I) without a Pd–Pd bond

The crystal structure of [Pd(dam)Cl]2CO (dam = Ph2AsCH2AsPh2) shows that the palladium atoms are not directly bonded or halogen bridged but that they are spin-paired via an unusual bridging carbonyl group.

Photocatalytic degradation of secondary alcohol ethoxylate: spectroscopic, chromatographic, and mass spectrometric studies.

Secondary alcohol ethoxylate (SAE) was photocatalytically degraded using a suspension of TiO 2 particles irradiated with long wavelength ultraviolet light. High starting concentrations of SAE were used (ca. 2000 mg/L), and changes in both SAE oligomer distribution and production of intermediates were monitored by using GC, GC/MS, NMR, and ESMS. Initial preferential cleavage of the ethoxyl groups over H0 . reactions with the aliphatic portions of the molecule is followed by cleavage at the secondary carbon. Relatively hydrophilic intermediates remained in solution, while the hydrophobic products adhered to the TiO 2 , causing agglomeration of the particles.

A quartz crystal microbalance study of the removal of solid organic soils from a hard surface in aqueous surfactant solution

Abstract A quartz crystal microbalance (QCM) has been employed to monitor the removal of two model solid organic soils, dotriacontane and tripalmitin, from the hard surface of the QCM crystal in aqueous surfactant solutions of octa-ethyleneglycol mono n -dodecyl ether (C 12 E 8 ). We have investigated the effect of varying the thickness of the soil coating on soil removal and the effect of soaking the soil in high-purity water for an extended period of time before adding surfactant. The QCM results support the view that net soil removal is preceded by a stage of water and surfactant penetration into the soil. The rate of penetration and rate of removal depends on the soil type. Water and surfactant take longer to penetrate dotriacontane compared to tripalmitin coatings. The removal process also occurs over a longer period of time in the case of dotriacontane coatings. The percentage of material removed is less for dotriacontane, compared to tripalmitin coatings. The initial coating thickness on the hard surface does not appear to govern the final percentage of soil removed, at least in the thickness range accessible to the QCM (approximately ≤800 nm). Immersing the soil coated surfaces in water for a relatively long time, hastens the onset of the removal stage after surfactant is added but does not significantly influence the rate and extent of removal from the hard surface.

Enhanced conductometric detection of cyanide in suppressed ion chromatography.

Weak-acid anions such as borate and cyanide, present problems in chemically suppressed ion chromatography, since the acids are weakly ionised, giving low conductivity and therefore decreased sensitivity. For borate this problem was overcome by converting the weak acid to its sodium salt, by the use of a second anion micromembrane suppressor (AMMS) as an ion exchange reactor (IER), flushed by EDTA reagent, to supply sodium ions for the conversion. This paper will discuss the use of this IER system to determine cyanide, which is also a very weak acid, with a similar pKa to borate. The detection limit for cyanide of 50 microM compare favourably with indirect conductivity detection.

Conductometric detection of anions of weak acids in chemically suppressed ion chromatography: critical point concentrations.

Previously we demonstrated that the conductometric determination of anions of weak acids in chemically suppressed ion chromatography could be enhanced, by conversion of the acid to a conjugate salt, if the anion was present above what we termed the critical point concentration (CPC). In this paper we have developed a simple theoretical model for the calculation of CPCs for weak acid/conjugate salt pairs. The CPC was found to be dependent on the acid ionization constant K(a) and the molar ionic conductivities (MICs) of the ions present. For monovalent anions with a MIC in the common range 25-75 S cm(2) mol(-)(1), with sodium or potassium as cations, the CPCs could be estimated from the expression pC ≈ pK(a) - 1, where pC = -log CPC. For formate, benzoate, and acetate, excellent agreement was found between the calculated and experimental CPCs, with a mean deviation of 0.05 mM. For fluoride, the calculated and experimental CPCs were 7.4 and 9.2 mM, respectively. Experimental CPCs could not be determined for other anions as their calculated CPCs were below the detection limits of the IC system. The simple theoretical model could also be used to estimate the expected conductivity enhancement for the conversion of weak acid to a particular conjugate salt. The effects of detector linearity and dispersion in the IC system on the use of CPCs are also discussed.

Enhancement of conductometric detection of weak acids in ion chromatography.

Anions of weak acids can represent a problem when determined via chemically suppressed ion chromatography as the acids can be weakly ionised, giving low conductivity and hence low sensitivity. Previous work showed that converting some weak acids back to their sodium salts, using a second micromembrane suppressor, greatly enhanced conductivity and thus sensitivity. This paper will discuss further work in optimising the conversion for boric acid by using sodium salts of EDTA and the mechanisms involved.

Silica and polyimide coated quartz crystal resonators for analysis of liquids

Abstract Silica and polyimide coatings were successfully applied to both sides of 10 MHz AT-cut quartz crystal resonators with silver and gold electrodes. A similar oscillation was observed for the uncoated and coated resonators in air, deionised water, 0.1 M NaCl and propylene glycol, in terms of the complex impedance analysis. The impedance module decreased with increasing conductance of the surrounding media while the resonant frequency appeared to depend on the liquid viscosity and density. However, differences in the oscillation were evident when these devices were immersed in waste water from a clean room for microelectronic fabrication. Relevant chemical analyses were also made on the waste water samples. Hourly testing results indicated that changes in the impedance were due to metal ions (Na+, K+, Ca2+, etc.) and the frequency shift comes from the complicated interaction between the solute molecules (propylene glycol) and the coatings or electrodes. This study highlights that the multi-sensors with various coatings and electrodes provide possibilities to monitor waste water in real-time.

Determination of Trace Levels of Diazinon and Propetamphos in Water and Sewage by Solid Phase Extraction

Abstract An analytical method is described for the determination of the organophosphorus pesticides diazinon and propetamphos in water and in sewage, at levels ranging from 0.01–1.0 mg/L. The method involves solid phase extraction using C-18 Bond Elut cartridges, elution with ether, and solvent change to hexane. Quantification of the pesticide is by temperature programmed capillary gas chromatography using a nitrogen-phosphorus detector. Recoveries of diazinon are between 98–102% from water and between 70–80% from activated sludge biomass. These results are compared with a more polar organophosphate, propetamphos, for which the recovery from both water and biomass is close to 100%.