Peter D. Carpenter

Enantiomeric separation of propranolol and selected metabolites by using capillary electrophoresis with hydroxypropyl-β-cyclodextrin as chiral selector

A capillary electrophoresis (CE) investigation of the enantiomeric separation of propranolol and some of its metabolites using CE was undertaken. Resolution of the enantiomers was achieved using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral selector. Parameters found to influence separation include cyclodextrin concentration, potential, pH and organic solvent/additive. It was observed that 17 mM HP-beta-CD gave optimum separation over the concentration range used in this study, however different racemates appear to have best resolution at different CD concentration. The potential does not have a great effect on enantiomer resolution, but appears to cause relative metabolite migration times to alter such that separation is affected. Carrier pH affects both migration time, and enantiomer resolution and metabolite separation. Above pH 5 inferior results are obtained. This is the first report of enantiomeric resolution of propranolol metabolites using CE.

Speciation of dissolved iodine in the waters of a humic-rich estuary

Abstract This paper reports the findings of a study into iodine speciation in the humic-rich waters of the Huon Estuary, Tasmania, Australia. Water samples were taken from the estuary at various locations during both summer and winter. The samples were analysed for a range of parameters including iodate, iodide, total iodine, nutrients, chlorophyll a , dissolved organic carbon (DOC) and salinity. Total iodine behaved conservatively within the estuary irrespective of season. Iodate concentrations varied linearly with salinity but became undetectable in the low salinity end of the estuary. Iodide concentrations showed no correlation with salinity, but showed a positive correlation with total dissolved phosphorus during summer suggesting iodide concentrations within the estuary are controlled by biological activity during, or immediately after, periods of high productivity. “Organic” iodine is produced within the estuary and the fraction of iodine present in this form increases in the low salinity waters where DOC concentrations are highest.

Detection of s-triazine pesticides in natural waters by modified large-volume direct injection HPLC

There is a need for simple and inexpensive methods to quantify potentially harmful persistent pesticides often found in our water-ways and water distribution systems. This paper presents a simple, relatively inexpensive method for the detection of a group of commonly used pesticides (atrazine, simazine and hexazinone) in natural waters using large-volume direct injection high performance liquid chromatography (HPLC) utilizing a monolithic column and a single wavelength ultraviolet-visible light (UV-vis) detector. The best results for this system were obtained with a mobile phase made up of acetonitrile and water in a 30:70 ratio, a flow rate of 2.0 mL min(-1), and a detector wavelength of 230 nm. Using this method, we achieved retention times of less than three minutes, and detection limits of 5.7 microg L(-1) for atrazine, 4.7 microg L(-1) for simazine and 4.0 microg L(-1) for hexazinone. The performance of this method was validated with an inter-laboratory trial against a National Association of Testing Authorities (NATA) accredited liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method commonly used in commercial laboratories.

Application of pentafluorophenyldimethylsilyl derivatization for gas chromatography-electron-capture detection of supercritically extracted sterols

We report a convenient method of extracting and detecting sterols in environmental water samples. Particle-associated sterols were extracted onto glass-fibre filters then the filters were supercritical fluid extracted (at 33 MPa, 80°C for 30 min) followed by pentafluorophenyldimethylsilyl (flophemesyl) derivatization for gas chromatographic–electron-capture detection (GC–ECD). Optimal derivatization of epicoprostanol, coprostanol, cholesterol, dihydrocholesterol, stigmasterol, β-sitosterol and stigmastanol with neat flophemesyl chloride was achieved under mild conditions (i.e., room temperature, 15 min) without the need for added solvent. These sterols gave linear GC–ECD calibrations (r2≥0.99) while detection limits in the final solutions were 0.1–0.6 μg/ml. Overall recoveries for the supercritical extraction and derivatization steps were 80–110% (mean 92%). The procedure was applied to raw sewage and to river water samples and 0–55%-higher results were obtained over those achieved by modified Bligh and Dyer extraction. Flophemesyl derivatization of sterols allows selective ECD, improved separation from other compounds such as polychlorinatedbiphenyls that may be found in environmental samples, and reduced clean-up requirements (e.g., removing lipids by saponification which may be needed when flame ionization detection is used). Characteristic mass spectra of the flophemesyl derivatives are reported; these were obtained in order to distinguish between sterol classes and individual sterols.

Aggregation of iron colloids in estuaries : a heterogeneous kinetics study using continuous mixing of river and sea waters

The kinetics of iron colloid aggregation in estuaries have been simulated with a model estuary in which seawater is continuously pumped into a reservoir initially containing river water. Profiles of colloidal Fe concentration versus salinity produced in this apparatus closely resembled field data for actual estuaries. Synthetic Fe colloids prepared by peptising Fe(OH)3 with humic acid and phosphate showed very similar kinetic behaviour. Aggregation rate was found to be almost independent of velocity shear rate, implying that most aggregations are induced by brownian interparticle collisions. A heterogeneous kinetic model is proposed to explain the kinetic behaviour of Fe colloids during seawater-induced aggregation. This model describes kinetic behaviour in terms of a log-normal distribution of rate constants characterised by a mean value 〈k〉 and a standard deviation γ. Experiments showed that 〈k〉 is linearly related to the rate constant for salinity increase during mixing. This coupling of salinity changes and aggregation rate leads to Fe-salinity profiles that are nearly independent of the rate of salinity change, but which are dependent on γ.

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.

Supercritical fluid extraction and gas chromatographic electron capture detection method for sterol analysis of environmental water samples

A standard additions technique was carried out by spiking standard sterol mixtures onto environmental water filtering glass fibre filters, which were then extracted by supercritical fluid extraction, derivatized into their pentafluorophenyldimethylsilyl ethers and analyzed by gas chromatography using electron capture detection. Calibration curves obtained from directly derivatized sterol standards, and also sterol standards spiked both onto blank filters and filters used to filter environmental water, were all r2 > 0.99 linearity. Spiked sterol recoveries ranged from 80 to 120% with good precision, allowing application of the method to the determination of sterol levels in environmental water samples. For a sample size of 0.5 l, the limit of detection of coprostanol was estimated to be 200 ng l–1. Water from the Prahran main drain outfall in Melbourne was analyzed and the coprostanol concentration was found to be about 400 ng l–1, which exceeds the equivalent primary contact limit (60 ng l–1) for this sterol in recreational waters in Australia.

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%.