Mary Meaney

Determination of pesticides in water using ATR-FTIR spectroscopy on PVC/chloroparaffin coatings

The objective of this study is to develop a novel in situ optical sensor for monitoring pesticides in water. The sensor consists of a polymer-coated attenuated total reflection (ATR) element or a silver halide optical fibre. The polymer film, which consists of PVC with a chloroparaffin plasticiser, acts to enrich the chlorinated pesticides and concentrates them within the penetration depth of the evanescent region of the ATR crystal or optical fibre. Measurements were performed by filling the sample cell with the aqueous pesticide solutions and recording a series of spectra over a period of time. Absorbance data were recorded for atrazine at 1577 cm-’ and alachlor at 1104cm-‘. Limits of detection in the region of 2 ppm have been achieved for atrazine and alachlor using a polymer-coated ATR element. Lower limits of detection can be achieved using polymer-coated optical fibres, especially with novel fibre configurations. These data establish the potential for this sensor for the use in pesticide analysis at alarm levels.

Determination of metal ions by capillary electrophoresis using on-column complexation with 4-(2-pyridylazo)resorcinol following trace enrichment by peak stacking

Co2+, Fe2+, Cu2+ and Zn2+ were separated and detected following derivatization with 4-(2-pyridylazo)resorcinol by capillary electrophoresis with UV-Vis detection. Parameters which were examined include both on-column and pre-column complexation, limit of detection, capillary loadability, linear dynamic range and reproducibility. A sample stacking technique was investigated in order to obtain better detection limits and greater sensitivity. Detection limits of 1 x 10(-8) M were achieved for Co2+, Fe2+ and Zn2+ and 4 x 10(-7) M for Cu2+. Mass detection limits were 0.2 fmol for Co2+, Fe2+ and Zn2+ and 7.0 fmol for Cu2+. The use of this method for the determination of metals in vitamin tablets and a pond water sample is presented.

Sensing of chlorinated hydrocarbons and pesticides in water using polymer coated mid-infrared optical fibres

An IR fibre optic sensor which operates in the 4–16 µm wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgClxBr1–x) optical fibre, coated with a polymer which both enriches the analyte in the evanescent wave region of the fibre and, when thick polymer coatings are used, minimizes water interference in the IR absorption. Using trichloroethylene and alachlor as representative pollutants, evanescent wave spectrometry in the mid-IR region is shown to provide good performance down to single ppm levels. Furthermore, it is shown that the technique can be applied to multi-analyte samples.

Determination of trace levels of copper(II), aluminium(III) and iron(III) by reversed-phase high-performance liquid chromatography using a novel on-line sample preconcentration technique

A column switching high-performance liquid chromatographic technique for the determination of copper(II), aluminium(III) and iron(III) as their 8-hydroxyquinolinate complexes using spectrophotometric detection at 400 nm is described. On-line preconcentration of the metal chelates was effected using a 10 × 1.5 mm i.d. pre-column packed with C18 reversed-phase sorbent. The pre-column was mounted before the analytical column; by manual actuation of a six-port switching valve it could be switched on-line. The metal chelates were resolved by reversed-phase high-performance liquid chromatography on the analytical column following elution from the pre-column with the appropriate mobile phase. A systematic approach to this type of trace enrichment is outlined, and the results show an increase in both sensitivity and selectivity over previous methods. The linear dynamic range is from 5 ppb to 10 ppm for AlIII and from 40 ppb to 5 ppm for both CuII and FeIII. Application of the technique to waste water from a mine and to beverage samples is reported.

Novel teflon-coated optical fibres for TCE determination using FTIR spectroscopy

The evaluation of a novel Teflon-coated fibre-optic chemical sensor for analysis of chlorinated hydrocarbons in water is described. The sensor which is based on evanescent wave absorption, consists of a Teflon-coated silver halide optical fibre. The Teflon coating is used to enrich the chlorinated hydrocarbon species within the penetration depth of the evanescent field of the fibre-optic sensor. The polymer-coated fibre was mounted in a glass cell containing inlet and outlet ports for the aqueous samples. Trichloroethylene (TCE) was used to calibrate the sensor and absorbance data were recorded at 938 cm- 1. The time constant for 90% saturation of the polymer with TCE was 3 min. The useful calibration range has a correlation coefficient of 0.9990 and relative standard deviation of 0.0002 in the range 5-50 ppm. A limit of detection of 1 ppm was achieved for TCE determination using the Teflon-coated optical fibre.

Development of a micro-electrochemical flow cell using carbon or gold fibres for voltammetric and amperometric analyses

The development of a micro-electrochemical flow cell using either carbon or gold fibre electrodes is described. The cell was tested using anodic and adsorptive stripping voltammetric determination of selenium(IV) and chromium(VI), respectively, and for the amperometric detection of salbutamol and hydroquinone after high-performance liquid chromatography. The cell is simple, easy to prepare and is compatible with many electroanalytical systems. The cost of the flow cell is considerably less than conventional electrochemical detectors equipped with glassy carbon macro-electrodes.

Midinfrared fiber sensor for the in situ detection of chlorinated hydrocarbons

An infrared fiber optic sensor has been developed for the in situ detection of chlorinated hydrocarbons and other pollutant species in water. The sensing element consists of a silver halide fiber, coated with an appropriate polymer. The polymer both enriches the chemical species to be measured in the evanescent wave region of the fiber and serves to exclude water from the measurement region. Evanescent wave spectrometry is then used to accurately quantify chemical species such as chlorinated hydrocarbons which have their strongest absorption bands above 10 micrometers . In order to increase the evanescent absorbance signal, and therefore the sensitivity of the sensor, a number of novel launch designs and fiber configurations has been examined. Results from a range of such configurations are presented and conclusions are drawn regarding optimum sensor design.

Determination of copper(II) and iron(III) in some anaerobic adhesive formulations using high-performance liquid chromatography

The determination of copper(II) and iron(III) in some anaerobic adhesive formulations has been investigated using reversed-phase high-performance liquid chromatography. A typical anaerobic adhesive formulation was first dissolved in dichloromethane before being extracted with 0.1 M HCl. After centrifugation, the aqueous layer was passed through a C18 Sep-Pak cartridge and the eluate mixed with 8-hydroxyquinoline (oxine) in order to form the corresponding CuII-and FeIII-oxine complexes. These complexes were then extracted into dichloromethane and the organic phase was passed through a silica Sep-Pak cartridge. After drying the cartridge, the complexes were eluted with methanol and injected on to a C18 reversed-phase column using a mobile phase of acetonitrile (made 1 × 10–2M in oxine) and 0.1 M acetate buffer, pH 6.0 (made 0.1 M in KNO3)(1 + 1). Detection of the metal complexes was achieved using a spectrophotometric detector operated at 400 nm. Limits of detection of the order of 100–250 p.p.b. of CuII and 250–600 p.p.b. of FeIII can typically be achieved.

Comparison of high-performance liquid chromatographic and atomic spectrometric methods for the determination of Fe(III) and Al(III) in soil and clay samples

Abstract A comparison has been made of high-performance liquid chromatographic and atomic absorption spectrometric methods for the determination of Fe(III) and Al(III) in soil and clay samples, following five different digestion/extraction schemes. Good correlations were obtained in the case of Fe(III) determinations in both matrices, but correlation was only achieved for Al(III) determinations following an hydrochloric acid digestion and a dithionite-citrate-bicarbonate extraction of the clay sample. Attempts have been made to explain the differences in results between the two methods in terms of the Al(III) species which are likely to be present following extraction. Confirmatory evidence to support some of the conclusions made with respect to the speciation of these metal ions in these matrices has been obtained using X-ray diffraction studies.

Application of Modified Electrodes for Analysis in Flowing Solutions

Analysis in flowing solutions, as performed in particular with high performance liquid chromatography (HPLC) and flow injection analysis, (FIA) has developed rapidly over the last decade and now plays an important function in most analytical laboratories throughout the world. There is little doubt, however, that even HPLC lacks the resolving power required to solve analytical problems in complex matrices with minimal sample preparation. Often, the resolving power of the detection method is called upon to assist in the solution of these problems. This is particularly true with electrochemical detection (ED) systems which offer a certain degree of selectivity based on differences in oxidation or reduction potentials of the species to be determined.1 In recent years, the advent of chemically modified electrodes (CMEs) has provided a stimulus to further improve both the sensitivity and selectivity of ED systems used in HPLC and FIA.