Terence J. Cardwell

Nafion-based optode for the detection of metal ions in flow analysis

Abstract An optical chemical sensor (optode) is described in which the colorimetric reagent 1-(2′-pyridylazo)-2-naphthol (PAN) is immobilized in a Nafion® membrane. The membrane, which is homogeneous, transparent and mechanically strong, changes color rapidly in the presence of one of several metal ions (Ni(II), Cd(II), Cu(II), Pb(II), Hg(II), Zn(II)), and the color change can readily be reversed by contact with acid. This optode has been incorporated into a modified sequential injection flow system which has been optimized for the determination of Ni(II) in the concentration range 0.02 to 0.12 mM. The advantages of the use of sequential injection with optode membranes are emphasized and the factors which are important in the discrimination between metal ions are discussed.

Spectrophotometric determination of dissolved organic phosphorus in natural waters using in-line photo-oxidation and flow injection

A rapid in-line photochemical digestion for use with flow injection (Fl) to determine the dissolved organic phosphorus (DOP) in natural waters is described. The Fl system includes a simple ultraviolet (UV) photoreactor and uses the tin(II) chloride reduction of phosphomolybdate for the spectrophotometric determination of the dissolved reactive phosphorus (DRP) produced by the photo-oxidation. Samples in the range 0.1–4 and < 0.1 mg l–1 of P can be analysed at rates of 72 and 50 samples h–1, respectively. The effective detection limit of the technique was 0.01 mg l–1. Comparison of the results for DOP obtained using the proposed method were in good agreement with those obtained using standard methods. The DRP could also be determined using the same Fl manifold but without UV irradiation.

Determination of total phenols in waters and wastewaters using flow injection with electrochemical detection; an alternative to the standard colorimetric procedure

Abstract A new flow injection (FI) method using a dual electrochemical detector is described for the analysis of total phenols in water and wastewater samples. The method relies upon in-line oxidative electrochemical removal or elimination of interferences at an upstream large surface area (coulometric) electrode combined with oxidative detection of all phenols at an amperometric electrode. Using the ESA dual electrode high sensitivity cell and a phosphate buffer carrier stream (pH 6.8), the ideal potentials were found to be +0.35 V for the coulometric electrode and +0.78 V for the sensing amperometric electrode. The method is fast, with sampling frequencies around 60 h −1 and precision is typically 0.1–4%. Several synthetic aqueous samples were analysed by the FI and colorimetric methods and compared with results obtained using reversed-phase liquid chromatography (LC). More reliable data were obtained for samples containing para -substituted phenols and nitrophenols with plots of FI vs. LC data resulting in correlation coefficients of r 2 = 0.71 and r 2 = 0.79, respectively, whereas the standard colorimetric method vs. LC data gave correlation coefficients of r 2 = 0.29 and r 2 = 0.04, respectively. The method was applied to the analysis of five industrial wastewaters.

Determination of Ammonia in Waste Waters by a Differential pHMethod Using Flow Injection Potentiometry and a Nonactin-BasedSensor

A method is described for the determination of total ammoniacal nitrogen in waters using an ammonium ion-selective sensor based on nonactin. The flow injection method relies on the measurement of the potential of the sensor at two pH values, 6.0 and 9.4, and the use of a mathematical expression to calculate the total ammoniacal nitrogen concentration. The method also compensates for the interference from moderate concentrations of other cations such as potassium and sodium.

Flow-injection technique for the determination of low levels of phosphorus in natural waters.

Abstract An inexpensive flow-injection instrument for determining low concentrations of dissolved reactive phosphorus in natural waters is reported. The unique feature is the use of an inexpensive detector consisting of a flow cell and a simple photometer that incorporates a super-bright light-emitting diode as the source and a photodiode as the detector. The tin(II) chloride-molybdate method was optimized using a modified simplex optimization method. Silicate interference up to 5 mg Si l−1 was removed by addition of 0.10% (w/v) tartaric acid. Using the tartaric acid-modified optimized reagents, a detection limit of 0.6 μg P l−1 was achieved. The method was linear over the range 0–100 μg P l−1 with an excellent precision (r.s.d. 2.9% at 2.0 and 0.5% at 50 μg P l−1). An in-line pre-concentration anion-exchange column was used to obtain an even lower detection limit of 0.1 μg P l−1 and applied to the analysis of real samples.

A multi-ion sensor cell and data-acquisition system for flow injection analysis

Abstract The flow-injection system described is used for the determination of four ions simultaneously with detection by solid-contact polymer-membrane ion-selective electrodes. The construction of the flow cell and data-acquisition system are discussed. The programming language FORTH facilitates the fast data acquisition required for flow injection analysis. The utility of the system is demonstrated by applying it to the simultaneous determination of potassium, calcium, nitrated and chloride in soil extracts; the results are compared with standard procedures.

Photo-cured polymers in ion-selective electrode membranes : Part 3. A Potassium Electrode for Flow Injection Analysis

Abstract The preparation of a calcium-selective electrode based on a photo-cured polymer membrane containing a neutral carrier is described. This electrode is suitable for use in flow injection analysis because of its fast initial response and the harness and mechanical strength of the membrane.

Pervaporation-flow injection with chemiluminescence detection for determination of iodide in multivitamin tablets

This paper describes the use of a pervaporation (PV) technique in a flow injection (FI) system for selective improvement in iodide analysis. Iodide in the sample zone is oxidized to iodine, which permeates through a hydrophobic membrane. Detection of the diffused iodine is achieved using the chemiluminescent (CL) emission at 425nm that results from the reaction between iodine and luminol. The method was applied for the analysis of some pharmaceutical products, such as nuclear emergency tablets and multivitamin tablets. Ascorbic acid present in multivitamin samples interfered seriously with the analysis, and off-line sample treatment using anion exchange resin was employed to successfully remove ascorbic acid before the analysis. Ascorbic acid was flushed from the column using 0.4M sodium nitrate followed by elution of iodide with 2M sodium nitrate. The detection limit (3S.D.) of the system was 0.5mgl(-1), with reproducibility of 5.2% R.S.D. at 5mgl(-1). Sample throughput was determined as 30injectionsh(-1). There was good agreement between iodide concentrations from extracted samples determined using four different methods, i.e., PV-FI, gas diffusion-flow injection, potentiometry and ICP-MS. A comparison of the analytical features of the developed pervaporation system with these of the previously reported chemiluminescence gas diffusion-flow injection previously reported is also described.

Versatile manifold for the simultaneous determination of ions in flow injection analysis

A flow injection analysis system is described for the simultaneous determination of several ions in a single sample using a combination of potentiometric and spectrophotometric detection. A composite manifold has been designed consisting of a flow cell containing four ion-selective electrodes and two spectrophotometric transducer flow cells. The system has been applied to the determination of K+, Ca2+, NH4+, Cl–, NO3– and PO43– ions in a number of plant nutrient solutions.

Use of immobilized 3-phytase and flow injection for the determination of phosphorus species in natural waters

A proportion of dissolved organic phosphorus (DOP) compounds found in natural waters may be utilized by algae and bacteria through hydrolysis by extracellular phosphomonoesterases such as alkaline phosphatase. The fraction of DOP remaining unhydrolysed may consist of organic phosphorus species such as myo-inositol hexakisphosphate (phytic acid), and comprise part of the pool of biologically unavailable or even refractory DOP. Of this bio-unavailable DOP fraction, a major portion is amenable to hydrolysis by 3-phytase, a phosphohydrolytic enzyme which is not found widely in aquatic systems. This paper describes the development and application of a flow injection system which utilises immobilized 3-phytase for the determination of phytase hydrolysable phosphorus (PHP) present in natural waters. The product of enzymatic hydrolysis is orthophosphate, and a conventional phosphomolybdenum blue detection method was used. The use of a suitable flow injection manifold and a multiple linear regression calibration procedure for quasi-simultaneous determination of phytase-hydrolysable and dissolved reactive phosphorus (DRP) coexisting in natural waters is outlined. The proposed technique is rapid (ca. 40 injections h−1), sensitive and reproducible, and the immobilized phytase exhibited good operational and storage stability over a period of several months.