Radiometric flow injection analysis with an ASIA (Ismatec) analyzer

Radiometric Flow Injection Analysis of a radioactive (¹³¹I) sample is described. For analysis an ASIA (Ismatec) analyzer with a NaI (Tl) scintillation detector was used.     

Radiometric determination of sulfate

A radiometric procedure for the determination of sulfate based upon the precipitation of barium sulfate is described with a sensitivity of about 0.01 μg/ml. Carrier-free³⁵SO₄ is added to the sample to measure the chemical recovery. The sulfate is precipitated with an excess of barium having a known specific activity of¹³³Ba. The amount of¹³³Ba determined by gamma counting is directly related by stoichiometry to the amount of sulfate in the precipitate.     

Low pressure ion chromatography with a low cost paired emitter-detector diode based detector for the determination of alkaline earth metals in water samples

The use of a low pressure ion chromatograph based upon short (25 mm × 4.6 mm) surfactant coated monolithic columns and a low cost paired emitter-detector diode (PEDD) based detector, for the determination of alkaline earth metals in aqueous matrices is presented. The system was applied to the separation of magnesium, calcium, strontium and barium in less than 7 min using a 0.15 M KCl mobile phase at pH 3, with post-column reaction detection at 570 nm using o-cresolphthalein complexone. A comparison of the performance of the PEDD detector with a standard laboratory absorbance detector is shown, with limits of detection for magnesium and calcium using the low cost PEDD detector equal to 0.16 and 0.23 mg L⁻¹, respectively. Finally, the developed system was used for the determination of calcium and magnesium in a commercial spring water sample.     

Studies on some experimental parameters of radiometric flow injection analysis (RFIA) using137Cs and60Co

A simple radiometric flow injection analyzer with NaI(Tl) detector was used for the study of some experimental parameters of¹³⁷Cs and⁶⁰Co determination. A sample transfer system was developed employing both merging zone and sample injection principle.     

Development of a selective post-column detector for phenols separated by high-performance liquid chromatography

An on-line post-column reactor based on air-segmented continuous flow is described for the determination of phenols. The reaction used is the coupling of diazotized sulfanilic acid with phenols to form highly colored azo dyes. The effect of experimental parameters on the detector response was inveestigated by both univariate and simplex approaches in order to establish optimum reaction conditions. The aqueous reaction system is compatible with common reverse-phase solvents. The detection limit for phneol with the derivatization detector (71 μg 1^?1 shows a 16-fold improvement over u.v. detection of the underivatized phenol. Imprecision, based on multiple injections of sample into the HPLC system and measurement of the peak heights, is ± 0.64% (RSD). The technique is applied to the determination of phenols added to river water and present in residual fuel oil samples.     

Comparison of Glassy Carbon and Copper Microparticles as a Renewable Working Electrode Material for Amperometric Determination of Amino Acids Using Flow Through Detector

Flow‐through detector with renewable working material based on glassy carbon or copper microparticles was used for flow injection determination of tyrosine by direct oxidation and phenylalanine via the complexation reaction with copper ions, respectively. Copper‐based detector allows the determination of electrochemically inactive amino acid, but the detection conditions are limited and fabrication and handling of the detector are more demanding. Low working potential, applied for the detection on copper microparticles, makes the determination very selective. Moreover, low baseline noise compensates lower sensitivity of copper‐based detector, enabling to reach quantification limit 4.7×10^?6 mol L^?1, in comparison with quantification limit 1.6×10^?6 mol L^?1 obtained for tyrosine on carbon‐based detector.     

Natural and fallout radionuclide concentrations in the environment of Islamabad

A study on the concentration of natural and fallout radionuclides in environmental samples collected from different localities of Islamabad was performed. For the determination of gamma-emitters such as ²³⁸U, ²³²Th, ⁴⁰K and ¹³⁷Cs high purity germanium (HPGe) detector was used while for the analysis of ⁹⁰Sr, a beta-emitter, liquid scintillation counting system was used. The indoor absorbed dose rate was measured by a CaF₂ : Dy thermoluminescence detector. Other radiation parameters were also determined to evaluate the radiation hazard. All the results were well within the permissible limits showing that there is no radiation hazard in the environment of Islamabad.     

Simple, stable and sensitive electrogenerated chemiluminescence detector for high-performance liquid chromatography and its application in direct determination of multiple fluoroquinolone residues in milk

A simple, stable and sensitive electrogenerated chemiluminescence (ECL) detector was developed. It was based on tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) immobilized on the surface of a Pt wire with Nepem-105D ion exchange solution. The detector was prepared by inserting a Pt wire with immobilized Ru(bpy)₃²⁺ (working electrode) into a capillary tube, followed by inserting another Pt wire (counter electrode) in this tube and sealing. ECL behavior was investigated using ofloxacin as an analyte. Under optimal conditions, stable ECL intensity was obtained. This detector has been used in HPLC-ECL for the determination of multiple target fluoroquinolone residues in milk. There is no post column reagent addition, which would dilute the analytes, potentially leading to chromatographic band-broadening. The system is very simple with low dead volume, low baseline and background noise, together with high sensitivity and stability. The as-prepared ECL detector, when was used for the determination of ofloxacin, pefloxacin, enrofloxacin and difloxacin in milk, demonstrated adequate sensitivity to allow quantification of trace FQ levels in commercial milk samples. One or more of the target FQ analytes were present at levels above the LOD of the new ECL detector in each and every one of the 22 milk samples analysed.     

Indirect determination of iron in a flow-injection system with amperometric detection

The change in peak current resulting from the reaction of Fe(II) with nitroso-R salt in a flow-injection system is used to quantify Fe(II) with either single- or dual-electrode amperometric detectors. The current change varies linearly with Fe(II) concentration from 0 to 200 mg 1^?1. The relative standard deviation was about 5% with the single-electrode detector and about 10% with the dual-electrode detector. The method is evaluated for the determination of iron in dietary supplements.     

Monitoring inorganic mercury and methylmercury species with liquid chromatography-piezoelectric detection

A piezoelectric detection system coupled with a liquid chromatographic system is developed for the speciation of inorganic mercury(II) and methylmercury. Piezoelectric detection has been demonstrated to be a very sensitive detection system for total mercury determination when a gold-coated piezoelectric quartz crystal was used. The analytical features of this detection unit make it very suitable to be used as a detector coupled with a liquid chromatographic system for monitoring mercury species. After separation by a chromatography column (Spherisorb ODS-2, 5 μm,  mm i.d.), mercury species are liberated and reduced, by using stannous chloride, and are detected as an amalgam on the gold-coated piezoelectric quartz crystal, the sensor subsequently was regenerated by passing a peroxydisulfate solution. This detector exhibits good sensitivity, it allows the determination of mercury at sub-ppb concentration levels (0.30-1.20 μg l⁻¹). The precision, expressed as relative standard deviation, was ±2.7% (n=11) for a 0.5 μg l⁻¹ total mercury concentration. The proposed method is free of interferences and it allowed the determination of inorganic mercury and methylmercury species in natural waters.     

Immobilized enzymes in clinical and biochemical analysis : Applications to the Simultaneous Determination of Acetylcholine and Choline and to Determination of Lipids

Uses of immobilized enzyme mini-columns in flow-injection systems are described Simultaneous determination of ? × 10^?5 M choline and acetylcholine is achieved by using acetylcholinesterase and choline oxidase columns. A home-made amperometric detector is used to detec the hydrogen peroxide produced enzymatically. An ion-exchange column is used on-line to remove interferences at the amperometric detector during analysis of blood and brain samples. Immobilization of the lipid enzymes phospholipase-C and -D is described. These enzymes are used for the determination of phospholipids. Total phospholipids (1– mM) are determined with a combination of phospholipase-D, lipase and glycerol-3-phosphate oxidase. All the methods described are simple and reproducible and the immobilized enzymes show good stability.     

Gas-chromatographic determination of the impurity composition of permanent gases,methane, carbon monooxide,and carbon dioxide in high-purity monogermane

A procedure is developed for the gas-chromatographic determination of trace impurities of permanent gases (H₂, O₂/Ar, N₂), methane, and carbon mono- and dioxide in high-purity monogermane using a helium discharge detector and a heat-conductivity detector. The procedure is based on the principle of two-dimensional gas chromatography with a flowing injection system and allows the determination of the specified impurities in the concentration range from 2 × 10⁻⁵ to 10 vol %. The procedure is tested in the analysis of monogermane obtained by an electrochemical method.     

Determination of Fe and Zn in healing plants by radionuclide X-ray fluorescence analysis

Radionuclide X-ray fluorescence method was used for the determination of Fe and Zn in healing plants (Sage, Peppermint, Stinging, Common Agrimony, Milfoil, Ribwort, Tansy, White Dead-Nettle).²³⁸Pu exciting source and Si/Li semiconductor detector were used for the determination.     

A simple method for self-attenuation correction in <Superscript>210</Superscript>Pb activity measurement in a well-type HPGe detector

A simple method for ²¹⁰Pb determination in a well-type detector for matrix with apparent densities ranging from ρ = 0.430 g cm^?3 to ρ = 2.037 g cm^?3 is presented. Ten spiked samples of ²¹⁰Pb were prepared to obtain the detector efficiency as a quadratic function of the matrix density. Then this equation was validated and successfully used to measure ²¹⁰Pb concentration activity in other samples. The equation proposed in this work is specific for each germanium detector; however it is proposed an extrapolation of the method to other well-type germanium detector by preparing a spiked sample and determining the efficiency for ²¹⁰Pb.     

Evaluation of an alternative convenient irradiation system for determination of emission rate of radio-isotopic neutron sources

In present work, an alternative irradiation system based on a symmetric cylindrical tank filled with a moderator containing hydrogen, which was equipped with a NaI(Tl) scintillation detector, was proposed for using in determination of neutron flux. This irradiation system was designed by MCNP4C code, with considering a ²⁴¹Am–Be neutron source in several volumes and different materials. When the neutron is captured by hydrogen, a 2.22 MeV prompt gamma-ray is emitted. The gamma pulse-height spectrum shows a photo-peak around 2.22 MeV whose net area is proportional to the total emission rate of neutron. The simulation result showed that a cylindrical tank with 110 cm diameter and height filled with water can be a suitable system for neutron source strength calibration. Furthermore, a proper two-layer shielding must be placed between the source and detector for preventing neutrons and gamma rays to directly enter the detector.     

Determination of purine bases by means of chromato-voltammetry

A detector working on the voltammetric principle was used for the liquid chromatographic analysis of purine bases.A new type of detector cell has been developed and its characteristic parameters were investigated. A linear correlation between the voltammetric sign and the concentration of the solution being analysed was obtained. The standard deviation was found to be 3% for 10 measurements. The lower limit of the determination was 10⁻¹⁰ mole for guanine.The cell was employed as a specific detector cell for purine bases.     

Determination of the pesticides fenthion and fenitrothion by flow injection with amperometric detection

The response of a glassy carbon amperometric detector in a flow system was studied. The values of the hydrodynamic variables were optimized. The detector functioned as a “thin-layer” cell. Methods are proposed for the determination of 1.6 × 10^?7?1.6 × 10^?5 Fenthion and 8 × 10^?6? 8× 10^?5 M Fenitrothion in a methanolic acetate-buffered carrier stream. The detection limits were 0.15 and 0.52 μM, respectively.     

A computer-controlled voltammetric flow-injection system

Voltammetric measurements are done with a laboratory-made digital voltameter; the detector is a thin-layer cell ith a glassy carbon working electrode. Three e-way and one 8-way magnetic valves are used to switch the flows to the detector. the 8-way valve can also be used as the injection valve. An ABC-80 computer controls the system, with a single-chip microcomputer as slave to control the voltammeter. The system was tested in continuous monitoring and in flow-injection determination of iodide. An authomatic stripping voltammetric method for the determination of chloride is also described.     

The use of an activation detector in the determination of beryllium by photon activation

The determination of traces of beryllium in large samples by the (γ, n) reaction, using a¹²⁴Sb gamma-source, is in general hampered by the rather high handling costs when a BF₃ counter is used for the neutron detection. When manganese dioxide is used as an activation detector, the analysis is possible with a simple facility which can be stored in a water basin. The lower limit of the determination is ∼ 1 μg/g for a sample weight of 50 g.