Determination of palladium in synthetic nuclear wastes by differential pulse voltammetry

A novel method for the determination of palladium in synthetic nuclear waste samples has been developed using a computerized voltammetric analyzer. The electrode system consists of hanging mercury drop electrode (HMDE)/glassy carbon/Ag-AgCl electrode. Various experimental conditions including electrolyte type, pH and concentration have been optimized, leading to a detection limit of 40 ng/ml. The mixture of 4^.10^-3M citric acid + 2^.10^-2M ammonia-ammonium chloride buffer + 4^.10^-3M EDTA was used as a supporting electrolyte at pH 9.0. Standard addition method was employed to determine the concentration of palladium present in the nuclear waste sample. The relative standard deviation of the proposed method was found to be 8% at 40 ng/ml of palladium content. The method is direct, simple, rapid and free from any possible interference.     

Flow-injection determination of paraoxon by inhibition of immobilized acetylcholinesterase

Two flow-injection methods (continuous-flow and stopped-flow) are proposed for the determination of paraoxon, applying the dual-injection technique and spectrophotometric detection. They are based on the inhibition of the acetylcholinesterase-catalysed hydrolysis of α-naphthyl acetate and subsequent reaction of the α-naphthol produced with p-nitrobenzenediazonium fluoroborate. For the continuous-flow system the calibration graph was linear from 5 × 10^?7 to 1.5 × 10^?5 M, the relative standard deviation (r.s.d.) (n=6) for an 8 × 10^?6 M standard was 1.4%, the limit of detection (3σ) was 4 × 10^?7 M and the sample throughput was ca. 60 h^?1. For the stopped-flow system the linear range was from 1 × 10^?8 to 4 × 10^?7 M, the r.s.d. for a 2.5 × 10^?7 M standard was 0.9%, the limit of detection was 8 × 10^?9 M and the sample throughput was 30 h^?1.     

A Sensitive Flow Injection Fluorimetry for the Determination of Carbamazepine in Human Plasma

Abstract

A simple, sensitive, and specific flow injection fluorimetric method has been developed for the determination of carbamazepine (CBZ). The proposed method is based on use of a solid‐phase reactor containing lead dioxide for on‐line oxidization of CBZ into a strongly fluorescent compound in a medium of phosphoric acid. The product has a green‐yellow fluorescence at a maximum excitation wavelength of 355 nm and an emission wavelength of 478 nm. Under the optimum conditions, the fluorescence intensity is proportional to the concentration of CBZ ranging from 0.0005 to 4.000 µg mL^?1. The detection limit is 5.7×10^?5 µg mL^?1 (2.4×10^?10 mol L^?1) and the relative standard deviation is 1.4% at the sampling rate of 45 h^?1. The proposed method has been applied to clinical estimation of CBZ in real patients' plasma samples with the results compared with those obtained by HPLC method.     

Bias-current modulation technique of a radio-frequency glow discharge plasma for atomic emission analysis associated with a fast Fourier transform analyzer

A measuring method using a fast Fourier transform (FFT) analyzer is suggested to estimate the emission intensity from a radio-frequency (RF)-powered glow discharge plasma for atomic emission analysis. The FFT analyzer has an ability to disperse the components by frequency from an overall signal, and thus works as a selective detector in modulation spectroscopy. In the RF glow discharge plasma, a dc bias current can be introduced by connecting an external electric circuit with the discharge lamp, which predominantly enhances the emission intensities. Further, the bias current can be pulsated with a switching device to modulate the emission intensities, and then the modulated component was selectively detected with the FFT analyzer. This method greatly improved the data precision. The emission intensity of the Cu I 324.75-nm line in an Fe-based alloy sample containing 0.043 mass% Cu could be estimated with a relative standard deviation of 0.20%. The 3σ detection limits of Cu in Fe-based alloys could be obtained to be 2.3 × 10^− 6 mass% Cu for Cu I 324.75 nm and 6.8 × 10^− 6 mass% Cu for Cu I 327.40 nm.     

Determination of rhodium by thermal neutron activation analysis using g-ray spectrometry

Trace amounts of rhodium have been determined by thermal neutron activation analysis using both destructive and non-destructive methods. With a neutron flux of 10¹² n cm^-2 sec^-1 the lower limits of detection are about 0.1 μg and 0.01 μg, respectively. A rapid sodium-peroxide fusion followed by a pyridine extraction was used in the destructive method to separate the 4.4-mm ^104mRh from its matrix. The 44-sec¹⁰⁴Rh was used in the non-destructive method. Both radioactive isomers were measured by γ-ray spectrometry with a multichannel pulse height analyzer. The average time required per non-destructive analysis was 7 min while the chemical method averaged 20 min.     

Flow injection spectrophotometric method for chloride determination in natural waters using Hg(SCN)(2) immobilized in epoxy resin

A flow injection (FI) spectrophotometric method was proposed for the determination of chloride ion in natural waters. The determination of chloride was carried out by reaction with Hg(SCN)₂ immobilized in an epoxy resin bead in a solid-phase reactor (SPR) and the thiocyanate ions released were determined spectrophotometrically at 480 nm after complexing reaction with Fe(III). The analytical curve for chloride was linear in the concentration range from 5.6 × 10⁻⁵ to 2.2 × 10⁻⁴ mol l⁻¹ with a detection limit of 1.4 × 10⁻⁵ mol l⁻¹. The relative standard deviation (R.S.D.) was 2.2% for a solution containing 2.2 × 10⁻⁴ mol l⁻¹ (n = 10). The simple manifold allows a routine analytical frequency of 100 determinations per hour. The main advantage of the developed method is the 400% reduction of the Hg waste solution generated when compared to conventional methods for chloride determination based on the same spectrophotometric reaction.     

Determination of Baicalin by High Performance Liquid Chromatography Coupling with Flow Injection Chemiluminescence Detection

A new method for the determination of baicalin in Scutellariae Radix extract and its preparations by high performance liquid chromatography (HPLC) coupling with flow injection chemiluminescence detection (FIA‐CL) has been developed. The method was based on the chemiluminescence reaction of potassium permanganate with baicalin in nitric acid medium; the CL intensity can be enhanced by formaldehyde. In this study, the conditions of chemiluminescence and chromatography were examined, and the schematic diagram of the HPLC‐FIA‐CL analyzer was optimized. The analytes were separated on Hypersil RP‐C18 columns (100 × 4.6 mm, I.D., 5 μm) by equality elution with 47:53 (v/v) methanol‐0.3% phosphoric acid as a mobile phase at a flow rate of 0.8 mL·min^?1 and a column temperature of 40 °C. Under the optimum condition, the CL intensity was proportional to the concentration of baicalin over the range of 4.10 × 10^?7 ? 6.15 × 10^?5mol·L^?1. The limit of detection (S/N = 3) was 2.79 × 10^?7mol·L^?1 with the relative standard deviation 2.5% (Cs = 6.15 × 10^?6 mol·L^?1, n = 5). The method has been applied to the determination of baicalin in Scutellariae Radix extract and its preparations, and satisfactory results were obtained.     

A flow injection analysis system for monitoring silver (I) ion and iodine residuals in recycled water from recovery systems used for spaceflight

A laboratory-built flow injection analyzer is reported for monitoring the drinking water disinfectants silver (I) ion and iodine in water produced from NASA's water recovery system. This analyzer uses spectrophotometric detection with a custom made 10 cm optical flow cell. Optimization and interference studies are discussed for the silver (I) ion configuration. Subsequent results using the silver (I) configuration with minor modifications and alternative reagents gave promising results for iodine determinations as well. The estimated MDL values for Ag⁺ and I₂ are 52 μg L⁻¹ Ag⁺ and 2 μg L⁻¹ I₂; the mean percent recoveries were 104% and 96.2% for Ag⁺ and I₂ respectfully; and percent relative standard deviations were estimated at 1.4% for Ag⁺ and 5.7% for I₂. The agreement of this potentially multifunctional analyzer to reference methods for each respective water disinfectant is measured using Bland–Altman analysis as well as more traditional estimates.     

A low-cost automated flow analyzer based on low temperature co-fired ceramic and LED photometer for ascorbic acid determination

An automated flow analyzer based on low temperature co-fired ceramic (LTCC), a solid-phase reactor (SPR) and a low-cost photometer was designed for ascorbic acid (AA) determination in pharmaceutical formulations. It consists of a peristaltic pump, three-way solenoid valves, SPR to chemically convert Cu(II) into Cu(I), and a LTCC device for mixing the liberated copper with bathocuproine and detection. The flow cell in the LTCC employed an ultrabright LED — photodiode photometer. The analyzer successfully determined AA in pharmaceutical formulations. The analytical curve from 8.5×10^?6 to 7.0×10^?4 M gave a detection limit of 7.0×10^?7 M and a RSD of 2.1% for a 2.0×10^?4 M AA solution (n = 10). A high sampling frequency of 102 h^?1 and low reagent and sample consumption (150 µL) resulted.      

Analysis of amino acids in complex samples by using voltammetry and multivariate calibration methods

A voltammetric method is proposed for the simultaneous determination of tryptophan, cysteine, and tyrosine using multivariate calibration techniques. Various electrodes and voltammetric techniques were explored to ascertain the optimum measurement strategy. Among them, differential pulse voltammetry (DPV) with a Pt electrode was selected as analytical technique since it provided a suitable compromise between sensitivity and reproducibility while allowing the oxidation peaks of the three compounds to be reasonably discriminated. The sensitivity of DPV with Pt electrode for Trp standards was 8.4×10⁻² A l mol⁻¹, the repeatability 3.7% and the detection limit below 10⁻⁷ M. The lack of full selectivity of the voltammetric data was overcome using multivariate calibration methods on the basis of the differences in the voltammetric waves of each compound. The accuracy of predictions was evaluated preliminarily from the analysis of three-component synthetic mixtures. Subsequently, this method was applied to the analysis of oxidizable amino acids in feed samples. Results obtained were in good concordance with those given by the standard method using an amino acid analyzer.     

Automated Assay for Fructose 2,6-Bisphosphate

Abstract

An automated procedure for the determination of Fructose 2,6-bisphosphate (Fru 2,6-P₂) is described. The method based on the degree of activation of the enzyme Pyrophosphate: D-fructose 6-phosphate 1-phosphotransferase from potato tuber by Fru 2,6-P₂, uses a discrete-sample automatic analyzer to perform the procedure and to monitor the spectrophotometric changes. The detection limit of Fru 2,6-P₂ levels is 0.016 pmol (6.25 × 10^?14 mol ml^?1). The coefficients of variation observed when assaying 0.5 nM of Fru 2,6-P₂ in the reaction mixture, 1.34% and 7.39% (n=10) for the automated and manual method are significantly different. Thus a 5-fold higher precision is shown by the automatic method. The same precision is observed when assaying biological samples from starved or refed animals.

In conclusion the assay is as sensitive as the manual spectrophotometric method previously described, but it shows higher precision and decreases the processing time allowing routine determinations. It is specially useful when purifying 6-phosphofructo 2-kinase or assaying a large number of tissue samples for Fru 2,6-P₂.     

Application of the laser microprobe mass analyzer (LAMMA) to qualitative and quantitative single cell analysis

The laser microprobe mass analyzer (LAMMA ) is a new type of analytical instrument. It is a combination of a laser microscope with a time-of-flight (TOF ) mass spectrometer. By focusing an UV pulse laser beam onto the specimen positive and negative atomic and molecular ions are formed which are detected by the TOF mass analyzer. The detection limits reach 10^–20 g for some elements in an excited sample volume of 10^–13 cm³. With the aim of finding out whether the LAMMA instrument is capable of quantitative measurements on very small biological samples the ²³Na⁺ and ³⁹K⁺ contents of single mycobacterial cells (M. tuberculosis H 37 Ra) were measured and the results were compared with those obtained from “integral” methods (AAS, NAA , tracer). Furthermore, the influence of different temperatures applied during the washing procedure of the bacteria on the distribution of the Na⁺/K⁺ ratio within the cell population was investigated. First attempts to trace isonicotinic acid hydrazide (INH) in bacteria were made by comparison of the LAMMA spectra of INH treated and untreated cells.     

Enzymatic determination of l-lysine by flow-injection techniques

An enzymatic assay that is highly selective for l-lysine, based on flow-injection techniques combined with spectrophotometric detection, is presented. l-Lysine-α-oxidase (E.C. 1.4.3.14) from Trichoderma viride and horseradish peroxidase were used in a coupled enzyme assay. Peroxide produced in the first reaction was converted by peroxidase with phenol and 4-aminoantipyrine to a quinoneimine dye detectable at 500 nm. An analytical enzyme reactor filled with coimmobilized enzymes was incorporated in the flow-injection system. The assay has a measuring frequency of 30 samples h^?1 and a response time of less than 2 min. To adapt the assay to high concentrations of l-Lysine and to minimize interferences, the injected sample volume was reduced to 2 μ-l, resulting in a linearity range of 1–16 mM l-lysine with a sensitivity of 6–7 mV 1 mmol^?1, a limit of detection (3σ) of 1 mM and a reproducibility of 0.5% (repetitive injection of a 10 mM l-lysine sample). The enzyme cartridge is stable for several months and thousands of measurements.     

Eine Methode zur Bestimmung der spezifischen Radioaktivität der „freien Aminosäuren“ in Gewebeextrakten von Säugetieren

Some experiences are given with a measuring device for the determination of the specific radioactivity of ¹⁴C-labelled brain amino-acids. The apparatus consists of an automatic amino-acid analyzer combined with a flow cell filled with anthracene. The reproducibility of the method is ±5% to ±1% m.e. in the range of 1×10^?3 μCi to 5×10^?2 μCi. A quantitative determination of 3×10^?4 μCi/ml eluant is still possible.     

Automatic polymerase chain reaction product detection system for food safety monitoring using zinc finger protein fused to luciferase

An automatic polymerase chain reaction (PCR) product detection system for food safety monitoring using zinc finger (ZF) protein fused to luciferase was developed. ZF protein fused to luciferase specifically binds to target double stranded DNA sequence and has luciferase enzymatic activity. Therefore, PCR products that comprise ZF protein recognition sequence can be detected by measuring the luciferase activity of the fusion protein. We previously reported that PCR products from Legionella pneumophila and Escherichia coli (E. coli) O157 genomic DNA were detected by Zif268, a natural ZF protein, fused to luciferase. In this study, Zif268–luciferase was applied to detect the presence of Salmonella and coliforms. Moreover, an artificial zinc finger protein (B2) fused to luciferase was constructed for a Norovirus detection system. In the luciferase activity detection assay, several bound/free separation process is required. Therefore, an analyzer that automatically performed the bound/free separation process was developed to detect PCR products using the ZF–luciferase fusion protein. By means of the automatic analyzer with ZF–luciferase fusion protein, target pathogenic genomes were specifically detected in the presence of other pathogenic genomes. Moreover, we succeeded in the detection of 10 copies of E. coli BL21 without extraction of genomic DNA by the automatic analyzer and E. coli was detected with a logarithmic dependency in the range of 1.0 × 10 to 1.0 × 10⁶ copies.     

Determination of90Sr by thin layer radiochromatography

A simple method for the determination of⁹⁰Sr by using thin layer chromatography on silica gel or cellulose pretreated with calcium oxalate is proposed. In these conditions a complete separation between strontium and its daughter yttrium is obtained. Radioactivity of separated elements was measured by a linear multiscanner analyzer and the results were computer processed to obtain the activity of⁹⁰Sr. The method has been applied to samples of water and milk subjected to a very simple extraction procedure. Under the experimental conditions used, the detection limit is about 25 mBq of deposited radioactivity, which corresponds to about 6 Bq/l.     

Electrochemical determination of hydrogen peroxide using o -dianisidine as substrate and hemoglobin as catalyst

A new electrochemical method for the determination of microamounts of hydrogen peroxide utilizing o-dianisidine (ODA) as substrate and hemoglobin (Hb) as catalyst is described in this paper. Hb can be used as mimetic peroxidase and it can catalyse the reduction of hydrogen peroxide with the subsequent oxidation of ODA. The oxidative reaction product is an azo compound, which is an electroactive substance and has a sensitive second-order derivative polarographic reductive peak at the potential of -0.58 V (vs. SCE) in pH 80 Britton-Robinson (B-R) buffer solution. The conditions of Hb-catalytic reaction and polarographic detection of the reaction product were carefully studied. By using this polarographic peak and under optimal conditions, the calibration curve for the H₂O₂ was constructed in the linear range of 2.0 x 10^-7 ∼ 10 x 10^-4 mol/l with the detection limit of 5.0 x 10^-8 mol/l. This method can also be used to the determination of Hb content in the range of 20 x 10^-9 ∼ 30 x 10^-7 mol/l with a detection limit of 10 x 10^-9 mol/l. The proposed method was further applied to the determination of the content of H₂O₂ in fresh rainwater with satisfactory results. The catalytic reaction mechanism and the electrode reductive process of the reaction product were carefully studied.     

A microfluidic chip analyzer for determining neurotransmitters

The fabrication of a chip analyzer based on polydimethylsiloxane and glass has been described. The possibilities of the treatment of the chip channel surface by atmospheric plasma and sodium dodecyl sulphate used as an additive to the working buffer solution has been studied. The rate of electroosmotic flow was evaluated. Using a model mixture of catecholamines, the effect of modification of the surface of microchip channels on efficiency and separation factor was revealed. Methods for enhancing the sensitivity of the electrochemical cell have been developed; the possibilities of online preconcentration in the chip format were evaluated. The limit of detection for catecholamines has been attained at 10^?6–10^?7 g/mL.     

A Novel Enzyme Membrane Electrode for Oxalate Determination in Foodstuffs

Abstract

An enzyme membrane electrode usable for the assay of oxalate in foodstuffs is described. A commercially available preactivated polyamide membrane was used for the immobilization of oxalate oxidase. The bioactive disk thus obtained was associated with an amperometric transducer. The resulting self-contained enzyme electrode wich allows oxalate determination in various materials with minimal pretreatment exhibits a linear calibration ranging from 10–7 M and 10–4 M in the cell. The response-time was comprised between 20 seconds and 1 minute, depending on the oxalate content in the sample. The electrode-response was very stable for at least 4 months, a period during which more than 150 assays were performed.

The results obtained with several food materials were in good agreement with those obtained with the conventional spectrophotometric method. Assays were also performed with a microprocessor-based analyzer normally used for glucose measurements with a glucose oxidase electrode When the analyzer is equipped with an oxalate oxidase membrane, without further setting, oxalate can be determined in the range 5 10^?3 M-10^?1 M in the sample.