Sensitive spectrofluorimetric determination of zinc at ultra-trace levels

An ultra-trace method based on the reaction of zinc with salicylthiocarbohydrazone (SATCH) and Triton X-100 as a non-ionic surfactant was developed for the fluorimetric determination of zinc at the picogram level. The reaction is carried out in the pH range 4.4–4.7 in an aqueous ethanolic medium [52% (v/v) ethanol]. The influence of the reaction variables is discussed. The detection limit is 10 pg ml^?1 and the range of application is 0.01–500 μg l^?1, with an optimum range of 0.04–400 μg l^?1. The relative standard deviations are 0.68% (0.01–0.1 μg l^?1 of zinc), 0.41% (0.1–1.0 μg l^?1 of zinc), 0.64% (1–10 μg l^?1 of zinc), 0.82% (10–100 μg l^?1 of zinc) and 0.15% (100–500 μg l^?1 of zinc). The method is highly sensitive and selective in the presence of Cd^II and Hg^II. The effect of interferences from other metal ions and anions was studied; the masking action is discussed. The advantages of the proposed method include its high sensitivity, simplicity and selectivity.     

Peroxidase-catalysed rupture of the CF bond as and indicator reaction for enzyme immunoassay : Kinetic determination of human immunoglobulin G, α-fetoprotein and placental lactogen

A fluoride ion-selective electrode is utilized as a sensor for the kinetic determination of peroxidase label in enzyme immunoassays. The method is based on a sandwich enzyme-linked immunosorbent assay (ELISA) technique, the peroxidase-catalysed rupture of the covalent CF bond in 4-fluorophenol and the subsequent release of fluoride ions. The determination of human immunoglobulin G (lgG), human α-fetoprotein (AFP) and human placental lactogen (HPL) was investigated. The potentiometric measurement of the rate of release of fluoride ion within 5 min provided a direct correlation with the concentration of analyte present in the sample. The concentration ranges investigated for the analytes were IgG 30 μg l^?1–10mg l^?1, AFP 5–500 μg l^?1 and HPL 60 ng l^?1–1 mg l^?1. Under the given experimental conditions, the detection limits were IgG 30, AFP 12.8 and HPL 1 μg l^?1. Replacing the rate method with the fixed-time mode (15–30 min) did not improve the detection limits. The performance of the present method was found to be comparable to that of the spectrophotometric detection technique.     

Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 μg l^?1 of tin in the MIBK solution or 0.2–0.3 μg g^?1 in the rock. The concentration range is linear between 2.5 and 500 μg l^?1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 μg l^?1 level and < 7% at the 10–30 μg l^?1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 μg g^?1 or less.     

Stripping voltammetry of aluminum based on adsorptive accumulation of its solochrome violet RS complex at the static mercury drop electrode

A very sensitive electrochemical stripping procedure for aluminum is reported. Accumulation is achieved by controlled adsorption of the aluminum/solochrome violet RS complex on the static mercury drop electrode. Optimal experimental parameters include an accumulation potential of ?0.45 V, solochrome violet RS concentration of 1 × 10^?6 M, and a linear-scan stripping mode. The detection limit is 0.15 μg l^?1, the response is linear over the 0–30 μg l^?1 concentration range, and the relative standard deviation (at the 10 μg l^?1 level) is 2%. Most cations do not interfere in the determination of aluminum. The interference of iron(III) is eliminated by addition of ascorbic acid. Results are reported for snow samples.     

The determination of gold by anodic stripping voltammetry

A method is described for the routine determination of gold as its chloride or cyanide complex by anodic stripping voltammetry at a glassy carbon electrode coupled to a microprocessor-controlled voltammeter. The preferred supporting electrolyte is 0.1 M HCl/0.32 M HNO₃, with plating at ?200 mV or ?1200 mV (vs. Ag/AgCl). The stripping peak potentials range from 830 to 1150 mV (vs. Ag/AgCl) depending on concentration and plating time. Precision (percent relative standard deviation) is better than 5 % for a range of concentrations between 5 μg l^?1 and 1000 μg l^?1. The detection limit is about 5 μg l^?1 for a 5-min plating period. Interferences from Cu, Hg, Ag and other electroactive species are overcome by preliminary extraction with diethyl ether.     

Determination of molybdenum in infant formula and human milk by electrothermal atomic absorption spectrometry with barium difluoride as matrix modifier

A method for the determination of molybdenum in infant formula and human milk by electrothermal atomic absorption spectrometry was developed and optimized. Samples were injected directly in the graphite tube with barium difluoride as the matrix modifier. The detection limit was 0.89 μg Mo l^?1. The molybdenum levels found in infant formula and human milk were 0.09–2.23 μg Mo g^?1 and 2.32–8.38 μg Mo l^?1, respectively.     

Multi‐Walled Carbon Nanotubes (MWCNT)‐Ionic Liquid‐Modified Carbon Paste Electrode: Probing FurazolidoneDNA Interactions and DNA Determination

The interactions of furazolidone (Fu) with double‐stranded calf thymus DNA (dsDNA) on the multi‐walled carbon nanotubes‐ionic liquid‐modified carbon paste electrode (MWCNT‐IL‐CPE) have been studied by cyclic voltammetry. In the presence of DNA, the cathodic peak current of Fu decreased and the peak potential shifted to a positive potential, indicating the intercalative interaction of Fu with DNA. The binding constant of Fu with DNA and stoichiometric coefficient has been determined according to the Hill's model. This electrochemical method was further applied to the determination of DNA. Two linear calibration curves were obtained for DNA detection in the concentration ranges of 0.03–0.10 and 0.10–4.0 μg l^?1 with a detection limit of 0.027 μg l^?1. The method was successfully applied to analyze Fu in serum samples.     

Determination of selenium(IV) by differential pulse voltammetry of the 3,3′-diaminobenzidine piazselenol

The determination of selenium(IV) by voltammetry through the formation of a piazselenol with 3,3′-diaminobenzidine (DAB) is described. At pH 1.5 and with a large excess of DAB, the formation of piazselenol is quantitative. In a borate-buffered electrolyte at pH 9, the piazselenol gives reduction peaks at potentials of ?0.64 V and ?0.82 V vs. SCE. The influence of DAB concentration on the sensitivity of the method is discussed. The calibration graphs are linear over the range 0–200 μg l^?1 Se(IV) and the detection limit is 0.10 μg l^?1. Copper(II) and lead(II) are tolerated in 500-fold amounts; the method is applicable to the determination of selenium in NBS Oyster Tissue.     

Spectrofluorimetric determination of trace amounts of thorium

A spectrofluorimetric method, based on the formation of a fluorescent complex with salicyladehyde carbohydrazone, is optimized for the determination of thorium (20–800 μg l^?1) at “pH” 1.3–1.7. The relative standard deviation is 2.7% for 100 μg Th l^?1. The method is applied to synthetic mixtures containing various amounts of thorium and to the determination of thorium in monazite samples.     

Flow-injection extraction spectrophotometric method for the determination of lead and its combination with minicolumn preconcentration

An automatic flow-injection method was developed for the determination of lead in the range 50–2000 μg l^?1. The method is based on the extraction of lead with the crown ether dicyclohexyl-18-crown-6 into chloroform from an acidic medium, subsequent addition of dithizone as chromogenic reagent to the extract and measurement of absorbance. The sample throughput is 45 h^?1. A microcolumn containing Chelex-100 chelating resin is used for on-line preconcentration of lead, giving a detection limit of 5 μg l^?1 with a sample throughout of 36 h^?1. The method compares favourably with the dithizone and diethyldithiocarbamate methods with respect to selectivity. Application to standard alloys, soil leachates and sea water is demonstrated.     

Spectrophotometric determination of vanadium using variamine blue and its application to synthetic, environmental and biological samples

A simple, rapid and accurate spectrophotometric method is described for the determination of trace amounts of vanadium using variamine blue (VB) as a chromogenic reagent. The method is based on the oxidation of variamine blue to form a violetcolored species on reaction with vanadium(V), having an absorption maximum at 570 nm. Beer’s law is obeyed in the range of 0.1–2.0 μg ml^?1. The molar absorptivity and Sandell’s sensitivity were found to be 1.65 × 10⁴ l mol^?1 cm^?1 and 0.003 μg cm^?2, respectively. Optimum reaction conditions were evaluated in order to delimit the linear range. The effect of interfering ions on the determination is described. The proposed method has been successfully applied to the determination of vanadium in steel, pharmaceutical, environmental, and biological samples.     

An efficient flow-injection system with on-line ion-exchange preconcentration for the determination of trace amounts of heavy metals by atomic absorption spectrometry

A flow-injection system with on-line ion-exchange preconcentration on dual columns is described for the determination of trace amounts of heavy metals at μg l^?1 and sub-μg l^?1 levels by flame atomic absorption spectrometry. The degree of preconcentration ranges from 50- to 105-fold for different elements at a sampling frequency of 60 s h^?1. The detection limits for Cu, Zn, Pb and Cd are 0.07, 0.03, 0.5, and 0.05 μg l^?1, respectively. Relative standard deviations were 1.2–3.2% at μg l^?1 levels. The behaviour of the different chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of sea water.     

Spectrophotometric determination of osmium with phthalimide dithiosemicarbazone by means of complex formation and catalytic reactions

Phthalimide dithiosemicarbazone forms a 1:1 complex with osmium at pH 3.3–4.5 (?₄₅₀ = 1.3 · 10⁴ l mol^?1 cm^?1 ) which is applied to the photometric determination of osmium; Beer's law is obeyed for the range 1–12 μg Os ml^?1. The oxidation of the reagent with cerium(IV) is catalyzed by osmium(VIII), and this reaction allows a more sensitive procedure for the determination of osmium; the calibration curve is linear over the range 0.05–0.4 μg Os ml^?1. The interferences in both procedures are described.     

Rapid spectrophotometric determination of ruthenium(III) with prochlorperazine maleate

A rapid, simple spectrophotometric method for the determination of μg amounts of ruthenium, based on the formation of a pink complex between the metal and prochlorperazine maleate (PCPM) in sulphuric or hydrochloric acid solution, is described. The complex has an absorption maximum at 530 nm and its molar absorptivity is 6.733·10³ l mol^?1 cm^?1. The sensitivity is 0.0151 μg Ru cm^?2 for log I_o/I = 0.001. Beer's law is valid over the range 0.2–10 μg Ru ml^?1 ; the optimal range for spectrophotometric determination is 0.8–8.0 μg Ru ml^?1. Job's method of continuous variation, the mole ratio method and the slope ratio method indicate a 1:1 composition for the complex. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions are reported.     

Spectrophotometric determination of copper(II) in natural waters, vitamins and certified steel scrap samples using acetophenone-p-chlorophenylthiosemicarbazone

A very simple, highly sensitive and selective spectrophotometric procedure was developed for the determination of copper(II). It is based on the reaction at pH 4–9 between the synthesized acetophenone-p-chlorophenylthiosemicarbazone (A-p-ClPT) and Cu(II) forming a green complex, Cu(II):A-p-ClPT (1:2), that floats quantitatively with oleic acid (HOL) surfactant. It exhibits a constant and maximum absorbance at 600 nm in both aqueous and surfactant layers. Beer’s law is obeyed over the concentration range 0.25–6.35 mg l^?1 with a detection limit of 0.021 mg l^?1 for a standard aqueous solution of Cu(II) with a concentration of 3.82 mg l^?1 (calculated on the basis of 3σ) and molar absorptivities of 5.5 × 10³ and 1.3 × 10⁴ mol l^?1 cm^?1 in aqueous and surfactant layers, respectively. Sandell’s sensitivity was calculated to be 0.244 μg cm^?2 and the relative standard deviation (n = 9) was 0.19%. The different analytical parameters affecting the flotation and determination processes were examined. The proposed procedure has been successfully applied to the analysis of Cu(II) in natural waters, certified scrap steel samples and vitamin samples. The results obtained agree well with those samples analyzed by atomic absorption spectrometry (AAS). Moreover, the flotation mechanism is suggested based on some physical and chemical studies on the solid complexes isolated from aqueous and surfactant layers.     

Flow-injection spectrophotometric determination of palladium in catalysts and dental alloys with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino)aniline

2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)aniline rapidly forms a water-soluble complex with palladium in an acetate-buffered medium at pH 3.2.The molar absorptivity of the complex is 9.84×10⁴l mol^?1 at 612 nm. The calibration graph is linear over the range of 10–100 μg l^?1 palladium; the detection limit is 2 μg l^?1 and the relative standard deviation is 0.6% for 100 μg l^?1 palladium. The sample throughput is 50 h^?1. Divalent transition metals (Fe, Ni, Co) do not interfere at levels from 2 to 10 mg l^?1. Interference from copper is prevented by adding 10^?3 M EDTA solution to the carrier stream. Palladium in solutions of catalysts and dental alloys can be determined selectively, sensitively and rapidly.     

Spectrophotometric Determination of Selected Antibiotics Using Prussian Blue Reaction

A simple, sensitive and accurate spectrophotometric method has been described for the determination of ampicillin(I), amoxicillin trihydrate(II) and cefazolin sodium(III). The procedure is based on the formation of Prussian Blue (PB) complex. The reaction between the acidic hydrolysis products of antibiotics (T = 60 °C) with mixture of Fe³⁺ and hexacyanoferrate(III) ions was evaluated for the spectrophotometric determination of the mentioned drugs. The maximum absorbance of the colored complex occurs at λ = 700 nm and the molar absorptivity is 3.0 × 10⁴ 1 mol^?1cm^?1. The effect of various parameters such as concentration of K₃Fe(CN)₆ and Fe³⁺, nature and amount of acids used, temperature and time of heating were investigated. Under optimum conditions the linear range of calibration graph was 2.0–12.0, 5.0–13.5 and 3.0–12.0 μg mL^?1 for ampicillin, amoxicillin and cefazolin, respectively. The relative standard deviation for the determination of 10 μg mL^?1 of antibiotics was about 0.5–1.5%. The proposed method was successfully applied to the determination of selected antibiotics from pharmaceutical preparations. The validity of the method was tested by the official methods and by the recovery studies of standard addition to pharmaceuticals.     

Comparison of four chromogenic reagents for the flow-injection determination of aluminum in water

Pyrocatechol violet (PCV), aluminon, eriochrome cyanine R (ECR) and eriochrome cyanine R with cetyltrimethylammonium bromide (ECR/CTA) are compared as chromogenic reagents for the flow-injection determination of aluminium in water. The detection limit of the ECR/CTA method is 1 μg Al 1^?1. The detection limits of the PCV and ECR methods are 5 μg Al 1^?1. The aluminon method is the least sensitive, with a detection limit of 50 μg Al l^?1. Interference from iron, fluoride, phosphate and the acidity of the sample were investigated. The interference from iron is suppressed by hydroxylammonium chloride/1,10-phenanthroline in the PCV and ECR/CTA methods at concentrations less than 5 mg Fe l^?1. In the ECR and aluminon methods, iron <5 mg l^?1) is masked by ascorbic acid. Fluoride at <0.2 mg l^?1 can be tolerated in all methods. The aluminon method can tolerate up to about 500 mg l^?1 in the three other methods. All methods are sensitive to changes in acidity of the samples; the acidity should be 0.08–0.12 M HCl.     

The fluoride ion-selective electrode in flow injection analysis: Part 1. General Methodology

A simple flow-injection system for determination of traces of fluoride by means of the fluoride-selective electrode is presented. A comparison of several flow-cell arrangements confirmed the advantages of a well-jet design. Systematic investigations of the parameters affecting response times (i.e., polishing procedure, flow rate, carrier composition) established the optimal experimental conditions for measurements down to 1 μg l^?1 fluoride. Calibration plots in the lower μg l^?1 range were neither Nernstein nor linear, but good precision (0.5–5%) was obtained even when the potential differences for concentration steps of one decade were as small as 3 mV.     

Automated method for the determination of boron in water by flow-injection analysis with in-line preconcentration and spectrophotometric detection

A sensitive, automated method for the determination of boron in water samples is described, involving flow injection with on-line ion-exchange preconcentration and spectrophotometric detection of the azomethine-H—boron complex. The method is applicable to various water samples and is free from interferences, even in coloured samples. Detection limits of 5 μg l^?1 at 20 samples h^?1 and 1 μg l^?1 at 10 samples h^?1 with relative standard deviations of < 10% at 1–10 μg l^?1 and < 5%at 10–200 μg l^?1 levels of boron were achieved. The recoveries for spiked natural water samples ranged from 96 to 101%. The method compares favourably with inductively coupled plasma atomic emission spectrometry.