Rapid determination of copper,nickel, lead and cadmium in small samples of estuarine and coastal waters by liquid/liquid extraction and electrothermal atomic absorption spectrometry

A rapid liquid/liquid extraction of 1.25-ml samples is used with graphite-furnace atomic absorption spectrometry for the determination of dissolved trace metals in saline waters. The metals are chelated with ammonium pyrrolidine dithiocarbamate and extracted into 1,1,1-trichloroethane; 20–40 μl of extract is injected into the furnace. Sample manipulation and overall time are greatly decreased compared to other similar large-scale extraction methods; all the chemical steps are done in the sample cups of an auto-sampler for graphite-furnace a.a.s. Detection limits (Cu 0.3 μg l^?1, Cd 0.02 μg l^?1, Pb 0.7 μg l^?1, Ni 0.5 μg l^?1 are low enough for applications in routine monitoring of filterable trace metal concentrations in coastal and estuarine waters to check for compliance with Environmental Quality Standards that apply in the European Community.     

Conversion techniques in flow injection analysis: Determination of Sulphide by Precipitation with Cadmium Ions and Detection by Atomic Absorption Spectrometry

A flow-injection system is described for on-line conversion of a soluble species to an insoluble compound by means of a tag-material which subsequently can be determined. This approach is used for the determination of sulphide by flame atomic absorption spectrometry, cadmium(II) ions being used as the precipitating tag-reagent. Excess of cadmium(II) is collected on a chelating ion-exchanger and later eluted. The detection limit for sulphide was 10 μg l^?1 and the sampling rate was 100 h^?1. Typical relative standard deviation was 1.2%. Of the potential interferences tested, only phosphate had any effect.     

Coulometric argentometric determination of microamounts of sulphur in iron and steel after reduction to hydrogen sulphide with iron(II) in strong phosphoric acid medium

A coulometric method was developed for the determination of microamounts of sulphur in iron and steel. Hydrogen sulphide is quantitatively evolved by reduction with iron(II) in strong phosphoric acid medium and is titrated with electrolytically generated silver ion from a silver anode. Microamounts of sulphide (2.96–224.3 μg) in sodium sulphide standard solutions could be determined with an error of only a few percent. Sulphur in a potassium sulphate standard solution is quantitatively reduced to hydrogen sulphide and could be separated from the solution by heating and determined accurately. Trace amounts of sulphur (7–100 μg g^?1) in iron and steels could be determined with a standard deviation of 0.7–2.1 μg g^?1.     

Application of the iron(III)/3,4-dihydroxybenzaldehyde 4-nitrophenylhydrazone complex for the analysis of sulphide/fluoride/phosphate mixtures by spectrophotometry or atomic absorption spectrometry

3,4-Dihydroxybenzaldehyde 4-nitrophenylhydrazone reacts with iron(III) to form a red complex extractable into methyl isobutyl ketone. Sulphide, fluoride and phosphate inhibit the formation of the complex. Sulphide and fluoride are masked with Cu(II) and Al(III), respectively. These properties are used to determine sulphide (0.15–4 mg l^?1), fluoride (0.3–9 mg l^?1) and phosphate (0.3–8 mg l^?1) in mixtures by spectrophotometry or atomic absorption spectrometry.     

Trace Analysis of Lead and Copper Ions in Fish Tissue Using Paste Electrodes

Abstract

DNA was immobilized onto a carbon nanotube surface through cyclic voltammetry, in which paste electrode (PE) was subjected to lead and copper trace ion analysis. Optimized conditions for square‐wave stripping voltammetry were then searched. The results indicated three other linear working ranges—3–21 mg l^?1, 2–16 µg l^?1, and 3–17 ng l^?1 Pb(II) Cu(II)—within an accumulation time of 190 s in 0.1‐M ammonium phosphate electrolyte solutions of pH 10.0. At the optimized conditions, the detection limit (S/N) was pegged at 0.4 ng l^?1 (1.93×10^?12 M Pb(II) and 6.29×10^?12 M Cu(II)). And the relative standard deviation at 10 mg l^?1 Pb(II) and Cu(II) was a 0.074 and 0.069% precision, in 15 measurements. The method can be applied to assays of fish tissue.     

The application of strongly reducing agents in flow injection analysis : Part 3. Vanadium(II)

The application of vanadium(II) as a powerful reducing reagent in flow injection analysis is described. Results are presented for the determination of various organic and inorganic substances. With spectrophotometric detection, based on the absorption by vanadium(II)-EDTA at 350 nm, limits of determination were about 5 X 10^?5 mol 1^?1. Nitrate, nitrite and hydroxylamine were measured with amperometric detection. The limit of determination was about the same as with spectrophotometric detection. In a slightly acidic medium, hydrazine could be determined with the amperometric detector, with a limit of determination of about 10^?4 mol l^?1. By coupling an ammonia detection device to the reduction system, the percentage conversions of nitrate, nitrite and hydroxylamine to ammonia were shown to be 26%, 54% and 47%, respectively.     

Determination of lead in whole blood with a simple flow-injection system and computerized stripping potentiometry

An automated (24 samples/hour) procedure is described for the determination of lead (0–1000 μg l^?1) in human blood based on flow-injection stripping potentiometry. The samples are diluted 20-fold with 0.5 M hydrochloric acid containing 100 mg l^?1 mercury and 40 μg l^?1 cadmium (II), and a 1.1 ml aliquot is injected into the flow system. With a mercury-coated carbon fibre as working electrode, lead (II) is determined by using cadmium (II) as internal standard and a calibration graph prepared from bovine blood. Analyses of two human blood reference samples yielded results of 335±37 and 691±24 μg l^?1 lead, the certified values being 332 and 663 μg l^?1, respectively.     

Ion chromatographic determination of selected ions in antarctic ice

Ion chromatography is used to measure the concentrations of chloride, nitrate, sulphate, ammonium and sodium ions at the μg l^?1 level in Antarctic ice and to investigate the occurrence of methanesulphonate, fluoride, formate, acetate and nitrite. Of the latter group of ions, only methanesulphonate was found in measurable concentrations.     

Extraction-spectrophotometric determination of sulphide and sulphite in waters based on formation of the bis(2,9-dimethyl-1,10-phenanthroline) copper(I) ion

A spectrophotometric method is described for the determination of sulphide or sulphite. The bis(2,9-dimethyl-1,10-phenanthroline)copper(II) ion is reduced at pH 10 by sulphide in the presence of formaldehyde and by sulphide and sulphite in its absence. The resulting copper(I) complex is extracted into chloroform and measured. With any convenient sample volume between 1 and 100 ml, the limits of detection are 0.1 mg for sulphide and 0.25 μg for sulphite. The method is unaffected by iron(II) and nitrite, in concentrations of 100 and 1000 mg l^-1, respectively.     

Determination of copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

Separation of trace rare earths and other metals from uranium by liquid-liquid extraction with quantitation by inductively-coupled plasma/mass spectrometry

N,N-Dihexylacetamide in toluene was used to extract uranium selectively from an aqueous phase containing 30 elements at 10 or 100 μg l^?1 concentrations. After three extractions, the uranium level fell from 119 000 mg l^?1 (0.5 M) to less than 3 mg l^?1. An inductively-coupled plasma/mass spectrometer (i.c.p./m.s.) was used to determine recoveries of the trace elements in the aqueous phase, which, in most cases, were in the range 90–110%. This combination of liquid-liquid extraction with i.c.p./m.s. offers determinations at the 10 ng g^?1 level in uranium for most of the elements studied.     

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.     

Applications of flow injection analysis in a power plant determination of pH,ammonia and hydrazine in an AVT-conditioned water steam cycle

The quality of information concerning management of systems and subsystems of industrial processes is greatly affected by the analytical techniques uses. Flow-injection methods are described for monitoring pH (in the range 4.5–95), ammonia (0.25–2 mg l^?1 N) and hydrazine (50?300 μg l^?1 N) in a water/steam cycle, based on the use of potentiometric sensors. The procedures are discussed in terms of both applicability to very dilute solutions (with simple management of the sytem) and measurability. The parameters considered were precision, analysis frequency and application range. The application range and analysis frequency were good for hydrazine but only the application range was good fro pH and ammonia. Data evaluation by means of a “measurability” model gave acceptable results for ammonia and hydrazine, but not for pH measurements. The frequency of analysis is the main factor affecting the quality of the results.     

Selective flow-injection determination of residual chlorine at low levels by amperometric detection with two polarized platinum electrodes

Flow-injection amperometry with two polarized platinum electrodes is used for the determination of residual chlorine based on the oxidation of iodide. Interferences of iron(III), copper(II), nitrite and atmospheric oxygen are eliminated in the proposed procedure. The detection limit for residual chlorine is 2 μg l^?1 at a sampling rate of 120 h^?1; linear calibration graphs are obtained up to 0.8 mg 1^?1. A method for the simultaneous flow-injection determination of residual chlorine and copper(II) is also proposed.     

Sensitive determination of traces of boron in waters,fertilizers na geological and biological materials by isotope-dilution mass spectrometry

A method is described for determining traces of boron in water, fertilizers, geological and biological (reference) materials by isotope-dilution mass spectrometry after separation on an Amberlite IRA-743 borate-selective ion-exchange column. Boron (–250 ng g^?1) in water can be determined with an accuracy of 5–20% (computed on a 2s basis). After correction for weighing errors and for moisture, content, which varied from 0 to 8% for the samples tested, 1–35 μg g^?1 boron in “dry” fertilizer, biological or geological sample can be assayed with an accuracy of 5–30% (2s). In an IAEA interlaboratory program on a simulated fresh water, the method yielded a value of 24.3 +? 2 μg l^?1, compared to the make-up value of 25 μg l^?1.     

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.     

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

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.     

Lead-selective electrodes based on lead(IV) oxide

Lead(IV) oxide electrodes are shown to give near-theoretical calibration slopes for lead(II) ions over the range 10^?3–10^?5 mol l^?1, and to have near-theoretical standard potentials in different acidic media. They are compared with lead sulphide-silver sulphide membrane electrodes and shown to be more tolerant of acidity and copper(II), mercury(II) and iron(III) ions. Iron(II) and manganese(II), however, interfere significantly. Some of the advantages of the lead(IV) oxide electrode are brought out in the determination of the solubility product of lead sulphate; implications for constructing phosphate- and sulphate-sensitive electrodes are mentioned.     

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.     

The spectrophotometric determination of arsenic in sea water,potable water and effluents

Procedures are described for the determination of arsenic in sea water, potable waters and effluents. The sample is treated with sodium borohydride added at a controlled rate. The arsine evolved is absorbed in a solution of iodine and the resultant arsenate ion is determined photometrically by a molybdenum blue method. The time required for a complete analysis is about 90 min, but of this only 15 min is operator time. For sea water the range, standard deviation, and detection limit are 1–4 μgl^-1, 1.4 % and O.14 μg l^-1, respectively; for potable waters they are 0–800 μg l^-1, about 1 % (at 20μg l^-1 level) and 0.5μg l^-1, respectively. Silver and copper cause serious interference at levels of 0.5 mgl^-1, and nickel, cadmium and bismuth interfere at concentrations of a few tens of mg l^-1; however, these elements can be removed either by preliminary extraction with a solution of dithizone in chloroform or by ion exchange. Arsenic present in organo-arsenic compounds is not directly determinable, but can be rendered reactive either by photolysis with ultraviolet radiation or by oxidation with permanganate or nitric—sulphuric acid mixture. Arsenic(V) can be determined separately from total inorganic arsenic after extracting arsenic(III) as its pyrrolidine dithiocarbamate into chloroform.