Determination of anionic surfactants by bis(ethylenediamine)copper(II) extraction and anodic stripping voltammetry

A stripping voltammetric finish for the measurement of total anionic surfactant has been developed. A limit of detection of 5.0 μg 1^?1 anionic surfactant was observed with a linear calibration from 5.0 to 500 μg 1^?1 in the original sample.     

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.     

Preconcentration of submicrogram amounts of nickel by liquid-liquid extraction and micro back-extraction from water for graphite furnace atomic absorption spectrometry

The effective preconcentration of submicrogram amounts of nickel from water is described. Nickel is extracted into xylene as a dithiocarbamate complex and subsequently back-extracted into 100 μl of nitric acid for graphite furnace atomic absorption spectrometry. Conditions for quantitative extraction and back-extraction are described. Data on interferences, precision and detection limits are presented. Sub-μg 1^?1 levels of nickel in water could be determined with concentration factors of 500–1000 by the proposed method. The concentrations of nickel in rain water and surface snow were found to be 0.39 and 0.19 μg 1^?1, respectively. The limit of determination can be lowered by using concentration factors larger than 10⁴, nickel determination at ng 1^?1 levels being feasible.     

Atomic absorption spectrometric determination of selenium with carbon furnace atomization

A Varian Techtron model 63 carbon rod atomizer is used for the atomic absorption spectrometric determination of nanogram quantities of selenium. The pronounced interferences from the matrices in biological digests can be obviated by isolating selenium from sample matrices by precipitation with ascorbic acid. The precision of the determination is improved by incorporating 5000 μg Ni ml^?1 in the analytical solutions. Selenium at μg g^?1 and sub-μg g^?1 levels in a variety of biological samples can be determined. The detection limit is 25 ng Se g^?1.     

New methods for the detection of cyanide based on displacement of the glutathione ligand of glutathionylcobalamin by cyanide

Glutathionylcobalamin (GSCbl) is a vitamin B₁₂ derivative that contains glutathione as the upper axial ligand to cobalt via a Co–S bond. In the present study, we discovered that cyanide reacted with GSCbl, generating cyanocobalamin (CNCbl) and reduced glutathione (GSH) via dicyanocobalamin (diCNCbl) intermediate. This reaction was induced specifically by the nucleophilic attack of cyanide anion displacing the glutathione ligand of GSCbl. Based on the reaction of GSCbl with cyanide, we developed new methods for the detection of cyanide. The reaction intermediate, violet-coloured diCNCbl, could be applied for naked eye detection of cyanide and the detection limit was estimated to be as low as 520 μg L^?1 (20 μM) at pH = 10.0. The reaction product, CNCbl, could be applied for a spectrophotometric quantitative determination of cyanide with a detection limit of 26 μg L^?1 (1.0 μM) at pH = 9.0 and a linear range of 26–520 μg L^?1 (1.0–50 μM). In addition, the other reaction product, GSH, could be applied for a fluorometric quantitative determination of cyanide with a detection limit of 31 μg L^?1 (1.2 μM) at pH = 9.0 and a linear range of 31–520 μg L^?1 (1.2–20 μM). These new GSCbl-based methods are simple, highly specific and sensitive with great applicability for the detection of cyanide in biological and non-biological samples.     

Trace Detection of Mercury(II) Using Gold Ultra‐Microelectrode Arrays

The electroanalytical detection of trace mercury(II) at gold ultra‐microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in nitric acid using linear sweep voltammetry where a linear response from mercury additions over the range 10 μg L^?1?200 μg L^?1 (10^?8?10^?6 M) was observed with a sensitivity and detection limit of 0.11 nC/μg L^?1 and 3.2 μg L^?1 (16 nM) respectively from using a deposition time of 30 s at ?0.2 V (vs. SCE). This methodology was explored in 0.1 and 1 M chloride media over the mercury range 10 μg L^?1?200 μg L^?1 (5×10^?8?10^?6 M) where similar sensitivities of 0.087 nC/μg L^?1 and 0.078 nC/μg L^?1 were observed with an identical detection limit. The protocol is demonstrated to be useful for the determination of mercury for analysis of environmental water samples.     

Entwicklung einer flieβinjectionsmethode zur bestimmung von chlorid im spurenbereich durch leitfähighkeitsdiffernzenA flow-injection method for the determination of trace amounts of chloride

The indirect determination of chloride in water is based on measurement of the difference in conductivity after the sample has passed through ion-exchange columns in the hydrogen form and silver form. The linear response range is about 0.5–10 μg g^?1 chloride (with 3 μg g^?1 nitrate and 5 μg g^?1 sulfate); the detection limit is about 50 ng g^?1 chloride but depends strongly on the concentrations of other anions.     

Development of Dispersive Liquid‐Liquid Microextraction Based on Solidification of Floating Organic Drop for the Determination of Trace Cobalt in Water Samples

A liquid‐phase microextraction technique was developed using dispersive liquid‐liquid microextraction based on solidification of floating organic drop combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of cobalt in water samples. Microextraction efficiency factors, such as the type and volume of extraction and dispersive solvents, pH, extraction time, the chelating agent amount, and ionic strength were investigated and optimized. Under optimum conditions, an enrichment factor of 160 was obtained from 10.0 mL of water sample. The calibration graph was linearin the range of 1.15‐110 μg L^?1 with a detection limit of 0.35 μg L^?1. The relative standard deviation for ten replicate measurements of 10 and 100 μg L^?1 of cobalt were 3.26% and 2.57%, respectively. The proposed method was assessed through the analysis of certified reference water or recovery experiments.     

Flow injection spectrophotometric determination of ascorbic acid in soft drinks and beer

Two spectrophotometric methods, a photochemical and a non-photochemical, for the determination of ascorbic acid in soft drinks and beer using a flow-injection system are proposed. The non-photochemical method is based on the redox reaction that takes place between ascorbic acid and Fe(III), yielding dehydroascorbic acid and Fe(II). Fe(II) reacts with 1,10-phenantroline, originating the reddish orange Fe(phen)₃ ²⁺ complex (ferroin). This complex is spectrophotometrically monitored at 512 nm, and the signal is directly related to the concentration of ascorbic acid in the sample. The photochemical method has the same basis, nevertheless, uses the irradiation with visible light to enhance the redox reaction and so achieve higher sensitivities in the analysis. The non-photochemical method shows a linear range between 5 and 80 μg mL^?1, with a relative standard deviation of 1.6% (n = 11), a detection limit of 2.7 μg mL^?1 and a sample throughput of ¶60 samples h^?1. The photochemical method shows a linear range between 1 and 80 μg mL^?1, with a relative standard deviation of 1.0% (n = 11), a detection limit of 0.5 μg mL^?1 and a sample throughput of 40 samples h^?1.     

Spectrophotometric determination of L-ascorbic acid in pharmaceutical preparations

The method is based on the oxidation of L-ascorbic acid with potassium hexacyanoferrate (III). Excess of oxidant is determined spectrophotometrically by oxidation of phthalophenone to phenolphthalein in alkaline solution. Linear calibration graphs are obtained for 0–7 μg ml^?1 ascorbic acid at 553 nm, with a detection limit of 0.1 μg ml^?1. Sugars and other organic compounds do not interfere when present in moderate amounts.     

Determination of soluble cyanide in soil samples by differential pulse polarography

Soluble cyanide can be determined ins oil samples by differential pulse polarography. Interference from sulphide is avoided by treating the alkali-stabilized sample solutions with lead carbonate prior to distillation of cyanide from the soil extract. Less than 10 μg l^?1 cyanide can be determined accurately, depending on teh weight of sample taken and the final collection volume. For a 100-g soil sample, the detection limit is 5 ng g^?1, which is similar to the limit of a standard spectrophotometric method. Relative standard deviations are 1–3%.     

Selective Kinetic Spectrophotometric Determination of Nitrite in Food and Water

Abstract

A highly selective and sensitive method for the kinetic spectrophothometric determination of sub-microgram amounts of nitrite has been development based on its reaction with Nile blue 2B in acidic medium. The reaction is monitored spectrophotometrically at 595 nm at a fixed time of 4.5 min. The change in absorbance at 595 nm is related to the concentration of nitrite in the range 0.005 - 1.100 μg.ml^?1 The detection limit is 0.001 μg.ml^?1. The relation standard deviation is 1% for 0.020 μg.ml^?1 of nitrite for ten replicate measurements. Most common anions and cations do not interfere. The procedure was applied to the determination of trace amounts of nitrite in sausage and water.     

Determination of selenium in human body fluids by hydride-generation atomic absorption spectrometry : Optimization of sample decomposition

The accuracy of the determination of selenium in human body fluids by hydride-generation a.a.s. depends critically upon the sample decomposition-method used. Digestion with HNO₃ alone gave low selenium recoveries, but with nitric, sulfuric and perchloric acids at a final temperature of 310°C gave results that agreed with those obtained by other techniques. The recovery of selenomethionine added to whole blood and of trimethylselenonium iodide added to urine was 97–104%. The average selenium values found for 6 healthy individuals were 88 μg l^?1 in whole blood, 75 μg l^?1 in blood plasma and 307 μg (kg Hb)^?1 in erythrocytes. A detection limit of 5 μg l^?1 Se in body fluids was found under routine conditions.     

Preconcentration and determination of trace chromium(III) by flow injection/inductively-coupled plasma/atomic emission spectrometry

A manifold incorporation an activated alumina (basic form) minicolumn is used to preconcentrate chromium(III), which is then eluted with 2 M nitric acid for detection. Calibration is linear up to 1000 μg l^? Cr, and the limit of detection for a 10-ml sample is 0.05 μg l^?1. The determination of chromium(III) in human urine is discussed.     

Integrated Retention/Spectrophotometric Detection Method for the Determination of Formaldehyde

Abstract

An integrated-sensor method for the determination of formaldehyde based on retention of the reaction product of the analyte with p-rosaniline and sulfite in a flow-cell packed with Dowex 1-X-8 anion exchange resin was developed. The method has a good selectivity with a detection limit of 0.3 μg ml^?1 (1 ml sample) or 75 ng ml^?1 (2 ml sample), and a linear range between 1–30 μg ml^?1. The relative standard deviations (n = 11) were 2.8 and 1.3% for 2 and 20 μg ml^?1 formaldehyde, respectively. Depending on the working conditions, the sampling frenquency ranged between 10 and 18 h^?1. The method was applied to the determination of formaldehyde in well water.     

Kinetic-Spectrophotometric Determination of Molybdenum(VI) Based on Its Catalytic Effect on the Thionine-Hydrazine Reaction

Abstract

A kinetic method for the determination of trace amounts of Mo(VI) (0.05-4 μg ml^?1) based on its catalytic effect on the reduction of thionine by hydrazine monochloride in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 605 nm after a fixed time (5 min.). The detection limit of the method is 23 ng ml^?1 and the relative standard deviation (RSD) for 0.05 μg ml^?1 of Mo(VI) is 1.2% (n=7). The method is almost free from interferences, especially from large amounts of tungsten. The procedure was successfully applied to the determination of trace amounts of molybdenum in steel.     

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.     

The direct determination of cadmium in urine by electrochemical atomic absorption spectrometry with the L'vov platform

A simple, direct procedure for the measurement of cadmium in urine is described. Graphite-furnace atomic absorption spectrometry is used in conjunction with selective atomisation at 800°C from a L'vov platform. Urine samples are diluted with an equal volume of deionised water and 20-μl aliquots are injected. Calibration is done by standard additions. The sensitivity is 0.016 μg Cd l^?1 for 1% absorption for a 20-μl sample. Within-run precision is 4.9% at 0.84 μg l^?1. The detection limit is 0.06 μg l^?1, which allows normal unexposed levels of cadmium in urine to be determined. The method is applicable to the determination of urinary cadmium levels of both occupationally non-exposed and exposed populations.     

Automated determination of total arsenic in sea water by flow constant-current stripping analysis with gold fibre electrodes

Total arsenic in sea water is determined in a fully automated flow system, by means of potentiostatic deposition for 4 min at a 25-μm gold fibre electrode and subsequent constant-current stripping in 5 M hydrochloric acid. Previously the sample is acidified with hydrochloric and arsenic(V) is reduced to arsenic(III) with iodide. During stripping, the potential vs. time transient is recorded with a real-time measurement rate of 26.5 kHz and a potential resolution of 1 mV. Cleaning and regeneration of the gold electrode are fully automated. The total arsenic concentrations in two reference sea waters (NASS-1 and CASS-1) were evaluated by single-point standard addition and found to be 1.58 and 1.14 μg l^?1 with standard deviations of 0.39 and 0.28 μg l^?1, respectively; certified values are 1.65 ± 0.19 and 1.04 ± 0.07 μg l^?1. The arsenic(III) content in these samples was below the detection limit (0.15 μg l^?1).     

Direct detection of acetaminophen in urine by liquid chromatography with electrochemical detection using dual electrodes. Preliminary application to a single-dose pharmacokinetic study

A method for the direct determination of acetaminophen in urine based on liquid chromatography with series dual-electrode detection has been developed. No sample pretreatment steps are required except for filtration. The method gives a linear range from 0.5 to 300 μg ml^?1 and a detection limit of 0.2 μg ml^?1 (10 μl). The analysis time of the assay is less than 7 min. The pharmacokinetics of acetaminophen in urine from a subject who had orally ingested 450 mg (table form) of the drug were studied and various pharmacokinetic parameters were determined.