Flow-injection extraction spectrophotometric determination of bismuth as tetraiodobismuthate(III) with the tetramethylenebis(triphenylphosphonium) cation

Bismuth can be determined spectrophotometrically at 495 nm after its extraction as tetramethylenebis(triphenylphosphonium) tetraiodobismuthate(III) into dichloromethane. The carrier stream is 2 M sulphuric acid and the reagent stream contains 2% (w/v) potassium iodine and 0.4% (w/v) tetramethylenebis(triphenylphosphonium) bromide. The injection rate is 20 h^-1. The calibration graph is linear up to 20 μ ml^-1 bismuth and the detection limit is 0.24 μ ml^-1 bismuth, based on injection volumes of 250μl. The system has been applied to determination of bismuth in pharmaceutical samples.     

Flow-injection extraction-spectrophotometric determination of permanganate with the ethylene-bis(triphenylphosphonium) cation

Permanganate is determined spectrophotometrically at 545 nm after extraction into chloroform of the ion-associate, ethylene -bis (triphenylphosphonium) permanganate. The carrier stream is pH 6 buffer containing 10% (w/v) ammonium fluoride and the reagent stream is 0.25% (w/v) ethylene-bis (triphenylphosphonium) bromide. The injection rate is 24 h^?1. Th calibration graph is linear up to 25 μg ml^?1 and the detection limit is 0.58 μg m^?1 Mn (VII), based on 250- μl injections. The system is applied to the determination of manganese in a range of steels.     

Flow-injection spectrophotometric determination of cobalt by extraction as tetrathiocyanatocobaltate(II) with the ethylenebis(triphenylphosphoniu) cation

Cobalt (0–10 μg) may be determined spectrophotometrically at 625 nm after flow-injection extraction into chloroform of the ion associate ethylenebis(triphenylphosphonium) tetrathiocyanatocobaltate(II). The carrier stream contained 10% (w/v) ammonium fluoride and the reagent stream contained 0.5% (w/v) ethylenebis (triphenylphosphonium) bromide and 5% (w/v) ammonium thiocyanate. The injection rate was 20 h^?1. The calibration graph is linear up to 20 μg ml^?1 and detection limit is 0.23 μg ml^?1 cobalt, based on injection volumes of 500 μl. The system has been applied to the determination of cobalt in a range of tool steels.     

Preconcentration and Spectrophotometric Determination of Chromium (VI) and Total Chromium in Drinking Water by the Sorption of Chromium Diphenylcarbazone with Surfactant Coated Alumina

Abstract

A simple and inexpensive method for determining chromium (VI) in drinking water by spectrophotometry after preconcentration with sodium dodecyl sulphate (SDS) coated alumina column is described. Chromium(VI) is reacted with diphenylcarbazide (DPC) and the Cr-DPC complex is quantitatively adsorbed onto a SDS coated alumina column from 800 ml of sample solution. The complex is then eluted with a 8 ml mixture of methanol, acetone and hydrochloric acid and determined by spectrophotometry. Total chromium can be determined after oxidation of chromium (III) to chromium (VI) by KMnO₄. The relative standard deviation (10 replicate analyses) at the 10 μg l^?1 of chromium (VI) and 10 μg l^?1 of total chromium were 3.5% and 3.4% and corresponding limits of detection (based on 3 σ) were 0.040 μg l^?1 and 0.033 μg l^?1, respectively.     

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.     

Flow-injection configurations for chromium speciation with a single spectrophotometric detector

The simultaneous or sequential determination of chromium(VI) and total chromium in water by flow injection analysis, using different configurations with a double- or single-beam spectrophotometer as detector, is investigated. The method is based on reaction between chromium(VI) and 1,5-diphenylcarbazide. Chromium(III) and (VI) are distinguished by using two carrier streams, one of which contains cerium(IV) to oxidize chromium(III) to chromium(VI). The determination range is 0.2–10.0 μg Cr ml^?1; the r.s.d. is 0.8% for 1 μg Cr. The sampling frequency is 40 h^?1. A wide study of interferences is reported.     

Speciation of chromium in sea water

Dissolved chromium(III) and (VI) are coprecipitated separately from sea water, and chromium in the precipitates and particulate matter is determined by thin-film x-ray fluorescence spectrometry. In combination with an ultraviolet irradiation procedure whch releases bound metals, the method provides information about the speciation of chromium in near-shore surface sea water. The ratios of labile Cr(III)/(IIO+VI) generally lie in a narrow range (0.4–0.5) as do the sums of labile Cr(III) and (VI) concentrations (0.3–0.6 μg l^?1). Bound chromium is variable (0–3 μg l^?1) and constitutes from 0 to 90% of total dissolved chromium. Acidification of the samples in the traditional manner for trace metal determination is shown to alter the proportion of Cr(III) to Cr(VI).     

Indirect spectrophotometric determination of chromium(VI)

A new simple and sensitive spectrophotometric method for the determination of chromium(VI) is established. It relies upon the oxidation of iron(II) with the titled ion, in acidic medium, to form iron(III) which is complexed with tiron to form a stable blue color with maximum absorption at 650 nm. Adherence to Beer's law is observed in the range 10–100 μg of chromium(VI) per 25 ml, with a molar absorptivity of 5.6 × 10³ liters mol^?1 cm^?1, sensitivity index of 0.0093 μg cm^?1, relative error of ?5.0 to +0.3%, and relative standard deviation of 0.3–4.0%, depending on the concentration level. Furthermore, the reaction needs neither temperature control nor an extraction step.     

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.     

Determination of hexavalent chromium in traditional Chinese medicines by high‐performance liquid chromatography with inductively coupled plasma mass spectrometry

An analytical method that combined high‐performance liquid chromatography with inductively coupled plasma mass spectrometry has been developed for the determination of hexavalent chromium in traditional Chinese medicines. Hexavalent chromium was extracted using the alkaline solution. The parameters such as the concentration of alkaline and the extraction temperature have been optimized to minimize the interconversion between trivalent chromium and hexavalent chromium. The extracted hexavalent chromium was separated on a weak anion exchange column in isocratic mode, followed by inductively coupled plasma mass spectrometry determination. To obtain a better chromatographic resolution and sensitivity, 75 mM NH₄NO₃ at pH 7 was selected as the mobile phase. The linearity of the proposed method was investigated in the range of 0.2–5.0 μg L^?1 (r² = 0.9999) for hexavalent chromium. The limits of detection and quantitation are 0.1 and 0.3 μg L^?1, respectively. The developed method was successfully applied to the determination of hexavalent chromium in Chloriti lapis and Lumbricus with satisfactory recoveries of 95.8–112.8%.     

Selective separation and determination of dissolved chromium species in natural waters by atomic absorption spectrometry

A procedure for determining the concentrations of dissolved chromium species in natural waters is described. Chromium(III) and chromium(VI), separated by co-precipitation with hydrated iron(III) oxide, and total dissolved chromium are determined separately by conversion to chromium(VI), extraction with APDC into MIBK and determination by a.a.s. The detection limit is 40 ng l^?1 Cr. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In the waters investigated, total concentrations were relatively high (1–5 μg l^?1) with Cr(VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species.     

The determination of chromium(VI) in natural waters by differential pulse polarography.

A method utilizing differential pulse polarography for the determination of chromium(VI) in natural water is described. Additions of 0.62 μg Cu(II) ml^-1 and 0.55 μg Fe(III) ml^-1 did not interfere with the determination of 0.050 μg Cr(VI) ml^-1. The natural water samples containing chromium(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylene diamine and analyzed. Natural water samples of chromium content from 0.035 μg ml^-1 to 2.0 μg ml^-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg ml^-1.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Spectrophotometric Determination of Phenols and Cyanides After Distillation from Natural Waters

Abstract

Total phenols were determined by molecular spectrophotometry, after distillation, complexation with 4-aminoantipyrine and extraction into chloroform. Cyanides were also determined spectrophotometrically after distillation from the acidified samples, and complexation in moderate acidic solution with barbituric acid. The dynamic ranges were 0 – 100 μg L^?1 for total phenols and 0 – 30 μg L^?1 for cyanides. The above methods were applied in the analysis of river, lake and stream waters collected from Northern Greece. The seasonal and spatial variation of concentrations was evaluated by two-way ANOVA. Background levels (4 – 12 μg L^?1 for total phenols and 0.3 – 3 μg L^?1 for cyanides), were found in almost all surface waters, with some exceptions.     

Determination of total organic carbon in water in the form of carbamate by means of a simple denuder/electrolytic conductivity flow cell system

A simple and sensitive technique for measuring both volatile organic carbon (VOC) and total organic carbon (TOC) in water is presented. The VOC fraction is stripped by a stream of oxygen and subjected to high-temperature catalytic combustion after removing the carbon dioxide, obtained from inorganic constituents at pH ? 2, with lithium hydroxide. The residual non-volatile organics (NVOC) are converted into carbon dioxide by injecting an aliquot of the stripped sample directly into the combustion tube. The carbon dioxide derived from the VOC/NVOC is preconcentrated from the gas stream by absorption in a stainless-steel capillary tube coated with a 2 M ethanolic solution of 3-methoxypropylamine. The carbamate formed in the liquid film is then eluted with a stream of the absorbent circulating through a microelectrolytic conductivity detector. The change in specific conductance due to the presence of the carbamate in the effluent stream is linearly related to the amount of VOC/NVOC/TOC up to 4.5 μg of carbon. The limit of detection for VOC is 0.5 μg l^?1 and for NVOC it is 100 μg l^?1. A simple determination takes 5 min. The precision was better than 5% (P=95%) for 0.5–4.5 μg of carbon. The method is also suitable for the determination of total carbon and inorganic carbon in water.     

Isomeric Transformation Of 4-Aminobiphenyl by U.V. Radiation and its Influence on the Determination by Flow Injection Analysis with Amperometric and Spectrophotometric Detection.

Abstract

Two flow-injection methods for the determination of 4-aminobiphenyl by amperometry (glassy carbon electrode) and spectrophotometry are proposed. A sample volume of 200 or 400 μl containing an analyte concentration of 0.1–1.0 μg ml^?1 or 0.8–24.0 μg ml^?1 for amperometric or spectrophotometric detection, respectively, is injected into a carrier stream containing 0.04 or 0.02 M Britton-Robinson buffer at pH 10.0 or 8.0, respectively.

The throughput thus achieved is 200 (amperometry) and 240 samples/h (spectrophotometry) and the relative standard deviation less than 2.5% and 4.2% respectively.

Both methods were applied to the determination of 4-aminobiphenyl in commercially available, legally permitted food colouring additive.     

Flow injection determination of hydrogen peroxide by means of a solid-state-peroxyoxalate chemiluminescence reactor

A solid-state reactor for detection of hydrogen peroxide in aqueous samples by peroxyoxalate chemiluminescence is described. Bis(2,4,6-trichlorophenyl)oxalate in solid form is packed into a bed reactor, which eliminates mixing problems and facilitates the instrumental development. Perylene is added as a sensitizer to a water/acetonitrile (20:80) carrier stream into which the samples (200–600 μl) are injected. Detection limits of 6 × 10^?9 M H₂O₂ (0.2 μg l^?1) are obtained with both a commercial and a home-made luminescence detector. Calibration graphs are linear up to 10^?5 M. The r.s.d. for 2 × 10^?7 M (6.7 μg^?1) hydrogen peroxide (n = 10) is 2.8%. Sample throughput is ca. 120 h^?1.     

The differential pulse polarographic determination of chromium in gallium arsenide

The method described for the determination of chromium in gallium arsenide is based on the catalytic current produced by nitrate in the electrolytic reduction of the chromium(VI)-diethylenetriaminepentaacetate complex. Matrix effects, primarily caused by gallium, are discussed in detail. The method is suitable for determinations of chromium at levels as low as about 1 μg g^?1 with about 50 mg of sample; the r.s.d. is better than 10%.     

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.     

Indirect determination of vanadium by atomic absorption spectrometry

An indirect method for the determination of vanadium as vanadate by atomic absorption spectrometry is described. In neutral medium, vanadate forms a stable ion-association complex with copper (II) and biguanide, which is extractable into butanol with an efficiency higher than 99%. The copper content in the extract (and hence indirectly VO^?₃) is determined by aspirating it directly into an acetylene flame. The calibration graph is linear up to 3.4 μg ml^?1 of VO^?₃. The limit of detection is 16 ng ml^?1. Only chromium interferes.