Fluorimetric trace determination of cerium(III) with sodium triphosphate

Sodium triphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III). The purpose of this study was to investigate the spectrofluorimetric determination of trace amounts of Ce(III) in sodium triphosphate solution. The excitation and emission wavelengths are 303.5 nm and 353 nm respectively. Optimum sodium triphosphate concentration is found to be 0.074 g l(-1) at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range 0.001-45 mug ml(-1). The detection limit is 9.4 x 10(-4)mug ml(-1). The relative standard deviations for 30 mug ml(-1) and 0.05 mug ml(-1) Ce(III) in 0.074 g l(-1) sodium triphosphate solution are 1.1% and 0.72% respectively. Quenching effects of other lanthanides and some inorganic anions are described. This method is a direct and rapid analytical method for the determination of Ce(III) in rare earth mixtures and cerium concentrates.     

Study on the solid phase extraction of Co(II)-QADEAB chelate with C(18) disk and its application to the determination of trace cobalt

A sensitive, selective and rapid method has been developed for the determination mug l(-1) level of cobalt based on the rapid reaction of cobalt(II) with 2-(2-quinolylazo)-5-diethylaminobenzoic acid (QADEAB) and the solid phase extraction (SPE) of the colored chelate with Waters Porapak(R) Sep-Park C(18) disk. The QADEAB can react with Co(II) in the presence of pH 3.8 acetic acid-sodium acetate buffer solution and cetyl trimethylammonium bromide (CTMAB) medium to form a violet chelate of a molar ratio 1:2 (cobalt to QADEAB). This chelate can retained on Waters Porapak(R) Sep-Park C(18) disk quantitatively when they passed the disk as aqueous solution. After the enrichment finished, the retained chelate can be eluted from disk by 2.5 ml of ethanol (contain 5% acetic acid). In the measured solution, the molar absorptivity of the chelate is 1.58x10(5) l mol(-1) cm(-1)at 635 nm, and Beer's law is obeyed in the range of 0.01-0.4 mug ml(-1). The relative standard deviation for 11 replicate sample of 0.01 mug ml(-1) level is 2.23%. The detection limit is 0.01 mug l(-1) (in original samples). This method can be applied to the determination of mug l(-1) level of cobalt in drinking water with satisfactory results.     

Comparison of ultrasound-assisted extraction and microwave-assisted digestion for determination of magnesium, manganese and zinc in plant samples by flame atomic absorption spectrometry

In this paper, a sample preparation method based on acid extraction of magnesium, manganese and zinc from plant tissue by means of high intensity probe ultrasonication is described. Acid extracts obtained upon sonication were directly nebulised into an air-acetylene flame for fast metal determination by atomic absorption spectrometry. Parameters influencing extraction such as sonication time, ultrasound amplitude, sample mass, particle size, extractant composition and volume were fully optimised. Optimum conditions for metal extraction were as follows: a 3-min sonication time, a 30% ultrasonic amplitude, a 0.1-g sample mass, a particle size less than 50 mum, a 0.3% m/v HCl concentration in the extractant solution and a 5-ml extractant volume. Six plant samples used in the human diet were analysed, the concentration range of the three metals approximately being in the range of 1500-3000 mug g(-1) for Mg, 30-735 mug g(-1) for Mn and 20-45 mug g(-1) for Zn. Limits of detection corresponding to the ultrasound-assisted extraction method were 0.10, 1.26 and 0.65 mug g(-1) for Mg, Mn and Zn, respectively. Between-batch precision, expressed as R.S.D., was about 0.5, 1.5 and 1% for Mg, Mn and Zn, respectively. Analytical results for the three metals by ultrasound-assisted extraction and microwave-assisted digestion showed a good agreement, thus indicating the possibility of using mild conditions for sample preparation instead of intensive treatments inherent with the digestion method. The advantages and drawbacks of ultrasound-assisted extraction in respect to the microwave-assisted digestion are discussed.     

A rapid, selective and sensitive spectrophotometric method for the determination of Ce(III) using some bisazophenyl-beta-diketone derivatives

A rapid, simple, selective and sensitive spectrophotometric method for the determination of cerium(III) using the title azo dyes [1,3-phenylenediamine bisazoacetylacetone (I(a));1,3-phenylenediamine bisazobenzoylacetone (I(b));1,4-phenylenediamine bisazoacetylacetone (I(c)); and 1,4-phenylenediamine bisazobenzoylacetone (I(d))] has been developed in neutral and slightly alkaline (pH 7.00, 7.50, 8.00 and 7.00) media. The 1:1 and 2:1 (M:L) complexes formed exhibit their highest absorbances in 30% (v/v) dioxane solutions, having formation constants (log K) of 4.44, 4.95. 5.63 and 5.22 and 8.51, 8.76, 9.73 and 9.37 respectively. Beer's law is obeyed over the concentration ranges 0.10-2.50, 0.05-3.00, 0.05-3.75 and 0.10-3.50 mug ml(-1) of cerium(III). More accurately, Ringbom optimum concentration ranges are 0.2-2.25, 0.2-2.6, 0.2-3.5 and 0.2-3.3 mug ml(-1) for the complexes of reagents I(a),I(b),I(c) and I(d) respectively. The molar absorptivities, Sandell sensitivities and relative standard deviations were also calculated. The interferences of 50 foreign ions on the determination of cerium(III) were studied. The method allows the determination of cerium(IV) after prior reduction to the trivalent state. The proposed method was used for cerium determination in two different monazite samples and the results were compared with certified values obtained using atomic absorption spectrometry, indicating that the procedure provided accurate and precise results.     

Fluorimetric determination of fluoride in a flow assembly integrated on-line to an open/closed FIA system to remove interference by solid phase extraction

A simple flow injection fluorimetric method for fluoride determination is proposed. The method is based on the enhanced fluorescence of quercitin-Zr(IV) complex when fluoride ion is present in the sample. An open/closed FIA manifold with a mini-column of Dowex 50W X8 resin was used to remove the most important interference (aluminum). The two FIA assemblies were integrated on-line to automate the pretreatment of the water sample and fluoride determination. The calibration graph was linear over the range 0.1-3.0 mug ml(-1) of fluoride with a correlation coefficient of 0.999 and LOD 0.06 mug ml(-1). The relative standard deviation was 2.5% and the sample throughput was 52 h(-1) without pretreatment and 10 h(-1) with pretreatment of the sample. The method was applied to the determination of fluoride in water samples.     

Selective extraction and photometric determination of trace vanadium with cinnamohydroxamic acid in MIBK and its application to steel and rock ore analysis

A sensitive and selective photometric method for the trace determination of vanadium with cinnamohydroxamic acid extracted from 1.8 M HCl in methyl isobutyl ketone is described. The wine-red chelate formed under an optimum acidity of 1.3-2.6 M HCl absorbs with a maximum at 525 nm. Beer's law is obeyed in the range 0-8 ppm of vanadium(V) and the optimum range of determination of vanadium is found to be 1-8 ppm. The molar absorptivity and Sandell's sensitivity are 6.0 x 10(3) l mol(-1) cm(-1) and 0.0086 mug cm(-2) of vanadium(V) at 525 nm. The photometric determination of trace amounts of vanadium in materials such as alloys, minerals and rock ores is also reported. The solvent extraction methods are simple, rapid and highly selective with fluoride used as a masking agent for Fe and Ti. The standard deviations are minimal and the mean error is only 0.015%.     

Extraction with long-chain amines-V Colorimetric determination of cobalt with nitroso-R salt

The colorimetric determination of cobalt with nitroso-R salt (NRS) has been modified and improved by the introduction of extraction of the Co-NRS chelate into a chloroform solution of trioctylmethylammonium chloride. Ammonium phosphate, fluoride and mainly citrate were used for masking iron, nickel, copper and calcium, which under the described conditions do not interfere even in 2000-fold excess. The method is very sensitive and permits determination of about 1 mug of cobalt per ml of the extractant.     

Kinetochromic spectrophotometry-III Determination of fluoride by catalysis of the zirconimn-Methylthymol blue reaction

The determination of 0.5-4.75 mug of fluoride ion by its catalytic action upon the slow reaction between Methylthymol Blue and zirconium(IV) in aqueous solution is described. Calibration curves obtained after 60 min under optimal conditions are smooth, and yield an effective molar absorptivity of 3.23 x 10(4) 1.mole(-1)mm(-1) at 586 nm. There is considerably less cationic interference than in the alizarin complexan-cerium(III) or lanthanum procedure, but more serious anionic interference is encountered when phosphate, arsenate and, to a lesser extent, sulphate ions are present in the sample solution.     

Sequential injection wetting film extraction applied to the spectrophotometric determination of chromium(VI) and chromium(III) in water

The spectrophotometric determination of Cr(VI) and Cr(III) via sequential injection was used to demonstrate the sensitivity enhancement provided by a newly developed wetting film extraction system. The reaction product of Cr(VI) with 1,5-diphenylcarbazide was ion-paired with perchlorate and extracted into an organic wetting film consisting of octanol and 4-methyl-2-pentanone on the inner wall of a Teflon tube. The wetting film, with the extracted analyte, was then eluted with 100 mul acetonitrile and the analyte determined spectrophotometrically at 546 nm. Important optimized parameters were the selection of wetting film and elution solvents, the flow rate, the length and diameter of the extraction coil and the conditions for the formation of the ion paired chelate. Cr(III) was previously oxidized to Cr(VI) and calculated as the difference between total Cr and Cr(VI). An enrichment factor of 25 and a detection limit of 2.0 mug l(-1) Cr(VI) were achieved with a sampling frequency of 17 h(-1). The calibration curve was linear up to 100 mug l(-1) Cr(VI) (r = 0.999). The relative standard deviations were 2.8 and 2.0% at the 25 and 100 mug l(-1) levels.     

Determination of trace phosphate ion in water by visual method after preconcentration on a membrane filter for field work

A sensitive visual method based on comparing the color intensity of precipitate as phosphomolybdenum blue on a membrane filter, has been developed for the determination of trace phosphate ion in water for field work. A sample solution containing 0.05-5.0 mug of phosphate was treated in a 25-ml polypropylene syringe, and the resulting precipitate was filtered through a membrane filter attached to the syringe. The color intensity of the precipitate on the membrane filter was measured visually following the standard series method. The coefficient of variation for five measurements at 0.5 mug of phosphate is 11%. The detection limit is 0.02 mug of phosphate ion in 22.5 ml (0.9 mug PO(3-)(4)/l) of water sample when the effective filtration area is 0.78 cm(2). The interference of various ions was studied and optimum conditions were developed for the determination of phosphate ion in natural water.     

Differential pulse polarography of some benzodiazepines and their determination in urine

A differential pulse polarographic method has been applied to the determination of diazepam, oxazepam, nitrazepam and flurazepam down to 2 x 10(-7)M (0.14 mug/ml). The method can also be used with biological materials such as urine, without prior extraction. Only a 2-ml volume of urine is necessary.     

Determination of fluoride in natural waters by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate

The most effective conditions for masking aluminium in the determination of mug/1. levels of fluoride in water by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate have been re-examined. The effectiveness of citrate for masking aluminium increases with pH, and up to 1.5 x 10(-2)M aluminium can be masked quantitatively at pH 8.5. Fluoride (5-100 mug in 500 ml of sample solution) is quantitatively co-precipitated at pH 4.7 with approximately 90 mg of aluminium phosphate. After dissolution of the precipitate and adjustment of the solution to pH 8.5 with TISAB, the fluoride content can be measured with a fluoride ISE. The method is simple and rapid, and is suitable for the determination of trace amounts of fluoride in various water samples.     

Indirect spectrophotometric determination of cerium(IV)

A simple and very fast photometric method for the determination of trace levels of cerium(IV) has been developed. Use has been made of the reaction in which iron (II), on oxidation with cerium(IV), gives iron(III) which is complexed with tiron, in acidic medium, to form a stable blue color, the intensity of which is in direct proportion to the amount of cerium(IV) originally present in the sample solution. In addition, the method has a wide range of determination and reasonable sensitivity, and it avoids both temperature control and the tedious extraction step.     

Spectrophotometric determination of bismuth with semi-xylenol orange and its application in metal analysis

Semi-Xylenol Orange forms a 2 : 1 chelate with bismuth(III), which has a logarithmic value of 3.08 for its conditional formation constant and a molar absorptivity of 4.2 x 10(4) l.mole(-1).cm(-1). Beer's law is obeyed at 540 nm over the range 10-30 mug of Bi(III), with a standard deviation of 1.1 mug (n = 18). Lactic acid is used as an auxiliary complexing agent to prevent olation and oxolation. Interference from up to 1.3 mg of copper can be eliminated by the combined use of masking Cu(II) with thiourea, ascorbic acid and thiosemicarbazide and "post-masking" Bi(III) with sodium chloride. The proposed method has been successfully applied to the direct determination of 0.002% of Bi in lead metal, with a coefficient of variation varying from 3.7 to 6.9%.     

Spectrophotometric determination of zinc with hydrazidazol in the presence of Triton X-100 and its application in metal analysis

A new spectrophotometric method for the determination of zinc is proposed. The chromogenic agent Hydrazidazol forms a 1:1 chelate with zinc in the presence of Triton X-100 in a medium containing 20-40% ethanol. The molar absorptivity and conditional formation constant have been found to be 2.7 x 1O(4) l.mole(-1).cm(-1) (at 640 nm) and 10(5.32) respectively. Beer's law is obeyed for zinc over the range of 0.2-0.8 mug/ml with a standard deviation of 0.024 mug/ml. The method can be applied to the determination of zinc in cadmium metal and its oxide after preconcentration by selective extraction of zinc thiocyanate into ethyl acetate in the presence of EDTA and thiosulphate as masking agents.     

Polarographic determination of fluoride using the adsorption wave of the Ce(III)-alizarin complexone-fluoride complex

A very sensitive electrochemical method for trace measurement of fluoride in water is discussed. The complex of cerium(III) with alizarin complexone (ALC) and fluoride ion is adsorbed at the dropping mercury electrode. In cathodic sweeps, the peak height is directly proportional to the concentration of fluoride over the range 8 x 10(-8)-5 x 10(-6)M (1.5 x 10(-9)-9.5 x 10(-8) g/ml), and the detection limit is 5 x 10(-8)M (9.5 x 10(-10) g/ml). The proposed method was applied to the determination of fluoride in water.     

Determination of Fluoride by Fluorescence Quenching

Abstract

A fluorescence quenching method for the determination of fluoride ion over the concentration range from 10^?9 to 10^?6M is presented. The fluoride ion is added to the fluorescent chelate of aluminum(III) and PAN [1- (2-pyridylazo)-2-naphthol]: the fluoride preferentially complexes the aluminum (III), displacing nonfluorescent PAN. Of the anions tested as possible interferences at equimolar levels, phosphate interferred seriously and iodide interferred somewhat.     

Indirect determination of fluoride in aqueous samples by inductively coupled plasma atomic emission spectrometry following precipitation of CeF3

An indirect fluoride determination method has been developed based on the ICP-AES determination of excess cerium(III) ion after precipitation. From four cations—Y(III), Sr(II), Ce(III), La(III)-cerium(III) proved to be the best precipitate forming cation in the 0-20 mg L⁻¹ fluoride concentration range with the limit of detection of 1.4 mg L⁻¹. The precision (RSD) of the proposed method is 0.71% at 8 mg L⁻¹ fluoride. The role of sulphate ions in the formation of the fluoride precipitate was studied as well. The applicability of the technique for the study of solid hazardous wastes as well as for groundwater monitoring of a fluoride contaminated area is demonstrated.     

Extraction of uranium(IV) from phosphoric acid solutions with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP)

The extraction of uranium(IV) from phosphoric acid solutions with PMBP and PMBP-TOPO mixtures has been studied. The synergic extraction with PMBP-TOPO is more effective than the simple chelate extraction with PMBP and both systems are more effective than the synergic extraction of uranium(VI) with DEHPA-TOPO. It is established that the complexes extracted are U(PMBP)(4) and U(PMBP)(4).TOPO for the chelate and synergic extraction respectively. The most probable uranium(VI) species in the aqueous phase (2.9-6.33M H(3)PO(4)) is the neutral complex U(H(5)P(2)O(8))(4). Analytical methods suitable for determination of uranium in phosphoric acid solutions have been developed. The highest sensitivity is achieved by combining the synergic extraction with the uranium(IV)-arsenazo III colour reaction.     

Separation of antimony(III) with iodide and dithizone by sorption on polyurethane foam from sulphuric acid medium for its spectrophotometric determination in glasses

A method for quantitative separation of antimony(III) by sorption on polyether based polyurethane foam and its spectrophotometric determination has been described. The method involves formation of a pink-red complex of antimony(III) with iodide (0.045M) and dithizone (2.3 x 10(-5)M) in 0.25-0.75M H(2)SO(4) medium, sorption of the complex on polyurethane foam (within 45 min) at room temperature followed by its elution with acidified acetone (acetone containing 0.008% H(2)SO(4)) and spectrophotometric measurement at 507.2 nm ( = 2.56 x 10(4) l mol cm). The method obeys Beer's law from 0.1 to 6.0 mug antimony(III). Tolerance limits of other ions are Co (100 mug), Ni (100 mug), Fe (10 mug), Cu (0.5 mug), Sn (20 mug), Zn (100 mug), As (100 mug), Mn (200 mug), Pb (50 mug), Ti (100 mug), V (50 mug), etc. Interference by iron and copper have been eliminated by treating with KOH prior to the extraction of antimony. The method has been standardized with glass samples spiked with known amounts of antimony and applied to the determination of antimony in various glasses.