Simultaneous spectrofluorimetric determination of europium, dysprosium, gadolinium and terbium using chemometric methods

A spectrofluorimetric method for the simultaneous determination of dysprosium, europium, gadolinium and terbium in ternary and quaternary mixtures by the use of pyridine-2,6-dicarboxylic acid as a chelating agent was developed. The influence of chemical variables affecting the analytical reaction was evaluated. A partial least-squares procedure and PC Quant software were used to assess data obtained from a variable number of calibration solutions and wavelengths. The ensuing method was validated by applying it to the analysis of synthetic ternary (Eu-Dy-Tb) and quaternary mixtures (Eu-Dy-Gd-Tb) over the concentration ranges 60-550 mug Eu l(-1), 30-400 mug Dy l(-1) and 30-400 mug Tb l(-1) in the former, and 20-220 mug Eu l(-1), 20-235 mug Dy l(-1), 25-230 mug Gd l(-1) and 75-230 mug Tb l(-1) in the latter. The results obtained by using the two quantitation procedures are compared. The relative errors in the determinations were less than 8% in most cases.     

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.     

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.     

Colour reaction of chromium (VI) with N,N-diethyl-1,4-phenylenediame in the presence of ethanol and cyclohexyldiamine tetraacetic acid as well as its application in the species analysis of chromium

A simple, rapid and precise spectrophotometric method for the determination of Chromium (III and IV) has been developed. The reaction of Cr(VI) with N,N-diethyl-1,4-phenylenediamine is almost complete in a twinkling, which yields a red product with a wavelength of maximum absorption at 530 nm. Beer's Law is obeyed in the Cr concentration range of 0-2.0 mug ml(-1). The molar absorptivity is 5.0x10(4) l mol(-1) cm(-1), limit of detection 0.002 mug ml(-1) and relative SD=1.13% for 5.04 mug Cr. The colouring rate and absorbance are not noticeably affected by temperature from 2 to 45 degrees C. The amounts of Cr(VI) and Cr(III) were measured by determining Cr(VI) first under the condition of masking Cr(III) by cyclohexyldiamine tetraacetic acid, and then the total amount by oxidation of Cr(III). The method was applied to the analyses of some industrial waste waters containing Cr with satisfactory results.     

Flow injection determination of iron by its catalytic effect on the oxidation of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide

A flow injection-photometric method has been developed for the determination of iron(II+III). The method is based on the catalytic effect of iron(III) on the hydrogen peroxide oxidation of 3,3',5,5'-tetramethylbenzidine to form a blue compound (lambda(max)=650 nm). In this catalyzed reaction, 1,10-phenanthroline acted as an effective activator. Iron(II) is also determined, being oxidized by hydrogen peroxide. Calibration graphs for iron(II) and iron(III) obtained under the optimized conditions were identical with each other and linear in the range 0.2-200 ng ml(-1) with a detection limit of 0.05 ng ml(-1) iron. The reproducibility was satisfactory with a relative S.D. of 1.0% for ten determinations of 5 ng ml(-1) iron(III). The proposed method was successfully applied to the determination of iron in river and lake water samples and can be determined free iron species.     

Chemometric study of selected polychlorinated biphenyls in ambient air of Madrid (Spain)

The formation of Fe(III) and Fe(II) chelates with pyridylazo and thiazolylazo reagents was examined. Optimum conditions for the formation of Fe(III) and Fe(II) chelates with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) were in detail evaluated. The LC method for simultaneous separation of Fe(III) and Fe(II) ions as 5-Br-PADAP chelates was evaluated using the PEEK column with C18 e.c. stationary phase and acetonitrile+water (90:10, v/v) eluent containing the 1x10(-3) mol l(-1) C(12)H(25)SO(3)Na, the ion-pairing reagent, pH 3.4-3.6. The simultaneous determination of 20-500 mug l(-1) Fe(II) ions (detection at 555 nm) and 20-500 mug l(-1) Fe(III) ions (detection at 585 nm) as 5-Br-PADAP chelates (for both ions, detection limit, 18 mug l(-1) for 20 mul loop) was established. The chromatographic method was applied to the water analysis. Although the present method is able to determine both Fe(III) and Fe(II) ions, the Fe(III) ion was not detected in all water samples. The Fe(II) was detected only in fresh gathered oligocene water at the level of 135 mug l(-1). The present method was used to the investigation of the distribution of Fe(III)/Fe(II) ions in aqueous and micellar solutions after action of external, ultrasonic field.     

Sensitive spectrofluorimetric determination of ruthenium at nanotrace levels using 2-(alpha-pyridyl) thioquinaldinamide [PTQA

A new spectrofluorimetric method for the determination of ruthenium with nonfluorescent 2-(alpha-pyridyl) thioquinaldinamide (PTQA) is described. The oxidative reaction of Ru(III) upon PTQA gives oxidised fluorescent product (lambda(ex(max))=347 nm; lambda(em(max))=486 nm). The sensitivity of the fluorescence reaction between ruthenium and PTQA is greatly increased in the presence of Fe (III). The reaction is carried out in the acidity range 0.01-0.075 M H(2)SO(4). The influence of reaction variables is discussed. The range of linearity is 1-400 microg l(-1) Ru(III). The standard deviation and relative standard deviation of the developed method are +/-1.210 microg l(-1) Ru (III) and 2.4%, respectively (for 11 replicate determinations of 50 microg l(-1) Ru (III)). The effect of interferences from other metal ions, anions and complexing agents was studied; the masking action is discussed. The developed method has been successfully tested over synthetic mixtures of various base metals and platinum group metals, synthetic mixtures corresponding to osmiridium, certified reference materials in spiked conditions and rock samples.     

Determination of clenbuterol in pharmaceutical preparations by reaction with o-phthalaldehyde using a flow-injection fluorimetric procedure

A new procedure for the determination of clenbuterol is proposed using flow-injection and fluorimetric detection. The method is based on the derivatization reaction of the primary amine group with o-phthalaldehyde in the presence of 2-mercaptoethanol. The calibration graph based on peak area was linear in the range 0.2-5 mug ml(-1) and the detection limit was 0.06 mug ml(-1). The method was validated using a reference spectrophotometric procedure and was applied to the determination of the drug in commercial pharmaceutical preparations.     

Spectrophotometric determination of bismuth(III) with o-hydroxyhydroquinonephthalein in the presence of Brij 58

A simple and sensitive spectrophotometric determination of bismuth(III) is based on the reaction between bismuth(III) and o-hydroxyhydroquinonephthalein in the presence of Brij 58 in acidic media. The calibration graph is linear over the range 0-3.5 mug/ml bismuth(III) in the final solution, and the apparent molar absorptivity at 520 nm is 9.03 x 10(4) l. mole(-1). cm(-1). The proposed method is 2-10 times more sensitive than other methods, and simpler. It has been applied to the assay of bismuth(III) in pharmaceutical preparations, such as dermatol and bismuth subnitrate, with good results.     

Spectrophotometric determination of Sb(III) in Sb(III)/Sb(V) binary mixtures using sodium dodecylsulfate/nonylphenoxy polyethoxyethanol mixed micellar media

Different micellar media had different effects on the absorption spectra of the complexes of bromopyrogallol red with Sb(III) and Sb(V). The mixed micellar medium composed of 0.7 ml of 0.2% sodium dodecylsulfate (SDS) and 0.3 ml of 2% nonylphenoxypolyethoxyethanol (OP) at 80 degrees C could be used for the sensitive determination of Sb(III) in Sb(III)/Sb(V) binary mixtures. Under the optimal conditions, Beer's Law was obeyed over the range 0.1-2.3 mug ml(-1) Sb(III) with molar absorptivity at 538 nm being 4.8 x 10(4) l mol(-1) cm(-1) and detection limit 0.04 mug ml(-1). For 10 mug Sb(III), more than 100 mug Sb(V) could be tolerated (error < 3%) in the presence of SDS/OP micellar medium as compared with 0.1 mug Sb(V) in the absence of SDS/OP micellar medium. In addition, the sensitivity of Sb(III) in the micellar medium was much higher than that in pure water medium. As compared with conventional extraction spectrometry, the proposed method produced a reproducible result. It did not need the conversion of Sb(III) to Sb(V) and a time-consuming extraction process. A detailed discussion on the selection of surfactants, the effect of temperature, and the role played by the mixed surfactants were also made.     

Preconcentration of Cr(III), Co(II), Cu(II), Fe(III) and Pb(II) as calmagite chelates on cellulose nitrate membrane filter prior to their flame atomic absorption spectrometric determinations

A method for the preconcentration and determination of Cr(III), Co(II), Cu(II), Fe(III) and Pb(II) ions by atomic absorption spectrometry has been described. The method was based the collection of metal-calmagite complexes on a soluble cellulose nitrate membrane filter. The detection of the solution was obtained by flame atomic absorption spectrometry (FAAS) after completely dissolving the membrane with 0.5 ml of nitric acid at 80 degrees C. The metal ions were recovered quantitatively at pH 8. Various factors which affect the collection and determination of metal ions such as, type and size of the membrane filter, solvent for dissolution of the species retained on the filter were investigated. The detection limits were varying 0.06 mug l(-1) for Cu to 2.5 mug l(-1) for Cr. An application of the proposed method for analyte ions in mineral and tap water samples was also described with satisfactory results (recoveries >95%, relative standard deviations <10%).     

Non-extraction batchwise and FIA determination of cationic and nonionic surfactants using Cu(II)-chromazurol S-surfactant complexes

Batchwise and FIA determinations have been developed for cationic and nonionic surfactants, based on the formation of ternary Cu(II)-chromazurol S-surfactant compounds. Optimum reaction conditions have been found (pH 8.0, lambda=590 and 630 nm, respectively). For the batchwise measurement, the molar absorption coefficient values epsilon(590)=5.1-5.7x10(4) l mol(-1) cm(-1) for cationic surfactants, epsilon(630)=0.7-1.5x10(4) l mol(-1) cm(-1) for nonionic surfactants. A factorial design has been carried out to determine the optimum flow conditions. Calibration curves were constructed and statistically evaluated for both the batchwise and FIA determination. For example, the linear concentration ranges for batch determination of the cationic surfactant cetyltrimethylammonium bromide and nonionic surfactant Marlophen NP 10 are 0-15 mug ml(-1) (R=0.9996, R.S.D.=6.62-0.64%) and 13-53 mug ml(-1) (R=0.9993, R.S.D.=4.48-1.40%), respectively; the respective detection limits are 0.02 and 4.0 mug ml(-1). For FIA determination of the same surfactants, the linear concentration ranges are 0-13 mug ml(-1) (R=0.9995, R.S.D.=4.44-0.49%) and 66-397 mug ml(-1) (R=0.9994, R.S.D.=8.92-1.12%), respectively, detection limits are 0.08 and 38 mug ml(-1), respectively.     

Determination of nitrite by sequential injection analysis of electrokinetic flow analysis system

A new sequential injection analysis (SIA) method of an electrokinetic flow analysis (EKFA) system for the determination of nitrite-nitrogen is presented in this paper. The proposed system mainly consisted of an electroosmotic pump, two solenoid valves and a spectrophotometer etc. All the pump and valves were controlled by a personal computer automatically. The determination method of nitrite-nitrogen was based on the reaction among nitrite, sulfanilamide and naphthylethylenediamine to form a colored compound, which was measured at 540 nm. The linear calibration range of nitrite-nitrogen was 10-800 mug l(-1). The detection limit was 1 mug l(-1) (K=3, n=11). The analytical method can provide a throughput of 33 samples per h.     

Determination of soluble chromium in simulated PWR coolant by differential-pulse adsorptive stripping voltammetry

An analytical method has been developed for the determination of dissolved chromium at concentrations less than 2 mug/l. in PWR coolant by differential-pulse adsorptive stripping voltammetry at a hanging mercury drop electrode. Concentrations above 2 mug/l. can be determined by appropriate dilution of the sample. The method is based on measurement of the current associated with reduction of a chromium(III)-DTPA (diethylenetriaminepenta-acetic acid) complex adsorbed at the surface of the mercury drop. The effects of boric acid, pH, DTPA concentration, accumulation potential and time were investigated together with the oxidation state of the chromium. No interference was observed from other transition metal ions expected to be present in PWR coolant. No alternative chemical technique of similar sensitivity was available for comparison with the results obtained in solutions containing <1 mug/l. chromium. Recoveries from simulated coolant solutions were greater than 95% and the relative standard deviations for single determinations were in the range 12-25%. The statistical limit of detection at the 95% confidence level was 0.023 mug/l. This method of analysis should prove valuable in corrosion studies and is uniquely capable of following the changes in soluble chromium concentration in PWR coolant that follow operational changes in the reactor.     

Indirect spectrophotometric determination of ascorbic acid with ferrozine by flow-injection analysis

A FIA indirect spectrophotometric determination of ascorbic acid was developed using its reducing action on Fe(III) in acidic medium and following the spectrophotometric determination of the reduced iron by using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine) as chromogenic reagent in buffered medium (pH 5.5) and monitoring the absorbance signal at 562 nm. A three-line manifold with two reaction coils was used: in the first reaction coil, ascorbic acid reduces Fe(III) to Fe(II); and in the second one, the complexation reaction is developed. The linear range of the method was 0.5-10 mug ml(-1) of ascorbic acid, the detection limit being 0.028 mug ml(-1). The proposed method was sensitive, rapid (sampling rate of 90 samples h(-1)) and reproducible (RSD 0.19%, n=10). Satisfactory results were obtained in the determination of ascorbic acid in pharmaceutical preparations, fruit juices and urine testifying the applicability of the method to real samples.     

Atomic fluorescence spectrometric determination of trace amounts of arsenic and antimony in drinking water by continuous hydride generation

A highly sensitive and simple method has been developed for the determination of As(III), total As, Sb(III) and total Sb in drinking water samples by continuous hydride generation and atomic fluorescence spectrometry (HGAFS). For As determination, water samples aspirated in a carrier of 2 mol l(-1) HCl were merged with a reducing NaBH(4) 3%(m/v) solution, with sample and NaBH(4) flow rates of 12.5 and 1.5 ml min(-1) respectively. The hydride generated in a 170 cm reaction coil was transported to the detector with an Ar flow of 400 ml min(-1), and a limit of detection between 5 and 20 ng l(-1) was obtained. For Sb determination, 2.5 mol l(-1) HCl and 2%(m/v) NaBH(4) were employed, with respective flow rates of 9.7 and 2 ml min(-1). The hydride generated in a 50 cm reaction coil was transported to the detector with an Ar flow rate of 300 ml min(-1), and a limit of detection between 6 and 14 ng l(-1) was obtained. Determination of the total concentration of these elements was obtained after a previous reduction with KI. Recovery studies of different added concentrations of these species in natural water samples were between 93 and 104% for As(III), 96-103% for As(V), 93-101% for Sb(III) and 90-119% for Sb(V).     

Photometric measurement of trace As(III) and As(V) in drinking water

A simple, fast and sensitive light-emitting diode (LED)-based photometric method for the differential determination of ppb-ppm levels of As(III) and As(V) in potable water in the presence of ppm levels of phosphate was developed. The detection chemistry is based on the well-known formation of arsenomolybdate, followed by reduction to heteropoly blue. The front-end of the measurement system is configured to selectively retain P(V) and As(V), based on the considerable difference of the pK(a) of the corresponding acids relative to As(III). Thus, it is As(III) that is injected into the medium, oxidized in-line with KBrO(3) to As(V) and forms Mo-blue that is detected by an LED-based detector. Only As(III) is measured if the sample is injected as such; if all As in the sample is prereduced to As(III) (by the addition of cysteine, in a provided in-line arrangement), the system measures As(V)+As(III). In the present form, limit of detection (LOD) (S/N=3) is less than 8 mug l(-1) As, and the linear range extends to 2.4 mg l(-1). Potential interference from dissolved silica and Fe(III) is eliminated by the addition of NaF to the sample.     

Malachite green as a reagent for detection and spectrophotometric determination of chromium(VI)

A sensitive and inexpensive method of spectrophotometric determination of chromium(VI), based on the absorbance of its complex with malachite green and acetic acid at pH 2.5 is reported. The complex shows a molar absorptivity of 8 x 10(4) l.mole(-1) cm(-1) at 560 nm, using malachite green and acetic acid as reference solution. The effect of time, temperature, pH and reagent concentration is studied and optimum operating conditions are established. Beer's law is applicable in the concentration range 2.0-22.8 mug/ml chromium(VI). The resin beads act as a catalyst and as little as 1.6 mug of chromium(VI) is detected in the resin phase as compared to 4.1 mug in the solution phase. The standard deviation in the determinations is +/-0.40 mug/ml for a 10.35 mug/ml 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.     

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.