[Show abstract][Hide abstract] ABSTRACT: The complextion reaction between Y3+ cation with macrocyclic ligand, 4′-nitrobenzo-18-crown-6 (4′NB18C6), was studied in acetonitrile-methanol (AN-MeOH), acetonitrile-1,2-dichloroethane (AN-DCE), acetonitrile-dimethylformamide (AN-DMF) and acetonitrile- ethylacetate (AN-EtOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most cases, the stoichiometry of complex formed between 4′NB18C6 and Y3+ cation is 1:1 [M:L], but in the case of AN-DCE binary solution (mol%DCE=50) at 15, 25 and 35°C, a 2:1 [M2:L] and also a 2:2 [M2:L2] complexes are formed in solution.The results show that the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation changes with the composition of the mixed solvents and even with temperature. The stability constant of the 1:1 complex was determined using a computer program, GENPLOT. The stability order of (4′NB18C6.Y)3+ complex in pure studied solvents at 25°C was found to be: EtOAc > AN > MeOH > DMF and in the case of the mixed solvent solutions with 25 mole percent of AN at 25°C was: AN-DCE > AN-EtOAc > AN-MeOH ∼ AN-DMF. The values of stability constant (logKf) of (4′NB18C6.Y)3+ complex which was obtained from conductometric data, show that the stability of the complex is not only affected by the nature and composition of the solvent system, but it is also influenced by the temperature. In all cases, a non-linear behavior is observed for changes of logKf of the (4′NB18C6.Y)3+ complex versus the composition of the binary mixed solvents. The values of standard thermodynamic quantities (ΔH°c and ΔS°c) for the complexation process which were obtaind from temperature dependence of the stability constant of (4′NB18C6.Y)3+ complex, show that depending on the solvent system, in most cases, the complex is enthalpy and also entropy stabilized, but in some cases, it is estabilized or destabilized from these view points.
Arabian Journal of Chemistry 08/2014; · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new flow injection method coupled to an electrochemical hydride generator with atomic absorption spectrometry was proposed for determination of cadmium. The influence of the experimental parameters such as cathode material, catholyte type, sample volume, catholyte flow rate, temperature of the atomizer, catholyte concentration, carrier gas flow rate, electrolytic current and cathode surface area on the analytical response was studied. Under the optimized conditions, the calibration curve was linear in the range of 2–50 ng mL− 1 of Cd. A concentration detection limit (3σb, n = 9) of 0.61 ng mL− 1 Cd and a relative standard deviation of 5.1% (RSD, n = 9) for 20 ng mL− 1 Cd were obtained. The potential interferences from various ions were also evaluated. The accuracy of the method was verified by the determination of cadmium in a certified reference material. The calculated concentration of Cd in CRM was found to be in good agreement with the certified value.
[Show abstract][Hide abstract] ABSTRACT: Headspace single-drop microextraction (HS-SDME) coupled with gas chromatography with electron capture detection (GC-ECD) was used for quantification of total iodine in milk based samples of infant formula. In this procedure 3 μL of a mixture containing 1-octanol and 3-pentanone was exposed to the headspace of a 5 mL acidic (H2SO4, 2 mol L−1) aqueous solution containing 1.5 mol L−1 ZnSO4 for 30 minutes followed by addition of 1 mL of 1 mol L−1 H2O2 for in situ generation of iodine. Optimization of the microextraction system was carried out using the Taguchi experimental design method. The limit of detection was determined to be 250 ng L−1 with an enrichment factor of 150. The repeatability, expressed as a relative standard deviation, was 1.9% (n = 6). The linear calibration working range was between 0.75 and 2000 μg L−1 (r2 = 0.998). The method was successfully applied for determination of iodine in milk based samples of infant formula.
[Show abstract][Hide abstract] ABSTRACT: A novel electrochemical hydride generation (ECHG) system working in flow-injection (FI) mode was developed for determination of cadmium coupled to an electrically heated quartz tube atomizer (QTA) by atomic absorption spectrometry (AAS). A Plackett-Burman experimental design for screening has been used to evaluate the influence of several variables on the analytical response. Then, the significant parameters such as the concentration of NaCl in catholyte, applied electrolytic current and flow rate of carrier gas have been simultaneously optimized using a central composite design (CCD). Under the optimized conditions, the detection limit (3σ(b), n=9) was found to be 0.51 ng mL(-1) Cd and the relative standard deviation (RSD) for nine replicate analyses of 20 ng mL(-1) Cd was 6.5%. The calibration curve was linear in the range of 2-50 ng mL(-1) of Cd. The potential interferences from various ions were also evaluated. The analysis of a reference material showed good agreement with the certified value. The proposed method was successfully applied to the determination of Cd in tap water sample.
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to compare the performance of an artificial neural network (ANN) model and a 3-phase segmented linear regression model to describe the relationship between flock age and hatchability in broiler breeder flocks. The predictive quality of these models was tested for an external validation set of 14 wk, randomly chosen from 39 wk. The accuracy of the models was determined by the r2 value, mean square error, bias, and Theil’s U-statistic parameters. The r2 values of the 3-phase segmented linear regression and ANN models were 0.4003 and 0.9984, respectively. Therefore, the ANN produced more accurate predictions of hatchability than the 3-phase segmented linear regression model. We conclude, based on the results of this study in commercial broiler breeder flocks, that hatchability is a function of flock age and that the relationship can be described by an ANN model.
The Journal of Applied Poultry Research 08/2011; 20(3):447-453. · 0.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An electrochemical hydride generation (ECHG) technique was developed to improve the determination of thallium by atomic spectrometry. The technique is based on the catholyte variation system for production of thallium hydride. Using Pb-Sn alloy as cathode, a transient peak shaped signal was achieved and its height, the maximum absorbance value, was taken as an analytical parameter. Parameters that might affect the hydride generation efficiency were investigated and the analytical performance of the method under the optimized experimental conditions was assessed. The linear range was 1-250 ng mL(-1) for thallium and the relative standard deviation of the method was 4.2% (RSD, n=7). The LOD for thallium was found to be 0.8 ng mL(-1), showing a significant improvement relative to conventional chemical hydride generation techniques. The proposed method was applied to the determination of thallium in unalloyed zinc standard reference material. This method offers high sensitivity, simplicity, rapidness, freeness from reagent and low acid consumption.
[Show abstract][Hide abstract] ABSTRACT: The complexation reactions between some rare earth metal cations (Ln; Y3+, La3+ and Ce3+) with 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), benzo-18-crown-6 (B18C6) and decyl-18-crown-6 (Dec18C6), have
been studied in methanol–acetonitrile (MeOH–AN) and methanol–water (MeOH–H2O) binary mixtures using a competitive spectrophotometric method. 2-(2-thiazolylazo)-4-methyl phenol (TAC or L) was used as
colorimetric complexant. It was found that the selectivity order of TAC for Ln cations is highly changed with changing the
composition of the mixed solvents. Moreover, as the concentration of acetonitrile increases in MeOH–AN binary mixture, the
stability of Ln–TAC complexes increases and passes through a maximum at a certain mole fraction of acetonitrile. In addition,
the stability of Ln–crown ether complexes increases with increasing the concentration of methanol in MeOH–H2O and acetonitrile in MeOH–AN binary solutions. A non linear behaviour was observed for variation of stability constants of
all complexes versus the composition of the mixed solvents. The results show that 18C6 generally forms more stable complexes
with La3+ and Ce3+ cations than DC18C6 in methanol and MeOH–H2O binary mixtures, while this sequence is reversed in the methanol-acetonitrile binary mixtures which are rich with respect
Journal of Inclusion Phenomena 01/2009; 63(1):43-52. · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aluminium was determined in a weakly alkaline medium by reaction with alizarin at trace level. Flotation of the complex was carried out with heptane, followed by dissolution in N, N-dimethylformamide (DMF) for subsequent spectrophotometric determination. The molar absorptivity was 2.92×10 mol cm at 518 run. Beer's law was obeyed in the range 5–80 μg/1 and the detection limit was 0.4μg/l.The reliability of the procedure was confirmed by determination of a sample of milk with Graphite Furnace Atomic Absorption Spectrophotometric method (GFAAS). The precision and accuracy of the method were both acceptable via F and tests at the 95% confidence level.
[Show abstract][Hide abstract] ABSTRACT: The kinetic methodology based on the difference of reaction rates, is based on the reaction between a common oxidizing agents such as tris(1,10-phenanthroline) and iron(III) complex (ferriin, [Fe (phen)3]3+) in the presence of citrate and spectrophotometrically, monitoring the changes of absorbance at the maximum wavelength of 511 nm. Experimental conditions such as pH, reagents and citrate concentrations were optimized, and the data obtained from the experiments were processed by several chemometric approaches, such as artificial neural network (ANN) and partial least squares (PLS). A set of synthetic mixtures of carbidopa (CD), levodopa (LD) and methyldopa (MD) was evaluated and the results obtained by the applications of these chemometric approaches were discussed and compared. It was found that the back propagation artificial neural network (BP-ANN) method afforded better precision relatively than those of radial basis function artificial neural networks (RBF-ANN) and PLS. The proposed method was also applied satisfactorily to the determination of carbidopa, levodopa and methyldopa in real samples.
[Show abstract][Hide abstract] ABSTRACT: The mechanistic aspects of a novel methodology for the electrochemical hydride generation (EcHG) of cadmium, entitled as the catholyte variation, have been studied. The hydrogen overvoltage of different cathode materials was determined in dilute electrolyte. The lead-tin alloy used as the cathode material for the EcHG of Cd had the highest hydrogen overpotential. In this technique, both electrolyte medium and cathode surface would change during electrolysis. The catholyte variation EcHG coupled with a flame heated quartz tube atomizer (QTA) atomic absorption spectrometer (AAS) produced peak-shaped transient signal of Cd. The analytical signal was significantly enhanced at neutralization time. The simultaneous production of lead and tin hydrides as well as the hydrogen at that time may speed up the desorption of cadmium species from the surface of the cathode. Also the high hydrogen overvoltage and the neutral medium aided the formation and separation of cadmium hydride molecules. The generated CdH2 vapour was kinetically stable.
[Show abstract][Hide abstract] ABSTRACT: 2,3-Bis(p-methoxybenzoyl)cyclopentadiene was studied as iron(III)-chelating agent. Its pK
a value was determined by spectrophotometry (pK
a = 8.27 ± 0.02 at 25 ± 0.1°C; λ = 421 nm). 2,3-Bis(p-methoxybenzoyl)cyclopentadiene reacts with Fe3+ ions in aqueous ethanol (1:1, by volume) to give a 2:1 ligandmetal complex. The effects of different factors on the complex
formation were studied. The reaction of 2,3-bis(p-methoxybenzoyl)cyclopentadiene with Fe3+ ions can be used as an alternative method for spectrophotometric determination of iron(III) in a range of concentrations
from 0.1 to 1 μg cm−3, where the Beer law is fulfilled with a correlation coefficient of 0.9992. The results of spectrophotometric determination
of iron(III) in geological materials (iron rock) showed very good agreement with those obtained by the atomic absorption measurements.
Russian Journal of General Chemistry 04/2006; 76(5):753-756. · 0.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purposes of the present study were to identify the correlation of total calcium (TCa) with albumin and total protein (TPro)
in normal, hypoproteinemic and/or hypocalcaemic cows and to determine the usefulness of adjusted Ca formulas in assessing
Ca levels in hypoproteinemic and/or hypocalcaemic conditions. Two hundred and nineteen clinically healthy Holstein dairy cows
were selected from 15 herds. Another 51 Holstein cows up to 48h after parturition were sampled. Ten out of these cows developed
parturient paresis. Serum Ca, albumin and TPro concentrations were measured using automated biochemical analytical techniques.
Results were analysed by Student’s t test, Pearson’s correlation coefficient test and regression analysis. TCa concentration correlated with the concentrations
of albumin (r=0.53, p<0.001) and TPro (r=0.603, p<0.001) in the serum of 219 lactating cows. Two correction formulas for Ca were derived on the basis of concentrations of
albumin and TPro: (1) adjusted Ca by albumin (mmol/L)=measured serum TCa (mmol/L)−0.02 serum albumin (g/L)+0.78; (2) adjusted
Ca by TPro (mmol/L)=measured serum TCa (mmol/L)−0.015 serum TPro (g/L)+1.2. The results indicate that TCa does not reflect
the true Ca situation of the body in hypoproteinemic conditions and adjusted formulas may be appropriately used to correct
TCa. In hypocalcaemic and normoproteinemic conditions (such as parturient paresis in cattle), TCa and adjusted Ca values correctly
reflect the true Ca situation of the body.
[Show abstract][Hide abstract] ABSTRACT: An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead–tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett–Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml−1of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml−1 and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml−1. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.
[Show abstract][Hide abstract] ABSTRACT: The possibility of applying headspace microextraction into a single drop for the determination of amines in aqueous solutions is demonstrated. A 1mul drop of benzyl alcohol containing 2-butanone as an internal standard was suspended from the tip of a micro syringe needle over the headspace of stirred sample solutions for extraction. The drop was then injected directly into a GC. The total chromatographic determination was less than 10min. Optimization of experimental conditions (sampling time, sampling temperature, stirring rate, ionic strength of the solution, concentration of reagents, time of extraction and organic drop volume) with respect to the extraction efficiency were investigated and the linear range and the precision were also examined. Calibration curves yielded good linearity and concentrations down to 2.5ngml(-1) were detectable with R.S.D. values ranging from 6.0 to 12.0%. Finally, the method was successfully applied to the extraction and determination of amines in tap and river water samples. This system represents an inexpensive, fast, simple and precise sample cleanup and preconcentration method for the determination of volatile organic compounds at trace levels.
[Show abstract][Hide abstract] ABSTRACT: An outbreak of cyanide poisoning that killed 56 ewes and 2 goats is reported. Fluid released into a ditch contained 1 g cyanide/L and produced toxicity in 3 ewes experimentally dosed with the liquid waste.
Veterinary and human toxicology 09/2004; 46(4):186-7.
[Show abstract][Hide abstract] ABSTRACT: For the selective separation of rare earth(III) ions (RE(III)), flotation spectrophotometric behaviors of these ions were investigated using alizarin both in the absence and in the presence of 1,10-phenanthroline (phen). The synergic effect of phen during the formation of stable ternary complexes with RE(III) ions, which influences the flotation process, was evaluated spectrophotometrically. After the pH of the media was varied and the other parameters were kept constant, the flotation process was followed with separation and dissolution of the complex in N,N-dimethylformamide (DMF) for measuring the absorbance. It was shown that after the pH was raised from 5, the synergic effect was observed for a number of light RE(III) ions followed for the others as the pH was increased to higher values. These observations, on one hand, are related to the others in terms of the characteristic properties of alizarin, phen, and their interactions, moreover to the type of RE(III) ions, so that the revealed differences between the properties of RE(III) ions can be realized for mutual separation of these ions.
Journal of Colloid and Interface Science 12/2002; 256(2):472-476. · 3.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel sample preparation technique, membrane extraction with a sorbent interface (MESI) has been optimized and used for continuous monitoring thermal degradation products in polyacrylonitrile (PAN) polymer headspace at different temperatures, followed by gas chromatography-mass spectrometry (GC-MS). MESI with a flat sheet poly(dimethyl siloxane)-polycarbonate (PDMS-PC) membrane and Tenax trap was used. The system is very simple, fast and reliable and allowed us to extract, enrich and continuously monitor major volatile compounds released from the polymer at different temperatures. The volatile and semi-volatile gaseous degradation products were identified. Sensitivity of the method depends on the length of time for trapping.
The Analyst 08/2002; 127(7):912-6. · 3.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The complexation of Pb2+, Tl+ and Cd2+ cationsby 18-crown-6 was studied in water/propanol (H2O/PrOH),water/acetonitrile (H2O/AN) and water/dimethylformamide(H2O/DMF) binary systems at 20 °C using squarewave polarography (SWP) and differential pulse polarography (DPP).It was confirmed that the stoichiometry of each of the complexes formed between 18C6 and the respective cations is 1 : 1. The formation constants of the complexes were found to increase with increasing concentration of the non-aqueous solvent. In all cases, a stability order of Pb2+ > Tl+ > Cd2+ was observed. In general,the stabilities of individual complexes were found to decrease as the binary solvent mixture varied from H2O/AN to H2O/PrOH to H2O/DMF.
Journal of Inclusion Phenomena 12/2000; 38(1-4). · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The complexation reaction between UO2
2+ cation with macrocyclic ligand, 18-crown-6 (18C6), was studied in acetonitrile–methanol (AN–MeOH), nitromethane–methanol
(NM–MeOH) and propylencarbonate–ethanol (PC–EtOH) binary mixed systems at 25°C. In addition, the complexation process between
2+ cation with diaza-18-crown-6 (DA18C6) was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–ethanol (AN–EtOH), acetonitrile–ethylacetate
(AN–EtOAc), methanol–water (MeOH–H2O), ethanol–water (EtOH–H2O), acetonitrile–water (AN–H2O), dimethylformamide–methanol (DMF–MeOH), dimethylformamide–ethanol (DMF–EtOH), and dimethylformamide–ethylacetate (DMF–EtOAc)
binary solutions at 25°C using the conductometric method. The conductance data show that the stoichiometry of the complexes
formed between (18C6) and (DA18C6) with UO2
2+ cation in most cases is 1:1 [M:L], but in some solvent 1:2 [M:L2] complex is formed in solutions. The values of stability constants (logKf) of (18C6·UO2
2+) and (DA18C6·UO2
2+) complexes which were obtained from conductometric data, show that the nature and also the composition of the solvent systems
are important factors that are effective on the stability and even the stoichiometry of the complexes formed in solutions.
In all cases, a non-linear relationship is observed for the changes of stability constants (logKf) of the (18C6·UO2
2+) and (DA18C6·UO2
2+) complexes versus the composition of the binary mixed solvents. The stability order of (18C6·UO2
2+) complex in pure studied solvents was found to be: EtOH>AN≈NM>PC≈MeOH, but in the case of (DA18C6·UO2
2+) complex it was : H2O>MeOH>EtOH.
Journal of Inclusion Phenomena 64(1):49-56. · 1.40 Impact Factor