An optimized on-line preconcentration system for analysis of trace gold in ore samples

A flow injection on-line preconcentration technique, combined with graphite furnace atomic absorption spectrometry for the determination of gold in ore samples has been presented. An alpha-amino pyridine resin (AP) was loaded onto a microcolumn as the preconcentration reagent and a solution of 90% acetone-5% HCl-5% H(2)O was used for the gold elution. The Scaled Simplex Method was employed to optimize the flow injection manifold. The selected factors were optimized by the simultaneous consideration of two responses, absorbance and column retention efficiency, with only 12 tests. A detection limit of 0.065 mug Au/l (3sigma) with a relative standard deviation of 4.3%, was achieved. Ore samples containing gold have been analysed successfully using the proposed method.     

Electrothermal atomic absorption spectrometric determination of ultra-trace amounts of tin by in situ preconcentration in a graphite tube using flow injection hydride generation with on-line ion-exchange separation

A method was developed for the ultra-trace determination of tin by in situ preconcentration in a graphite tube using a flow injection hydride generation technique with on-line ion-exchange separation. The sample was prepared in 2M hydrochloric acid before being passed through an incorporated micro-column packed with a strongly basic anion-exchanger D-201. The tin was retained as its chlorostannate complex and subsequently eluted by de-ionized water into the hydride generation system. The hydride and hydrogen gases evolved were separated from the liquid phase in a gas-liquid separator and transferred into a palladium-coated graphite tube pre-heated to 300 degrees C to collect the analyte, which was later atomized at 2300 degrees C. With the reported system, tin was determined at a sampling frequency of 30/hr with a detection limit (3sigma) of 0.01 mug/l. using 10.7 ml sample. The precision was 1.5% RSD at the 0.5 mug/l. level. The proposed method was applied to the determination of tin in tap water, hair, serum samples and geological reference samples.     

The design of an on-line flow injection system with a gravitational phase separator for flame atomic absorption spectrometry and its analytical performance

A liquid-liquid flow extraction system associated with a specifically designed phase separator has been developed. A common trisectional confluence connector was used for segmentation. The system was connected on-line with a flame atomic absorption spectrometer. The performance of the system was studied with respect to determining copper and gold. The detection limits were 1 mug/l. for copper and 1.8 mu/1. for gold, and the precision was 1.8 and 2.5%, respectively, with medium signal enhancement factor 70 for gold, and 78 for copper. Analytical results of real sample analysis were in good agreement with certified values.     

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.     

Preconcentration of trace amounts of manganese from natural waters by means of a macroreticular poly(dithiocarbamate) resin

A chelating poly(dithiocarbamate) resin (PDTC) with macroreticular support is characterized as effective collector for traces of manganese from natural waters. Using small PDTC columns preconcentration of manganese can be achieved even at high flow-rates (5-6 ml/min) and sample volumes (1500 ml). Accordingly, PDTC resin is used for the preconcentration of manganese from water samples prior to its determination by flame atomic-absorption spectrometry. A series of ions abundant in natural waters do not interfere. The sensitivity and detection limit were 2.5 and 0.5 mug/l., respectively. The relative standard deviations of the results for a manganese concentration of 40-400 mug/l. are in the range 1.1-6.2%. In mineral and tap waters analysed, the manganese concentration range was between 2.9 and 30.8 mug/l.     

Determination of cadmium, lead and copper in water samples by flame atomic-absorption spectrometry with preconcentration by flow-injection on-line sorbent extraction

Cadmium, lead and copper were determined in synthetic sea-water, drinking water and the NBS 1643b Trace Elements in Water standard reference material at mug/l. levels by flame atomic-absorption spectrometry after on-line preconcentration by sorbent extraction with a flow-injection system. Bonded silica with octadecyl functional groups packed in a micro column of 100 mul capacity was used to collect diethylammonium diethyldithiocarbamate complexes of the heavy metals in the aqueous samples. The sample loading time was 20 sec at a flow-rate of 3.3 ml/min. Ethanol or methanol was used to elute the adsorbed analytes into the spectrometer. The sample loading rate, elution rate and pH were optimized. Enrichment factors of 19-25 for Cd, Pb and Cu were achieved at sampling frequencies of 120/hr with precisions of 1.4, 1.0 and 1.3% rsd (n = 11), respectively. The detection limits (3sigma) for Cd, Pb and Cu were 0.3, 3 and 0.2 mug/l., respectively. Determination of Cd, Pb and Cu in NBS SRM 1643b showed good agreement with the certified values. Recoveries of Cd and Pb added to sea-water were 95 and 102%, respectively.     

Determination of strontium in human serum by inductively coupled plasma mass spectrometry and neutron activation analysis: A comparison

Strontium has been determined in a human serum reference material by ICP-MS and by NAA. By ICP-MS, results for (88)Sr and (86)Sr in both 10- and 5-fold diluted serum were in good agreement. For (88)Sr the precision was better than 3% and the detection limit was 0.05 mug/l. under the conditions used. The results were 25.5 mug/l. in the liquid serum or 0.281 mug/g in the lyophilized reference material. In the NAA the (87m)Sr produced was radiochemically separated by extraction with oxine in chloroform. The precision was about 10% and the detection limit 0.02-0.05 mug/g.     

Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO(4), as oxidizing agent. The method has a limit of detection of 5 x 10(-7)M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05M NaOH at 90' degrees C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol(-1) l and a limit of detection of 1.9 x 10(-7)M, which corresponds to 50 mug/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 x 10(-6)M which corresponds to 500 mug/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol(-1) l but the limit of detection remains of the order of 44 mug/l.     

Determination of trace hydrazine by differential pulse voltammetry using magnetic microspheres

A new type of magnetic polymer microspheres containing ketone groups on the surface was synthesized. It can be reacted with hydrazine to produce electroactive adduct. Reduction of this derivative that was aggregated on the magnetic electrode is possible and effective in indirect determination of hydrazine. The experimental conditions and electrode structure were discussed. Under optimum conditions, It was found that the peak potential (Ep) of hydrazine is -1.06 V (vs. Ag/AgCl). Hydrazine in the range 0.3-500 mug l(-1) can be determined. The detection limits for hydrazine is 0.1 mug l(-1). The relative standard deviation for determination of 100 mug l(-1) hydrazine was 2.43 %. The method was applied to the determination of hydrazine in water samples with satisfactory results.     

Determination of arsenic, cadmium, lead and selenium in highly mineralized waters by graphite-furnace atomic-absorption spectrometry

A graphite-furnace AAS method using the stabilized-temperature platform furnace (STPF) concept, mixed palladium and magnesium nitrates as chemical modifier and Zeeman background correction has been applied to the direct determination of As, Cd, Pb and Se in highly mineralized waters used for medicinal purposes. These contain 20-40 g/l. concentrations of salts, mainly sodium and magnesium chlorides, bicarbonates and sulphates. The use of a pre-atomization cool-down step to 20 degrees in the graphite-furnace programme reduced the background absorption. Increasing the mass of magnesium nitrate modifier to 5 times that originally proposed improved the analyte peak shape. Under these conditions, no interference was found in analysis of the chloride/bicarbonate type of water, but the sodium and magnesium sulphate type of water had to be diluted, and even then an interference remained. Calibration with matrix-free standard solutions was used, but use of spike recovery is strongly recommended for testing the accuracy. The limits of determination (4.65sigma) of the proposed method for undiluted samples are 2.0 mug/l. for As, 0.05 mug/l. for Cd, 1.0 mug/l. for Pb and 1.5 mug/l. for Se.     

Rapid determination of zinc and iron in foods by flow-injection analysis with flame atomic-absorption spectrophotometry and slurry nebulization

A rapid method of determining zinc and iron in food by flame atomic-absorption spectrophotometry with slurry nebulization into an air-acetylene flame has been developed. A V-groove, clog-free Babington-type nebulizer, coupled to a single-line flow-injection analysis (FIA) system, was employed to introduce the slurry into the spray chamber. Under the FIA conditions described, an injection frequency of 120/hr is possible, with negligible carry-over and memory effects. The calibration graphs were obtained by using various concentrations (up to 0.1 g/ml) of white bean homogenate as standards, rather than solutions. The method has been applied to various kinds of foods, including grains, vegetables, fruits and sausage. Homogenization of semi-prepared samples to form slurries took only 4 min. Relative deviations between results by the slurry and solution methods for both elements averaged 2-3%. Detection limits by the slurry method were 0.3 mug/ml Zn and 0.6 mug/ml Fe.     

Capillary electrophoretic determination of zinc dimethyldithiocarbamate (Ziram) and zinc ethylenebisdithiocarbamate (Zineb)

A simple and sensitive capillary electrophoretic method was developed for the separation and determination of Ziram and Zineb in boric acid buffer by direct UV absorbance detection at lambda=254 nm. The separation is dependent on pH and nature of the buffer. The detection limits (S/N=3) are 1.88x10(-6) mol/l (0.57 mug/ml) and 2.48x10(-6) mol/l (0.68 mug/ml) for Ziram and Zineb, respectively. The method was successfully applied to the analysis of wheat samples spiked with Ziram and Zineb.     

Cyclodextrin enhanced spectrofluorimetric determination of fluoxetine in pharmaceuticals and biological fluids

The characteristics of host-guest complexation between methyl-beta-cyclodextrin and fluoxetine were investigated by fluorescence spectrometry. A 1:1 stoichiometry of the complex was established and association constant of 4.35x10(-3) M(-1) at 20 degrees C was calculated. A spectrofluorimetric method for the determination of fluoxetine, with a range of application between 40 and 1000 mug l(-1) was developed. Overall least squares regression was used to find the straight line that fitted the experimental data. The detection limit, according to the error propagation theory, was 9.6 mug l(-1) and the detection limit proposed by Clayton was 15.8 mug l(-1). Repeatability and relative standard deviation were also determined according to this theory, with satisfactory results. The method was successfully applied to the determination of fluoxetine in pharmaceuticals and biological fluids.     

Determination of submicrogram amounts of Mercury(II) with 5-(2'-carbomethoxyphenyl)azo-8-quinolinol in presence of anionic surfactant by derivative spectrophotometry

A new sensitive, rapid and selective method is proposed for the determination of mercury in submicrogram level. Mercury(II) forms an insoluble complex with 5-(2'-carbomethoxyphenyl)azo-8-quinolinol in aqueous medium at pH 4-4.8 which can be made soluble by the action of anionic surfactant. The dissolution of the complex results in an orange red colour which is stable for at least 20 hr. The molar absorptivity and Sandell's sensitivity are at 512 nm 8.00 x 10(4) l. mol(-1) . cm(-1) and 0.0025 mug/cm(2), respectively. Derivative spectrophotometry is used to achieve selectivity.     

Spectrophotometric determination of chromium(III) and rhodium(III) after extraction with oxine into molten naphthalene

Conditions have been developed for the extraction of chromium(III) and rhodium(III) as their 8-hydroxyquinolinates into molten naphthalene. The naphthalene is allowed to solidify, separated by filtration, dried with filter paper and dissolved in chloroform. The solution is diluted to 10 ml and its absorbance measured at 410 nm for chromium and 425 nm for rhodium, against a reagent blank. In both cases the solution is stable for 24-36 hr. Beer's law is obeyed over the range of 2.7-48.6 mug of chromium or 2.7-57.5 mug of rhodium in 10 ml of the chloroform solution. The molar absorptivity is 3 x 10(3) l. mole(-1) . cm(-1) for chromium and 3.6 x 10(4) for rhodium. Solutions containing 27.0 mug of chromium or 10.95 mug of rhodium give a mean absorbance of 0.140 and 0.395 respectively, with standard deviations of 0.002(2) and 0.004(7). Most metal ions that form oxinates may interfere, but can be removed beforehand by normal liquid-liquid extraction.     

On-line preconcentration and determination of copper, lead and chromium(VI) using unloaded polyurethane foam packed column by flame atomic absorption spectrometry in natural waters and biological samples

A simple, sensitive and low cost, flow injection time-based method was developed for on-line preconcentration and determination of copper, lead and chromium(VI) at sub mug l(-1) levels in natural waters and biological samples. At the optimum pH, the on-line formed metal-ammonium pyrrolidine dithiocarbamate (APDC) complexes were sorbed on the unloaded commercial polyurethane foam (PUF), and subsequent eluted quantitatively by isobutylmethylketone and determined by flame atomic absorption spectrometry (FAAS). All chemical, and flow injection variables were optimized for the quantitative preconcentration of each metal and a study of interference level of various ions was also carried out. The system offered improved flexibility, low backpressure and applicability to all the studied metals. At a sample frequency of 36 h(-1) and a 60 s preconcentration time, the enhancement factor was 170, 131 and 28, the detection limit was 0.2, 1.8 and 2.0 mug l(-1), and the precision, expressed as relative standard deviation (s(r)), was 2.8 (at 10 mug l(-1)), 3.4 (at 50 mug l(-1)) and 3.6% (at 50 mug l(-1)) for Cu(II), Pb(II) and Cr(VI), respectively. The accuracy of the developed method was sufficient and evaluated by the analysis of certified reference materials and spiked water samples. Finally, the method was applied to the analysis of environmental samples.     

Enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide using internal standard and derivative spectrophotometry

In the present work, erioglaucine A was applied as internal standard to enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide. The following procedure was used: (1) addition of internal standard and formation of ion pairs of Cr (VI) with benzyltributylammonium bromide (BTAB) (sample volume 100 ml), (2) extraction to 10 ml of methylene chloride, (3) evaporation in nitrogen stream, and (4) redissolution in a micro-volume with addition of diphenylcarbazide for color development (final volume 200 mul). The preconcentration factor achieved was about 400 and it was shown that, using internal standard, the analytical errors due to sample treatment were reduced. The analytical signals for chromium and internal standard were obtained at 591.30 and 653.50 nm from first derivative spectra, normalized against (1)D(653.50nm). The analytical characteristics evaluated were: detection limit = 0.06 mug l(-1), quantification limit = 0.19 mug l(-1), precision for 1 mug l(-1) 14.2%, and for 10 mug l(-1) 3.2%, correlation coefficient of linear regression was 0.9985. The proposed procedure was applied to determination of chromium (VI) in tap water. Total chromium was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent chromium added was then evaluated and compared with the results of the proposed procedure. In this experiment, good agreement was obtained between results obtained by the two methods.     

Spectrophotometric determination of gold(iii) with p-dimethylaminobenzilidenerhodanine in hydrochloric acid-ethanol medium

The reaction between gold(III) and p-dimethylaminobenzilidenerhodanine in hydrochloric acid medium containing 20% v/v ethanol has been studied spectrophotometrically. It has been established that the process is very complicated: gold(III) is reduced to gold(I) which reacts with unchanged reagent. The value of the equilibrium constant is 2.56 +/- 0.45. Conditions are proposed for the determination of 2-8 mug of gold in 25 ml, with a standard deviation of 0.04 mug 25 ml .     

Chemical composition, antioxidant and antibacterial properties of Achillea collina Becker ex Heimerl s.l. and A. pannonica Scheele essential oils

The in vitro antioxidant and antimicrobial activities of two Achillea millefolium (Adanson) Koch s.l species essential oils (A. collina Becker ex Heimerl s.l. and A. pannonica Scheele, Asteraceae) originating from the Golija and Radan mountains (Serbia) were investigated. The chemical profiles of the essential oils were evaluated by GC-MS. Antioxidant activity was assessed as free radical scavenging capacity (RSC) towards 2,2-diphenyl-1-picrylhydrazil (DPPH) radicals, together with effects on lipid peroxidation (LP). Antibacterial activity was examined on 21 bacterial strains. Based on the chemical composition of the essential oil, A. collina s.l. from Mount Golija was classified as a chamazulene chemotype (tetraploid). The high percentage of oxygenated monoterpenes and absence of azulene in the essential oil obtained from A. pannonica from Radan pointing that this population is octaploid. Essential oil of A. pannonica expressed stronger antimicrobial activity on almost all tested bacteria. Furthermore, this essential oil expressed higher scavenging effects on DPPH radical (IC(50) = 0.52 comparing to 0.62 mug/mL). Only in the LP evaluation, essential oil of A. collina s.l. from Golija exhibited stronger antioxidant activity (IC(50) = 0.75 comparing to 2.12 mug/mL).     

Ion-exchanger colorimetry-VIII Microdetermination of copper in natural waters

A microdetermination method for copper by ion-exchanger colorimetry has been developed. The porphyrin alpha,beta,gamma,gd-tetrakis(4-N-methylpyridyl)porphine was used as the colour reagent. After the complexation at pH 4.5 and 40 degrees , the surplus ligand was converted into the protonated species by addition of sulphuric acid. The complex and the ligand were easily sorbed on the cation-exchange resin, Dowex 50W-X2-H(+) (100-200 mesh). The resin-phase absorbances of the complex species at 424 nm and of the resin background at 510 nm were used for the measurements. There were no interferences by the foreign ions expected to be present in natural waters, at up to 1000 times the concentration of copper. With a 1 -litre sample the detection limit is 0.072 mug/l. It is possible to determine copper at mug/l. or lower levels in natural waters.