Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Spectrophotometric determination of nitrite in natural waters using diazotization-coupling method with column preconcentration on naphthalene supported with ion-pair of tetradecyldimethylbenzyl-ammonium and iodide

 A column preconcentration method has been established for the spectrophotometric determination of traces of nitrite using diazotization and coupling on an naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) adsorbent. Nitrite ion reacts with sulfanilic acid (SA) in the pH range 1.8–3.0 for the SA-1-naphthol system and in the pH range 2.3–3.2 for the SA-1-naphthylamine-4-sulfonate system (SA-NAS system) in hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were coupled with 1-naphthol in the pH range 1.6–4.6 and with NAS in the pH range 2.6–5.0 to be retained on naphthalene-TDBA-I packed in a column. The solid mass was dissolved from the column with 5 mL of dimethylformamide (DMF) and the absorbance measured at 418 nm for the SA-1-naphthol system and at 485 nm for the SA-NAS system. The calibration curve was linear over the concentration range 0.02–0.87 mg/L for SA-1-naphthol and 0.02–0.80 mg/L in the sample for SA-NAS. The molar absorptivity was calculated to be 1.70×10⁴ L mol^-1 cm^-1 for SA-1-naphthol and 1.66×10⁴ L mol^-1 cm^-1 for SA-NAS. The detection limits were found to be 0.014 and 0.016 mg/L for SA-1-naphthol and SA-NAS, respectively. The preconcentration factors were 8 and 6 for SA-1-naphthol and SA-NAS, respectively. Replicate determinations of seven sample solutions containing 6.6 μg of nitrite for SA-1-naphthol and 5.3 μg of nitrite for SA-NAS gave mean absorbances of 0.486 and 0.382 with relative standard deviations of 0.49 and 0.58%, respectively. Interferences due to various foreign ions have been studied and the method has been applied to the determination of 27–65 μg/L levels of nitrite in natural waters. The recovery and relative standard deviation for water samples were 98–102% and 0.49–0.58% for both systems. Received: 1 December 1995/Revised: 22 April 1996/Accepted: 22 April 1996     

Simultaneous separation and microdetermination of cobalt(II), nickel(II) and copper(II)

 A sensitive and selective flotation procedure for the separation of microamounts of Co(II), Ni(II) and Cu(II) separately or in admixture is described. The maximum separation rate (∼1) for 0.1 mmol/L of each analyte is achieved using 1 mmol/L of both oleic acid (HOL) surfactant and 4-phenylthiosemicarbazide (HPTS) as a collector in the pH range 6–7. A method for the simultaneous separation and microdetermination of the analytes is elaborated, based on adding excess HPTS and floating the species with HOL at pH ∼6. The filtrate (which is clear brownish-yellow) obtained from the scum is used for the spectrophotometric determination of Co(II) at 350 nm. The formation constants of 1:1 and 1:2 [Co(II):HPTS] species are 6.9×10⁵ and 1.22×10¹⁰ L mol^-1, respectively. Beer’s law is obeyed up to 9 μg/mL of Co(II) with a molar absorptivity of 1.15×10⁴ L mol^-1 cm^-1. The precipitate in the scum layer is quantitatively collected, dissolved in aqua regia and aspirated directly into the flame for the (AAS) determination of Ni and Cu. The procedure is successfully applied to some natural water samples. A mechanism for the separation of the analytes is proposed. Received: 23 January 1996/Revised: 1 April 1996/Accepted: 9 April 1996     

Determination of palladium by adsorptive stripping voltammetry

 Adsorptive accumulation of the Pd(II) complex with dimethylglyoxime was evaluated for stripping voltammetry with respect to different parameters. The sensitivity of the method and the linearity between the peak current and the concentration of Pd(II) depends on the ionic strength, the electrode area, the preconcentration time, the transport rate to the electrode, and the potential scan rate. The most appropriate medium was 0.1 mol/L acetate buffer between pH 3.5 and 4. Using 2 min of preconcentration at a 2.6 mm² electrode and the differential pulse mode, a detection limit of 0.05 μg/L Pd was achieved for liquid samples and 50 ng/g for solid samples. Different aqueous and solid samples were analysed and the recovery from biological and inorganic materials investigated. Received: 29 February 1996/Revised: 29 July 1996/Accepted: 1 August 1996     

Determination of copper by anodic stripping voltammetry on a glassy carbon electrode using a continuous flow system

 A successful flow-through system was developed for trace analysis of copper using DPASV with a glassy-carbon electrode. Periodical chemical regeneration of the electrode with a 1 mol/L NaOH solution increased sensitivity and precision. The method was shown to be applicable with a detection limit of 0.56 μg/L, with a determination time of less than 7 min per measurement (without deaeration time). The drawback of the system is the 10 min deaeration time. The system gave an accuracy of 0.090±0.005% for a certified reference material of low alloy steel containing 0.090±0.004% Cu. Applicability to various fresh water samples with a Cu content between 1.57 and 13.11 μg/L with an RSD<2.36% is illustrated. Received: 11 March 1996/Revised: 1 July 1996/Accepted: 4 July 1996     

Determination of copper by anodic stripping voltammetry on a glassy carbon electrode using a continuous flow system

 A successful flow-through system was developed for trace analysis of copper using DPASV with a glassy-carbon electrode. Periodical chemical regeneration of the electrode with a 1 mol/L NaOH solution increased sensitivity and precision. The method was shown to be applicable with a detection limit of 0.56 μg/L, with a determination time of less than 7 min per measurement (without deaeration time). The drawback of the system is the 10 min deaeration time. The system gave an accuracy of 0.090±0.005% for a certified reference material of low alloy steel containing 0.090±0.004% Cu. Applicability to various fresh water samples with a Cu content between 1.57 and 13.11 μg/L with an RSD<2.36% is illustrated. Received: 11 March 1996/Revised: 1 July 1996/Accepted: 4 July 1996     

Analytical characterization of manganese in rainwater and snow samples

 Seven rain and 2 snow samples collected in October and November 1993 were analyzed by GFAAS. Manganese concentrations ranging from 0.3 to 11.3 μg/L were found. pH-values (4.04–4.89, mean 4.52) and redox potentials (528–665 mV, mean 581 mV) were additionally determined. This is important with respect to a qualified specification of Mn in atmospheric samples. A 0.45 μm-filtration of the samples prior to GFAAS-analysis showed the same manganese concentrations in the filtrate as in the unfiltered samples. Hence, the amount of solid Mn species in the investigated samples is negligible. For an examination of the oxidation state of Mn some investigations concerning the stability of Mn(III) were carried out. They indicated that Mn(III) is unstable under atmospheric conditions. For checking whether all the manganese in rainwater exists as Mn(II), a sensitive IC method for the detection of Mn(II) was developed. By adapting a photometric procedure based on the oxidation of Leucomalachite Green (LMG) to Malachite Green (MG) by permanganate (MnO^- ₄) to the IC-flow-through-system, a limit of determination of 1 μg/L Mn(II) could be achieved. A comparison of the IC measurements with GFAAS-results of the filtered samples showed agreeing results. Thus, manganese in rainwater and snow exists entirely as soluble Mn(II). Received: 24 May 1996/Revised: 7 July 1996/Accepted: 14 July 1996     

Analytical characterization of manganese in rainwater and snow samples

 Seven rain and 2 snow samples collected in October and November 1993 were analyzed by GFAAS. Manganese concentrations ranging from 0.3 to 11.3 μg/L were found. pH-values (4.04–4.89, mean 4.52) and redox potentials (528–665 mV, mean 581 mV) were additionally determined. This is important with respect to a qualified specification of Mn in atmospheric samples. A 0.45 μm-filtration of the samples prior to GFAAS-analysis showed the same manganese concentrations in the filtrate as in the unfiltered samples. Hence, the amount of solid Mn species in the investigated samples is negligible. For an examination of the oxidation state of Mn some investigations concerning the stability of Mn(III) were carried out. They indicated that Mn(III) is unstable under atmospheric conditions. For checking whether all the manganese in rainwater exists as Mn(II), a sensitive IC method for the detection of Mn(II) was developed. By adapting a photometric procedure based on the oxidation of Leucomalachite Green (LMG) to Malachite Green (MG) by permanganate (MnO^- ₄) to the IC-flow-through-system, a limit of determination of 1 μg/L Mn(II) could be achieved. A comparison of the IC measurements with GFAAS-results of the filtered samples showed agreeing results. Thus, manganese in rainwater and snow exists entirely as soluble Mn(II). Received: 24 May 1996/Revised: 7 July 1996/Accepted: 14 July 1996     

Determination of cadmium in indium phosphide by electrothermal atomic absorption spectrometry and ion-selective electrode potentiometry

 Two independent methods for the determination of cadmium in cadmium-doped indium phosphide have been developed. Electrothermal atomic absorption spectrometry (ETAAS) utilized both platform atomization and a chemical modifier composed of magnesium nitrate and orthophosphoric acid. As the matrix mass was found to influence the cadmium sensitivity, matrix matched calibration standards were necessary. The detection limit (3s_B) is 0.20 μg/g for a 100 mg sample. The electrochemical method employed a solid-state cadmium sulfide-silver sulfide electrode as potentiometric sensor. An excess of indium (III) influenced the electrode response. A preliminary chelation-extraction of indium with acetylacetone at pH 5.0 in acetate buffer overcame the interference. The detection limit of the ISE-potentiometric method is 10 μg/g for a 200 mg sample. Two indium phosphide single crystals grown from melts doped with cadmium sulfide or cadmium telluride were analyzed for their cadmium content. Received: 27 August 1996/Revised: 27 January 1997/Accepted: 30 January 1997     

Determination of acetaldehyde in liquid, solid and semi-solid food after pervaporation-derivatization

 A spectrophotometric method for the determination of acetaldehyde in liquid, semi-solid and solid food samples, employing the coupling of a continuous flow configuration to a pervaporation unit, has been proposed. It is based on the reaction of the analyte with fuchsin in acidic medium and subsequent formation of a coloured product (alkylsulphonic acid chromophore) with sodium sulphite, which was monitored spectrophotometrically. Variable sensitivity was obtained by altering the pervaporation temperature and the thickness of the membrane. The detection limits went down to 4.2 μg/mL and the precision was between 1.2 and 3.6%. Received: 5 August 1996/Revised: 16 October 1996/Accepted: 18 October 1996     

Cyclodextrin-based optosensor for the determination of quinine

 A flow-through optosensor for quinine is described. It has been developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The detection limit for quinine was 0.20 ng ml^-1 with a relative standard deviation of 2.1% for the determination of 0.05 μg ml^-1 (n=7) of quinine. The method has been successfully tested for the determination of quinine in some pharmaceutical preparations. Received: 4 June 1996 / Revised: 23 August 1996 / Accepted: 24 August 1996     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Cyclodextrin-based optosensor for the determination of quinine

 A flow-through optosensor for quinine is described. It has been developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The detection limit for quinine was 0.20 ng ml^-1 with a relative standard deviation of 2.1% for the determination of 0.05 μg ml^-1 (n=7) of quinine. The method has been successfully tested for the determination of quinine in some pharmaceutical preparations. Received: 4 June 1996 / Revised: 23 August 1996 / Accepted: 24 August 1996     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Determination of acetaldehyde in liquid, solid and semi-solid food after pervaporation-derivatization

 A spectrophotometric method for the determination of acetaldehyde in liquid, semi-solid and solid food samples, employing the coupling of a continuous flow configuration to a pervaporation unit, has been proposed. It is based on the reaction of the analyte with fuchsin in acidic medium and subsequent formation of a coloured product (alkylsulphonic acid chromophore) with sodium sulphite, which was monitored spectrophotometrically. Variable sensitivity was obtained by altering the pervaporation temperature and the thickness of the membrane. The detection limits went down to 4.2 μg/mL and the precision was between 1.2 and 3.6%. Received: 5 August 1996/Revised: 16 October 1996/Accepted: 18 October 1996     

Colorimetric determination of iron in infant fortified formulas by sequential injection analysis

 A procedure is described for the colorimetric determination of iron in infant fortified formulas based on sequential injection analysis (SIA). Iron(III) complexation with thiocyanate is used as colour developing reaction. The system enables the determination of iron in the samples (after digestion by dry ashing and treatment with 0.2 mol/L nitric acid in the range of 0.50–20.0 mg/L, consuming 140 μL of the sample and 8 mg thiocyanate per determination. The reactor geometry and the adjustment of the ionic content of the calibration solutions is important for the accuracy of the results. A regression line according to the equation [Fe(III) (mg/L)]_SIA=−0.3(±0.4)+1.03(±0.04) [Fe(III) (mg/L)]_FAAS was obtained after comparative analysis of a set of 12 samples. The measurement rate was 34 s, thus allowing to analyze 100 samples per hour with a relative standard deviation lower than 2%. Received: 30 July 1996/Revised: 1 October 1996/Accepted: 4 October 1996     

Novel dissolution procedure using a mixture of manganese dioxide and hydrochloric acid for the matrix-independent determination of gold

 A mixture of manganese dioxide and hydrochloric acid has been used for the accurate and precise determination of gold in various gold-bearing matrices. Results of intermethod comparison studies, F-test on variances, Mann-Whitney U-test, Spearman rank correlation and regression analyses are presented. The recommended method can be applied to a quality control programme and for the evaluation of reference materials. Various standard reference materials (SRM) of diverse matrices have been examined to check the validity of the method and the results were found to be in very good agreement with the certified data. Sample decomposition is straight forward [1–10 g sample (roasted at 600–700 °C)+5 g of MnO₂+30 mL of 2 mol/L HCl]. Gold is coprecipitated with potassium tellurite using tin (II) chloride solution. The precipitate is extracted into toluene and finally stripped back into aqua-regia solution for final nebulization into an air-acetylene flame for atomic absorption spectrophotometry. The method is very simple and easily adaptable, and more convenient than conventional methods involving aqua regia or a hydrobromic acid-bromine water mixture. Received: 23 October 1995/Revised: 18 March 1996/Accepted: 23 March 1996     

Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition

 The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film. Received: 17 June 1996 / Revised: 26 July 1996 / Accepted: 2 August 1996     

Kinetic determination of carminic acid by its inhibition of lanthanide-sensitized luminescence

 The stopped-flow mixing technique was used to develop a simple and fast kinetic method for the determination of carminic acid based on its inhibitory effect on the fluorescence intensity of the europium(III)- diphacinone-ammonia system in the presence of Triton X-100. Analytical data can be obtained within 10 s after the reactants are mixed, which minimizes manipulation and enables the ready application of the proposed method to routine analyses for carminic acid in orange soft drinks. The dynamic range of the calibration graph was 0.5–15 μg ml^-1 and the relative standard deviation less than 4%. The analytical recoveries obtained by applying the method directly to the analysis of samples ranged from 90.0 to 111.8%. Received : 11 November 1995/Revised: 2 February 1996/Accepted: 6 February 1996