Indirect determination of chloride and carbonate by reversed flow-injection analysis coupled with atomic-absorption spectrometry and in-line preconcentration by precipitation

Chloride and carbonate are determined indirectly by reversed flow-injection analysis with preconcentration by precipitation. The anions are precipitated in a Tygon tube containing glass beads and connected to an atomic-absorption spectrophotometer, and are then dissolved by suitable reagents. Chloride is precipitated as silver chloride, which is then dissolved with ammonia, sodium thiosulphate or potassium cyanide solution. Carbonate is precipitated as calcium carbonate, which is dissolved with hydrochloric acid. The response of the system has been optimized with respect to concentration, precipitation time, solution flow-rate and other AAS variables. Detection limits are 3 × 10⁻⁷ and 5 × 10⁻⁷M for chloride and carbonate, respectively, with thiosulphate and hydrochloric acid as the dissolution agents.     

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at μg L^–1 level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3σ) in the sample digest was 0.25 μg g^–1 (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 μg L^–1 and 2.0% for 50 μg L^–1. The sampling frequency was 45 h^–1. The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples. Received: 1 November 2000 / Revised: 8 January 2001/ Accepted: 11 January 2001     

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at microg L(-1) level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3sigma) in the sample digest was 0.25 microg g(-1) (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 microg L(-1) and 2.0% for 50 microg L(-1). The sampling frequency was 45 h(-1). The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples.     

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 trace levels of sulphate in water using flow-injection and in-line preconcentration

Sulphate is preconcentrated on a strong anion-exchange resin and determined using the effect of sulphate ions on the complexation of methylthymol blue and barium. A computer-controlled flow-injection analyser is used to automate the whole procedure. The resin has two functions: it preconcentrates sulphate and also separates sulphate from divalent cations that may interfere in the determination step. The system can handle 30 samples per hour and has a working range from 25 to 1000 μg 1^?1 of sulphate. Lower detection limits can be obtained by changing the preconcentration conditions. The effect of both anionic and cationic interferents was studied.     

Determination of copper in powdered chocolate samples by slurry-sampling flame atomic-absorption spectrometry

Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L^–1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L^–1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 g g^–1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 g g^–1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 g g^–1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.     

Determination of cadmium and lead at low levels by using preconcentration at fullerene coupled to thermospray flame furnace atomic absorption spectrometry

A new and sensitive method for Cd and Pb determinations, based on the coupling of thermospray flame furnace atomic absorption spectrometry and a preconcentrator system, was developed. The procedure comprised the chelating of Cd and Pb with ammonium pyrrolidinedithiocarbamate with posterior adsorption of the chelates on a mixture (40 mg) of C₆₀ and C₇₀ at a flow rate of 2.0 ml min⁻¹. These chelates were eluted from the adsorbent by passing a continuous flow of ethanol (80% v/v) at 0.9 ml min⁻¹ to a nickel tube placed in an air/acetylene flame. After sample introduction into the tube by using a ceramic capillary (0.5 mm i.d.), the analytical signals were registered as peak height. Under these conditions, improvement factors in detectability of 675 and 200 were obtained for Cd and Pb, respectively, when compared to conventional flame atomic absorption spectrometry. Spiked samples (mineral and tap waters) and drinking water containing natural concentrations of Cd were employed for evaluating accuracy by comparing the results obtained from the proposed methodology with those using electrothermal atomic absorption spectrometry. In addition, certified reference materials (rye grass, CRM 281 and pig kidney, CRM 186) were also adopted for the accuracy tests. Due to the good linearity ranges for Cd (0.5–5.0 μg l⁻¹) and Pb (10–250 μg l⁻¹), samples with different concentrations could be analyzed. Detection limits of 0.1 and 2.4 μg l⁻¹ were obtained for Cd and Pb, respectively, and RSD values <4.5% were observed (n=10). Finally, a sample throughput of 24 determinations per hour was possible.     

Determination of gold in ore by flame atomic absorption spectrometry with flow-injection on-line sorbent extraction preconcentration

Gold in ores was determined by flame atomic absorption spectrometry following on-line preconcentration by sorbent extraction in a flow-injection system. The medium polarity adsorption resin Amberlite XAD-8 packed in a 220-μl micro-column was used to collect gold(III) from hydrochloric acid sample solutions for 40 s at 7.6 ml/min. Ethanol was used to elute the adsorbed analytes into the nebulizer. Optimization studies were made on sample loading rate, elution rate and sample acidity. Some possible interferences on the determination are discussed. A 35-fold enrichment was achieved at a sampling frequency of 60 h^?1 and with an RSD of 1.4%. The detection limit (3σ) and 2 μg l^?1. Results for gold in ore samples showed good agreement with those obtained using activated carbon adsorption preconcentration. The recoveries were 97–108%.     

Determination of cadmium in biological materials by flame atomic absorption spectrometry with flow-injection on-line sorption preconcentration

A new on-line preconcentration flame atomic absorption spectrometry (FAAS) system for trace element determination was developed based on sorption of soluble metal complexes on the walls of a PTFE knotted reactor using flow injection techniques. The system was applied to the determination of cadmium in biological materials. Cadmium complexed with sodium diethyldithiocarbamate was sorbed on the inner walls of the reactor and eluted on-line by isobutyl methyl ketone. The retention efficiency was 81% at a sampling loading rate of 5.2 ml/min. The enhancement factor was 66 and the concentration efficiency was 61/min with a 50 sec preconcentration period, consuming 4.2 ml sample. A detection limit of 0.1 μg/l. Cd (3σ) was obtained with a sampling frequency of 55/hr. The precisions were 1.2% RSD for 20 μg/l. Cd (N = 11). Thiourea and ascorbic acid/phenanthroline were used to overcome interferences from copper and iron, respectively. The analytical results obtained for powdered rice and human hair standard reference materials were in good agreement with the certified values.     

Application of the slotted quartz tube in flow-injection flame atomic-absorption spectrometry

The slotted quartz has been applied to flow-injection flame atomic-absorption spectrometry (FI-FAAS) showing several important advantages. The tube life was improved by a factor of 5-6 compared to conventional continuous aspiration. Flow impact systems were found not to be necessary in the applications so that larger enhancement factors may be achieved without sacrifice in precision. For 1.0 mg/l. copper, 1.0 mg/l. lead, 0.1 mg/l. cadmium and 1.0 mg/l. gold sensitivity enhancement factors of 3.1, 5.5, 5.3 and 4.0 were obtained with precisions of 1.3%, 1.1%, 1.6% and 1.7% RSD (n = 11) respectively. Application of the slotted quartz tube FI-FAAS method to the determination of heavy metals in urine has shown improved tolerance to interfering matrices. Recoveries obtained by spiking undiluted urine samples with 0.1 mg/l. copper and lead, and 0.01 mg/l. cadmium were in the range 100-102%.     

Determination of heterocyclic aromatic amines by capillary electrophoresis coupled to mass spectrometry using in-line preconcentration

This paper shows the potentiality of capillary electrophoresis (CE) coupled to mass spectrometry (MS) for the analysis of heterocyclic aromatic amines obtaining good results in terms of sensitivity and precision. These compounds have a special interest since they can be carcinogenic for humans. The optimization of a CE-MS method was performed and the best conditions were obtained using a 16 mM formic acid/ammonium formate solution at pH 4.5 with 60% methanol as running electrolyte. For CE-MS coupling, a sheath liquid methanol/20 mM formic acid (75/25) solution at a flow rate of 3 microL/min and hydrodynamic injection of methanol mixtures for 10 s were used. Detection limits ranging from 18 ng/g to 360 ng/g and precisions up to 1.4% and 12% for migration time and concentration, respectively, were obtained. In order to improve sensitivity, field-amplified sample injection was applied as an in-line preconcentration method. Methanol/5 mM formic acid (50/50) as a sample solvent, 3 s hydrodynamic injection (0.5 psi) of a methanol plug, and 25 s of electrokinetic injection (10 kV) of the sample were found to be the optimum conditions. Detection limits up to 25 times lower and similar precisions than those reported for hydrodynamic injection were obtained.     

Determination of strontium at low concentration levels by flame atomic absorption spectrometry associated on-line with continuous coprecipitation preconcentration

A sensitive method for the determination of strontium has been developed. In this work strontium was determined by flame atomic absorption spectrometry using a continuous copreconcentration dissolution procedure based on the formation of lead sulfate followed by elution with hot EDTA solution. Manifold parameters and chemical conditions are described in detail. A concentration factor of up to 61 can be achieved at a sampling rate of 20-30 h(-1). The detection limit for strontium was 0.9 ng ml(-1) (3sigma) and the relative standard deviation was 3.5% (n = 8) at a concentration level of 100 ng ml(-1).     

The determination of trace amounts of tin by flow-injection hydride generation atomic-absorption spectrometry with on-line ion-exchange separation and preconcentration

A hydride generation atomic-absorption spectrometric (AAS) method with flow-injection (FI), aimed at developing a practical routine assay for the determination of tin in food digests, is described. In order to modify the sample matrix and to achieve optimized and reproducible conditions for the hydride generation reaction, the analyte is initially converted into its chlorostannate-complex thereby allowing it to be separated and preconcentrated on-line on an incorporated micro-column packed with a strongly basic anion exchanger and subsequently to be eluted by diluted nitric acid under strictly controlled conditions. Optimum acidic conditions for the FI hydride generation AAS system was found to be 0.01-0.05M nitric acid. At a consumption of 2.7-ml sample volume, aspirated by time-based injection, the procedure resulted in an enrichment factor of 3.5 and yielded a detection limit of 0.08 microg/l. (3sigma) at a sampling frequency of 72/hr. The precision was 2.5% rsd at the 10 microg/l. level. Potential interferents, such as Ni(II), Co(II), Zn(II) and Fe(III) could, at a Sn level of 10 microg/l., be tolerated at an excess of 1000 times without impairing the assay, while a 100-1000-fold excess of Cu(II) decreased the signal by 10-15%. Recoveries in the range 94-102% were obtained for canned food sample digests spiked with 10 microg/l. Sn.     

Determination of chromium in steel by atomic-absorption spectrometry with an air-acetylene flame

A new atomic-absorption procedure is described for the determination of chromium, at levels up to 1%, in steel. The method involves the use of the air-acetylene flame and incorporates 8-hydroxyquinoline as a releasing agent to suppress metallic interferences. Chemical operations have been reduced to a minimum in order to provide a simple, rapid and accurate procedure.     

Determination of trace metals in urine with an on-line ultrasound-assisted digestion system combined with a flow-injection preconcentration manifold coupled to flame atomic absorption spectrometry

A flow analysis method with on-line sample digestion/minicolumn preconcentration/flame atomic absorption spectrometry is described for the determination of trace metals in urine. First, urine sample was on-line ultrasound-assisted digested exploiting the stopped-flow mode, and then the metals were preconcentrated passing the pre-treated sample through a minicolumn containing a chelating resin. A home-made minicolumn of commercially available imminodiacetic functional group resin, Chelite Che was used to preconcentrate trace metals (Cu, Fe, Mn and Ni) from urine. The proposed procedure allowed the determination of the metals with detection limits of 0.5, 1.1, 0.8 and 0.8 μg L⁻¹, for Cu, Fe, Mn and Ni, respectively. The precision based on replicate analysis was less than ±10.0%, and the enrichment factor obtained was between 21.3 (Mn) and 44.1 (Ni), for sample volumes between 2.5 and 5.0 mL, and an eluent volume of 110 μL. This procedure was applied for determination of metals in urine of workers exposed to welding fumes and urine of unexposed persons (urine control).     

Determination of indium in aluminium alloys by flame atomic-absorption spectroscopy and flame atomic-emission spectrometry

The use of flame atomic-absorption and atomic-emission spectrometry for the determination of indium in aluminium alloys is described. Two types of flame are used: air—acetylene and nitrous oxide—acetylene. The efrect of other ions, especially aluminium, has been studied, and the use of lanthanum as a releasing agent is proposed for both techniques, the amount used depending on the amount of aluminium present.     

Automated method for the determination of boron in water by flow-injection analysis with in-line preconcentration and spectrophotometric detection

A sensitive, automated method for the determination of boron in water samples is described, involving flow injection with on-line ion-exchange preconcentration and spectrophotometric detection of the azomethine-H—boron complex. The method is applicable to various water samples and is free from interferences, even in coloured samples. Detection limits of 5 μg l^?1 at 20 samples h^?1 and 1 μg l^?1 at 10 samples h^?1 with relative standard deviations of < 10% at 1–10 μg l^?1 and < 5%at 10–200 μg l^?1 levels of boron were achieved. The recoveries for spiked natural water samples ranged from 96 to 101%. The method compares favourably with inductively coupled plasma atomic emission spectrometry.     

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.     

Determination of iron and lead by flame atomic absorption spectrometry after preconcentration with sepiolite

By using a new adsorbent (sepiolite) an adsorption-elution and atomic absorption spectrometric method has been developed for the preconcentration and determination of Fe and Pb. Recoveries of the analytes were 82 ± 3% for Fe and 91 ± 2% for Pb at 95% confidence level. For Cu it was only 5 ± 1%. The recovery of iron could be increased to about 97 ± 1% by complexing with EDTA, the recovery of copper only to 57 ± 2%. The optimised method was applied to the determination of lead in metal materials (e.g. brass). Received: 20 February 1996 / Revised: 7 May 1996 / Accepted: 11 May 1996     

Determination of antimony in rocks and sulphide ores by flame and electrothermal atomic-absorption spectrometry

Atomic-absorption methods for determination of antimony at mug/g levels in rocks and sulphide ores by flame atomization (FAA) and electrothermal atomization (ETAA) have been described. The FAA method involves the separation of antimony from matrix elements by extraction as the iodide into methyl isobutyl ketone containing tri-n-octylphosphine oxide, from dilute hydrochloric acid solution, followed by direct aspiration of the extract into an air-acetylene flame. If necessary, antimony is first separated from copper and lead by co-precipitation with hydrous ferric oxide from ammoniacal medium and by precipitation of lead as lead sulphate. The ETAA method involves co-precipitation of antimony with hydrous ferric oxide followed by dissolution of the precipitate in dilute nitric acid, mixing with nickel solution as releasing agent, and ETAA measurement by use of a tungsten strip atomizer.