Determination of trace elements in seawater by electrothermal atomic absorption spectrometry with and without a preconcentration step

The determination of the trace metals Cd, Pb and Cu in seawater by electrothermal atomic absorption spectrometry (ETA-AAS) has been investigated. A combination of the platform with mixed palladium nitrate-magnesium nitrate as matrix modifier and Zeeman background correction allows Cd an Pb to be determined by aqueous standard calibration in appropriately diluted seawater samples. Copper can be determined in undiluted seawater samples without chemical modification using a standard additions method. Detection limits (3) of 2.97,5.27 and 1.1 gl^–1 are obtained for Cd, Pb and Cu respectively. A Kelex-100 impregnated silica C18 material (Kelex 100-C18) has been tried and has proved to be effective as a column packing for extraction/preconcentration of these metals from seawater. Using the column extraction method, the sensitivity of the graphite furnace technique is enhanced 50-fold using a 10 l injection volume. Thus, the determination of the studied three metals in seawater at the ng.l^–1 level could be achieved.     

Determination of osmium in waste water by graphite furnance atomic absorption spectrometry

The determination of osmium in waste water by electrothermal atomic absorption spectrometry (AAS) with a graphite furnace atomiser has been investigated. The atomisation characteristics of osmium on the atomiser were found to result in optimal ashing and atomisation temperatures of 300–500 and 3180 °C, respectively.The characteristic mass (the mass of element giving 0.0044 abs.) of osmium after optimization was found to be 1.6ng, which is better than obtained with flame AAS and ultraviolet/visible (UV) absorption spectrophotometry. The detection limit (s/n = 3) was 3.6ng (or 0.36 (g ml^–1). The relative std. deviation obtained with graphite furnace AAS was 3.0%.The interference caused by large amounts of common cations and anions in waste water were evaluated and thiourea as matrix modifier was shown to be able to eliminate many interferences. The recovery of osmium spiked in waste water was considered almost satisfactory at the 1–50 g ml^–1 range and the results were shown to well agree with the analytical values obtained by UV absorption spectrophotometry.     

Simultaneous enrichment of aluminium and lead with cupferron on activated carbon for determination in milk and fruit juices by atomic absorption spectrometry

An enrichment method has been modified for the determination of Al in animal milk and fruit juices by flame atomic absorption spectrometry (FAAS). The samples were digested by wet ashing. 8-Hydroxyquinoline and cupferron were used as complexing reagents for adsorption of the Al complexes on activated carbon. The pH values for maximum recovery of Al were in the ranges 4.4–6.0 for cupferron and 8.0–9.0 for oxine. The relative standard deviation was 4% for an aluminium concentration of 120 gL^–1 using cupferron. Optimum conditions for lead enrichment were taken from previous work on the cupferronactivated carbon enrichment method. The optimized procedure was applied to the determination of Al and Pb in animal milk and fruit juices by FAAS. Simultaneous enrichment of these two elements was achieved at the same pH.     

Determination of traces of silver in copper by direct Zeeman graphite furnace atomic absorption spectrometry

Summary A method was developed to determine traces of silver in copper by direct Zeeman graphite furnace atomic absorption spectrometry (ZAAS) on solid samples. The system is calibrated using quantitatively doped copper, whose blank silver content is determined using an iterative process. The method has been applied to the analysis of several candidate reference materials. Relative standard deviations of 2 to 5% are obtained in the range 1 to 12 g·g^–1. Furthermore, it was also applied to assess the homogeneity of a neutron dosimetry candidate reference material.     

Pre-concentration of traces of tin by coprecipitation with yttrium hydroxide for electrothermal atomisation atomic absorption spectrometry

Summary Trace amounts of tin were concentrated by coprecipitation and determined by electrothermal atomisation atomic absorption spectrometry. Yttrium hydroxide coprecipitated quantitatively 0.1–3 g of tin from 50–500 ml of sample solution at pH 9.5–11.2. The atomic absorbance of tin increased about twice by using an impregnated graphite tube with yttrium. The impregnated graphite tube, furthermore, improved the reproducibility of the measurement of tin. A linear calibration graph was obtained in the range of 0.004–0.12 g/ml of tin. Twenty-three foreign ions did not interfere seriously. The method was applicable to the determination of tin in zinc metal.     

Determination of traces of silver in human scalp hair slurries by electrothermal atomic absorption spectrometry

A simple and rapid method for the determination of traces of silver in human hair by slurry sampling and electrothermal atomic absorption spectrometry was optimized. Hair pulverization and the particle size reduction were achieved using a vibrational zirconia mill ball for 20 min. Palladium nitrate, magnesium nitrate and palladium-magnesium nitrate were investigated as chemical modifiers to thermally stabilize silver. Glycerol was used as wetting agent to stabilize the hair slurries. A limit of detection of 21.6 g kg^–1 was obtained for the use of palladium nitrate as best chemical modifier. The repeatibility of the overall procedure (slurry preparation and atomic absorption spectrometric determination) corresponding to eleven measurements was 14.3%. Matrix effect was significant and so, the standard addition method was used to determine silver in hair samples from healthy people. The levels found varied between 0.10 and 1.62 mg kg^–1.     

Determination of total selenium and selenium distribution in the milk phases in commercial cow’s milk by HG-AAS

A procedure has been developed for determining the selenium in cows milk using hydride generation–atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 g l^–1, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5–100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5–21 g l^–1 range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2–73.6%), while the lowest level was found for the fat phase (4.8–16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components.     

Human albumin as a reference material for trace elements

Summary An investigation through interlaboratory comparison using different analytical techniques has been carried out in order to assess the suitability of a plasma protein solution as a source for a trace element reference material in clinical analysis. Reasonable agreement was obtained for a number of elements from the range studied: Al, Ba, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Sr, V and Zn. The techniques used included flame and furnace atomic absorption spectrometry (FAAS and ETA-AAS), furnace atomic emission spectrometry (ETA-AES), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), and simultaneous multi-element atomic absorption spectrometry (SIMAAC). Results indicated that this plasma protein solution may prove useful as a source for a reference material covering trace element levels outwith the range found in normal human plasma.

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Humanalbumin als Referenzmaterial für Spurenelemente

     

Inductively coupled plasma atomic emission spectrometric determination of arsenic in mussel products

Summary A precise, accurate procedure is proposed for the determination of arsenic in mussel products by inductively coupled plasma atomic emission spectrometry. Organic matter is destroyed by dry ashing. Experimental conditions for the determination of arsenic were selected and an interference study was carried out. The methodology developed has a detection limit of 0.1 g g^–1, a relative standard deviation of 3%, and a recovery percentage of 98±2%. The accuracy of the method was checked by analysis of a certified sample of NIST oyster tissue (certified 14.0±1.2 g g^–1; found 14.1±1.1 g g^–1). The proposed procedure was used to analyze real samples of mussel products.     

Direct determination of copper and iodine in milk and milk powder in alkaline solution by flow injection inductively coupled plasma mass spectrometry

The development and evaluation of a flow injection inductively coupled plasma mass spectrometric (FI-ICP-MS) method for the determination of copper and iodine in milk and milk powder has been described. The sample preparation is based simply on the dilution of the sample by an alkaline solution containing 0.05 mol/l potassium hydroxide and 0.07 mol/l tetramethylammonium hydroxide. Possible matrix interferences on the determination of copper were alleviated by the use of standard addition calibration. Detection limits (3s) were 0.94 gl^-1 and 0.45 gl^-1 for copper and iodine, respectively. Four different certified milk powder reference materials were analysed and the concentrations found were in a good agreement with the certified values indicating that the method is unbiased. Due to the simplicity of the method a high sample throughput is possible, approximately 90 samples can be analysed in one day. More than 100 samples of Danish raw milk were analysed and median values of 0.050 mgkg^-1 of Cu and 0.084 mgkg^-1 of I were found.     

Separation and preconcentration of trace quantities of copper ion using modified alumina nanoparticles, and its determination by flame atomic absorption spectrometry

We report on a sensitive, reliable and relatively fast method for separation, preconcentration and determination of trace quantities of copper(II) ion. It is making use of nanometer-sized γ-alumina nanoparticles modified with sodium dodecyl sulfate (SDS). The adsorptive potential was assessed via a Langmuir isotherm and the maximal sorption capacity was found to be 138 mg g^-1. The effects of pH values, amount of ligand, flow rate, type of eluting agent, volume of eluent, and the volume of sample were examined. The effects of interfering ions on the recovery of the analyte were also investigated. Copper ion was then determined by flame atomic absorption spectrometry. The relative standard deviation for five replicate determinations (at 50 μg L^?1 of copper) is 3.3%. The detection limit (at 3 s) is 2.5 μg L^?1. This method was validated with a certified reference material of oyster tissue (NIST SRM 1566b) and the results coincided well with the certified values. The procedure was successfully applied to the determination of Cu in water and food samples.

Simultaneous determination of chromium(VI) and chromium(III) by flame atomic absorption spectrometry with a chelating ion-exchange flow injection system

Summary Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h^–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml^–1 and 0.67% for Cr(III) (0.10,g ml^–1) and the corresponding limits of detection were 85 ng ml^–1, and 16 ng ml^–1, respectively.On leave from University of Belgrade.     

Determination of trace alkaline metals in quartz by flame atomic emission and atomic absorption spectrometry

Flame Atomic Emission Spectrometry (FAES) and Electrothermal Atomizer Atomic Absorption Spectrometry (ETA-AAS) were assessed for the determination of K and Na in quantities of less than 10 μg g⁻¹ in quartz. The advantages of the direct AAS technique (samples were atomized directly in solid form) are described as less time-consuming and do not require extensive sample preparation. The FAES technique was applied as the control method using water standard solutions for calibration. The results obtained by the two methods agree well in the concentration ranges from 0.5 to 20 μg ml⁻¹.     

High-performance flow atomic spectrometry: New nebulization techniques, on-line speciation and on-line sample pretreatment

An interface-free combination of HPLC separation techniques and methods for element determination by atomic spectrometry can be achieved by hydraulic high-pressure nebulization (HHPN). With high-temperature HHPN (300^°C) super heated liquids can be nebulized providing aerosol yields of up to 90% in flame AAS. This new nebulization method combines the advantages of HHPN and thermospray techniques (very small aerosol droplets, high aerosol yield, nebulization of saturated salt solutions).     

Analytical application of atomic emission and atomic absorption spectrometry for the determination of imidazoline derivatives based on formation of ion-associates with sodium cobaltinitrite and potassium ferricyanide

Ion-association complexes of Naphazoline HCl (I), Tolazoline HCl (II) and Xylometazoline HCl (III) with [Co(NO₂)₆]^3– and [Fe(CN)₆]^3– were precipitated and the excess of the unreacted iron or cobalt comples was determined. A new method using atomic emission and atomic absorption spectrometry for the determination of the above drags in pure solutions and in pharmaceutical preparations is given. The drugs have been determined in the ranges 0.98–14.76, 0.78–11.80 and 1.12–16.80 g/ml solutions of I, II and III. respectively, using [Co(NO₂)₆]^3–], with mean relative standard deviations of 0.4–1.5% and 1.92%–19.68, 1.52–5.68 and 2.24–22.4 g/ml solutions of I, II and III, respectively using [Fe(CN)₆]^3– with mean relative standard deviations of 0.6–1.6%. The recovery values of 98.12–101.26% indicate high precision and accuracy.     

Indirect flow-injection determination of ascorbic acid by flame atomic absorption spectrometry

A continuous-flow procedure is proposed for the indirect determination of ascorbic acid, based on its reducing properties because of the oxidation of its 1,2-enediol group. Iron(III) was injected into a 1,10-phenanthroline stream, which was mixed with a sample carrier and then with a sodium picrate solution stream. In these conditions the iron(III) was reduced to iron(II) by the ascorbic acid. Thus, the iron(II) formed reacts with 1,10-phenanthroline to form a charged red complex, which with picrate ion forms a stable red-orange uncharged ion-association complex that is adsorbed on-line on a non-ionic polymeric adsorbent (Amberlite XAD-4), proportionally to the ascorbic acid in the sample. The unadsorbed iron was determined by flame atomic absorption spectrometry. The proposed method allows the determination of ascorbic acid in the range 0.5–25 g ml^–1 with a relative standard deviation of 2.9% at a rate of ca. 90 samples h^–1. This method has been applied to the determination of ascorbic acid in pharmaceutical preparations, fruit juices and sweets. The results obtained in the analysis are compared with those provided by the 2,6-dichloroindophenol method.     

Indirect flame atomic absorption detection for the liquid chromatographic separation of alkaline metals

Alkaline metals and ammonium ion are separated by cationic exchange liquid chromatography using a 60 g ml^–1 aqueous copper solution as the mobile phase at 1.5 ml min^–1. Detection is carried out by measuring copper with an atomic absorption spectrometer directly interfaced to the chromatograph. A simple T-piece is used to compensate the difference between the nebulizer uptake rate and the chromatographic flow-rate with air. The method is applicable to the analysis of alkaline metals and ammonium in waters. Average recovery (n = 16) was 100.3 ± 4.0%.     

Determination of Se(IV) using solidified floating organic drop microextraction coupled to ultrasound-assisted back-extraction and hydride generation atomic fluorescence spectrometry

A method is presented for matrix separation, preconcentration and determination by hydride generation atomic fluorescence spectrometry of trace amounts of Se(IV). It is based on solidified floating drops of 1-undecanol that are capable of extracting the target analyte after chelation with a water soluble ligand and subsequent ultrasound-assisted back-extraction into a aqueous solution. Hydride generation was then accomplished by reaction with a solution of sodium borohydride. Under optimized conditions, an enrichment factor of 15 and a linear calibration plot in the range from 0.01 to 5.0 μg L^?1 were achieved using a 10.0 mL sample. The detection limit (3σ) is 7.0 ng L^?1, and the relative standard deviation (RSD) is 2.1% at 1.0 μg L^?1 (n?=?11). The method was applied to determination of Se(IV) in different real water samples through recovery experiments and subsequently validated against two certified reference materials.

Detection of silver nanoparticles in parsley by solid sampling high-resolution–continuum source atomic absorption spectrometry

In this work, we present a fast and simple approach for detection of silver nanoparticles (AgNPs) in biological material (parsley) by solid sampling high-resolution–continuum source atomic absorption spectrometry (HR-CS AAS). A novel evaluation strategy was developed in order to distinguish AgNPs from ionic silver and for sizing of AgNPs. For this purpose, atomisation delay was introduced as significant indication of AgNPs, whereas atomisation rates allow distinction of 20-, 60-, and 80-nm AgNPs. Atomisation delays were found to be higher for samples containing silver ions than for samples containing silver nanoparticles. A maximum difference in atomisation delay normalised by the sample weight of 6.27?±?0.96 s mg^?1 was obtained after optimisation of the furnace program of the AAS. For this purpose, a multivariate experimental design was used varying atomisation temperature, atomisation heating rate and pyrolysis temperature. Atomisation rates were calculated as the slope of the first inflection point of the absorbance signals and correlated with the size of the AgNPs in the biological sample. Hence, solid sampling HR-CS AAS was proved to be a promising tool for identifying and distinguishing silver nanoparticles from ionic silver directly in solid biological samples.

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.