Characterization of interfering effects in the determination of molybdenum by atomic absorption spectrometry

The effect of anions on molybdenum absorbance depends on the pH; low pH causes the formation of iso- or heteropoly anions which change the atomization process in the flame. Organic ligands also depress the release of molybdenum atoms but cyanide radicals in the flame scavenge, e.g., OH radicals from such ligands and prevent their depressive effect. Certain cations (La, Ce, Mg, Ca, Sr and Ba) appear to form spinels; boric acid minimizes this effect.     

Characterization and elimination of the interfering effects of foreign species in the atomic-absorption determination of iron

The inhibition-release titration method has been used to study interference effects in flame atomic-absorption determination of iron. Interferences from anions, cations and complexing agents with the atomic-absorption of iron when a stoichiometric air-acetylene flame is used, can be obviated by a preliminary treatment of the sample solution with sulphosalicylic acid to convert the iron into the same complex before aspiration, thus giving a constant environment for the iron in the flame processes.     

Elimination of the interfering effects of ligands in the determination of cobalt by atomic absorption spectrometry

In atomic absorption spectrometric determinations of cobalt(II) and cobalt(III), the interfering effects of different complex-forming substances can be completely eliminated by addition of excess of cyanide. Cyanide has a double role: first, it forms very stable cyano complexes, so that the cobalt species reaching the flame will normally be independent of the original composition of the solution; secondly, the high excess of cyanide produces favourable physical and chemical conditions for cobalt atomization.     

Selective separation and determination of dissolved chromium species in natural waters by atomic absorption spectrometry

A procedure for determining the concentrations of dissolved chromium species in natural waters is described. Chromium(III) and chromium(VI), separated by co-precipitation with hydrated iron(III) oxide, and total dissolved chromium are determined separately by conversion to chromium(VI), extraction with APDC into MIBK and determination by a.a.s. The detection limit is 40 ng l^?1 Cr. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In the waters investigated, total concentrations were relatively high (1–5 μg l^?1) with Cr(VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species.     

Determination of chromium in sea water by atomic absorption spectrometry

A method for the determination of chromium in sea water is described which requires minimal sample preparation. The chromium from filtered samples is oxidized with permanganate, extracted with ammonium pyrrolidine dithiocarbamate into MIBK, and analyzed by atomic absorption spectrometry in a fuel-rich air-acetylene flame. Non-filterable solids are extracted with 12 M hydrochloric acid and analyzed. Detection limits for the methods are 0.05 μg 1^-1 in the soluble phase and 0.06 μg 1^-1 in the particulate phase.     

Determination of aluminium and chromium in serum by atomic absorption spectrometry

Summary The optimal conditions for the determination of aluminium and chromium in blood serum are proposed. Several sample pretreatment procedures for the purpose are compared. The best results are obtained by sample dilution with nitric acid (0.1 mol/l) and addition of Mg(NO₃)₂ as modifier with a magnesium concentration of 0.2 mg/ml. This procedure has been used for studying the intestinal intake of aluminium by patients after oral administration of aluminium compounds.     

Mechanism of interference elimination by thiourea in electrochemical atomic absorption spectrometry

The mechanism of interference elimination by thiourea in electrothermal atomization is discussed. Activation energies of atomization were measured. The experimental values for bismuth, lead, copper and cadmium were not altered in the presence of concomitants, provided that thiourea was added before atomization. These elements from complexes with thiourea which are converted to sulphides during the charring stage. Atom formation occurs from the sulphides without compound formation between analyte and concomitants.     

Determination of chromium in human serum by electro-thermal atomic absorption spectrometry

An accurate and sensitive method for serum chromium determinations by graphite-furnace atomic absorption spectrometry is described. Samples containing a small amount of magnesium nitrate as an ashing aid/matrix modifier are lyophilized and dry-ashed in silanized quartz tubes; the residue is dissolved in 0.1 M HCl. Because of the very low levels of chromium in serum, strict contamination control measures must be used throughout the procedures for collection, storage, preparation and quantitation. Standard curves are prepared by using a bovine serum pool, which also serves as a quality control measure. The uniform nature of sera obviates the need to use the method of standard additions. The detection limit of the method is about 0.03 ng ml^?1 Cr and the accuracy of the method is evaluated by comparison with stable-isotope-dilution mass spectrometry.     

Determination of chromium in gallium arsenide by electrothermal atomic absorption spectrometry

The sample is decomposed with 50% (v/v) aqua regia and the diluted solution is injected into the graphite furnace. The temperature program developed minimizes non-specific background signals, so that correction is not required. For a 100-mg sample, the 3σ detection limit is 70 ng Cr g^?1. The relative standard deviation of the overall procedure is 5–7%.     

Chemical reactions of chromium and vanadium in graphite furnace atomic absorption spectrometry

The chemical reactions of V and Cr in the graphite furnace are determined by absorption measurements, X-ray diffraction and electron microscopy techniques. It is shown that both elements form carbides, VC and Cr₃C₂, respectively. An increase in absorption is obtained in tubes coated with pyrolytic graphite. Interferences of carbideforming elements on the absorption signal are studied. Reaction paths are proposed for both elements during their heat treatment in graphite furnace AAS.     

Determination of total chromium traces in tannery effluents by electrothermal atomic absorption spectrometry, flame atomic absorption spectrometry and UV-visible spectrophotometric methods

Three different analytical methods comprising colorimetric method with 1,5-diphenyl-carbazide, electrothermal atomic absorption spectrometry (ET AAS) and flame atomic absorption spectrometry were utilized in a study to determine traces of chromium (Cr) in synthetic tannery effluent from laboratory scale treatment process variations. All the results obtained using the three different methods showed good agreement and met the requirement of Brazilian regulation for total Cr for effluent discharges (<0.5 mg l(-1)). However, ET AAS has been the proposed method because it was faster, less laborious, needed smaller volume of sample and presented lower limit of quantification (LOQ=2.2 mug l(-1)).     

Separation and preconcentration of chromium species by selective absorption on Lemna minor and determination by slurry atomisation electrothermal atomic absorption spectrometry

A novel method for the separation and preconcentration of Cr(III)/Cr(VI) with Lemna minor and determination by slurry atomization electrothermal atomic absorption spectrometry (ETAAS) was developed. A sample solution was added to a polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 1.0, stirred for 8 min for selective absorption of Cr(III) and then centrifuged. The upper layer of solution was transferred into another polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 5.0, stirred for 12 min for adsorption of the residual Cr(VI) and centrifuged. The two residues in two centrifuge tubes were washed twice with water, 2 ml of agar solution added, stirred for 2 min, then two slurries were prepared and used for the determination of Cr(III) and Cr(VI) by ETAAS. Detection limits (3sigma) of 0.01 microg L(-1) for Cr(III) and 0.03 microg L(-1) for Cr(VI) were obtained. The relative standard deviation was 2.8% for Cr(III) and 3.3% for Cr(VI) at the 1 microg L(-1) level. The method was applied to the determination of Cr(III)/Cr(VI) in water samples. The analytical recoveries of Cr(III) and Cr(VI) added to samples were 97-102 and 96-103%, respectively.     

Determination of chromium in human milk and urine by graphite-furnace atomic absorption spectrometry

Low-temperature ashing and dry ashing at 500°C are compared for the analysis of urine and human milk. Dry ashing gives superior accuracy. The importance of contamination control, background correction and temperature control are stressed. Both urine and human milk contain about 1 ng Cr ml^-1.     

Stray light effects in Zeeman atomic absorption spectrometry

A transverse Zeeman atomic absorption spectrometer has been modeled using a polychromatic, optical calculus simulation software program. The models were found to be realistic and greatly facilitated the study of the effects of various Zeeman spectrometer parameters and their interactions. The behavior of the Zeeman spectrometer calibration curves, in the presence of three different types of stray light, was modeled. From the initial results, it seems most likely that the major stray light source in real Zeeman experiments is due to polychromaticity of the light source, even when the source profile is relatively narrow in spectral bandwidth.     

石墨炉原子吸收光谱法测定蚕蛹中Cr、Se量

建立了石墨炉原子吸收光谱法测定蚕蛹中Cr、Se的方法,为蚕蛹新资源食品的开发及明确其营养价值提供科学数据。利用石墨炉原子吸收光谱法,偏振塞曼效应扣除背景,石墨炉程序升温方式进行Cr、Se的原子化,检测峰值吸收。加入硝酸镍、吐温X-100为基体改进剂,在体积分数0.5%HNO3介质中对桑蚕蛹中Cr、Se进行测定。方法的精密度:4.0%(Cr),3.1%(Se)。加标回收率:96.8%~105.3%(Cr),92.1%~108.8%(Se)。Cr、Se的线性范围和检出限分别为:0~10μg/L(Cr),0~40μg/L(Se);LOD=1.22μg/L(Cr),1.86μg/L(Se)。建立的分析方法适用于蚕蛹中Cr、Se的测定。     

The reduction and elimination of matrix interferences in graphite furnace atomic absorption spectrometry

The approaches to reduction or elimination of matrix interferences encountered in graphite furnance atomic absorption spectrometry is reviewed. These techniques include matrix modification, application of active gas, and coating tubes with metallic compounds. The research work carried out in the author's laboratory is emphasized. A more universal matrix modifier, palladium, is proposed for the determination of mercury, lead, tellurium, bismuth, arsenic, thallium and indium in environmental samples.     

Direct determination of chromium in human urine by electrothermal atomic absorption spectrometry

A rapid, accurate and direct method for urinary chromium determinations by graphite-furnace atomic absorption spectrometry is described. Few reagents are used and very little sample preparation and manipulation are required, greatly reducing the incidence of sample contamination. The method of standard additions is used to compensate for changes in sensitivity as the furnace tube ages, and for the widely different matrices encountered in urine samples. Furnace parameters must be carefully controlled. The detection limit is in the order of 0.03 ng Cr ml^-1. Agreement with independent methods is evaluated.     

Preconcentration and speciation of chromium in waters using solid-phase extraction and atomic absorption spectrometry

A method for the preconcentration and speciation of chromium was developed. After formation of an anionic compound with ethylenediaminetetraacetic acid (CrY(-)), Cr (VI) and Cr (III) are retained on a strong anionic phase (SAX) and controlled elution with 0.5 M NaCl permits their speciation. The retention and elution conditions were optimised, and interferences due to the presence of other ions such as Mg(II), Mn(II), Sn(II), Fe(III), Ba(II), Al(III), Ca(II), chloride, iodine, bromide, fluoride, sulphate, phosphate, bicarbonate and nitrate were studied. The detection limits were 0.4 mug l(-1) and 1.1 mug l(-1) for Cr(III) and Cr(VI), respectively, and reproducibility was 9%. The results obtained for speciation of chromium by the proposed method in wastewaters are in agreement with the values obtained by a reference method for a 95% confidence level.     

Segmented approximation of interference effects in atomic absorption spectrometry

A segmented approximation method is used for empirical modelling of interference effects in atomic absorption spectrometry. First- and second-degree polynomials are used in the modelling. The examples presented concern the determination of iron in presence of sodium, and calcium in the presence of strontium. In each case, the split polynomial models are more accurate and reliable than the single high-degree polynomial models.     

Determination of traces of chromium in cocaine and heroin by flameless atomic absorption spectrometry

A method for the determination of total chromium in cocaine and heroin by flameless atomic absorption spectrometry is presented. Cocaine samples were dissolved in 2 ml of HNO(3) 35.0% (v/v) and diluted to 10 ml with ultrapure water; heroin samples were dissolved in ultrapure water, adding 0.4 ml of HNO(3) 35.0% (v/v) to dissolve inert species, and also diluted to 10 ml. Mg(NO(3))(2) and HNO(3), as chemical modifiers, were compared in terms of sensitivity, precision and accuracy, a lower detection limit being obtained for the use of Mg(NO(3))(2), 5.77 mug kg(-1) (7.23 mukg(-1) for HNO(3)). Within-batch precision was found to be 6.19% and 1.48% for drug solution spiked with 0 and 10 mug l(-1) of Cr(3+), respectively, when using Mg(NO(3))(2), and 7.45 and 1.19% for the same respective concentration levels when using HNO(3). Similar results on analytical recovery were obtained for both Mg(NO(3))(2) and HNO(3). Mg(NO(3))(2) was selected as the more adequate of the two chemical modifiers. A study of the introduction of a cooling-down step of 50 degrees C was carried out and compared in terms of sensitivity to the programme without a cooling-down step, but no advantage was observed. Studies on the variation in precision and analytical recovery with the amount of sample, and interferent effects of different species on chromium determination were developed. Finally, chromium concentrations obtained in cocaine samples varied between 0.02 and 0.14 mg kg(-1), the levels in the heroin samples being in the 0.05-0.59 mg kg(-1) range.