Study of chemical modifiers for the determination of chromium in biological materials by tungsten coil electrothermal atomic absorption spectrometry

The determination of Cr in digest solutions of mussels and non-fat milk powder by tungsten coil electrothermal atomic absorption spectrophotometry (TC-ETAAS) is affected by interferences. This study reports a critical evaluation of chemical modifiers that could be employed to correct these interferences. The chemical modifiers tested were: Mg [as Mg(NO₃)₂], Pd [as Pd(NO₃)₂], NH₄NO₃, ascorbic acid, and mixtures of these compounds. The less effective modifier was NH₄NO₃. The best effects, considering thermal stabilization and sensitivity, were obtained in mixtures of ascorbic acid plus Mg. Chromium was determined by TC-ETAAS in certified reference materials of mussels and non-fat milk powder, and results were comparable with those obtained by graphite furnace atomic absorption spectrophotometry (GFAAS). Received: 19 June 1998 / Revised: 11 January 1999 / Accepted: 16 January 1999     

The selection of a chemical modifier for vanadium determination in various types of natural waters by electrothermal atomic absorption spectrometry

Various modifiers (ascorbic acid, NH₄NO₃, EDTA, NH₄SCN and a mixture of Pd/Mg(NO₃)₂) are compared for the accurate determination of vanadium in natural waters by electrothermal atomic absorption spectrometry. The interferences of compounds commonly present in natural waters, such as NaCl, CaCl₂, MgCl₂ and FeCl₃ are studied. Matrix interferences were effectively eliminated by ascorbic acid or ammonium nitrate. For comparison, the standard addition method was applied without a modifier which provided satisfactory results. The accuracy of the method was confirmed by analysis of certified reference materials of waters (‘Trace Metals in Drinking Water’ and SRM 1643e ‘Trace Elements in Water’) as well as by recoveries of vanadium spiked to tap water, mineral water, synthetic riverine and synthetic sea waters. The limits of detection and characteristic masses for ascorbic acid and ammonium nitrate as the modifiers were 1.71 and 1.56?µg?L^?1 and 70 and 67?pg, respectively. Recovery was in the range of 98–105% and RSD was less than 5%.     

Some observations on the use of matrix modifiers in the determination of aluminum by electrothermal atomic absorption spectrophotometry

Some evidence demonstrating that the use of matrix modifiers is necessary to obtain good calibration lines in the determination of aluminum by graphite furnace atomic absorption spectrophotometry is provided. It was found that the most sensitive results were obtained when Mg(NO₃)₂ was used instead of NH₄H₂PO₄.     

Direct and simultaneous determination of copper and manganese in seawater with a multielement graphite furnace atomic absorption spectrometer

The direct and simultaneous determinations of Cu and Mn in seawater using a multielement graphite furnace atomic absorption spectrometer (Perkin-Elmer SIMAA6000) are described. Three kinds of chemical modifier (Mg(NO₃)₂, Pd(NO₃)₂ and a mixture of these) were tested. The matrix interferences were removed completely so that a simple calibration curve method could be used to determine Cu and Mn in seawater from the open ocean using Pd or a mixture of Pd and Mg as the chemical modifier. The relative standard deviations (RSDs) for the simultaneous determination of Cu and Mn in seawater from open ocean are 10% or less, and the detection limits were 0.07 μg 1⁻¹ for Cu and 0.10 μg 1⁻¹ for Mn, using Pd as the chemical modifier. The accuracy of the method is confirmed by analysis of four kinds of certified reference saline waters.     

Determination of cadmium, copper and lead in soils, sediments and sea water samples by ETAAS using a Sc + Pd + NH(4)NO(3) chemical modifier

Cadmium, copper and lead in soils, sediments and spiked sea water samples have been determined by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background corrector using NH₄NO₃, Sc, Pd, Sc + NH₄NO₃, Pd + NH₄NO₃, Sc + Pd and Sc + Pd + NH₄NO₃ as chemical modifiers. A comprehensive comparison was made among the modifiers and without modifier in terms of pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations. Sc + Pd + NH₄NO₃ modifier mixture was found to be preferable for the determination of analytes in soil and sediment certified and standard reference materials, and sea water samples because it increased the pyrolysis temperature up to 900 °C for Cd, 1350 °C for Cu and 1300 °C for Pb. Optimum masses of mixed modifier components found are 20 μg Sc + 4 μg Pd + 8 μg NH₄NO₃. Characteristic masses of Cd, Cu and Pb obtained are 0.6, 5.3 and 15.8 pg, respectively. The detection limits of Cd, Cu and Pb were found to be 0.08, 0.57 and 0.83 μg l⁻¹, respectively. Depending on the solid sample type, the percent recoveries were increased up to 103% for Cd, Cu and Pb by using the proposed modifier mixture. The accuracy of the determination of analytes in the sea water samples was also increased.     

Parameter optimization of electrothermal vaporization inductively coupled plasma mass spectrometry for oligoelement determination in standard reference materials

The operational parameters of the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), i.e. the internal carrier gas flow rate, the total carrier gas flow rate, the sample pretreatment temperature and the volatilization temperature, are optimized for oligoelement determinations (⁷⁵As, ⁹Be, ¹¹²Cd, ⁵⁰Cr, ⁶⁵Cu, ¹⁰³Rh, ¹²³Sb). The volatilization temperatures of As and Cr are compared to those obtained by graphite furnace atomic absorption spectrometry (GFAAS). Several modifiers Mg(NO₃)₂, Pd(NO₃)₂, Mg(NO₃)₂/Pd(NO₃)₂, Ni(NO₃)₂, KI, (NH₄)H₂PO₄ have been tested using the concentrations recommended for GFAAS. The concentration of Mg(NO₃)₂ alone and in combination with NaCl has been varied to find the optimal modifier conditions. ETV-ICP-MS signal enhancements by a factor of 10 to 130 respective to those of conventional nebulization have been obtained. The optimized parameters are evaluated by analyzing the water standard reference NIST 1643c and the aqua regia solution of the lake sediment reference material BCR 280.     

Parameter optimization of electrothermal vaporization inductively coupled plasma mass spectrometry for oligoelement determination in standard reference materials

The operational parameters of the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), i.e. the internal carrier gas flow rate, the total carrier gas flow rate, the sample pretreatment temperature and the volatilization temperature, are optimized for oligoelement determinations (⁷⁵As, ⁹Be, ¹¹²Cd, ⁵⁰Cr, ⁶⁵Cu, ¹⁰³Rh, ¹²³Sb). The volatilization temperatures of As and Cr are compared to those obtained by graphite furnace atomic absorption spectrometry (GFAAS). Several modifiers Mg(NO₃)₂, Pd(NO₃)₂, Mg(NO₃)₂/Pd(NO₃)₂, Ni(NO₃)₂, KI, (NH₄)H₂PO₄ have been tested using the concentrations recommended for GFAAS. The concentration of Mg(NO₃)₂ alone and in combination with NaCl has been varied to find the optimal modifier conditions. ETV-ICP-MS signal enhancements by a factor of 10 to 130 respective to those of conventional nebulization have been obtained. The optimized parameters are evaluated by analyzing the water standard reference NIST 1643c and the aqua regia solution of the lake sediment reference material BCR 280.     

Evaluation of tungsten–rhodium coating on an integrated platform as a permanent chemical modifier for cadmium,lead, and selenium determination by electrothermal atomic absorption spectrometry

A tungsten–rhodium coating on the integrated platform of a transversely heated graphite atomizer is proposed as a permanent chemical modifier for the determination of Cd, Pb, and Se by electrothermal atomic absorption spectrometry. It was demonstrated that coating with 250 μg W+200 μg Rh is as efficient as the conventional Mg(NO₃)₂+NH₄H₂PO₄ or Pd+Mg(NO₃)₂ modifiers for avoiding most serious interferences. The permanent W–Rh modifier remains stable for 300–350 firings of the furnace, and increases tube lifetime by 50%–100% when compared to pyrolytic carbon integrated platforms. Also, there is less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifiers, resulting in a decreased need of re-calibration during routine analysis. The characteristic masses and detection limits achieved using the permanent modifier were respectively: Cd 1.1±0.4 pg and 0.020 μgL⁻¹; Pb 30±3 pg and 0.58 μgL⁻¹ and Se 42±5 pg and 0.64μgL⁻¹. Results from the determination of these elements in water reference materials were in agreement with the certified values, since no statistical differences were found by the paired t-test at the 95% level.     

Determination of cadmium by electrothermal atomic absorption spectrometry after microwave-assisted digestion of animal tissues and sewage sludges

The determination of cadmium in different sample types has been carried out by electrothermal atomization atomic absorption spectrometry with D₂-background correction using a unpyrocoated graphite tube, after pressurized microwave-assisted digestion. Five chemical modifiers [(NH₄)₂HPO₄, Pd(NO)₃)₂, Ni(NO₃)₂, thiourea and Triton X-100] have been assayed and nickel nitrate has been found to be most effective for an accurate determination of cadmium in mussel tissue, pig kidney and sewage sludge. The characteristic mass of the method is of the order of 1 pg and the limit of detection is lower than 0.1 ng/ml.     

On-line pre-concentration of Cr(III) and Mn(II) in FI-FAAS: A critical study involving interference effects and analytical use of an immobilized 8-hydroxyquinoline minicolumn

A flow injection system with a pre-concentration minicolumn based on a chelating resin was coupled to a flame atomic absorption spectrometer. The focus of this work was the investigation of interference effects and the analytical applicability of the azo-immobilized 8-hydroxyquinoline on controlled-pore glass for the determination of Cr and Mn in mussel and non-fat milk powder. All studied concomitants affected the retention of Cr(III). These effects are probably related to the formation of hydroxo-complexes at the optimum pH range 9.0-10. The positive effect caused by Ca(II) was exploited to increase the retention of Cr(III) species and to improve the slope by 70%. The interferences on Mn(II) retention were less severe. The quantification of Cr and Mn was performed by standard additions. The proposed methodology was validated by analysis of three certified reference materials of mussels (Cr and Mn) and non-fat milk powder (Mn) with a mean relative percent error of <6.5% and mean relative standard deviation of <13%. Chromium and Mn were determined in typical Chilean mussels samples, and Mn was determined in non-fat milk powder samples. Results agreed at the 95% confidence level with those obtained by electrothermal atomic absorption spectrometry (ETAAS) using graphite furnace atomization. The method detection limits for a 30 s pre-concentration time were 0.9 and 1.1 micro g L(-1) for Mn, and 2.2 and 2.5 micro g L(-1) for Cr in acid digested solutions of mussel and non-fat milk, respectively. The methodology is simple, fast (sampling frequency 60-72 h(-1)), reliable, of low cost, and can be applied to the determination of traces of Cr (> or =0.18 micro g g(-1)) and Mn (> or =0.6 micro g g(-1)) in mussel samples, and Mn (> or =0.37 micro g g(-1)) in non-fat milk powder.     

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l⁻¹ HNO₃ and in 1+1 v/v diluted wine using mixtures of Pd(NO₃)₂+Mg(NO₃)₂ and NH₄H₂PO₄+Mg(NO₃)₂ as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l⁻¹ HNO₃, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l⁻¹ Cd and 5.0–50 μg l⁻¹ Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l⁻¹ for Cd, 0.8 μg l⁻¹ for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l⁻¹ and for Pb at 500 μg l⁻¹. The relative standard deviations (n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.     

Effect of nitric acid for equal stabilization and sensitivity of different selenium species in electrothermal atomic absorption spectrometry

Determination of selenium by electrothermal atomic absorption spectrometry (ETAAS) is complicated by the presence of different species of this analyte. The presence of different oxidation states (−II, IV and VI) may result in different sensitivities obtained for each species rendering impossible the use of a single species for calibration. These species also exhibit different behaviours regarding thermal stabilities; the temperature program must be provided to conform to this problem. Chemical modifiers are commonly used for thermal stabilization of selenium species. In this study, experiments were carried out to demonstrate the effect of nitric acid in the presence of chemical modifiers. Nickel and palladium + magnesium were selected as the most commonly used chemical modifiers. Using both aqueous and human serum solutions it has been demonstrated that although chemical modifiers provide thermal stabilization of species so that higher ashing temperatures can be used, equal sensitivities cannot be achieved unless nitric acid is also present. Selenite, selenate, selenomethionine and selenocystine were used in experiments. When equal sensitivities for all these species are achieved, determination of total selenium by ETAAS can be performed by using a single species as the standard; selenite was used in this study. Precision was 5.0% or better using peak height signals. There was no significant difference in detection limits (3s) when Ni or Pd + Mg(NO₃)₂ was used as chemical modifier; 37 and 35 pg of selenium were found to be the detection limits for Ni and Pd + Mg(NO₃)₂ chemical modifiers, respectively. For chemical modifications, either 5 μg of Ni or 0.5 μg of Pd and 5 μg of Mg(NO₃)₂ were used; final solutions contained 2.5% HNO₃. In serum analyses, 10 μg of Ni was used in presence of 2.5% HNO₃.     

Use of hydrogen for the elimination of matrix interferences in the determination of lead by graphite furnace atomic absorption spectrometry

Summary Comparatively high sulphur contents in brown algae (Fucus vesiculosus) cause interferences in the determination of lead by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). These cannot always be eliminated by the application of the L'vov platform, matrix modifiers recommended for lead as (NH₄)₂HPO₄ and Mg(NO₃)₂, Zeeman-effect background correction and peak area evaluation.The behaviour of the lead absorbance signal obtained from the L'vov platform inserted into an uncoated as well as a pyrolytically coated graphite tube was examined in the presence of sodium and magnesium sulphate and (NH₄)₂HPO₄ and Mg(NO₃)₂ matrix modifiers.Accurate lead determinations could only be performed if hydrogen was used as alternate gas during drying and charring steps since this eliminated the interferences caused by sulphates.

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Verwendung von Wasserstoff zur Eliminierung von Matrixstörungen bei der Bleibestimmung durch Graphitofen-AAS

Zusammenfassung Vergleichsweise hohe Schwefelgehalte in Braunalgen (Fucus vesiculosus) verursachen Störungen bei der Bestimmung von Blei mit Grahitrohrofen-AAS. Diese können nicht immer durch Anwendung der L'vov-Plattform und den für Blei empfohlenen Matrix-Modifizierer (NH₄)₂HPO₄ und Mg(NO₃)₂, Zeeman-Effekt-Untergrundkorrektur und Peakflächenauswertung behoben werden.Das Verhalten des Blei-Absorbance-Signals, das von einer L'vov-Plattform, die sowohl in ein unbeschichtetes wie in ein mit Pyrokohlenstoff beschichtetes Graphitrohr eingebracht wurde, erzeugt wird, wurde in Gegenwart von Natrium- und Magnesiumsulfat sowie (NH₄)₂HPO₄ und Mg(NO₃)₂-Matrix-Modifizierern untersucht.Richtige Bleibestimmungen konnten nur durchgeführt werden, wenn Wasserstoff als Alternativgas während des Trocknens und der thermischen Zersetzung verwendet wurde, was die durch Sulfat hervorgerufenen Störungen eliminierte.

     

The determination of low lead levels in the bone of lead-depleted mice by graphite furnace atomic absorption spectrometry

Low lead levels in the femurs of mice fed with a lead-depleted diet have been determined by use of electrothermal atomic absorption spectrometry with Zeeman-effect background correction. The method is based on the use of Mg(NO₃)₂/Pd as matrix modifier which enables significant reduction of the spectral interferences prevalent if chemical modifiers based on NH₄H₂PO₄ with either Ca or Mg are used for samples rich in Ca₃(PO₄)₂ matrix. The method was developed and validated by use of the NIST standard reference material 1486 bone. Bones were decomposed in a pressurized microwave-heated system using 70% nitric acid. Forty-three mice femurs, with a mass of 74.62 ± 12.54 mg, were dissolved in concentrated nitric acid. The lead results found in SRM 1486 (1.25 ± 0.15 μg g^–1, n = 9) were in good agreement with the certificate (1.335 ± 0.014 μg g^–1). Recoveries of 200 ng lead added to the SRM before or after digestion were 99.0 ± 1.4% and 98.5 ± 1.6%, respectively. The lead detection limit in bone samples is 0.06 μg g^–1 dry mass. This method is, therefore, suitable for the determination of very low lead levels (0.06–0.20 μg Pb kg^–1 bone) in the femurs of mice fed a diet with lead level of < 20μg kg^–1.     

Direct determination of lead in sweet fruit-flavored powder drinks by electrothermal atomic absorption spectrometry

A simplified method for direct determination of lead in sweet fruit-flavored powder drinks, syrups and honeys by electrothermal atomic absorption spectrometry without sample digestion is proposed. Samples were dissolved in water, acidified to 0.2% (v/v) HNO₃, and directly injected into an end-capped transversely heated graphite atomizer (THGA). Building up of carbonaceous residue inside the atomizer was effectively precluded for sugar solutions not exceeding 8.0% (m/v) when a heating program with two pyrolysis steps (600 and 1000°C) was carried out without air-ashing. Under these conditions one atomizer supported about 250 firings. Among various chemical modifiers tested, better recovery and repeatability results were obtained with a 5 μg Pd + 3 μg Mg(NO₃)₂ mixture. Tests carried out with individual concomitants containing up to 1.0 μg Na, K, Ca or Cl, and up to 10.0 μg phosphate or sulphate, and several mixtures of these six concomitants, did not reveal significant interferences on lead atomization. Characteristic mass and detection limit based on integrated absorbance were 15 and 11 pg Pb, respectively. The relative standard deviation based on 10 measurements for typical samples (20–60 ng g⁻¹ Pb) was always lower than 5.5%. The detection limit of 7.0 ng g⁻¹ Pb attained the Codex recommendation for the maximum allowed lead contents in the sugar samples. Application of t-test to the results obtained by the proposed direct analysis, and the official method adopted by Food Chemical Codex, demonstrated that there were no significant differences at the 5% probability level.     

Slurry sampling for determination of lead in marine plankton by electrothermal atomic absorption spectrometry

A slurry sampling method has been developed for the determination of Pb in marine plankton by ETAAS using a freshwater plankton certified reference material (CRM 414). Slurries were prepared in 1–3% m/v range with 1% v/v HNO₃ by ultrasonic agitation for 5 min. The effects of several chemical modifiers, including Ir(NO₃)₂, Mg(NO₃)₂, Pd(NO₃)₂, Pd(NO₃)₂ + Mg(NO₃)₂, and Mg(NO₃)₂ + NH₄H₂PO₄, were investigated for the stabilization of Pb during thermal pretreatment. Lead in slurries was effectively stabilized up to 1000 °C with Ir, Pd and Pd + Mg modifiers among which Pd + Mg provided the best results with complete atomization at 1850 °C. Firings in the presence of Ir were, problematic due to ash formation inside the atomizer. Water, dilute HNO₃ and HF were examined as suspension medium. Dilute HNO₃ (1–2% v/v) proved to be advantageous over water as it afforded extraction of Pb from plankton almost quantitatively in 5 min agitation. Hydrofluoric acid was the least suitable medium. Increasing HF concentration up to 5% v/v resulted in inaccuracy and substantial background absorption. Fast-heating furnace method provided comparable accuracy and precision to that of conventional-heating in slurries of CRM 414. Detection limits and characteristic masses were, respectively, 0.49 μg L^− 1 and 32 pg for the conventional method and 0.62 μg L^− 1 and 37 pg for the fast-heating method. However, fast-heating approach suffered from distorted peaks at high temperatures and incomplete pyrolysis of matrix at lower temperatures. Analysis of marine plankton samples for Pb was performed by using the conventional furnace program. The results showed a high correlation with those obtained by solution ICP-MS. Differences were statistically insignificant within 95% confidence interval.     

Determination of cadmium and lead in mussels by tungsten coil electrothermal atomic absorption spectrometry

In this work it was evaluated the determination of Cd and Pb in mussels by tungsten coil electrothermal atomic absorption spectrometry (TCA-AAS). A critical and comprehensive study of the effects caused by Pd, Mg, ascorbic acid, and binary mixtures of these compounds on the atomization of Cd and Pb in acid digested solutions of mussels was performed. Palladium and mixtures containing it were useful to increase sensitivity and thermal stability of Cd and Pb. Additionally, the coil lifetime was increased and the background signals were decreased in these modifiers. All these favorable effects were analytically exploited to determine Cd and Pb in samples of mussels. The proposed methodology was validated using two certified reference materials (oyster tissue and mussel). No statistical difference was observed between determined and certified values at a 95% confidence level. Cadmium and Pb in Chilean bivalve mussels were determined by TCA and by graphite furnace-AAS. Again, the results showed statistical agreement.     

Direct copper determination in whole milk, non-fat milk and whey milk by electrothermal atomic absorption spectrometry

A method for the direct determination of copper in samples of whole milk, non-fat milk and whey milk by electrothermal atomic spectrometry (ETAAS) was studied. The fat separation by centrifugation at 3200 rpm and the separation of casein mycelles to obtain the whey milk by ultracentrifugation at 31 000 g were investigated. In all cases Mg(NO₃)₂ was used as chemical modifier and Triton X-100 (0.2% w/v) as emulsifying agent. The optimum pyrolysis temperature was 1500° C. The detection limit was 0.4 μg/l of copper. The precision was studied for the whole milk and the coefficients of variation (CV) were 5.7, 4.0, 2.4 and 2.8% for 0, 5, 10 and 20 μg/l of copper added. The accuracy was determined by using the Reference Material Milk A-11 (IAEA) with a certified content of 378.4 ± 24 ng Cu/g; 359 ± 16 ng/g were found. The method was applied to ten cow milk samples, the levels of copper being determined for whole milk, non-fat milk and whey milk. A statistical study was applied and it was concluded that the majority of copper is in the non-fat milk. Received: 29 February 1996 / Revised: 19 April 1996 / Accepted: 28 April 1996     

Comparative study on the use of Ir, W and Zr-coated graphite tubes for the determination of chromium in slurries of human scalp hair by electrothermal atomic absorption spectrometry

The use of Ir, W and Zr-coated graphite tubes, as permanent chemical modifiers, was studied for the determination of chromium in human scalp hair by ETAAS using the slurry sampling technique. The use of Mg(NO₃)₂ and Pd, as aqueous chemical modifiers, was also investigated and compared to the use of the permanent chemical modifiers. Scalp hair samples were pulverized using a Zr vibrational ball mill, (mean particle diameter of 0.8 μm) and suspended in ultrapure water. The lowest limit of detection, 44.5 μg kg^–1,was achieved for the use of W-coated graphite tubes. The repeatability of the overall procedures (slurry preparation and ETAAS determination) were 15.7, 14.5 and 16.7% for W- and Zr-coated graphite tubes and Mg(NO₃)₂, respectively. The methods were applied to several reference materials, CRM 397 (human hair), DOLT-1 (dogfish liver) and DORM-1 (dogfish muscle), and the results obtained were in agreement to the certified values. Finally, the methods were applied to several human scalp hair samples from healthy adults.     

Comparative study on the use of Ir, W and Zr-coated graphite tubes for the determination of chromium in slurries of human scalp hair by electrothermal atomic absorption spectrometry

The use of Ir, W and Zr-coated graphite tubes, as permanent chemical modifiers, was studied for the determination of chromium in human scalp hair by ETAAS using the slurry sampling technique. The use of Mg(NO₃)₂ and Pd, as aqueous chemical modifiers, was also investigated and compared to the use of the permanent chemical modifiers. Scalp hair samples were pulverized using a Zr vibrational ball mill, (mean particle diameter of 0.8 μm) and suspended in ultrapure water. The lowest limit of detection, 44.5 μg kg^–1,was achieved for the use of W-coated graphite tubes. The repeatability of the overall procedures (slurry preparation and ETAAS determination) were 15.7, 14.5 and 16.7% for W- and Zr-coated graphite tubes and Mg(NO₃)₂, respectively. The methods were applied to several reference materials, CRM 397 (human hair), DOLT-1 (dogfish liver) and DORM-1 (dogfish muscle), and the results obtained were in agreement to the certified values. Finally, the methods were applied to several human scalp hair samples from healthy adults. Received: 3 April 1997 / Revised: 12 May 1997 / Accepted: 15 May 1997