Permanent Chemical Modifier Research Articles

Noble metals as permanent chemical modifiers for the determination of mercury in environmental reference materials using solid sampling graphite furnace atomic absorption spectrometry and calibration against aqueous standards

Iridium, palladium, rhodium and ruthenium, thermally deposited on the platform, were investigated as permanent modifiers for the determination of mercury in ash, sludge, marine and river sediment reference materials, ground to a particle size of 50 μm, using solid sampling graphite furnace atomic absorption spectrometry. A total mass of 250 μg of each modifier was applied using 25 injections of 20 μl of modifier solution (500 mg l −1), and executing a temperature program for modifier conditioning after each injection. The performance of palladium was found to be most consistent, taking the characteristic mass as the major criterion, resulting in an excellent correlation between the measured integrated absorbance values and the certified mercury contents. Mercury was found to be lost in part from aqueous solutions during the drying stage in the presence of all the investigated permanent modifiers, as well as in the presence of the palladium and magnesium nitrates modifier added in solution. A loss-free determination of mercury in aqueous solutions could be reached only after the addition of potassium permanganate, which finally made possible the use of aqueous standards for the direct analysis of solid samples. A characteristic mass of 55–60 pg Hg was obtained for the solid samples, using Pd as a permanent modifier, and also in aqueous solutions after the addition of permanganate. The results obtained for mercury in ash, sludge and sediment reference materials, using direct solid sapling and calibration against aqueous standards, as well as the detection limit of 0.2 mg kg −1 were satisfactory for a routine procedure.

Metals distribution and investigation of L'vov platform surface using principal component analysis, multi-way principal component analysis, micro synchrotron radiation X-ray fluorescence spectrometry and scanning electron microscopy after the determination of Al in a milk slurry sample

This work describes the use of different strategies/techniques, such as scanning electron microscopy (SEM), multivariate analysis (principal component analysis (PCA) and multi-way PCA) and micro synchrotron radiation X-ray fluorescence (μSRXRF), in order to extract information about platform morphology, metals distribution on its surface, and the performance of conventional and permanent modifiers after slurry analyses using electrothermal atomic absorption spectrometry (ET AAS). With multivariate analysis it was possible to select Zr (500 μg for each 50 heating cycles) as a permanent chemical modifier for the determination of Al in milk powder slurry samples. Employing multi-way PCA and SEM, it was possible to note the differences in morphology between platforms permanently treated with Zr and those conventionally treated with Mg(NO 3) 2. The use of PCA and SEM also allowed finding similarities between new platforms, and those with and without Zr treatment. Using the μSRXRF it was possible to establish metals distribution on the L'vov platform and compare the performance of conventional [Mg(NO 3) 2] and permanent (Zr) modifiers.

Investigations of a W-Rh permanent modifier for the determination of Pb in blood by electrothermal atomic absorption spectrometry

A tungsten-rhodium coating (250 μg W+200 μg Rh) on the integrated platform of a transversely heated graphite atomizer (THGA) was used as a permanent chemical modifier for the direct determination of lead in whole blood by electrothermal atomic absorption spectrometry (ETAAS). Blood samples were diluted 1+9 with a diluent consisting of 0.2% v/v HNO 3 and 0.5% v/v TritonX-100, and 12 μl of the diluted sample was deposited on the platform. With use of the W-Rh modifier, tube lifetime was improved by a factor of 2–3 when compared with a conventional NH 4H 2PO 4 modifier. With a standard THGA tube, use of the W-Rh permanent modifier allows simple calibration with aqueous standard solutions for blood Pb measurement. However, matrix-matched calibration is still necessary when an end-capped THGA tube is used. The method detection limit (3σ) based on integrated absorbance measurements is 1.5 μg dl −1 (0.092 μmol 1 −1) for the standard THGA and 1.0 μg dl −1 (0.048 μmol l −1) for the end-capped tube. Various blood-based certified reference materials and proficiency testing samples, certified for Pb, were analyzed for validation purposes. All results were well within the range considered acceptable. Analysis of human blood samples for blood Pb measurement provided additional validation data against an established blood Pb ETAAS method that uses phosphate modifier.

Zirconium–iridium coating as a permanent modifier for determination of tin in stream sediment, oyster tissue and total diet slurries by electrothermal atomic absorption spectrometry

A slurry atomization procedure has been developed for the determination of total tin in different types of environmental samples such as stream sediment, oyster tissue and total diet using a Zr–Ir permanent chemical modifier and transverse heated electrothermal atomic absorption spectrometry (THETAAS). Reference materials such as GBW07312 Stream Sediment, NIST SRM 1566a Oyster Tissue and NIST SRM 1548 Total Diet were used to validate the method. Slurries were prepared in a mixture of 1% v/v HNO3, 2% v/v HCl and 0.2% Triton X-100 solution by using magnetic stirring and ultrasonication. Addition of Triton X-100 after sonication of the slurries rather than before was found to improve the precision of measurement. With the Zr–Ir-coated tube the characteristics mass obtained was 38 ± 2 pg, which is an improvement of nearly five times compared to using an uncoated tube. The tube lifetime using aqueous standards and slurries was nearly 500 atomization cycles. The Zr–Ir permanent chemical modifier was found to effectively reduce the interference effects from chloride, phosphate and silica, as nearly 90–100% recovery was obtained in the presence of 100 μg of the matrix. In the presence of 100 μg of sulfide, aluminum nitrate and sodium silicate, 30–60% recovery was obtained, indicating the presence of matrix interferences.

Flow system with in-line separation/preconcentration coupled to graphite furnace atomic absorption spectrometry with W–Rh permanent modifier for copper determination in seawater

A flow system was coupled to a graphite furnace with a platform coated with tungsten–rhodium permanent chemical modifier for in-line separation and preconcentration of copper by employing a minicolumn loaded with 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C 18-bonded silica fixed in the tip of the autosampler arm. Elution was made by sampling 35 μl of 0.50 mol l −1 HCl with further delivering into a coated platform. Remarkable improvements in both selectivity and sensitivity were observed. Copper(II) was effectively separated from solutions containing up to 20 g l −1 Na +; 10 g l −1 K +, Ca 2+ and Mg 2+; 1.0 g l −1 Fe 3+ and Zn 2+. For a sample flowing at 3.0 ml min −1 and a loading of 60 s, the detection limit was estimated as 5 ng l −1 Cu(II) at the 99.7% confidence level, and an enrichment factor of 33 was calculated. Coefficient of variation was estimated as 4% for a 0.30 μg l −1 copper solution ( n=20). The W–Rh permanent chemical modifier was used to improve system stability, analytical performance and atomizer lifetime. More than 1500 firings were carried out with the same atomizer without significant variations in sensitivity and precision. On account of the reagent immobilization, its consumption was lower than 0.2 μg per determination. In addition, TAN purification was unnecessary.

Emprego de planejamento fatorial para a otimização das temperaturas de pirólise e atomização de Al, Cd, Mo e Pb por ETAAS

This work describes a factorial design for the optimization of pyrolysis and atomization temperatures in ETAAS. As examples, Cd and Pb were determined using lower pyrolysis and atomization temperatures and Al and Mo with higher pyrolysis and atomization temperatures. Good results were obtained for Cd employing Rh (mo = 1.4 pg) as a permanent modifier with pyrolysis and atomization temperatures of 640 and 1500 °C, respectively. For Zr, W or Zr+W, the Cd pyrolysis and atomization temperatures were 500 and 1500 °C, respectively, with mo = 1.4 pg using Zr or W and 1.5 pg using Zr+W. The best results for Pb were those using Rh, Zr, W and Zr+Rh, obtaining characteristic masses of 42, 37, 34 and 36 pg, respectively. Pyrolysis and atomization temperatures of 910 and 1850 °C, respectively, were achieved for this metal. For Al, the best results were obtained when Zr or Zr+W were used. Mo was also tested as a possible permanent modifier for Al, but the results were not satisfactory. The results obtained for Mo without modifier were similar to those with conventional modifiers (Mg or Pd+Mg) and the results obtained using permanent chemical modifiers were not satisfactory. In all situations, the experiments were performed faster than those using the univariate procedure.

Copper determination in biological materials by ETAAS using W–Rh permanent modifier

A tungsten–rhodium treatment on the integrated platform of a transversely heated graphite atomiser was used as a permanent chemical modifier for the determination of copper in biological materials by using digested samples as well as slurry sampling in electrothermal atomic absorption spectrometry. The W–Rh permanent modifier was as efficient as Pd+Mg(NO 3) 2 conventional modifier for obtaining good Cu thermal stabilisation in the digested and slurry samples. The permanent W–Rh modifier remained stable by approximately 300 and 250 firings when 20 μl of digested sample and 20 μl of slurry were delivered into the atomiser, respectively. In addition, the permanent modifier increased the tube lifetime up to 1370 and 744 analytical measurements in the digested and slurry samples, respectively. Also, when the W–Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of re-calibration during routine analysis, increasing the sample throughput, and consequently diminishing the variable analytical costs. Detection limits obtained with W–Rh permanent modifier were 0.64 and 0.33 μg g −1 Cu for digested (dilution factor 100 ml g −1) and 1.0% m/v slurries of biological materials, respectively. Results for the determination of copper in the samples were in agreement with those obtained with decomposed sample solutions by using Pd+Mg(NO 3), since no statistical differences were found after applying the paired t-test at the 95% level.

Electrothermal behavior of sodium, potassium, calcium and magnesium in a tungsten coil atomizer and review of interfering effects

The electrothermal behavior of Na, K, Ca and Mg in a 150-W tungsten coil atomizer was investigated in order to gather information about the atomization processes and the underlying factors responsible for chemical interferences of them on atomization of Al, Ba, Cd, Co, Cr, Pb and Yb. The interference effects were discussed considering the thermal stability of the species that could be formed in the condensed phase, the effect of protective gas composition in the atomization process and the pyrolysis temperature curves. Ca is the most serious interferent due to its high thermal stability (up to 1600°C) and to the possibility of double oxides formation. As hydrogen is decisive for the atomization of Na, K, Ca and Mg, some interference processes caused by these elements seem to be related to the competition towards hydrogen present in the protective gas composition. The knowledge of the correct temperature of the tungsten coil surface shows that most strategies for overcoming interferences based on chemical modifiers will fail for Cd and Pb, because tungsten acts as a natural permanent chemical modifier. It seems that in many applications previous separation and masking will be necessary.

Determination of cadmium, copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry

Solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated as a potential technique for the routine determination of trace elements in mineral coal and cadmium, copper and lead were chosen as the model elements. Cadmium and lead could be determined at their main resonance lines at 228.8 nm and 283.3 nm, respectively, but an alternate, less sensitive line had to be used for the determination of copper because of the high copper content in coal. No modifier was necessary for the determination of copper and calibration against aqueous standards provided sufficient accuracy of the results. For the determination of cadmium and lead two different modifiers were investigated, palladium and magnesium nitrates in solution, added on top of each sample aliquot before introduction into the atomizer tube, and ruthenium as a ‘permanent’ modifier. Both approaches gave comparable results, and it is believed that this is the first report about the successful use of a permanent chemical modifier in SS-GF AAS. Calibration against solid standards had to be used for the determination of cadmium and lead in order to obtain accurate values. The agreement between the values found by the proposed procedure and the certificate values for a number of coal reference materials was more than acceptable for routine purposes. The detection limits calculated for 1 mg of coal sample using the ‘zero mass response’ were 0.003 and 0.007 μg g −1 for cadmium with the permanent modifier and the modifier solution, respectively, approximately 0.04 μg g −1 for lead, and 0.014 μg g −1 for copper.

Uma célula eletroquímica de fluxo para modificação permanente de tubo de grafite empregado em absorção atômica

A flow cell assembled on the original geometry of a graphite tube to achieve permanent chemical modifier is proposed. The graphite tube operates as the working electrode. A stainless steel tube, positioned downstream from the working electrode, was used as the auxiliary electrode. The potential value applied on the graphite electrode was measured against a micro reference electrode (Ag/AgCl) inserted into the auxiliary electrode. Palladium solutions in acetate buffer (100 mmol L-1, pH = 4.8), flowing at 0.5 mL min-1 for 60 min was used to perform the electrochemical modification. A mercury solution (1 ng) was used to evaluate the performance of the permanent palladium modifier.

Lead determination in slurries of biological materials by ETAAS using a W-Rh permanent modifier.

A tungsten-rhodium coating on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of lead in biological materials by slurry sampling in electrothermal atomic absorption spectrometry (ETAAS). Slurries were sonicated during 20 s before being delivered to the previously W-Rh treated platform. The number of particles of biological materials introduced into the atomiser for delivering 20 microL slurry aliquot ranged from 5,100 to 39,000. The permanent W-Rh modifier remained stable during approximately 300 analytical measurements when 20 microL of slurries containing up to 1.5% m/v were delivered into the atomiser. In addition, the permanent modifier increases the tube lifetime by approximately 100% when compared to untreated integrated platforms. Also, there is less decrease of sensitivity during the atomiser lifetime when compared with the conventional modifiers, resulting in a decreased need of re-calibration during routine analysis and consequently increasing the sample throughput. The atomiser lifetime was limited to the THGA wall durability, because the W-Rh treated platform was intact after more than 650 analytical firings in a medium containing up to 1.5% m/v slurry of biological material. The detection limit based on integrated absorbance was 20 ng g(-1) Pb for 1.50% m/v slurries. Results from the determination of lead in slurries of biological materials using the W-Rh permanent modifier were in agreement with those obtained with digested solutions using Pd + Mg(NO3)2.

Determination of selenium by tungsten coil atomic absorption spectrometry using iridium as a permanent chemical modifier

Permanent chemical modifiers have been shown to prolong graphite tube lifetime while reducing the furnace cycle time, thus improving cost-effectiveness. In this work, iridium is used as a permanent chemical modifier for the first time in the determination of selenium by tungsten-coil atomic absorption spectrometry (W-Coil AAS). The iridium modifier is thermally coated onto the tungsten coil. After coating, the coil can be used for 300–400 firings without further application of the modifier. Thermal treatment with iridium permits operating with higher pyrolysis temperature and coil lifetime is extended up to 1600 firings. The sensitivity and linearity of the method is improved, and the analytical procedure allows the use of analyte solutions containing up to 8% nitric acid. The short-term stability of the absorbance measurements is demonstrated by the reproducibility in the measurements of a Se amount (6 ng) 30 times higher than the limit of detection (0.2 ng). A 7% relative standard deviation (R.S.D.) was observed for 10 consecutive measurements of 6 ng Se. The long-term stability is almost as good: less than 9% R.S.D. over a 3-week period and 1500 firings. The surface of the tungsten-coil treated with iridium is examined before and after intensive use by scanning electron microscopy. Finally, the thermal treatment of the tungsten-coil with iridium appears to delay the appearance of selenium atoms by approximately 0.2 s although the integrated absorbance measurements are unaffected. The magnitude of delay decreases with coil age.

The utility of a W–Ir permanent chemical modifier for the determination of Ni and V in emulsified fuel oils and naphtha by transverse heated electrothermal atomic absorption spectrometer

A ‘water in oil’ emulsification procedure has been applied to a transverse heated electrothermal atomic absorption spectrometer (TH-ETAAS) for direct determination of Ni and V in petroleum products such as naphtha, NIST SRM 1618 Residual Oil and NIST SRM 1634c Residual Fuel Oil. The utility of permanent chemical modifiers such as W, W–Rh and W–Ir, has been examined in determining these elements. The furnace with an integrated platform coated with W and Ir was found to provide 25–30% improved sensitivity than other coatings for Ni. In the case of V, a pyrocoated tube with an integrated platform was found to give the best results. The W–Ir coated tube could be used for nearly 400 firings. The limit of detection for naphtha emulsion was 0.002 and 0.006 µg g−1 for Ni and V, respectively, indicating that the method is well suited for matrices containing very low concentration of trace elements. The method can also be applied to dense matrices such as SRMs Residual Oil and Residual Fuel Oil. In this case, the limit of detection was 0.1 µg g−1 for Ni and 0.5 µg g−1 for V with a precision of less than 5%.

Application of Tungsten-Rhodium Permanent Chemical Modifier in Slurry Analysis: Determination of Cadmium

A tungsten-rhodium coating on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of Cd in sediment slurries by electrothermal atomic absorption spectrometry. Slurries were ultrasonicated during 20 s before being delivered to the previously W-Rh treated platform. The permanent W-Rh modifier remains stable by approximately 250 measurements when 20 μl of slurries containing up to 1.0% m/v are delivered into the atomiser. In addition, the permanent modifier increases the tube lifetime up to 720 analytical firings. Also, when the W-Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of re-calibration during routine analysis, increasing the sample throughput.

The use of tungsten–rhodium permanent chemical modifier for cadmium determination in decomposed samples of biological materials and sediments by electrothermal atomic absorption spectrometry

A 250 μg W + 200 μg Rh coating (W–Rh) on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of Cd in digests of biological materials and dissolved sediments by electrothermal atomic absorption spectrometry (ETAAS). The W–Rh permanent modifier was as efficient as NH 4H 2PO 4 + Mg(NO 3) 2 and Pd + Mg(NO 3) 2 conventional modifiers for obtaining good Cd thermal stabilisation in the decomposed samples. The permanent W–Rh modifier remained stable by approximately 300–350 firings when 20 μl of digested sample were delivered into the atomiser. In addition, the permanent modifier increased the tube lifetime up to 1450 analytical measurements in the decomposed samples containing 1.0% v/v HNO 3. Also, when the W–Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of recalibration during routine analysis, increasing the sample throughput, and consequently diminishing the variable analytical costs. The atomiser lifetime was limited to the THGA wall durability, because the W–Rh treated platform was intact after more than 1200 analytical firings. The W–Rh permanent modifier withstood acidic concentrations up to 5.0% v/v HNO 3 without changes in the coating lifetime as well as in the analytical signal. Detection limits obtained with W–Rh permanent modifier were 1.0 and 6 ng g −1 Cd for biological materials and sediments, which were 1.25 and 2.5 times better than NH 4H 2PO 4 + Mg(NO 3) 2 and Pd + Mg(NO 3) 2 mixtures, respectively. Results for the determination of cadmium in the samples were in agreement with those obtained with decomposed sample solutions by using NH 4H 2PO 4 + Mg(NO 3) 2 and Pd + Mg(NO 3), since no statistical differences were found after applying the paired t-test at the 99% level.

Determination of arsenic in sediment and soil slurries by electrothermal atomic absorption spectrometry using W–Rh permanent modifier

A simple method is described for the determination of As in sediments and soils by electrothermal atomic absorption spectrometry (ETAAS). The procedure combines slurry sampling ETAAS with a 250 μg W + 200 μg Rh permanent chemical modifier. Slurries were sonicated for 20 s before being delivered to the previously W–Rh treated platform. The detection limit for 0.50% m/v slurries was 0.4 μg g−1. The RSD for 783 consecutive measurements of 20 μl of 0.50% m/v soil-5 slurry was 3.8%. In order to verify the accuracy and precision of the proposed method, five sediment and two soil certified reference materials were analysed and the results obtained were in agreement with the certified values.

Tungsten-rhodium permanent chemical modifier for cadmium determination in fish slurries by electrothermal atomic absorption spectrometry

A tungsten carbide–rhodium coating on the integrated platform of a transversely heated graphite atomiser was used as a permanent chemical modifier for the determination of Pb in sediment slurries by electrothermal atomic absorption spectrometry. Slurries were sonicated for 20 s before being delivered to the previously W–Rh treated platform. The number of sediment particles introduced into the atomiser for delivery of a 20 µl slurry aliquot ranged from 1300 to 3400. The permanent W–Rh modifier remains stable for approximately 250 firings when 20 µl of slurry containing up to 0.5% m/v are delivered to the atomiser. In addition, the permanent modifier increases the tube lifetime by 50–95% when compared with untreated integrated platforms. Also, there is less degradation of sensitivity during the atomiser lifetime when compared with conventional modifiers, resulting in a decreased need for re-calibration during routine analysis. Detection limits, based on integrated absorbance for 0.50% m/v slurries, were 61 ng g–1 Pb for the 250 µg W + 200 µg Rh permanent modifier and 125 ng g–1 Pb for 5 µg Pd + 3 µg Mg(NO3)2. The RSD for 735 consecutive measurements of 20 µl of a 0.50% m/v sediment slurry was 3.6% for the proposed permanent chemical modifier. Results for the determination of Pb in sediment slurries using the W–Rh permanent modifier were in agreement with those obtained with digested solutions by using Pd + Mg(NO3)2, since no statistical differences were found by the paired t-test at the 99% level.

Tungsten–rhodium permanent chemical modifier for lead determination in sediment slurries by electrothermal atomic absorption spectrometry

Tungsten–rhodium permanent chemical modifier for lead determination in sediment slurries by electrothermal atomic absorption spectrometry

Tungsten-rhodium permanent chemical modifier for lead determination in digests of biological materials and sediments by electrothermal atomic absorption spectrometry

É. C. Lima, F. Barbosa Jr., F. J. Krug and U. Guaita, J. Anal. At. Spectrom., 1999, 14, 1601 DOI: 10.1039/A903270C

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 250μg W+200μg 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±0.4pg and 0.020μgL−1; Pb 30±3pg and 0.58μgL−1 and Se 42±5pg 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.