Jean-Yves Cabon

Determination of Cd and Pb in seawater by graphite furnace atomic absorption spectrometry with the use of hydrofluoric acid as a chemical modifier

Abstract High concentration of added hydrogen fluoride converted the seawater chloride to the corresponding fluoride matrix, and the liberated hydrochloric acid could be removed during the drying step. The atomization of cadmium and lead could be performed at a relatively low temperature (∼1300 °C) at which the vaporization of the fluoride matrix was relatively slow, and the corresponding weak background signals could be separated from the analytical signals in time. Experimental conditions for the determination of Cd and Pb in seawater in the presence of HF were optimized with the use of the a priori calculation of the limit of detection. The experimental limit of detection obtained for Cd and Pb were, respectively, 0.007 and 0.25 μg l−1 for a 15-μl seawater sample (3σ, 20 replicates). The concentrations of Cd determined in a SLEW-1 estuarine water and a CASS-2 seawater were 0.020±0.002 and 0.016±0.002 μg l−1 Cd, respectively, in good agreement with the 0.018±0.003 and 0.019±0.004 μg l−1 Cd certified values (At the 95% confident level, 10 replicates).

The determination of Cr, Cu and Mn in seawater with transversely heated graphite furnace atomic absorption spectrometry

Abstract The atomization signals of Cr, Cu and Mn in the presence of seawater salts have been investigated using a new transverse heated atomic absorption spectrometer and longitudinal Zeeman-effect background correction system. In unmodified seawater, the vaporization of the chloride matrix at a relatively low background absorption signal level may induce errors of correction which cannot be neglected at low metal concentration levels. Even without charring, seawater salts do not interfere with the recovery of Cr; however, due to temporal overlap of analytes and chloride vapours, seawater salts interfere severely with the recovery of Cu and Mn. For diluted seawater solutions ( S ) a charring step at about 500°C almost suppresses the chloride chemical interference effect in the case of Cu and Mn, Mn being sufficiently stabilized through MgCl2 hydrolysis to permit the elimination of NaCl at 1000°C before atomization. However, for more saline solutions, due to mass effect the hydrolysis of MgCl2 is not complete; the recovery of Mn is lowered to about 80% and the recovery of Cu is less than 20%. In the presence of nitric acid (more than 0.15 M) or oxalic acid (more than 0.1 M) which hydrolyses MgCl2 to MgO and stabilizes Cr, Cu and Mn in their oxide forms, the recovery for Cr, Cu and Mn is good and a charring step at about 1150°C permits the elimination of the major part of the matrix (Na species) before atomization at 2150°C; these conditions are almost optimal for the simultaneous determination of Cr, Cu and Mn. The detection limits obtained for 20 μl seawater 0.15 M in HNO3 or 0.1 M in oxalic acid are respectively 0.042 μg l−1 for Cr, 0.075 μg l−1 for Cu and 0.026 μg l−1 for Mn (3σ).

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L(-1) (20 microL, 3sigma) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3sigma) of 3 ng L(-1) (i.e. 54 pM) for total Fe concentration with the use a 20 microL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 microg L(-1)) seawater sample were in good agreement with the certified values.

Determination of lead in seawater by electrothermal atomic absorption spectrometry with transversely heated furnace by using oxalic acid or Pd/Mg as modifiers☆

Abstract The simultaneous volatilization of seawater salts and lead free atoms induces chemical interferences. Moreover, an under-compensation related to the vaporization of seawater salts is observed; the systematic error depends on the magnitude of the background absorption signal to be corrected and can be very important at low Pb concentrations. In the presence of oxalic acid, which modifies the seawater matrix and promotes a lower atomization temperature, the chemical interference is suppressed and the background absorption signal is dramatically reduced. In the presence of the Pd/Mg modifier and nitric acid, Pb is stabilized at a higher temperature and the major part of the seawater matrix can be removed before atomization, but the integrated absorbance remains depressed. The detection limits obtained for 10 μ1 of seawater in the presence of oxalic acid or Pd/Mg and nitric acid used as modifiers are respectively 0.3 μg 1−1 and 0.5 μg 1−1.

Interference of salts on the determination of lead by electrothermal atomic absorption spectrometry. Ion chromatographic study

Abstract The influence of various salts on the atomization signal of lead has been examined by using a transverse heated atomic absorption spectrometer. To get more information about interference mechanisms, volatilization of salts has been studied by ion chromatographic analysis of the residue left on the furnace after drying or charring. The use of a Pd/Mg chemical modifier in these model solutions has also been examined. In 0.1 M chloride medium, NaCl, MgCl 2 and CaCl 2 do not interfere significantly. However, their different behaviour in the furnace, and particularly hydrolysis of MgCl 2 influence greatly the charring curves of Pb. The use of a Pd/Mg modifier appears interesting only in the case of NaCl. Indeed, Pd stabilizes Pb sufficiently to permit the removal of NaCl by charring. In the case of MgCl 2 , Pb is not sufficiently stabilized to remove chloride through hydrolysis of MgCl 2 or volatilization of MgCl 2 . In the presence of CaCl 2 , the Pb signal is delayed and coincides with the background absorption signal of CaCl 2 ; the stabilization effect is not sufficient to eliminate CaCl 2 by charring before atomization. At 0.1 M nitrate concentration, the presence of NaNO 3 , Mg(NO 3 ) 2 , and particularly Ca(NO 3 ) 2 , greatly modifies the atomization signal shape of Pb. Pb is more stabilized in nitrate medium, but losses are observed at the decomposition step of nitrate salts. In this medium, the stabilization effect of Pd leads to a single peak signal and permits elimination of nitrate decomposition products before atomization. Interference effects are more important in the presence of 0.1 M sulphate salts and increase with the acidity of the medium. Na 2 SO 4 , which is reduced to Na 2 S on the graphite, does not interfere significantly. However, the decomposition products of MgSO 4 and CaSO 4 induce an important interference effect on the determination of Pb which is stabilized in the furnace. In the case of Na 2 SO 4 , the use of the Pd/Mg modifier delays the atomization signal which coincides with the background absorption signal, leading to an important interference effect which cannot be eliminated by charring. In the presence of MgSO 4 and CaSO 4 , the stabilizing effect of Pd permits the elimination of decomposition products of sulphate salts before atomization and suppresses the chemical interference effect.

Electrothermic factors optimization in electrothermal atomic absorption spectrometry via an optimal experimental design matrix

Abstract A new approach is proposed to optimize some instrumental electrothermic parameters, i.e. injected volume, calcination duration, calcination and atomization temperatures, gas flow, in electrothermal atomic absorption spectrometry. It is based on the monitoring of the detection limit estimation variation by using an unconventional experimental design well adapted to a particular experimental domain. This method was tested on Cd, Mn and Cu in sea water. By comparison with the default operating conditions, the limits of detection were improved in some cases and always obtained on carrying out less experiments than usual.

Electrochemical Reduction of a Bridging Imide: Generation of Ammonia at a Dimolybdenum Tris(μ‐thiolate) Site

The electrochemical reduction of the imide complex [Mo2(cp)2(mu-SMe)3(mu-NH)]+ (1+) has been investigated in THF and MeCN electrolytes by cyclic voltammetry, controlled-potential electrolysis and coulometry. In the absence of free protons, the electrochemical reduction produces the amide derivative [Mo2(cp)2(mu-SMe)3(mu-NH2)] (2) after consumption of 1 Fmol(-1) of 1+. In THF in the presence of acid, the reduction of 1+ occurs through a two-electron process. The presence of acid also results in the shift of the equilibrium between 1+ and amide dication 2(2+) (MeCN electrolyte) or induces an isomerisation of the imide ligand (THF electrolyte). This allows the electrolysis to be conducted at a potential 600 mV less negative than the reduction potential of 1+. Controlled-potential electrolyses in the presence of acid (2 equiv HTsO) produce the ammine derivative. Ammonia is released from these compounds either by coordination of the solvent (MeCN electrolyte) or by the binding of chloride to the ammine-tosylate complex (electrolyses in THF in the presence of acid and chloride). The final products, isolated almost quantitatively (>95%), are [Mo2(cp)2(mu-SMe)3(MeCN)2]+ and [Mo2(cp)2(mu-SMe)3(mu-Cl)], respectively.

Direct determination of cadmium in sea-water using electrothermal atomization atomic absorption spectrometry with Zeeman-effect background correction and oxalic acid as a chemical modifier

A method for the determination of cadmium in sea-water using an electrothermal atomization atomic absorption spectrometry system with Zeeman-effect background correction is presented. The effect of various inorganic and organic acids, used as chemical modifiers, on the atomization of cadmium and the sea-water background absorption signals were examined. Of all the different modifiers studied, oxalic acid suppresses chloride interference, promotes a lower atomization temperature and does not introduce any simultaneous significant background absorption signal, and was therefore of particular interest. Optimization of the experimental conditions gave a characteristic mass of 0.23 pg. For an injection of 99 µl of sea-water into the furnace, the detection limit was 3 ng l–1.

Direct determination of zinc in sea-water using electrothermal atomic absorption spectrometry with Zeeman-effect background correction: effects of chemical and spectral interferences

The determination of zinc in sea-water using an electrothermal atomic absorption spectrometry system with Zeeman-effect background correction is presented. The influence of various chloride and nitrate salts on the atomization signal of zinc was examined. In chloride medium particularly, the interference effect induced through losses of zinc chloride, by the thermohydrolysis of magnesium chloride and simultaneous generation of HCl during the pyrolysis step is noted. In nitrate medium, zinc is more stabilized by Mg > Ca > Na > NH+4. The effect of various inorganic and organic acids, used as chemical modifiers, on the atomization of zinc and background absorption signals in sea-water were examined. In unmodified sea-water, a Zeeman interference effect related to the vaporization of the chloride matrix leading to a systematic under-compensation and consequently to erroneous zinc concentration values was observed. In sea-water, modified with 1 mol l–1 nitric acid, a spectral Zeeman interference effect induced by the Zeeman splitting of the absorption bands of NO molecules generated during the decomposition–reduction of nitrate was observed; the induced over-compensation is eliminated by selective pyrolysis at about 850 °C. The chemical interference effect (25%) is related to the simultaneous vaporization of zinc and sodium oxides; the detection limit (3σ) being about 80 ng l–1 for a 10 µl injected volume of sea-water. In sea-water modified with 0.7 mol l–1 oxalic acid, there is no significant interference effect and the detection limit in this medium is about 60 ng l–1 for a 10 µl injected volume of sea-water.

Improvement of direct determination of Cu and Mn in seawater by GFAAS and total elimination of the saline matrix with the use of hydrofluoric acid

Hydrofluoric acid, added to seawater, can assist in the removal of chloride in the drying step by precipitating fluoride salts, thus suppressing the chloride interference effects induced on the atomization signals of Cu and Mn. By adding HF to seawater before the analysis, MgF(2) and CaF(2) are precipitated at the bottom of the sampling flask, without precipitating Cu and Mn, and are consequently not introduced into the graphite furnace. Because sodium salts are eliminated at the pretreatment step, the whole seawater matrix is eliminated before the atomization of Cu or Mn. Therefore, the analyzed volume of seawater can be increased by using the multi-injection procedure without degradation of the limit of detection and risks of spectral interferences. The limit of detection obtained for Cu and Mn are 0.05 and 0.01mugL(-1), respectively, for a 50muL analyzed seawater volume.