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

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, MgCl₂ and CaCl₂ do not interfere significantly. However, their different behaviour in the furnace, and particularly hydrolysis of MgCl₂ 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 MgCl₂, Pb is not sufficiently stabilized to remove chloride through hydrolysis of MgCl₂ or volatilization of MgCl₂. In the presence of CaCl₂, the Pb signal is delayed and coincides with the background absorption signal of CaCl₂; the stabilization effect is not sufficient to eliminate CaCl₂ by charring before atomization. At 0.1 M nitrate concentration, the presence of NaNO₃, Mg(NO₃)₂, and particularly Ca(NO₃)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. Na₂SO₄, which is reduced to Na₂S on the graphite, does not interfere significantly. However, the decomposition products of MgSO₄ and CaSO₄ induce an important interference effect on the determination of Pb which is stabilized in the furnace. In the case of Na₂SO₄, 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 MgSO₄ and CaSO₄, the stabilizing effect of Pd permits the elimination of decomposition products of sulphate salts before atomization and suppresses the chemical interference effect.     

Direct determination of traces of molybdenum in synthetic sea water by atomic absorption spectrometry with electrothermal atomization and selective volatilization of the salt matrix

A simple and rapid method is described for the direct determination by graphite-furnace atomic absorption spectrometry (HGA-2100) of traces of molybdenum (O.1–4 ng) in synthetic sea water. It is shown that the salt matrix can be removed completely by selective volatilization at 1700–1850°C, but the original presence of NaCl, Na₂SO₄, and KCl causes a considerable decrease in molybdenum absorbance, and MgCl₂ and CaCl₂ a pronounced enhancement. The presence of MgCl₂ prevents the depressive effects. Samples of less than 50 μl can be analyzed directly without using a background corrector, with a precision of<10%.     

High temperature thermogravimetry of chlorides and sulphates : A study of the application to soils

Quantitative volatilization of NaCl and KCI occurs between 900 and 1200°. CaCl₂ and MgCl₂ are converted to the oxides at lower temperatures. CaSO₄, Na₂SO₄ and K₂SO₄ require the admixture of quartz to catalyse their decomposition with a total loss of SO₃ between 1150 and 1335°. MgSO₄ does not require quartz for its decomposition. The catalytic effects of Al₂O₃ and Fe₂O₃ on sulphate decomposition were also examined. The findings were applied to the analysis of saline soils. The thermogravimetric determination of chlorides in soils is subject to several interferences, but the conditions are more favourable for sulphates.     

Effect of low-salinity water on asphaltene precipitation

The effect of low-salinity (1000 to 5000?ppm) and intermediate-salinity (5000 to 40000?ppm) water (MgSO₄, MgCl₂, Na₂SO₄, CaCl₂, NaCl and KCl) on asphaltene precipitation was investigated in this work. The results revealed that all brines intensify the amount of asphaltene precipitation. All cases exhibited initial downward trend followed by the upward trend for the amount of asphaltene precipitation with increasing the brine concentration. A similar trend was also observed for Interfacial Tension (IFT) between crude oil and brine in this study. IFT was tested for MgSO₄, MgCl₂, Na₂SO₄, CaCl₂, NaCl and KCl brines with concentrations of 1000 to 40000?ppm. Finally, experimental results showed that an increase in volume of all brines in the mixture (brine +oil) led to increase and decrease of the asphaltene precipitation in low and intermediate salinity regions, respectively.     

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%.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant.     

La matrice eau de mer et le signal du cuivre en spectrometrie d'adsorption atomique sans flamme : Partie 1: Etude de l'influence des principaux composants

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 1: study of the effects of principal inorganic ions.)The effects of the main inorganic ions of seawater (Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO^2?₄), and of nitrate as modifier, on the electrothermal atomic absorption spectrometric signal of copper are studied. Sodium chloride, sulfate or nitrate, magnesium chloride or nitrate, and calcium chloride can cause serious interferences. Thermal treatment at about 700°C prevents the interference of MgCl₂ by its hydrolysis. Ashing can be done without loss of copper at higher temperatures in the presence of sulfate salts (1300°C) and nitrate salts (1200°C) than in the presence of chloride salts (1100°C). This is ascribed to the stabilising effect of oxides and sulfides. A study of the influence of two-component matrices, MCl-MNO₃ or MCl-MSO₄, on the atomization signal of copper confirms this stabilizing effect which adds to the decrease in interference connected with removal of chloride in acidic medium.     

Effects of Surfactant and Salt Species in Reverse Micellar Forward Extraction Efficiency of Isoflavones with Enriched Protein from Soy Flour

Suitability of reverse micelles of anionic surfactant sodium bis(2-ethyl hexyl) sulfosuccinate (AOT) and sodium dodecyl sulfate (SDS), cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) and nonionic surfactant polyoxyethylene p-t-octylphenol (TritonX-100) in organic solvent isooctane for extraction of soy isoflavone-enriching proteins was investigated. The results showed that the order of combined isoflavone contents was SDS>CTAB>Triton X-100>AOT, while the order of protein recovery was SDS>AOT>TritonX-100>CTAB. As compared with ACN-HCl extraction, the total amount of isoflavones was lower than reverse micellar extraction. Ion strength was one of the important conditions to control extraction of isoflavone-enriching proteins with AOT reversed micelles. For the six salt systems, KNO₃, KCl, MgCl₂, CaCl₂, NaCl, and Na₂SO₄, extracted fraction of isoflavone-enriching proteins was measured. Salt solutions greatly influenced the extraction efficiency of isoflavones in an order of KNO₃>MgCl₂>CaCl₂>KCl>NaCl>Na₂SO₄, while protein in an order of MgCl₂>CaCl₂>NaCl>KNO₃>Na₂SO₄>KCl.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant. Received: 23 February 1998 / Revised: 18 December 1998 / Accepted: 25 December 1998     

Effects of various salts on the determination of arsenic by graphite furnace atomic absorption spectrometry. Direct determination in seawater

The effect of Na, Mg, Ca and Sr as their nitrate, chloride and sulfate salts and seasalt, with and without the use of palladium, on the determination of arsenic by electrothermal atomic absorption spectrometry was investigated. In the absence of any stabilizing agent, arsenic was partially lost as molecular species at low temperatures. The effect of salts on the shape of the atomization signal, the integrated absorbance and the stabilizing effect were highly dependent both on their nature and mass. By trapping arsenic, oxide species resulting from the decomposition of nitrate salts induced a high stabilization effect depending on their vaporization temperatures: MgO～CaO>SrO>Na₂O. The stabilization effect of chlorides occurred about 200?°C lower and depended on mass, volatility and hydrolytic properties: SrCl₂>CaCl₂>MgCl₂～NaCl. The effect of sulfates was mainly dependent on their decomposition/vaporization mechanisms, and in the presence of Na₂SO₄ or CaSO₄ a strong chemical interference effect was observed. Palladium stabilized arsenic in the presence of nitrates, chlorides or even sulfates, leading to a similar delaying effect, signal shape and integrated absorbance. Seasalt induced also important modifications to the atomization signal of As. Moreover, an interference effect was observed, which could probably be attributed to the simultaneous vaporization of sulfate in seasalt. In seawater, Pd suppressed this interference effect and permitted to use a high pyrolysis temperature up to 1400?°C to remove the major part of the seawater matrix before atomization. Under optimized conditions, the detection limit for As obtained in unmodified seawater in the presence of Pd was 0.34 μg L^–1 for a 10 μl sample.     

Investigation of aluminum interferences using the stabilized temperature platform furnace

Al was determined in the stabilized temperature platform furnace with very few interferences. No interferences were found for several metal nitrates, sulfates or phosphates, or for NaCl. The Al absorbance signal was delayed in the presence of MgCl₂ but there was no interference. This led to the use of 50 μg Mg(NO₃)₂ as a matrix modifier for Al. There were no interferences for CaCl₂ but it was particularly important to use new pyrolytically coated tubes to avoid “aging” effects. CuCl₂ provided a very persistent interference that was reduced when the Mg(NO₃)₂ matrix modifier was used that permitted a char temperature of 1700°C. Perchloric acid interferences were severe with improperly coated graphite tubes but did not exist up to 0.5 M HClO₄ when the new pyrolytically coated tubes were used. A serum Al method was tested briefly and no problems were found. Al was determined in seawater with no influence from the salinity of the sample and less than 0.6 μg/1 Al in seawater could be detected.     

Acid Effects on the Measurement of Mercury by Cold Vapor Atomic Absorption Spectrometry

Abstract

The influence of nitric, hydrochloric and sulfuric acids on the measurement of mercury by cold vapor atomic absorption spectrometry has been investigated. Small pre-reduction peaks associated with the instability of mercury were observed in solutions containing ≤ 12.5, < 2 and ≥ 12.5% v/v of each acid, respectively. Mercury was found to be most stable in ≥, 2% v/v hydrochloric acid and the measured absorbance was not greatly influenced by varying concentration of the acid. The mercury absorbance measurements were more sensitive in solutions containing ≤ 6.3% v/v hydrochloric acid than in similar concentrations of nitric and sulfuric acids. The use of the three acids as a digestion mixture result in serious interference from nitrogen oxides. The interferant was removed by use of expelling agents such as urea and sulfamic acid or overcome by use of excess stannous chloride, prior to the reduction of mercury(II) ions. The determination of mercury in NBS albacore tuna using both of these approaches to overcome the interference problem proved to be successful.     

Organophosphorus acid interferences in flame atomic absorption spectrometry

The interference of the organophosphorus acids, 1-hydroxyethane-1,1-bisphosphonic acid, aminotris(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid) and hexamethylenediaminetetrakis(methylenephosphonic acid) on the determination of eighteen metal ions by flame atomic absorption spectrometry is reported. Comparisons with the effect of orthophosphoric acid reveal similarities and distinct differences in their interfering effects. In the air/acetylen flame, depressive interferences are attributed to the formation of phosphates, M₃(PO₄)₂, or hydroxynpatite-like compounds, M₅(OH)(PO₄)₃, in the flame aerosol particles for Mg, Ca, Sr, Ba, Mn, Co and Ni. Iron(III) and chromium(III) appear to form stable oxide phosphates, M₂O₃?MPO₄ or M₃O₄?MPO₄. Evidence for the formation of stable molybdenum carbides, MoC and MoC₂, is also presented. In the nitrous oxide/acetylene flame, serious interferences perssisted only for molybdenum but were eliminated by the addition of sodium sulphate.     

Inelastic collisional deactivation in plasma-related non-spectroscopic matrix interferences in inductively coupled plasma atomic emission spectrometry

Inelastic collisional deactivation of the analyte excited state is demonstrated as a dominant cause for non-spectroscopic matrix interference in inductively coupled plasma atomic emission spectrometry (ICP-AES) for commonly used plasma operating conditions in routine analysis. A mathematical simulation of the inelastic collisional model was examined. Comparison between the theoretical model and experimental results using atomic and ionic lines of the analytes Zn, Ba, Mg, Mn and Sr validates the inelastic collisional deactivation model as a dominant cause for non-spectroscopic matrix effect. Matrices evaluated were NH₄Cl, NH₄SCN, (NH₄)₂SO₄, and H₂SO₄ to represent difficult-to-ionize matrices (DIE) and NaCl and CaCl₂ to represent easy-to-ionize element matrices (EIE).     

Extraction and chemical investigation of Kulthi (Macrotylona uniflorus,Lam.) seed protein

Studies have been carried out on the protein solubility profile of Kulthi (Macrotylona uniflorus, Lam.) seed in aqueous solution over various pHs and at different concentrations of NaCl, Na₂SO₃, CaCl₂, and MgCl₂ at pH 8.0. Amino acid analysis of isolated protein identified 17 amino acids, 9 of which are essential. Gel-permeation chromatography on Sephadex G-200 revealed the presence of seven components in the protein fraction. Their molecular weights were determined by two comparable standard methods. Extractable Kulthi seed proteins in salt solutions were separated electrophoretically into eight fractions whose molecular weights were found to be 186,200, 131,800, 108,400, 91,200, 53,700, 44,700, 38,000, and 27,500.     

老山汉墓土遗址盐分调查与分布规律探索

老山汉墓土遗址中可溶-微溶盐导致遗址表面酥碱、起甲、泛白和块状脱落等病害较为严重.利用X射线荧光光谱(XRF)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)以及离子色谱(IC)等方法测定了老山汉墓遗址不同取样位置及距遗址表面不同深度处可溶盐的成分及含量,并分析了盐分对遗址破坏的可能机制.结果表明,该遗址的主要有可溶盐有Na2SO4、Na2SO4·10H2O、Na Cl、Na12Mg7(SO4)13·15H2O,微溶盐有Ca SO4、Ca SO4·2H2O,此外还含有少量的Ca Cl2、KNO3、KCl、Mg Cl2、K2SO4、Mg SO4等盐分.随着取样深度增加,各盐分的种类及含量有所减少,此分布规律可能与可溶盐的赋存环境及水分运移有关.试验结果对于老山汉墓土遗址的保护措施具有一定的参考价值.     

Use of iridium plus rhodium as permanent modifier to determine As, Cd and Pb in acids and ethanol by electrothermal atomic absorption spectrometry

The most severe interferences in atomic absorption spectrometry are caused by the presence of anions when they are in different concentrations in the samples and in the calibration solutions. The analyte addition technique or matrix matching calibration can be employed to minimize or compensate the non-spectral interferences, but they are time consuming or difficult to be carried out. The use of chemical modifiers usually allows higher pyrolysis temperatures and consequently the removal of components of the sample matrix, equalizing the analyte signal in the sample and in the calibration solution. In this work, a mixture of Ir and Rh is proposed as permanent modifier to determine As, Cd and Pb in diluted hydrochloric, sulfuric and phosphoric acids and in ethanol and methanol by electrothermal atomic absorption spectrometry (ET AAS) with calibration against 1% v/v nitric acid aqueous solutions. The performance of the proposed permanent modifier was compared to that of Pd plus Mg nitrates in solution. Better recoveries, low background levels and faster analysis were obtained with the permanent modifier. The permanent modifier was also successfully employed for the determination of As, Cd and Pb in different concentrations of sulfuric and hydrochloric acids. For the phosphoric acid, the proposed modifier was only efficient for acid concentrations up to 2% v/v for As and up to 5% v/v for Cd and Pb. The precision, expressed as the relative standard deviation (n=3), was lower than 10%, for all samples, including ethanol and methanol.     

Influence of ionic composition in aqueous solution on wettability of rock surface-experiment and economics evaluation

In this study, the influence of different ionic composition in aqueous solution on the minerals surface wettability was studied. The differences effect of monovalent ion and divalent ions onto the wettability alteration were studied. The anions were Cl^- and SO₄^2-. The SO₄^2- could make the minerals surface more hydrophilic. Besides, the influence of NaCl, MgCl₂, CaCl₂, Na₂SO₄, K₂SO₄ and MgSO₄ on the mineral wettability alteration were studied. The results indicated that divalent ions showed significant impact on the minerals wettability alteration, compared with monovalent ion. The reasons were due to the fact that divalent ions showed higher ions adsorption than monovalent ion, and divalent ions have higher effect on compressing the electric double layer. The static contact angle and dynamic contact angle were measured. Different heavy oils were studied, including heavy oil with 100 ppm, heavy oil, heavy oil without resins, heavy oil without asphaltenes. The results showed that the asphaltenes would make it difficult for the heavy oils to liberate from minerals, thus decreasing the oil drops contact angle. Then the resins would decrease the heavy oil contact angles. CaCl₂/MgCl₂ and K₂SO₄ have synergistic effect on the change of the minerals surface wettability. Atomic force microscope (AFM) measurement indicated that the ions would effectively decrease the interaction force on the surface of heavy oil-minerals, which was beneficial to the heavy oil liberation. The roughness measurement indicated that the different ions would effectively increase the minerals surface wettability.     

A Study of Concentration Polarization on Ion Exchange Membrane Electrodialysis

The concentration polarization phenomena in ion exchange membrane electrodialysis have been studied with single exchange membrane cell. The limiting current densities of Asahi ion-permselective membranes CK-1 and CK-2, Selemion ion-exchange membranes CMV, AMV, DMV and ASV have been measured with Ag-AgCl reversible electrode in various electrolyte solutions under 25°C and constant flow rate. In sodium chloride solution, the cation exchange membrane is easier to occur concentration polarization than the anion exchange membrane. The limiting current density increases as the concentration of solution increases for the same kind of ion exchange membrane. The experimental limiting current densities of Selemion CMV and AMV in NaCl, KCl, MgCl₂, CaCl₂, BaCl₂, Na₂SO₄, NaOH and HCl aqueous solutions are measured. The results show that the limiting current density increases as the ion mobility and diffusivity increase, and is affected by the transference number of ion. For the mixture of electrolyte solution, there are linear relationship between limiting current density and equivalent fraction of electrolytes.     

La matrice eau de mer et le signal du cuivre en spectrometrie d'absorption atomique sans flamme: Partie 2: Proposition d'un schéma explicatif des phénomènes observés pour une eau de mer

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 2: model for phenomena observed with sea water.)A model to explain the variations of copper signals in seawater is proposed on the basis of the results of Part 1 of this study and data obtained by ashing simulated seawaters under different conditions. The model is confirmed by the results found with nitric of sulfuric acid as modifier. In this model, ashing at 800°C hydrolyses MgCl₂ to MgO, and the consequent formation of sodium sulfide from the matrix stabilizes the copper in the furnace. The addition of a small nitrate concentration (0.2 M) induces, when magnesium is present, a complementary decrease of the interference.