High-resolution Molecular Absorption Spectrometry Research Articles

Determination of bromine and fluorine via sequential vaporization of TlBr and CaF molecules from the same aliquot by high-resolution continuum source graphite furnace molecular absorption spectrometry

This work describes the development of a multielement method for determination of bromine and fluorine, via sequential vaporization of TlBr and CaF molecules, from the same sample aliquot, using high resolution molecular absorption spectrometry. The molecular absorption of TlBr and CaF was measured at 342.9797 nm and 606.4322 nm, respectively. Studies were conducted by injecting 10 μL of sample or standard of bromine and fluorine into the graphite furnace. The source of the molecule-forming agents was 10 μL of solutions at 8.0 g L−1 of thallium and calcium, individually prepared from TlNO3 and Ca(NO3)2·4 H2O. The optimized vaporization temperatures were at 900 °C (TlBr) and 2100 °C (CaF). No chemical modifiers were used, and calibration against aqueous standard was employed. The limits of detection (LOD) were 2 ng (Br) and 0.02 ng (F). The linear ranges were 5–5000 ng (Br) and 0.5–100 ng (F). The evaluation of potentially interfering species showed no interference due to the presence of bromide over the signal for CaF or fluorine over the signal for TlBr. No interference was observed for TlBr with up to 20 μg of chlorine. However, for the CaF molecule, significant depreciation of the signal for 5 ng of fluorine was observed in the presence of 10 μg of chlorine. This interference is visually indicated by the appearance of a structured background, relative to the formation of CaCl, in the region next to CaF absorption. To verify the accuracy and performance of the proposed method, drug samples were analyzed with reported values for bromine or fluorine, sea lettuce reference material BCR 279 with informed value for bromine and road dust sample CW7 with no reported values. The determined values closely agreed with the reference values for the drugs and BCR 279 samples. However, for the road dust sample, non-spectral interference was observed. Nevertheless, the results here are promising and indicate the way to develop similar studies.

An Improved Methodology for Determination of Fluorine in Biological Samples Using High-Resolution Molecular Absorption Spectrometry via Gallium Fluorine Formation in a Graphite Furnace

Nowadays growing attention is paid to the control of fluorine content in samples of biological origin as it is present in the form of various biologically active organic compounds. Due to the chemically-rich matrix of biological tissues, the determination of fluorine becomes a very difficult task. Furthermore, a required complex sample preparation procedure makes the determination of the low contents of F by ion chromatography UV-Vis or ion-selective electrodes not possible. High-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) seems to be the best option for this purpose due to its high robustness to matrix interferences, especially in the presence of carefully selected modifiers. In this work the possibility of quantitative F determination in water and animal tissues was examined by measuring the molecular absorption of gallium monofluoride (GaF) at 211.248 nm with the use of a commercially available HR-CS GF MAS system. Experimental conditions for the sensitive and precise determination of fluorine were optimized, including the time/temperature program as well as addition of gallium and modifier mixture in combined mode. Under these conditions the fluoride present in the sample was stabilized up to 600 °C, and the optimum vaporization temperature for GaF was 1540 °C. Palladium and zirconium deposited onto the graphite surface served as solid modifiers; sodium acetate and ruthenium modifiers were added directly to the sample. The limit of detection and the characteristic mass of the method were 0.43 μg/L and 8.7 pg, respectively. The proposed procedure was validated by the use of certified reference materials (CRMs) of lake water and animal tissue; the acceptable recovery was obtained, proving that it can be applied for samples with a similar matrix.

Iodine determination by high-resolution continuum source molecular absorption spectrometry – A comparison between potential molecules

This work presents an overview of four diatomic iodine molecules for iodine quantification by high-resolution molecular absorption spectrometry, a comparison between the optimal conditions for CaI SrI, BaI, and InI, the consequences of these parameters for the method development and the quantification of iodine in supplements using the diatomic molecules and a simple dilute-and-shoot sample preparation. The thermal behavior of I using Ir, Pt, Zr and W as permanent modifier were studied and compared for each molecule. The concentrations of the forming reagent and the influence of Cl as an interferent were also investigated. The absolute LOD and LOQ values found for iodine using the CaI SrI, BaI, and InI molecules were between 20 ng – 60 ng and 60 ng −200 ng respectively. The concentrations of iodine were in agreement with the producer's stated values, and since there was no significant interference in these samples for this diatomic molecule, an external calibration with aqueous solutions was possible.

Assessment of the Halogen Content of Brazilian Inhalable Particulate Matter (PM10) Using High Resolution Molecular Absorption Spectrometry and Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry, with Direct Solid Sample Analysis.

Halogens in the atmosphere play an important role in climate change and also represent a potential health hazard. However, quantification of halogens is not a trivial task, and methods that require minimum sample preparation are interesting alternatives. Hence, the aim of this work was to evaluate the feasibility of direct solid sample analysis using high-resolution continuum source molecular absorption spectrometry (HR-CS MAS) for F determination and electrothermal vaporization-inductively coupled plasma mass spectrometry (ETV-ICP-MS) for simultaneous Cl, Br, and I determination in airborne inhalable particulate matter (PM10) collected in the metropolitan area of Aracaju, Sergipe, Brazil. Analysis using HR-CS MAS was accomplished by monitoring the CaF molecule, which was generated at high temperatures in the graphite furnace after the addition of Ca. Analysis using ETV-ICP-MS was carried out using Ca as chemical modifier/aerosol carrier in order to avoid losses of Cl, Br, and I during the pyrolysis step, with concomitant use of Pd as a permanent modifier. The direct analysis approach resulted in LODs that were proven adequate for halogen determination in PM10, using either standard addition calibration or calibration against a certified reference material. The method allowed the quantification of the halogens in 14 PM10 samples collected in a northeastern coastal city in Brazil. The results demonstrated variations of halogen content according to meteorological conditions, particularly related to rainfall, humidity, and sunlight irradiation.

Determination of sulfur in diesel via CS molecule by high-resolution molecular absorption spectrometry applying palladium nanoparticles as chemical modifier

Crude oil contains a high concentration of sulfur, an element that poses serious environmental and health risks. Sulfur occurs mostly in heavier petroleum fractions, like diesel, and it is possible to reduce its concentration by using methods such as catalytic hydrodesulfurization. High-resolution continuum source molecular absorption spectrometry (HR-CS MAS) allows for determination of non-metals. Sulfur is generally analyzed as the CS molecule at 258 nm, which corresponds to the electronic transition X1Σ+ → A1Π. This study aimed to apply graphite furnace HR-CS MAS to determine sulfur in diesel, using palladium nanoparticles as chemical modifier. To evaluate the proposed method, seven diesel samples (including two reference samples) were employed as emulsions with surfactants and alcohols. Direct diesel analysis was also evaluated, in an attempt to improve sulfur detection. Sodium sulfate, thiourea, and 2-mercaptoethanol were used as sulfur standards. Two types of synthesized palladium nanoparticles were compared with other chemical modifiers in graphite furnace vaporization. Measurements were conducted at 258.056 nm, with detection of three pixels. The ethanol emulsion was stable (4 h). PdCl2 nanoparticles provided the best results as chemical modifier, and thiourea was the most suitable sulfur standard under the experimental conditions. The following figures of merit were obtained: limit of detection (LOD) = 120 mg kg−1, limit of quantification (LOQ) = 400 mg kg−1, R2 = 0.9972, and relative standard deviation = 1–5%. The method's accuracy, evaluated with two reference samples, agreed with a confidence interval of 95%. It was not possible to determine sulfur in one sample only (sulfur concentration 10 mg kg−1), due to the LOD. This drawback was circumvented by applying direct diesel analysis. Using Pd nanoparticles as chemical modifier it was possible to obtain better sensitivity, LOD (7.2 ng absolute or 3 mg kg−1 for direct analysis), and LOQ (24 ng or 9 mg kg−1).

Determination of sulfur in coal by solid sampling graphite furnace high-resolution molecular absorption spectrometry

An analytical procedure for quantitative analysis of sulfur in coal by direct solid sampling graphite furnace high-resolution continuum source molecular absorption spectrometry (HR-CS GF MAS) is described, which is based on the molecular absorption of tin sulfide. The heating program is optimized, and a series of chemical modifiers (Ir, Mg, Pd, Ru, W, Zr) are tested. All measurements are accomplished with an Ir coated platform and Pd as modifier, because the best results are achieved.Accurate results are obtained using the central SnS line of the band found at 271.578nm with precision values between 1 and 6%. A limit of detection of 10ngS absolute is achieved. Furthermore, the trueness of the procedure is verified by analysis of certified reference materials. Several coal samples with a concentration range from 0.8 to 21.7mgg−1S and three certified reference materials are analyzed. In all cases, simple calibration with aqueous standards is found to be possible and the sample throughput is 2–3 samples per hour (6 replicates per sample).

Determination of fluorine in plant materials via calcium mono-fluoride using high-resolution graphite furnace molecular absorption spectrometry with direct solid sample introduction

Fluorine reacts with calcium forming gaseous CaF, which can be determined by high-resolution molecular absorption spectrometry.

Determination of fluorine in tea using high-resolution molecular absorption spectrometry with electrothermal vaporization of the calcium mono-fluoride CaF

High-resolution continuum source molecular absorption of the calcium mono-fluoride molecule CaF in a graphite furnace has been used to determine fluorine in tea after acid digestion, alkaline solubilization and preparation of a conventional aqueous infusion. The strongest absorption ‘line’ of the CaF molecule is at 606.440nm, which is part of the rotational fine structure of the X2Σ+−A2Π electronic transition; it has a bond dissociation energy of 529kJmol−1, which is comparable with other molecules used for fluorine determination. One advantage of using Ca as the molecule-forming reagent is that spectral interferences are extremely unlikely in the spectral range of its strongest absorption. Another advantage is that Ca acts both as molecule forming reagent and chemical modifier, so that no other reagent has to be added, making the method very simple. The only disadvantage is that Ca has a somewhat negative influence on the graphite tube lifetime. The limit of detection was found to be 0.16mgL−1 F, corresponding to 1.6ng F absolute, and the calibration curve was linear in the range between 0.5 and 25mgL−1 with a correlation coefficient of R=0.9994. The results obtained for a certified tea reference material were in agreement with the certified value on a 95% confidence level. There was also no difference between the results obtained after an acid digestion and an alkaline solubilization for 10 tea samples, based on a paired t-test. The values found in the 10 samples ranged between 42μgg−1 and 87μgg−1 F; the tea infusions contained between 21μgg−1 and 56μgg−1 F, with an extraction rate between 48% and 74%.

Feasibility of high-resolution continuum source molecular absorption spectrometry in flame and furnace for sulphur determination in petroleum products

For the first time, high-resolution molecular absorption spectrometry with a high-intensity xenon lamp as radiation source has been applied for the determination of sulphur in crude oil and petroleum products. The samples were analysed as xylene solutions using vaporisation in acetylene-air flame or in an electrothermally heated graphite furnace. The sensitive rotational lines of the CS molecule, belonging to the ∆ν = 0 vibrational sequence within the electronic transition X 1∑ + → A 1П, were applied. For graphite furnace molecular absorption spectrometry, the Pd + Mg organic modifier was selected. Strong interactions with Pd atoms enable easier decomposition of sulphur-containing compounds, likely through the temporal formation of Pd xS y molecules. At the 258.056 nm line, with the wavelength range covering central pixel ± 5 pixels and with application of interactive background correction, the detection limit was 14 ng in graphite furnace molecular absorption spectrometry and 18 mg kg −1 in flame molecular absorption spectrometry. Meanwhile, application of 2-points background correction found a characteristic mass of 12 ng in graphite furnace molecular absorption spectrometry and a characteristic concentration of 104 mg kg −1 in flame molecular absorption spectrometry. The range of application of the proposed methods turned out to be significantly limited by the properties of the sulphur compounds of interest. In the case of volatile sulphur compounds, which can be present in light petroleum products, severe difficulties were encountered. On the contrary, heavy oils and residues from distillation as well as crude oil could be analysed using both flame and graphite furnace vaporisation. The good accuracy of the proposed methods for these samples was confirmed by their mutual consistency and the results from analysis of reference samples (certified reference materials and home reference materials with sulphur content determined by X-ray fluorescence spectrometry).

Determination of sulfur in biological samples using high-resolution molecular absorption spectrometry in a graphite furnace with direct solid sampling

The determination of sulfur in biological materials using high-resolution continuum source molecular absorption spectrometry and electrothermal vaporization of the carbon monosulfide (CS) molecule has been investigated in detail using direct solid sampling. Best results have been obtained coating the platform with tungsten as a permanent modifier, adding 40 μg Pd in solution as a chemical modifier, and the only sulfur compound that showed sufficient sensitivity and thermal stability to be used for calibration purposes under the conditions established for biological materials was thiourea. A pyrolysis temperature of at least 900 °C could be used and the optimum vaporization temperature was 2500 °C. Under optimized conditions a limit of detection of 0.015 μg S absolute or 0.03 mg g−1 S in the solid sample, based on a sample mass of 0.5 mg could be obtained; the characteristic mass was m0 = 18 ng. Five certified biological reference materials have been analyzed using direct solid sampling and calibration against aqueous standards; the results were in agreement with the certified values on a 95% confidence interval.