Electrothermal Molecular Absorption Research Articles

Application of MgF2 as a new sorbent for preconcentration and isolation of sulphur in food samples before the determination by molecular absorption spectrometry

This study proposes, for the first time, the development of an analytical method using the new sorbent - magnesium fluoride (MgF2) and ultrasound-assisted dispersive micro solid-phase extraction (UA DMSPE) for accurate preconcentration and isolation of sulphur in food samples. The further determination was conducted with high-resolution continuum source electrothermal molecular absorption spectrometry (HR-CS ET MAS). The main UA DMSPE parameters were investigated. Satisfying extraction efficiencies were obtained using 10 mL of sample solution, 20 mg of MgF2 and 20 s extraction time. The limit of detection and the preconcentration factor were 0.001 μg mL−1 and 18, respectively, and no matrix effect was observed. The relative standard deviation (RSD) was 2–13%. The proposed method was applied, inter alia, to corn flakes and flour, dried raisins and goji berries as well as different types of tea leaves. The accuracy of the developed method was evaluated by analysis of certified reference materials: mixed polish herbs (INCT-MPH-2), soya bean flour (INCT-SBF-4), tea leaves (INCT-TL-1), wheat (NCS ZC73009) and corn (NCS ZC73010). Sulphur concentrations determined in these materials were in satisfactory agreement with the certified values (recoveries in the range of 94% to 101%).

Determination of Sulfur in Grape and Apricot Samples Using High-resolution Continuum Source Electrothermal Molecular Absorption Spectrometry.

The determination of sulfur in apricot and grape samples was performed by using high-resolution continuum source electrothermal molecular absorption spectrometry based on vaporization of the carbon monosulfide (CS) molecule. CS forms in the gas phase without the addition of any molecule-forming element, since graphite cuvette contains plenty of carbon as well as food samples. A mixture of 15 μg Pd + 10 μg Mg was used in solution as the chemical modifier. The best sensitivity was obtained at 900°C of the pyrolysis temperature with a K2SO4 calibration solution. The calibration plot drew a linear path between 50 and 1600 ng of sulfur, and the limit of detection was found to be 23 ng. The accuracy of the method was confirmed with the use of a standard reference material (Rice Flour, NIST SRM 1568a). The sulfur content in chemically dried apricot samples (1987 ± 45 mg/kg) was determined to be higher than that of apricot samples dried under sunshine.

A new approach for the determination of sulphur in airborne particles by HR-CS ETAAS

ABSTRACTIn this work, water and nitric acid extractable sulphur concentrations in PM2.5 fraction of urban aerosols were determined by high-resolution continuum source electrothermal molecular absorption spectrometry using most suitable CS molecular absorption band at 258.056 nm. For this purpose, the PM2.5 airborne particulates were collected on quartz filters using a high-volume sampler (500 L/min) in Istanbul (Turkey) during six months (January–June) of two consecutive years. The instrumental and experimental parameters (pyrolysis temperature, molecule formation temperature and leaching reagents) were optimised. The validity of the method for the sulphur was tested using standard reference material and the results were found to be in the uncertainty limits of the certified value.

Theoretical study of the formation mechanism of molecules СaF for fluoride determination using electrothermal molecular absorption spectrometry

In order to select the temperature-time heating program, the calibration method, the prediction of matrix interference and to increase the sensitivity and accuracy of the halogens determination using the electrothermal molecular absorption spectrometry it is essential to know the formation mechanism of the measured molecules. Thermochemical processes of gaseous molecules CaF formation, which are used in the electrothermal molecular absorption determination of fluorine, were studied using the method of the thermodynamic simulation. All calculations were performed using the HSC 6.1 software package with its own database of thermodynamic data. For calculations, the non-equilibrium thermodynamic system, which was realized in the graphite furnace, was divided into the thermodynamic subsystems that correspond to the main stages of time-temperature program: drying of the sample, pyrolysis, vaporization and formation of gaseous diatomic molecules. The composition of the condensed sample residues after drying and pyrolysis stages, the composition of the gas phase in the analytical zone of the graphite furnace during vaporization and the formation of molecules stages were determined by the calculations. This study theoretically describes thermochemical processes of the formation of gaseous CaF molecules using thermodynamic simulation for electrothermal molecular absorption determination of fluorine. The calculations make it possible to establish that gaseous molecules CaF g are formed during the course of the thermal decomposition of the condensed fluoride (CaF 2 c ). The correct execution of thermodynamic simulation was confirmed by the comparison of the theoretical temperature curves of pyrolysis and the formation of molecules CaF g with the experimental curves. The developed procedure of the thermodynamic simulation can be applied to study the formation of other dimeric molecules used for molecular absorption analysis with electrothermal atomization. Keywords: high-resolution continuum source molecular absorption spectrometry, thermodynamic simulation, fluorine, calcium mono-fluoride, temperature of drying, pyrolysis and vaporization. Polina V. Zaitceva*, Alexander A. Pupyshev Ural Federal University named after the fist President of Russia B.N.Yeltsin (UrFU), ul. Mira, 19, Ekaterinburg, 620002, Russian Federation DOI: http://dx.doi.org/10.15826/analitika.2015.20.1.003

Determination of sulphur in various vegetables by solid sampling high-resolution electrothermal molecular absorption spectrometry

Sulphur was determined in various vegetables via molecular absorption of carbon monosulphide (CS) at 258.056nm using a solid sampling high resolution continuum source electrothermal atomic absorption spectrometer (SS HR-CS ETAAS). Samples were dried, ground and directly introduced into the ruthenium coated graphite furnace as 0.05 to 0.50mg. All determinations were performed using palladium+citric acid modifier and applying a pyrolysis temperature of 1000°C and a volatilisation temperature of 2400°C. The results were in good agreement with certified sulphur concentrations of various vegetal CRM samples applying linear calibration technique prepared from thioacetamide. The limit of detection and characteristic mass of the method were 7.5 and 8.7ng of S, respectively. The concentrations of S in various spinach, leek, lettuce, radish, Brussels sprouts, zucchini and chard samples were determined. It was showed that distribution of sulphur in CRM and grinded food samples were homogeneous even in micro-scale.

О механизме образования молекул SrF при электротермическом молекулярно-абсорбционном определении фтора

О механизме образования молекул SrF при электротермическом молекулярно-абсорбционном определении фтора

Development of a simple method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry

In this work, it was developed a method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry of NO produced by thermal decomposition of nitrate in a graphite furnace. The NO line at 215.360nm was used for all analytical measurements and the signal obtained by integrated absorbance of three pixels. A volume of 20μL of standard solution or groundwater sample was injected into graphite furnace and 5μL of a 1% (m/v) Ca solution was co-injected as chemical modifier. The pyrolisis and vaporization temperatures established were of 150 and 1300°C, respectively. Under these conditions, it was observed a difference of thermal stability among the two nitrogen species in the presence of hydrochloric acid co-injected. While that the nitrite signal was totally suppressed, nitrate signal remained nearly stable. This way, nitrogen can be quantified only as nitrate. The addition of hydrogen peroxide provided the oxidation of nitrite to nitrate, which allowed the total quantification of the species and nitrite obtained by difference. A volume of 5μL of 0.3% (v/v) hydrochloric acid was co-injected for the elimination of nitrite, whereas that hydrogen peroxide in the concentration of 0.75% (v/v) was added to samples or standards for the oxidation of nitrite to nitrate. Analytical curve was established using standard solution of nitrate. The method described has limits of detection and quantification of 0.10 and 0.33μgmL−1 of nitrogen, respectively. The precision, estimated as relative standard deviation (RSD), was of 7.5 and 3.8% (n=10) for groundwater samples containing nitrate–N concentrations of 1.9 and 15.2μgmL−1, respectively. The proposed method was applied to the analysis of 10 groundwater samples and the results were compared with those obtained by ion chromatography method. In all samples analyzed, the concentration of nitrite–N was always below of the limit of quantification of both the methods. The concentrations of nitrate–N varied from 0.58 to 15.5μgmL−1. No significant difference it was observed between the results obtained by both methods for nitrate–N, at the 95% confidence level.

Determination of sulfur in coal and ash slurry by high-resolution continuum source electrothermal molecular absorption spectrometry

We propose a procedure for the determination of sulfur in coal slurries by high resolution continuum source electrothermal molecular absorption spectrometry. The slurry, whose concentration is 1mgmL−1, was prepared by mixing 50mg of the sample with 5% v/v nitric acid and 0.04% m/v Triton X-100 and was homogenized manually. It sustained good stability. The determination was performed via CS molecular absorption at 257.592nm, and the optimized vaporization temperature was 2500°C. The accuracy of the method was ensured by analysis of certified reference materials SRM 1632b (trace elements in coal) and SRM 1633b (coal fly ash) from the National Institute of Standards and Technology, using external calibration with aqueous standards prepared in the same medium and used as slurry. We achieved good agreement with the certified reference materials within 95% confidence interval, LOD of 0.01% w/w, and RSD of 6%, which confirms the potential of the proposed method.

Determination of fluorine in milk samples via calcium-monofluoride by electrothermal molecular absorption spectrometry

The determination of fluorine in milk samples via the molecular absorption of calcium mono-fluoride (CaF) was performed using a HR-CS-ETAAS. For this purpose, calcium was pipetted to graphite furnace together with samples. The amount of Ca and the graphite furnace program were optimised. Fluorine was determined in pyrolytically coated platforms at 606.440nm applying a pyrolysis temperature of 700°C and a molecule forming temperature of 2250°C. Finally, applying standard addition technique, F contents of several milk samples were determined. The results obtained by linear calibration and standard addition techniques were significantly different which can be attributed to non-spectral interferences in milk due to matrix concomitants. Therefore, in order to tolerate the errors, the F contents of several milk samples were determined applying standard addition technique. However, since the ingredients of milk samples change for different kinds, the F in each sample was determined from its own standard addition curve. The range of F content for the milk samples were 0.027–0.543μgmL−1. The limit of detection and characteristic mass of the method were 0.26 and 0.13ng of F, respectively.

Effect of matrix modifier and furnace material on the determination of traces of fluoride by electrothermal molecular absorption spectrometry of aluminum monofluoride

In the determination of fluoride by AlF absorbance measurements, the interference from strontium nitrate is avoided by using magnesium nitrate or barium nitrate added to aluminum solution as the matrix modifier. The effects of the graphite-furnace material on AlF absorbance are investigated. Glassy carbon and synthetic carbon gave longer furnace lifetimes and better sensitivity than the other materials tested. The maximum sensitivity (4.2 μg ml −1 fluoride for 0.0044 absorbance with a 10-μl injection) was obtained with synthetic carbon. The r.s.d, was <5% for 0.1 μg ml −1 fluoride ( n=10). Na +, K +, Pb 2+, Zn 2+, Cu 2+ and Ag + did not affect the measurements up to 500 μg ml −1, but Ni 2+, Co 2+, Fe 2+, Sr 2+ and especially Ca 2+ depressed the absorbance.