Molecular Absorption Spectrometry Research Articles

General Applicability of High-Resolution Continuum-Source Graphite Furnace Molecular Absorption Spectrometry to the Quantification of Oligopeptides Using the Example of Glutathione

This communication introduces the first-time application of high-resolution continuum-source molecular absorption spectrometry (HR CS MAS) for the quantification of a peptide. The graphite furnace technique was employed and the tripeptide glutathione (GSH) served as a model compound. Based on measuring sulfur in terms of carbon monosulfide (CS), a method was elaborated to analyze aqueous solutions of GSH. The most prominent wavelength of the CS molecule occurred at 258.0560 nm and was adduced for monitoring. The methodological development covered the optimization of the pyrolysis and vaporization temperatures. These were found optimally to be 250 °C and 2250 °C, respectively. Moreover, the effect of modifiers (zirconium, calcium, magnesium, palladium) on the absorption signals was investigated. The best results were obtained after permanent coating of the graphite tube with zirconium (total amount of 400 μg) and adding a combination of palladium (10 µL, 10 g L−1) and calcium (2 µL, 1 g L−1) as a chemical modifier to the probes (10 µL). Aqueous standard samples of GSH were used for the calibration. It showed a linear range of 2.5–100 µg mL−1 sulfur contained in GSH with a correlation coefficient R2 > 0.997. The developed method exhibited a limit of detection (LOD) and quantification (LOQ) of 2.1 µg mL−1 and 4.3 µg mL−1 sulfur, respectively. The characteristic mass accounted for 5.9 ng sulfur. The method confirmed the general suitability of MAS for the analysis of an oligopeptide. Thus, this study serves as groundwork for further development in order to extend the application of classical atomic absorption spectrometry (AAS).

High-resolution continuum source graphite furnace molecular absorption spectrometry for the monitoring of Sr isotopes via SrF formation: a case study

A new approach for monitoring Sr isotopes via HR CS GFMAS is described.

Study on the Optimization of Determination of Total Nitrogen in Water by Gas Phase Molecular Absorption Spectrometry

Study on the Optimization of Determination of Total Nitrogen in Water by Gas Phase Molecular Absorption Spectrometry

Evaluation of dried matrix spot sampling for total sulphur determination in automotive gasoline by high-resolution continuum source molecular absorption spectrometry and direct solid sample analysis

In this work, a method for total sulphur determination in automotive gasoline using dried matrix spot sampling is proposed. The method is based on the deposition of the sample on a cellulose-based filter paper and subsequent sulphur quantification via CS diatomic molecule using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). The sample deposition was carried out, along with the chemical modifier, on a 20-mm filter paper disc previously adapted into a polytetrafluoroethylene (PTFE) mould. The liquid phase was removed by heating the PTFE mould, and then the gasoline sample-embedded filter paper was punched in smaller discs (procedure A) or pulverised (procedure B) before the analyses. The mixture of Pd and Mg was used as chemical modifier to stabilise the sulphur compounds on the filter paper and on the graphite furnace. All the calibration curves constructed using seven different sulphur-containing compounds had a coefficient of determination higher than 0.995 and a linear range from 2 to 150 mg kg−1 S. By using the optimised conditions, the best characteristic mass, limits of detection and quantitation were 6 ng, 0.6 and 1.8 mg kg−1, respectively. The two sampling procedures (A and B) were evaluated for real samples, and procedure B was chosen since it markedly improved the precision. Using this procedure, satisfactory recovery values from 95 to 106% were obtained in the spike-recovery tests. In addition, the S concentrations for the certified reference materials were not statistically different from the certified values at 95% confidence level. Sulphur concentrations from 20 to 46 mg kg−1 were found in the six analysed gasoline samples, and these values were statistically assessed using a reference method (ASTM 5453). Spectral interference caused by MgF and MgCl diatomic molecules was observed and investigated.

Calcium monofluoride as a target molecule for determination of organic fluorine in gasoline and its components using high-resolution continuum source flame molecular absorption spectrometry

High-resolution continuum source molecular absorption spectrometry (HR-CS MAS) is widely applied to determine fluorine in various materials, and its graphite furnace option with calcium monofluoride as a target molecule is popular. However, up to now, the idea of using the molecule in flame molecular absorption spectrometry seemed impossible or impractical due to the expected low sensitivity and detectability. The following paper completely changes this view. The CaF molecule has been proven to be an excellent tool for determining organic fluorine in gasoline using flame molecular absorption spectrometry, giving benefits over previously used gallium monofluoride. The following favourable circumstances decide about it: 1) relatively high population of CaF molecules in preferable air-acetylene flame, 2) possibility of using oil calcium “standard” as a source of calcium, which is well dissoluble in both xylene (solvent) and gasoline, 3) extremely good stability of baseline in the used spectrum range, 4) relatively high freedom from spectral and chemical interferences and 5) possibility of summing of many pixels response. The analysis relies on simple sample dilution in xylene, with the addition of oil calcium “standard” to obtain 1500 mg L−1 Ca in measured solutions. Simplified standard addition calibration is used to overcome the effect of variability of samples (various physical properties and combustion characteristics). The signals of four CaF rotational “lines” are summed. The only undesirable spectral effect is a molecular absorption at the second “line” (606.0368 nm), which is attributed to the absorption by the CaOH molecule formed in the flame. The effect can be easily overcome by using the least square background correction, LSBC. The characteristic concentration and the detection limit for solutions are 6 and 0.6 mg L−1, respectively. The detection limit recalculated for the original sample is 2 mg kg−1 in the case of alkalyte, reformate and gasoline, while it is 6 mg kg−1 in the case of volatile isomerizate, mainly due to necessary higher sample dilution. The calibration curve is linear over at least two orders of magnitude. Heptafluorobutanol has been found a suitable standard. The agreement of the results of the proposed method and standard combustion ion chromatography is satisfactory.

Silicon determination via a SiO rotational line using high-resolution graphite furnace molecular absorption spectrometry: A straightforward approach for the analysis of solid samples prepared as suspensions

High-resolution graphite furnace molecular absorption spectrometry combined with samples prepared as suspensions were used for the quantification of Si in geological samples and in spent catalysts used for petrochemical processing. Measurements at the main Si resonance line at 251.6110 nm were proven unfeasible due to the formation of a quasi-continuous signal, which resulted in significant memory effect. An alternative was to monitor the fine rotational spectrum of SiO, which allowed memory effect-free measurements. A SiO rotational line centered at 231.9373 nm was selected to carry out quantitative analysis of Si at high percent concentrations in a variety of solid samples. Pyrolysis and vaporization temperatures were evaluated and optimized as 800 °C and 2400 °C, respectively, without the need to use a chemical modifier. Attempts to produce SiO molecules from acidified aqueous standards containing Si were unsuccessful, as the molecule could only be produced from solid samples, likely due to the formation mechanism that involves thermal decomposition of silicates. Hence, solid samples were prepared as suspensions in 0.14 mol L−1 HNO3. Calibration was performed using a series of suspensions prepared from a gabbro rock certified reference material (CRM), resulting in a limit of detection of 0.5% (m/m). The accuracy of the method was attested by the analysis of several CRM, including rocks, soils and sediments. Solid spent petrochemical catalyst samples were also analyzed and 97–114% recovery was obtained by spiking the catalyst suspensions with a CRM. The good accuracy demonstrated that the formation of SiO is free from matrix effects and highly efficient under the adopted conditions. Overall, the method was proven accurate and consists on a simple and fast alternative to determine Si in silicate-rich samples.

Recently Developed Adsorbing Materials for Fluoride Removal from Water and Fluoride Analytical Determination Techniques: A Review

In recent years, there has been an increase in public perception of the detrimental side-effects of fluoride to human health due to its effects on teeth and bones. Today, there is a plethora of techniques available for the removal of fluoride from drinking water. Among them, adsorption is a very prospective method because of its handy operation, cost efficiency, and high selectivity. Along with efforts to assist fluoride removal from drinking waters, extensive attention has been also paid to the accurate measurement of fluoride in water. Currently, the analytical methods that are used for fluoride determination can be classified into chromatographic methods (e.g., ionic chromatography), electrochemical methods (e.g., voltammetry, potentiometry, and polarography), spectroscopic methods (e.g., molecular absorption spectrometry), microfluidic analysis (e.g., flow injection analysis and sequential injection analysis), titration, and sensors. In this review article, we discuss the available techniques and the ongoing effort for achieving enhanced fluoride removal by applying novel adsorbents such as carbon-based materials (i.e., activated carbon, graphene oxide, and carbon nanotubes) and nanostructured materials, combining metals and their oxides or hydroxides as well as natural materials. Emphasis has been given to the use of lanthanum (La) in the modification of materials, both activated carbon and hybrid materials (i.e., La/Mg/Si-AC, La/MA, LaFeO3 NPs), and in the use of MgO nanostructures, which are found to exhibit an adsorption capacity of up to 29,131 mg g−1. The existing analytical methodologies and the current trends in analytical chemistry for fluoride determination in drinking water are also discussed.

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.

Au-on-Pd bimetallic nanoparticles applied to the voltammetric determination and monitoring of 4-nitroaniline in environmental samples

Palladium@Gold bimetallic nanoparticles (Au-on-PdNP) were synthesized and characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The nanomaterial was successfully applied in the modification of a glassy carbon electrode (GCE). By using the modified electrode and cyclic voltammetry (CV), a pronounced current response was obtained for the noxious compound 4-nitroaniline (4-NA), an environmental pollutant. Using differential pulse voltammetry (DPV), the anodic peak currents increased by increasing 4-NA concentrations in the range of 0.5–50 µmol L−1, with a limit of detection of 0.17 µmol L−1. The proposed method was successfully applied to the determination of 4-NA in river water samples, at different levels, with a recovery range of 90–106%. Selectivity was investigated, showing that, at a significance level of 95%, the matrix did not interfere with the analysis. Accuracy was evaluated using molecular absorption spectrometry. Consistent results were obtained with accuracy and precision showing that the novel method can be successfully used for environmental purposes as an alternative strategy. The electrode also presents long-term stability, showing that Nf/Au-on-Pd/GCE may be applied as an electrochemical sensing platform for the 4-NA detection in environmental analysis with a focus on management and in-loco monitoring.

N-compounds speciation analysis in environmental samples using ultrasound-assisted solid-liquid extraction and non-chromatographic techniques.

A fast, efficient, and non-chromatographic method was presented in this study for nitrite, nitrate, and p-nitrophenol (N-compounds) extraction and speciation analysis of environmental samples. By applying ultrasound-assisted solid-liquid extraction (USLE), analytes were efficiently extracted from water, soil, or sediment collected in areas of environmental disaster. These analytes were selectively converted to NO(g) through UV photolysis (NO3-), H2O2/UV photocatalysis (PNP), and direct conversion (NO2-). Following conversion, NO(g) was separated from the liquid phase and determined by high-resolution continuum source molecular absorption spectrometry (HR-CS MAS). The LODs obtained were 0.097 ± 0.004mgL-1 for nitrite, 0.119 ± 0.004mgL-1 for nitrate, and 0.090 ± 0.006mgL-1 for p-nitrophenol. On applying this speciation method to environmental samples, concentrations were found to be up to 0.99 ± 0.03mgL-1 (NO2-), 49.80 ± 2.5mgL-1 (NO3-), and 0.10 ± 0.02mgL-1 (PNP). Finally, addition/recovery study of real water, soil, and sediment samples showed 101 ± 2% recovery for NO2-, 100 ± 1% for NO3-, and 96 ± 5% for PNP.

Method development for determination of organic fluorine in gasoline and its components using high-resolution continuum source flame molecular absorption spectrometry with gallium fluoride as a target molecule

High-resolution continuum source molecular absorption spectrometry (HR-CS MAS) has been developing fast for fluorine determination, but neither flame nor graphite furnace technique have ever been applied for the analysis of petroleum or its products. Hydrogen fluoride can be applied in technologies of gasoline components production, unfortunately, arising organic fluorides can contaminate final product. The aim of this work was development of fast and simple HR-CS MAS method, with an ordinary air-acetylene flame, for determination of organic F in gasoline and its components. Gallium fluoride as a target molecule was the imposing choice, because Ga undergoes atomization at relatively low temperature, and the GaF molecule is known to provide good sensitivity in F determination. Severe difficulties have arisen to get higher concentration of gallium (as Ga(III)acetylacetonate) in the measured (xylene) solution. Furthermore, depending on the flame character, the spectrum of the GaF molecule at the most sensitive 211.248 nm rotational “line”could have been disturbed by intensive noise (a case of too rich flame) or overlapped by the OH molecule spectrum (a case of too lean flame). The effects, as well as sensitivity of F determination, depended on the sample volatility and its dilution ratio. The difficulties have been overcome by adjusting the solution aspiration rate and the additional air flow rate to get not-disturbed baseline. The least square background correction (LSBC) with the OH molecule spectrum as the correction spectrum (the OH molecule spectrum intentionally generated for the first time) and the standard addition calibration have been also applied. Huge difference in sensitivity, up to one order of magnitude, depending on the F compound volatility and its chemical character was stated. A standard giving the best sensitivity (heptafluorobutanol) turned out to be the most suitable for calibration in analysis of real samples (satisfactory agreement with results of combustion ion chromatography). It was found that HF introduced into the solution of the investigated sample does not contribute to the increase of F signal. Using 5000 mg L−1 of Ga in a solution, the best characteristic concentration and detection limit are 3.2 mg L−1 and 0.93 mg L−1, respectively. The developed method enabled to identify high contamination of some gasoline components with organic F species, which constituted significant corrosion and environmental threat.

The use of microwave-induced plasma optical emission spectrometry for fluorine determination and its application to tea infusions

This study presents a novel method for fluorine quantification determination by microwave-induced plasma optical emission spectrometry (MIP-OES). Due to the low temperature of this plasma, atomic emission of fluorine could not be measured, instead CaF molecular emissions were measured by using a calcium solution mixed in the spray chamber with the sample using a T-piece. Several wavelengths were studied to find the best signal to noise ratio for fluorine determination and 530.45 nm was chosen. The limit of detection for the determination of fluorine via CaF using MIP-OES was 1.1 mg L−1. A linear response was observed over two orders of magnitude (R2 = 0.998). The developed method was applied to ten tea infusion samples from the UK and Saudi Arabia. The results were not significantly different (paired Student's t-test, p = 0.97) to the results obtained using the reference method, high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-GF MAS). The total fluorine in the tea infusions varied between 2.7 and 7.8 mg L−1; all of which were above the WHO recommended level of fluoride (0.8–1.5 mg L−1) in drinking water. This method can potentially be used for total fluorine determination and might be useful for fluorine speciation analysis when coupled with HPLC.

Determination of organic chlorine in water via AlCl derivatization and detection by high-resolution continuum source graphite furnace molecular absorption spectrometry.

High-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GF-MAS) was employed for determining adsorbable organic chlorine (AOCl) in water. Organic chlorine was indirectly quantified by monitoring the molecular absorption of the transient aluminum monochloride molecule (AlCl) around a wavelength of 261.42 nm in a graphite furnace. An aluminum solution was used as the molecular-forming modifier. A zirconium coated graphite furnace, as well as Sr and Ag solutions were applied as modifiers for a maximal enhancement of the absorption signal. The pyrolysis and vaporization temperatures were 600 °C and 2300 °C, respectively. Non-spectral interferences were observed with F, Br, and I at concentrations higher than 6 mg L-1, 50 mg L-1, and 100 mg L-1, respectively. Calibration curves with NaCl, 4-chlorophenol, and trichlorophenol present the same slope and dynamic range, which indicates the chlorine atom specificity of the method. This method was evaluated and validated using synthetic water samples, following the current standard DIN EN ISO 9562:2004 for the determination of the sum parameter adsorbable organic halides (AOX) for water quality. These samples contain 4-chlorophenol as the chlorinated organic standard in an inorganic chloride matrix. Prior to analysis, organic chlorine was extracted from the inorganic matrix via solid-phase extraction with a recovery rate >95%. There were no statistically significant differences observed between measured and known values and for a t-test a confidence level of 95% was achieved. The limits of detection and characteristic mass were found to be 48 and 22 pg, respectively. The calibration curve was linear in the range 0.1-2.5 ng with a correlation coefficient R2 = 0.9986.

Method for organic fluorine determination in gasoline and its components using high-resolution continuum source flame molecular absorption spectrometry with gallium fluoride as a target molecule

Organic fluorides can arise due to the usage of HF in technologies of gasoline production, therefore, it is necessary to identify contamination of gasoline or its components with organic fluorine. For this aim, simple and fast method is proposed. The method relies on sample dilution in xylene, followed by the solution aspiration to a high-resolution continuous source spectrometer for measurement of absorption of radiation by GaF molecule, arisen in air-acetylene flame. Gallium(III) acetylacetonate is carefully dissolved and introduced to all measured solutions at Ga concentration 5000 mg L−1. For standard addition calibration three types of samples solutions are prepared to contain: none, 50 mg L−1 and 100 mg L−1 of added fluorine. As fluorine standard 2, 2, 3, 3, 4, 4, 4-heptafluoro-1-pentanol is applied. The lowest possible flow rate of acetylene is recommended. The solution flow rate and the additional air flow rate should be adjusted to obtain not-disturbed baseline. The overlap of the GaF signal with residual signal of the OH molecule can be overcome using least square background correction. Five pixels are recommended for signal evaluation at the most sensitive 211.248 nm rotational “line”. Using such conditions characteristic concentration was 3.2 mg L−1. Detection limit recalculated for initial sample was 4-10 mg L−1.•High-resolution continuum source flame molecular absorption spectrometry turned out to be an excellent tool for determination of pollution of gasoline with organic fluorine.•Due to application of GaF as a target molecule, it is possible to use a low-temperature and easy for operation air-acetylene flame.•The proposed method can be applied for analysis of alkylate, reformate, isomerizate, ethanol as well as commercial automotive and aviation gasoline.

Determination of residual dimethyl sulfoxide by high-resolution continuum source graphite furnace molecular absorption spectrometry

High-resolution continuum source molecular absorption spectrometry (HR-CSMAS) has been extended to the determination of sulfur-containing organic molecule, on the example of dimethyl sulfoxide (DMSO) as a residual solvent in CH3NH3PbI3 perovskite thin films. For this purpose, DMSO molecules were converted into CS molecules by pyrolysis in a graphite furnace at low temperature and the sulfur content was determined by measuring molecular absorption of CS at 258.055 nm. An aqueous solution of DMSO was used for calibration. A characteristic mass of 17 ng was achieved for S after pyrolysis at 160 °C by using Pd as a chemical modifier. Furthermore, the content of DMSO was normalized to that of Pb whereas the content of Pb was determined by reducing the Pb in the perovskite to metallic Pb with Zn powder and measuring absorption of the weak Pb line at 261.418 nm by high-resolution continuum source atomic absorption spectrometry (HR-CSAAS). The Pb content remained constant whereas the S/Pb molar ratio decreased with increasing annealing time. Our results open new opportunities for the characterization of residual DMSO in wide classes of materials.

Determination of organically bound fluorine sum parameters in river water samples\u2014comparison of combustion ion chromatography (CIC) and high resolution-continuum source-graphite furnace molecular absorption spectrometry (HR-CS-GFMAS)

In this study, we compare combustion ion chromatography (CIC) and high resolution-continuum source-graphite furnace molecular absorption spectrometry (HR-CS-GFMAS) with respect to their applicability for determining organically bound fluorine sum parameters. Extractable (EOF) and adsorbable (AOF) organically bound fluorine as well as total fluorine (TF) were measured in samples from river Spree in Berlin, Germany, to reveal the advantages and disadvantages of the two techniques used as well as the two established fluorine sum parameters AOF and EOF. TF concentrations determined via HR-CS-GFMAS and CIC were comparable between 148 and 270 μg/L. On average, AOF concentrations were higher than EOF concentrations, with AOF making up 0.14–0.81% of TF (determined using CIC) and EOF 0.04–0.28% of TF (determined using HR-CS-GFMAS). The results obtained by the two independent methods were in good agreement. It turned out that HR-CS-GFMAS is a more sensitive and precise method for fluorine analysis compared to CIC. EOF and AOF are comparable tools in risk evaluation for the emerging pollutants per- and polyfluorinated alkyl substances; however, EOF is much faster to conduct.Graphical abstract

Chemical modification for sulfur determination in human hair by high-resolution continuum source graphite furnace molecular absorption spectrometry

This paper presents the study of chemical modification for sulfur determination in human hair samples by high-resolution continuum source molecular absorption spectrometry in a graphite furnace (HR-CS GF MAS) via molecular absorption of CS. The thermal behavior of inorganic and organic S species was studied without and with the use of chemical modifiers. Without chemical modification, sulfur species were lost in the pyrolysis step, especially when using organic standards. The combination of a mixture of modifiers Pd + Mg (15 + 10 μg) in solution and W (800 μg) as a permanent modifier allowed the accurate determination of S in hair samples at 900 °C pyrolysis and 2400 °C vaporization temperatures, by using an inorganic sulfur standard for constructing the calibration curve. Accuracy was checked by the analysis of the certified reference material NSC DC73347a (human hair), with the recovery of the certified value better than 98%. The results obtained for 14 human hair samples by the proposed method were in agreement with those obtained by ICP OES, according to the paired t-test, with a 95% level of confidence.

Green Synthesis, Characterization and Antimicrobial Evaluation of Silver Nanoparticles for an Intracanal Dressing.

Green chemistry has been applied in different areas due to the growing demands for renewable processes and one of them is nanotechnology. The aim of this study was to characterize a formulation containing silver nanoparticles (AgNPs) produced by a green synthesis and to evaluate its antimicrobial activity. The formulation will be used as an intracanal dressing exploiting the AgNPs' antimicrobial properties, which are crucial to prevent infections and bacterial reinfections that can compromise endodontic treatments. In the green synthesis, silver nitrate was employed as the precursor salt, maltose as a reducing agent, and gelatin as a stabilizing agent. The formulation was prepared mixing 50 % of a liquid containing the AgNPs and 50 % of hydroxyethylcellulose gel at 1.5 % with proper evaluation of the process inherent parameters. Techniques such as molecular absorption spectrometry and dynamic light scattering were used in characterization step. The antimicrobial activity of the AgNPs against Escherichia coli ATCC 25922, Enterococcus faecalis NCTC 775, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923 and Streptococcus mutans ATCC 25175 was verified according to National Comittee for Clinical Laboratory Standards (NCCLS) by determining minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). The obtained results indicated the formulation containing AgNPs produced by a green synthesis was properly characterized by the selected techniques. Furthermore, the formulation assessment proved that it is suitable for the proposal as well as it has potential to be used as an intracanal dressing since presented antimicrobial activity against all bacterial strains evaluated.

Sulfur determination using the SiS diatomic molecule via HR-CS GF MAS and direct analysis of solid samples: A versatile method for different matrices

In this work, a simple and reliable method was proposed for sulfur determination in different matrices using the diatomic molecule SiS via high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) and direct analysis of solid samples. This investigation was carried out using six sulfur standard solutions, Na2S, Na2SO4, BeSO4, thiourea, l-cysteine and sulfamic acid, and nine certified reference materials (CRMs). All measurements were performed using the SiS analytical line at 282.910 nm with 400 μg Zr as permanent modifier and 20 μg Si in basic media as molecule forming reagent. The optimized pyrolysis and vaporization temperatures were 1200 and 2000 °C, respectively. The investigated sulfur sources presented similar analytical signals and statistically equal Aint values for the SiS molecule. Calibration curves with aqueous sulfur standard solutions were used to achieve the limits of detection (LOD) and quantification (LOQ) and the characteristic mass (m0) of 8.8, 29 ng mg−1 and 9.8 ng, respectively, and to determine sulfur in the CRMs. Considering that the investigated wavelength range contained multiple SiS lines, the LOD (2.5 ng mg−1), LOQ (8.4 ng mg−1), m0 (1.0 ng) and the working range (0.008–2.5 μg) were improved by using ten SiS lines (30 pixels) for the measurements. Despite differences in the CRM matrices, the SiS molecule was successfully employed to determine their sulfur concentrations, which were in agreement with the certified values at a confidence level of 95% through Student or Welch t-tests. Therefore, a simple, versatile and reliable method using the SiS molecule was developed to perform sulfur determination in a great variety of sample matrices via HR-CS GF MAS and direct analysis of solid samples.

Sequential and simultaneous determination of chlorine, iron, and silicon in beer samples by high-resolution continuum source graphite furnace molecular and atomic absorption spectrometry

An analytical method was proposed for the determination of Cl (via the InCl molecule at 267.2181 nm), Fe (252.7435 nm), and Si (252.8508 nm) in beer samples using sequential and simultaneous determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) in combination with high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). First, Cl was determined using 600 °C and 1800 °C as the pyrolysis and vaporization temperatures, respectively, using In as a forming agent of the InCl molecule. Then, Si and Fe were simultaneously determined from the same sample aliquot using 2600 °C as the atomization temperature. A solution of Pd/Mg was used as a chemical modifier. The matrix effect was evaluated, and the results indicated that external calibration was possible using aqueous standard solutions. The limit of detection and quantification were 0.05 and 0.17 mg L–1 for Cl, 0.08 and 0.26 mg L–1 for Si, and 2.0 and 6.7 μg L–1 for Fe, respectively. Recovery tests presented interval between 85 and 120% for the three analytes. Accuracy was confirmed by comparing the results obtained by the proposed method with those obtained by inductively coupled plasma optical emission spectrometry for Si and Fe and by ion chromatography for Cl. The concentration range found in ten beer samples was 106–277 mg L–1 for Cl, 15–37 mg L–1 for Si, and < 20–73 μg L–1 for Fe.