Continuum Source Molecular Absorption Spectrometry Research Articles

Sulfur fractionation using high-resolution continuum source molecular absorption spectrometry with calcium and hydrophobic palladium nanoparticles as chemical modifiers

The unprecedented use of high-resolution continuum source molecular absorption spectrometry (HR-CS MAS) for the fractionation of organic and inorganic sulfur (S) species through monitoring the CS molecule is presented here. Two separate methods for determining organic (CSorg) and inorganic (CSino) sulfur were developed to work sequentially. The optimized temperature program for both methodologies has two pyrolysis steps and one vaporization step (1st Tpyr: 1800 and 2ndTpyr: 800 °C, and Tvap: 2500 °C). The fractionation was achieved by implementing hydrophobic Pd NPs and Ca as chemical modifiers for the CSorg and CSino methods. Method development was performed by applying different statistical models, allowing the definition of optimal conditions for the chemical modifier mass, and minimizing the S species interconversion, i.e., Doehlert design, and central composite design. The limits of detection (LoD) for CSorg and CSino were 2.4 and 2.1 mg L−1, respectively. Recovery tests evaluated the method's specificity and accuracy; over 92 % recovery was found for both CSorg and CSino. Thus, the proposed methods offer a reliable alternative for fractionating organic and inorganic S by using HR-CS MAS.

Feasibility of high-resolution continuum source molecular absorption spectrometry for vanadium determination

This work aimed to evaluate high-resolution continuum source molecular absorption spectrometry (HR-CS MAS), traditionally used to determine non-metals, for the determination of a new element, metal, vanadium.

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).

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.

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.

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.

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.

The use of high resolution graphite furnace molecular absorption spectrometry (HR -MAS) for total fluorine determination in extractable organofluorines (EOF)

The determination of total fluorine content using high-resolution graphite furnace continuum source molecular absorption spectrometry (HR- MAS) has been employed in a variety of samples for over 10 years. However, most of the samples analysed by HR- MAS are rich in fluoride, with negligible levels of organic fluorinated species. With an increase in concern surrounding per- and polyfluoroalkyl substances (PFASs), new methods to measure total fluorine of organofluorine using different techniques have been developed. However, no studies focused on PFASs behaviour in HR-MAS have been performed. As these compounds encompass a wide range of different structures, boiling points, decomposition temperatures and matrix interactions, a loss of accuracy can occur when an aqueous external calibration is performed using only one compound. To overcome this issue, an investigation into permanent modifiers for the graphite furnace was performed. After optimisation similar sensitivity for different PFCA was achieved when 400 μg of W was used as a permanent modifier together with an optimised temperature program. The relative deviation between the different PFCA standard slopes relative to the PFOA slope was lower than 15%. The instrumental limit of detection and quantification (LOD and LOQ, respectively) of total fluorine as total PFCA was 0.1 mg L−1 and 0.3 mg L−1, respectively, while the method LOD and LOQ (using solid phase extraction) was 0.3 μg L−1 and 1.0 μg L−1, respectively. The developed method gave satisfactory recoveries for the spiked PFCA into seawater, river water and effluent using PFOA calibration standards. The optimised method is useful for measuring extractable organofluorines (EOF) when only ionic PFASs such as PFCA are expected. When other organofluorines are expected, the results using HR GF-MAS should be taken with caution.

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.

Multi-energy calibration for the determination of non-metals by high-resolution continuum source molecular absorption spectrometry

Spectra of diatomic molecules are rich in fine structures which may be used for different analytical applications in high-resolution continuum source molecular absorption spectrometry (HR-CS MAS).

Formation of calcium monofluoride in graphite furnace molecular absorption spectrometry, part 2: interference mechanisms of chloride, bromide and sulfate salts

In this study, the interference mechanisms of chloride, bromide and sulfate together with sodium in the determination of CaF by high resolution continuum source molecular absorption spectrometry were investigated.

Method development for the determination of bromine via molecular absorption of barium monobromide by high-resolution continuum source molecular absorption spectrometry

A challenging novel method was developed for the determination of bromine via molecular absorption of barium monobromide (BaBr) using a high-resolution continuum source electrothermal atomic absorption spectrometer (HR-CS ETAAS).

Speciation of nitrite, nitrate and p-nitrophenol by photochemical vapor generation of NO using High-Resolution Continuum Source Molecular Absorption Spectrometry

This paper presents a new speciation method of n-compounds in food samples using the technique of High-Resolution Continuum Source Molecular Absorption Spectrometry (HR-CS MAS). The nitrite ion was determined in a quartz cell of the HR-CS MAS by generating NO steam. Speciation methods of nitrite and nitrate were studied, using the reduction of nitrate to nitrite. The most efficient alternative was the irradiation of ultraviolet light (UV) in the samples containing nitrate in an ammonium bufferand EDTA. Therefore,the nitrate concentration in the samples, using the reduction process to nitrite,was added to the previous nitrite concentration and was specified by subtracting the initial concentration to the final one. The p-nitrophenol was determined by its degradation throughUV in the presence of H2O2, generating, among other products, nitrite, which was determined through the reduction of nitrite to NO steam. After that, samples of natural water and canned foods were analyzed. The R2, LOD (mg L−1), LOQ (mg L−1) and m0 values were, respectively 0.990; 0.047,0.16 and 0.25 μg, for nitrate; 0.990; 0.090 and 0.30 and 0.52 μg, for nitrate, and 0.996; 0.034, 0.11 and 0.29 μg, for p-nitrophenol.

Determination of free and total sulfur(IV) compounds in coconut water using high-resolution continuum source molecular absorption spectrometry in gas phase

This work proposes a method for the determination of free and total sulfur(IV) compounds in coconut water samples, using the high-resolution continuum source molecular absorption spectrometry. It is based on the measurement of the absorbance signal of the SO2 gas generate, which is resultant of the addition of hydrochloric acid solution on the sample containing the sulfating agent. The sulfite bound to the organic compounds is released by the addition of sodium hydroxide solution, before the generation of the SO2 gas.The optimization step was performed using multivariate methodology involving volume, concentration and flow rate of hydrochloric acid. This method was established by the sum of the absorbances obtained in the three lines of molecular absorption of the SO2 gas. This strategy allowed a procedure for the determination of sulfite with limits of detection and quantification of 0.36 and 1.21mgL−1 (for a sample volume of 10mL) and precision expressed as relative standard deviation of 5.4% and 6.4% for a coconut water sample containing 38.13 and 54.58mgL−1 of free and total sulfite, respectively.The method was applied for analyzing five coconut water samples from Salvador city, Brazil. The average contents varied from 13.0 to 55.4mgL−1 for free sulfite and from 24.7 to 66.9mgL−1 for total sulfur(IV) compounds. The samples were also analyzed employing the Ripper´s procedure, which is a reference method for the quantification of this additive. A statistical test at 95% confidence level demonstrated that there is no significant difference between the results obtained by the two methods.

Determination of boron isotope ratios by high-resolution continuum source molecular absorption spectrometry using graphite furnace vaporizers

Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+→A1Π were evaluated around wavelengths 433.1nm and 437.1nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1nm and 437.1nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k=2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.

Method development and validation for sulfur determination via CS molecule in petroleum green coke by high resolution continuum source molecular absorption spectrometry

Development and validation of a method for determination of sulfur via CS molecule in petroleum green coke samples by high resolution continuum source molecular absorption spectrometry (HR-CS MAS) is the aim of this work. The protocol adopted for the method validation followed criteria based on international guidelines. Optimizations and determination of the analyte in the samples were carried out at the wavelength 258.0330nm, at the same spectral interval of the analytical line of Tl. Slurry prepared using Triton X-100 (0.05% v/v) without the use of HNO3, is proposed as a simple and fast sample treatment. Chemical modifier KOH (1.0% m/v) was important to promote the formation and stabilization of CS molecule. Pyrolysis and Vaporization temperatures were optimized using different compounds, ammonium sulfate, l-cysteine monohydrochloride and thiourea aqueous solutions, and also certified reference material, NIST 2718, and petroleum green coke. Compromise temperature conditions were 1000°C and 2600°C, for pyrolysis and vaporization, respectively. Aqueous calibration with thiourea presented the best condition and was chosen for the determination of the analyte. The obtained concentrations of sulfur in coke samples were between 6.20mgg−1 and 9.40mgg−1. The following parameters were evaluated as validation protocol: accuracy, precision, linearity, limits of detection and quantification, sensitivity, selectivity, robustness, working range and measurement uncertainty. Weighted least square (WLS) method was employed to estimate LOD and LOQ, since it leads to lower final uncertainty. The evaluation of the validation parameters, especially the measurement uncertainty, confirmed the satisfactory performance of the method.

Determination of sulfur in bovine serum albumin and l-cysteine using high-resolution continuum source molecular absorption spectrometry of the CS molecule

In this study, the content of sulfur in bovine serum albumin and l-cysteine was determined using high-resolution continuum source molecular absorption spectrometry of the CS molecule, generated in a reducing air-acetylene flame. Flame conditions (height above the burner, measurement time) were optimized using a 3.0% (v/v) sulfuric acid solution. A microwave lab station (Ethos Plus MW) was used for the digestion of both compounds. During the digestion step, sulfur was converted to sulfate previous to the determination. Good repeatability (4–10%) and analytical recovery (91–106%) was obtained.

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.