Molecular Absorption Spectrometry Research Articles

Multi-walled carbon nanotubes/nickel hydroxide composite applied as electrochemical sensor for folic acid (vitamin B9) in food samples

Folic acid (FA) acts as an essential nutrient for body functions. Several countries have already proposed a resolution for flour fortification with iron and FA; thus, of food industry concern. Therefore, a new electroanalytical method based on a composite material of functionalized MWCNTs with nickel hydroxide (f-MWCNT-Ni(OH)2) is hereby proposed. This composite material was characterized by FT-IR, TGA, SEM and TEM techniques. An inorganic ionic silsesquioxane polymer (Si4Pic+Cl−) was used to disperse the composite and applied on the modification of a glassy carbon electrode (GCE). Linear response from 0.5–26 μmol L−1 was obtained based on FA electrochemical oxidation through differential pulse voltammetry. The LoD and LoQ values obtained were 0.095 μmol L−1 and 0.3 μmol L−1 of FA, respectively. The GCE/f-MWCNT-Ni(OH)2-Si4Pic+Cl− was applied for the quantification of FA in wheat flour, fortifier, and dietary supplement. Validation was performed through a comparison with molecular absorption spectrometry, showing the accuracy of the newly proposed method.

Present-Day Possibilities of High-Resolution Continuous-Source Electrothermal Atomic Absorption Spectrometry

The review covers modern directions of the implementation of high-resolution continuous-source electrothermal atomic absorption spectrometry (HR CS ETAAS) for quantitative analysis. Approaches to the direct analysis of solid samples of various compositions, including determination using aqueous reference solutions, analysis of suspensions and sorbates after sorption separation, use of various modifiers, and optimization of the program of heating graphite furnace are systematized. Restrictions of HR CS ETAAS in the determination of poorly volatile elements are noted, methods for increasing the rate of their atomization in a graphite furnace are described. The potentials of HR CS ETAAS for the simultaneous and consecutive monitoring of atomic lines are investigated. The difference between the simultaneous multielement determination and consecutive determination in one aliquot portion is noted. Restrictions of simultaneous multielement analysis by HR CS ETAAS in the number of elements, their thermochemical properties, and intensities of corresponding absorption lines are described. Possibilities of molecular absorption spectrometry for the determination of analytes whose atomic absorption lines are outside the continuous spectrum range of 190–900 nm are discussed. A promising approach to the determination of sulfur, phosphorus, halogens, and aluminum by absorption lines of diatomic molecules is presented.

Determination of Chemical Oxygen Demand in Water Samples Using Gas-phase Molecular Absorption Spectrometry.

Chemical oxygen demand (COD) is important for water quality assessment as it represents the level of reductive organic pollution from eutrophication in aquatic systems. For surface water quality monitoring, permanganate is usually applied as an oxidizing reagent, and the routine CODMn determination is mostly achieved by titration method. However, this titration method is tedious and time consuming, and the results suffer from environmental temperature fluctuations and complicated operation techniques. In this study, a novel CODMn determination method was developed using gas-phase molecular absorption spectrometry equipped with an online automated digestion device for the first time. The effects of digestion temperature, digestion time and sulfuric acid content were thoroughly studied. This method exhibited good linearity (0.35 to 12 mg/L), a low detection limit (0.12 mg/L), and good RSD from various water samples (0.71 - 2.37%). When used for CODMn determination in routine water quality monitoring, this automated GPMAS can considerably improve analysis speed, efficiency, accuracy and stability compared to the traditional titration method.

MAIN MINERALS AND ORGANIC COMPOUNDS IN COMMERCIAL ROASTED AND GROUND COFFEE: AN EXPLORATORY DATA ANALYSIS

Coffee is one of the most popular beverages in the world, however, little information is found regarding the mineral composition of commercial roasted and ground coffees (RG) and its correlation with organic bioactive compounds. 21 commercial Brazilian RG coffee brands - 9 traditional (T) and 12 extra strong (ES) roasted ones - were analyzed for the Cu, Ca, Mn, Mg, K, Zn, and Fe minerals, caffeine, 5-caffeoylquinic acid (5-CQA) and melanoidins contents. For minerals determination by flame atomic absorption spectrometry (FAAS), the samples were decomposed by microwave-assisted wet digestion. Caffeine and 5-CQA were determined by liquid chromatography and melanoidins by molecular absorption spectrometry. The minerals and organic compounds contents association in RG coffee was observed by a principal component analysis. The thermostable compounds (minerals and caffeine) were related to dimension 1 and 2, while 5-CQA and melanoidins were related to dimension 3, allowing for the T coffees segmentation from ES ones.

Molecular absorption and mass spectrometry for complementary analytical study of fluorinated drugs in animal organisms

Comprehensive methodology for investigation of the interaction of fluorinated drugs with animals organisms.

Introducing multi-energy ratios as an alternative to multi-energy calibration for Br determination via high-resolution continuum source graphite furnace molecular absorption spectrometry. A case study

Two different multi-signal calibration approaches are examined and their benefits for solving matrix effects for HR CS GFMAS demonstrated.

Understanding polyatomic interference in the determination of phosphorus via PO molecules using high-resolution continuum source graphite furnace molecular absorption spectrometry with direct solid analysis

Study of the occurrence of a molecular interference affecting the determination of phosphorus by the molecular absorption of PO at 213.647 nm using HR CS SS-GF MAS.

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.

Simultaneous determination of procaine hydrochloride, procainamide hydrochloride and lidocaine by molecular absorption spectrometry

Two spectrometric methods have been developed for quantitative simultaneous determination of procaine hydrochloride (PH·HCl), procainamide hydrochloride (PHA·HCl) and lidocaine (Lid) from synthetic mixture. The methods employed are first derivative spectrometry, using zero crossing method and multicomponent analysis which is based on the additivity law. Using first derivative spectrometry, the wavelength selected for the quantitative determination of PH·HCl was 237 nm for Lid was 242 nm and for PHA·HCl was 290 nm in mixture. The method is linear when the concentration ranged between 6.62-9.93 μg/mL for PH·HCl, 6.43-9.64 for PHA·HCl and 5.56-8.35 for Lid. The multicomponent analysis is a direct method and involves the absorbance measurements of at three different wavelengths. The molar absorption coefficients values were calculated at each wavelength and the concentration of PH·HCl, PHA·HCl and Lid from mixture was determined by solving matrix using Cramer's rule. The recovery of each compound in mixture was calculated and it is 101.4 % for PH·HCl, 100.4 % for PHA·HCl and 98.4 % for Lid.

Shake, shut, and go – A fast screening of sulfur in heavy crude oils by high-resolution continuum source graphite furnace molecular absorption spectrometry via GeS molecule detection

A fast and simple method for sulfur quantification in crude oils was developed by using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). For this, heavy crude oil samples were prepared as microemulsion (shake) and injected into a graphite furnace (shut). Finally, the concentration of sulfur was determined by monitoring in situ the transient molecular spectrum of GeS at wavelength 295.205 nm after adding a germanium solution as molecular forming agent (and go). Zirconium dioxide in the form of nanoparticles (45–55 nm) was employed as a permanent modifier of the graphite furnace. Calibration was done with an aqueous solution standard of ammonium sulfate, and a characteristic mass (m0) of 7.5 ng was achieved. The effectiveness of the proposed method was evaluated analizing, ten heavy crude oil samples with sulfur amounts ranging between 0.3 and 4.5% as well as two NIST standard reference materials, 1620c and 1622e. Results were compared with those obtained by routine ICP-OES analysis, and no statistical relevant differences were found.

Quaternary protoberberine alkaloids and their interactions with DNA

The G-quadruplex DNA is commonly present in several protooncogenic-DNA promoters and participates in many important biological processes such as replication, transcription, and translation. Because of their supposed role in cancer, G-quadruplex DNA is often studied as a target for anti-cancer drugs. Quaternary protoberberine and tetrahydroprotoberberine alkaloids (corysamine, coptisine, stylopine), which are supposed to selectively bind these structures, have been compared in terms of stability with selected types of DNA. Influence of selected alkaloids on the stability of double-stranded DNA and non-canonical forms of DNA was observed by determining association constants of alkaloid–DNA complexes using spectroscopic methods—molecular absorption spectrometry, fluorescence spectrometry, and mass spectrometry. Furthermore, the effect of given alkaloids on the melting temperature of these DNA structures was determined using CD spectrometry. Competitive dialysis and electrospray mass spectrometry were performed for affinity comparison of certain alkaloids to different DNA structures including G-quadruplexes. These experiments have proven that corysamine and coptisine prefer interaction with G-quadruplexes in comparison to dsDNA and ssDNA, whereas tetrahydroprotoberberine alkaloid stylopine does not interact with any DNA whatsoever.

Application of the Multicomponent Spectral Fitting Algorithm in the Estimation of the Correct Value of Phosphorus determined by ICP OES in Soil Samples

ABSTRACTPhosphorus (P) determination by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) in soil extracts is affected by copper (Cu) content and may lead to misinterpretation of the results. In this study, Multicomponent Spectral Fitting (MSF) method for the quantitative determination of P in the presence of Cu was tested. Phosphorus determination by UV/Vis molecular absorption spectrometry (COL) was free from copper interference. Phosphorus determination by ICP OES at wavelengths of 213.618 and 214.914 nm without use of MSF were subject to interference when Cu concentration was greater than 1.5 and mg L−1 and 3.5 mg L−1, respectively. When the P: Cu ratio in solution was 1:1 and 2:1, on average, there was no significant difference between the P determined by COL and by ICP-OES using MSF. In matrices containing Cu, it is indicated to use the P spectral line at 214.914 nm because it was less sensitive to Cu concentration than spectral line at 213.618 nm.

Investigation of different chemical modifiers based on the Pd/Mg mixture for the determination of sulfur in shale oil by high-resolution continuum source graphite furnace molecular absorption spectrometry

This study investigated different combinations of Pd/Mg, as chemical modifier, for sulfur determination, via CS molecule, in shale oil samples by high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). It was evaluated the mixture Pd/Mg in aqueous solution, Pd/Mg in propan-1-ol and the Pd/Mg in propan-1-ol plus Ru as a permanent modifier. The best sensitivity was achieved with Pd/Mg mixture in propan-1-ol. The high solubility of the samples in propan-1-ol promotes a better interaction with the modifier and, consequently, a more efficient thermal stability of the CS molecules. Due to the high sulfur content in the samples, the analytical line at 258.288 nm was used. Only a minimum sample preparation was required, i.e., a dilution in propan-1-ol by a factor of 1:10 (w/w). Temperatures of 800 °C and 2200 °C were the optimized conditions for pyrolysis and vaporization, respectively. The calibration curve was constructed with l-cysteine aqueous standard solutions. The characteristic mass was 27 ng; detection and quantification limits were 0.012% (w/w) and 0.039% (w/w), respectively. The accuracy of the proposed method was confirmed by the statistical agreement (Student's and Welch's t-test at 95% confidence level) using the certified reference material CRM NIST 1084a and an OTE oil sample whose sulfur content was previously determined by the standard method ASTM D4294. The method was successfully applied in three shale oil samples. The sulfur content in the investigated samples ranged from 1.0% (w/w) to 1.3% (w/w).

Phenolic and Mineral Composition of Wild Chicory Grown in Romania

The paper presents original results concerning phenolic and mineral composition of different parts of wild chicory grown in Romania (flowers, leaves, stems and roots). Total and some individual phenols concentrations were determined using molecular absorption spectrometry (modified Folin Ciocalteu method) and HPLC-DAD. Metals concentrations were measured by FAAS. The highest total phenolic compounds concentration was founded in flowers (1531.2 mg GAE/100g d.w.), followed by leaves (1180.3 mg GAE/100g d.w.), roots (167.86 mg GAE/100g d.w.) and stems (142.36 mg GAE/100g d.w.). HPLC-DAD analysis revealed the presence of seven phenolic acids in the range of 30-50% from total phenols concentration. The main determined phenolic compounds are: in flowers methyl gallic acid (301.55 mg/100g d.w.) in leaves, roots and stems ellagic acid (389.68 mg/100g d.w., 67.93 mg/100g d.w. respectively 22.97 mg/100g d.w.). Metals analyses by FAAS indicate that Cd, Cr, K, Ni and Pb are in concentrations under the detection limits. Except iron and sodium, all others metals are in higher concentration in leaves. Rank for the metal concentration from chicory was Ca]Mg]Zn]Na]Cu]Fe]Mn.

Validation of a Quantitative Analysis Method for Collagen Extracted from Grey Mullet Marine Fish

The Black Sea offers numerous harnessing possibilities for the medical and pharmaceutical, agricultural, food industry and cosmetic fields. Collagen extraction from the Black Sea fish is a research area of great interest. The purpose of this paper is to optimize the collagen quantitative analysis method based on hydroxyproline reagent through visible molecular absorption spectrometry. The adapted method was validated, achieving the following performance criteria: linearity, detection and quantification limits, accuracy/fidelity, stability/sturdiness, repeatability, and measurement uncertainty. The validated method was applied for the quantitative determination of collagen content in Grey Mullet fish and for the evaluation of collagen extraction output.

Evaluation of Antioxidant Capacities and Phenols Composition of Wild and Cultivated Berries

The study presents original results concerning analytical characterization of alcoholic extracts of four wild berries (blueberries, blackberries, red currants and raspberries) and two cultivated berries (black cherries and strawberries). Total and some individual phenols concentrations were determined using molecular absorption spectrometry (modified Folin Ciocalteu method) and HPLC-DAD technique. The measurement of lipid-soluble antioxidant capacity (ACL) was done by photochemiluminescence method using trolox as standard.The highest total phenolic content was registered in blueberries (543.5 mg/100g f.w.), while the lowest was found in raspberries (344.5 mg/100g f.w.).HPLC � DAD analysis indicated the presence of six individual polyphenolic compounds in different concentrations: gallic acid (62.664 - 178.821 mg/100 g f.w); chlorogenic acid (30.152 - 243.923 mg/100g f.w.); 3-O-methyl-gallic acid (2.035 - 4.907 mg/100 g f.w.); caffeic acid (0.401 - 5.664 mg/100 g f.w.); p-coumaric acid (4.252 - 10.806 mg/100 g f.w.) and cinnamic acid (0.665-0.958 mg/100 g f.w.). ACL results showed values between 54.00 and 1152 �mols trolox/100 g f.w.

Screening method for extractable organically bound fluorine (EOF) in river water samples by means of high-resolution-continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS).

The introduction of fluorine into organic molecules leads to new chemical/physical properties. Especially in the field of pharmaceutical as well as technical applications, fluorinated organic substances gain in importance. The OECD identified and categorized 4730 per- and polyfluoroalkyl substances-related CAS numbers. Thus, an increasing release of fluorinated compounds into the environment is expected. In particular, perfluorinated compounds often show higher environmental stability leading to the risk of bioaccumulation. Polyfluorinated compounds undergo decomposition; thus, further possible fluorine species occur, which may exhibit different toxic/chemical properties. However, current target methods based on, e.g., HPLC/MS-MS, are not applicable for a comprehensive screening of fluorinated substances as well as assessment of pollution. Thus, within this work, a sum parameter method for quantitative determination of extractable organically bound fluorine (EOF) in surface waters was developed. The method is based on solid-phase extraction (SPE) for extraction of fluorinated compounds as well as separation of interfering inorganic fluoride in combination with high-resolution-continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) for organic fluorine quantification. Upon optimization of the SPE procedure (maximum concentration of extractable organic fluorine), enrichment factors of about 1000 were achieved, allowing for highly sensitive fluorine detection. HR-CS GF MAS allows for selective fluorine detection upon in situ formation of a diatomic molecule ("GaF"). Next to a species-unspecific response, limits of detection in the low nanogram per liter range (upon enrichment) were achieved. Upon successful method development, surface water samples (rivers Moselle and Rhine) were analyzed. Furthermore, a sampling campaign along the river Rhine (from the south-close to the French border; to the north-close to The Netherlands border) was conducted. EOF values in the range of about 50-300ng/L were detected. The developed method allows for a fast and sensitive as well as selective/screening detection of organically bound fluorine (EOF) in surface water samples, helping to elucidate pollution hotspots as well as discharge routes. Graphical abstract A solid phase extraction (SPE) HR-CS GF MAS screening method was developed for the quantitative analysis/screening of extractable organically bound fluorine (EOF) in river water samples. Highly sensitive EOF analysis (low ppq range) was obtained upon SPE and HR-CS GF MAS analysis. Sampling campaign along the river Rhine was conducted.

A Novel Electrochemical Sensor Based on Silsesquioxane/Nickel (II) Phthalocyanine for the Determination of Sulfanilamide in Clinical and Drug Samples

AbstractThis paper describes the immobilization of nickel (II) phthalocyanine‐tetrasulfonic acid tetrasodium salt (NiTsPc) in 3‐n‐propyl(3‐methylpyridinium) silsesquioxane chloride (Si3Pic+Cl−). This hybrid material was synthetized and characterized by 29Si NMR CP‐MAS, FTIR and DRS. The modified material, designated as Si3Pic+Cl−/NiTsPc, was used to build carbon paste electrodes to determine sulfanilamide (SFL) by differential pulse voltammetry. The modified electrode showed a higher current response when compared to the bare carbon paste electrode. The evaluation of SFL was possible in the presence of salicylic acid, commonly used in solid ointment compositions in a high concentration. Theoretical calculations using density functional theory were done aiming to shed light at dimerization process at SFL. The oxidation peak increased with increasing concentrations of SFL in the range of 35–301 μmol L−1. The LOD and LOQ values obtained were 12 and 35 μmol L−1 of SFL, respectively. The novel electrochemical sensor was successfully applied for the determination of SFL in pet drug samples, urine and serum through the standard addition method. Validation was performed through a comparison with values obtained by the molecular absorption spectrometry method and there were no significant differences in the results, as confirmed by the statistical paired t‐test. This demonstrates the promise of a new approach for analytical application in clinical and drug samples of sulfonamide compounds.

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.

Feasibility of pyrohydrolysis as a clean method for further fluorine determination by ISE and IC in high purity nuclear grade alumina

In this work, a method based on pyrohydrolysis of high purity nuclear grade alumina and subsequent F determination by ion chromatography (IC) and ion selective electrode (ISE) was developed. After pyrohydrolysis, F was absorbed in a suitable solution (50 mmol L−1 (NH4)2CO3, 50 mmol L−1 NH4OH, and also water were evaluated). Using the selected conditions, it was possible to digest a high sample mass (500 mg) in only 10 min. The following analytical parameters were evaluated: pyrohydrolysis temperature (550 to 1050 °C), time of reaction (2.5 to 20 min), air flow-rate (0.1 to 0.4 L min−1), water flow-rate (0.1 to 1.0 mL min−1), and the use of V2O5 (200 mg), as an auxiliary reagent. Quantitative F recoveries were obtained using air and water flow-rates pumped through the reactor at 0.2 L min-1 and 0.5 mL min−1, respectively. Only water was required as absorbing solution and the use of V2O5, generally recommended for inorganic matrices, was not necessary. Detection limits of 2.0 and 3.6 μg g−1 using IC and ISE, respectively, were obtained. Accuracy was evaluated by recovery tests and also by comparison with the results obtained by high resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). Suitable recoveries for F were obtained (95%) and no statistical difference (95% of confidence level) was observed for the results obtained by HR-CS GF MAS. Pyrohydrolysis allowed the F volatilization in a relatively short time avoiding the use of concentrated reagents and making possible further determination by both analytical techniques (IC or ISE). The pyrohydrolysis method was considered suitable for further F determination, avoiding excessive dilution of digests or matrix matching approaches, making this method a suitable option for routine F determination in nuclear grade alumina samples.