Direct Analysis Of Solid Samples Research Articles

Marine sediments monitoring studies for trace elements with the application of fast temperature programs and solid sampling high resolution continuum source atomic absorption spectrometry

Analytical procedure for the determination of As, Cd, Cu, Ni, Co and Cr in marine sediment samples using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS AAS) and direct solid sample analysis has been developed. The application of fast programs in combination with direct solid sampling allows to eliminate the drying and pretreatment steps, however makes impossible the use of liquid standards for calibration. Iridium treated platforms were applied throughout the present study. Calibration technique based on the use of solid certified reference materials (marine sediments) similar to the nature of the analyzed sample and statistics of regression analysis were applied to the real sediment samples. The instrumental parameters were optimized in order to obtain reproducible and interference free analytical signals. The ISO-17025 requirements and Eurachem guidelines were followed in the validation of the proposed analytical procedure. Accordingly, blanks, selectivity, calibration, linearity, working range, trueness, repeatability reproducibility, limits of detection and quantification and expanded uncertainty (k=2) for all investigated elements were assessed. Two different approaches for the estimation of measurement uncertainty were applied and obtained results compared. The major contributors to the combined uncertainty of the analyte mass fraction were found to be the homogeneity of the samples and the microbalance precision. The influence of sample particle sizes on the total combined uncertainty was also evaluated.Traceability to SI system of units of the obtained by the proposed analytical procedure results was demonstrated.Additionally, validation of the methodology developed was effectuated by the comparison of the obtained results with independent method e.g. ICP-MS with external calibration. The use of solid sampling HR CS AAS for the determination of trace elements in marine sediment matrix gives significant advantages, such as straightforward calibration, a high sample throughput, sufficient precision, suitable limits of detection, appropriate for monitoring studies concentration range and reduced risk of analyte loss and contamination. This approach allows comparatively simple and reliable evaluation of uncertainty of the results and the basic validation parameters and in a natural way provides traceability of the obtained results. A comparison between the proposed fast programs with solid standard calibration and the conventional ones with liquid standard calibration demonstrates advantages of the new methodology. It provides faster, accurate and unbiased results typically with significantly lower uncertainties.The potential of the HR CS AAS technique is demonstrated by direct analysis of marine sediments form the Caribbean region and various sediment CRMs within the frame of monitoring program for this region.

Method development for the determination of chromium and thallium in fertilizer samples using graphite furnace atomic absorption spectrometry and direct solid sample analysis

A method has been developed for the determination of chromium and thallium in fertilizer samples using line source graphite furnace atomic absorption spectrometry (LS-GF AAS) with Zeeman-effect background correction and direct solid sample analysis. The results obtained with this equipment were compared with those obtained with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) to verify the absence of spectral interferences. For chromium, it was necessary to employ magnesium as a chemical modifier, and the optimum pyrolysis and atomization temperatures were 1600°C and 2500°C, respectively. For thallium, these temperatures were 900°C and 1700°C, and the determinations were made without a modifier. For chromium, the limit of detection (LoD) for LS-GF AAS and HR-CS GF AAS were 150ngg−1 and 60ngg−1, respectively. For thallium the LoD were 15ngg−1 for LS-GF AAS and 3ngg−1 using HR-CS GF AAS. The accuracy of the methods was verified using the certified reference materials NIST SRM 695 and NIST SRM 2704. The results obtained with the two spectrometers showed no significant difference at the 95% level of confidence. Using HR-CS GF AAS, it was possible to confirm the absence of spectral interferences in the determination of both elements in the investigated fertilizers.

An LA-ICP-MS trace element classification of ochres in the Weld Range environ, Mid West region, Western Australia

Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) is successfully used to distinguish ochre from two nationally heritage listed Aboriginal ochre mines in the Mid West region of Western Australia: Wilgie Mia and Little Wilgie. The same technique is then used to test whether either ochre mine is the likely source of ochre used at archaeological sites in the local landscape. The archaeological samples were retrieved from rock-art and the surface of artefacts in excavated and surface contexts. LA-ICP-MS offers advantages over other techniques for the geochemical characterisation of ochre including direct analysis of solid sample, reduced laboratory preparation and breadth of trace element isotopes analysed. This work highlights the potential for trace elemental analyses and profiling to develop an understanding of the past cultural significance of ochre, from sources which are also important mythological sites.

Determination of total mercury for marine environmental monitoring studies by solid sampling continuum source high resolution atomic absorption spectrometry

The most critical step in almost all commonly used analytical procedures for Hg determination is the sample preparation due to its extreme volatility. One of the possible solutions of this problem is the application of methods for direct analysis of solid samples. The possibilities for solid sampling high resolution continuum source atomic absorption spectrometry (HR CS AAS) determination of total mercury in various marine environmental samples e.g. sediments and biota are object of the present study. The instrumental parameters were optimized in order to obtain reproducible and interference free analytical signal. A calibration technique based on the use of solid standard certified reference materials similar to the nature of the analyzed sample was developed and applied to various CRMs and real samples. This technique allows simple and reliable evaluation of the uncertainty of the result and the metrological characteristics of the method. A validation approach in line with the requirements of ISO 17025 standard and Eurachem guidelines was followed. With this in mind, selectivity, working range (0.06 to 25ng for biota and 0.025 to 4ng for sediment samples, expressed as total Hg) linearity (confirmed by Student's t-test), bias (1.6–4.3%), repeatability (4–9%), reproducibility (9–11%), and absolute limit of detection (0.025ng for sediment, 0.096ng for marine biota) were systematically assessed using solid CRMs. The relative expanded uncertainty was estimated at 15% for sediment sample and 8.5% for marine biota sample (k=2). Demonstration of traceability of measurement results is also presented. The potential of the proposed analytical procedure, based on solid sampling HR CS AAS technique was demonstrated by direct analysis of sea sediments form the Caribbean region and various CRMs.Overall, the use of solid sampling HR CS AAS permits obtaining significant advantages for the determination of this complex analyte in marine samples, such as straightforward calibration, a high sample throughput (15min per sample), sufficient precision, a suitable limit of detection, and reduced risk of analyte loss and contamination.

Direct solid sample analysis with graphite furnace atomic absorption spectrometry—A fast and reliable screening procedure for the determination of inorganic arsenic in fish and seafood

Direct solid sample analysis with graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated initially with the intention of developing a method for the determination of total As in fish and other seafood. A mixture of 0.1% Pd+0.06% Mg+0.06% Triton X-100 was used as the chemical modifier, added in solution over the solid samples, making possible the use of pyrolysis and atomization temperatures of 1200°C and 2400°C, respectively. The sample mass had to be limited to 0.25mg, as the integrated absorbance did not increase further with increasing sample mass. Nevertheless, the recovery of As from several certified reference materials was of the order of 50% lower than the certified value. Strong molecular absorption due to the phosphorus monoxide molecule (PO) was observed with high-resolution continuum source AAS (HR CS AAS), which, however, did not cause any spectral interference. A microwave-assisted digestion with HNO3/H2O2 was also investigated to solve the problem; however, the results obtained for several certified reference materials were statistically not different from those found with direct SS-GF AAS. Accurate values were obtained using inductively coupled plasma mass spectrometry (ICP-MS) to analyze the digested samples, which suggested that organic As compounds are responsible for the low recoveries. HPLC–ICP-MS was used to determine the arsenobetaine (AB) concentration. Accurate results that were not different from the certified values were obtained when the AB concentration was added to the As concentration found by SS-GF AAS for most certified reference materials (CRM) and samples, suggesting that SS-GF AAS could be used as a fast screening procedure for inorganic As determination in fish and seafood.

Fluorine determination in coal using high-resolution graphite furnace molecular absorption spectrometry and direct solid sample analysis

The absorption of the calcium mono-fluoride (CaF) molecule has been employed in this study for the determination of fluorine in coal using direct solid sample analysis and high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). The rotational line at 606.440nm was used for measuring the molecular absorption in the gas phase. The pyrolysis and vaporization temperatures were 700°C and 2100°C, respectively. Different chemical modifiers have been studied, such as Pd and Ir as permanent modifiers, and Pd and the mixed Pd/Mg modifier in solution. The limit of detection and the characteristic mass were 0.3 and 0.1ng F, respectively. One certified reference material (CRM) of coal (NIST 1635) and four CRMs with a non-certified value for F (SARM 18, SARM 20, BCR 40, BCR 180) were used to evaluate the accuracy and precision of the method, obtaining good agreement (104%) with the certified value and with the informed values (ranging from 90 to 103%).

Application of direct solid sample analysis for the determination of chlorine in biological materials using electrothermal vaporization inductively coupled plasma mass spectrometry

This work describes a methodology developed to carry out Cl determination in biological materials using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis. The solid samples were directly weighed into graphite ‘cups’ and inserted into the graphite furnace. The RF power and the carrier gas flow rate were optimized at 1300W and 0.7Lmin−1, respectively. Calibration could be carried out using aqueous standard solutions with pre-dried modifiers (Pd+Nd or Pd+Ca) or using solid certified reference materials with the same pre-dried modifiers or without the use of modifiers. The limit of quantification was determined as 5μgg−1 under optimized conditions and the Cl concentration was determined in five certified reference materials with certified concentrations for Cl, in addition to three certified reference materials, for which certified values for Cl were unavailable; in the latter case, the results were compared with those obtained using high-resolution continuum source molecular absorption spectrometry. Good agreement at a 95% statistical confidence level was achieved between determined and certified or reference values.

Determination of palladium, platinum and rhodium in used automobile catalysts and active pharmaceutical ingredients using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

This work investigates the potential of high-resolution continuum source graphite furnace atomic absorption spectrometry for the direct determination of Pd, Pt and Rh in two samples of very different nature. While analysis of active pharmaceutical ingredients is straightforward and it is feasible to minimize matrix effects, to the point that calibration can be carried out against aqueous standard solutions, the analysis of used automobile catalysts is more challenging requiring the addition of a chemical modifier (NH4F·HF) to help in releasing the analytes, a more vigorous temperature program and the use of a solid standard (CRM ERM®-EB504) for calibration. However, in both cases it was possible to obtain accurate results and precision values typically better than 10% RSD in a fast and simple way, while only two determinations are needed for the three analytes, since Pt and Rh can be simultaneously monitored in both types of samples.Overall, the methods proposed seem suited for the determination of these analytes in such types of samples, offering a greener and faster alternative that circumvents the traditional problems associated with sample digestion, requiring a small amount of sample only (0.05mg per replicate for catalysts, and a few milligrams for the pharmaceuticals) and providing sufficient sensitivity to easily comply with regulations. The LODs achieved were 6.5μgg−1 (Pd), 8.3μgg−1 (Pt) and 9.3μgg−1 (Rh) for catalysts, which decreased to 0.08μgg−1 (Pd), 0.15μgg−1 (Pt) and 0.10μgg−1 (Rh) for pharmaceuticals.

Strontium mono-chloride — A new molecule for the determination of chlorine using high-resolution graphite furnace molecular absorption spectrometry and direct solid sample analysis

A new method has been developed for the determination of chlorine in biological reference materials using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) of the strontium mono-chloride (SrCl) molecule and direct solid sample analysis. The use of the SrCl molecule for high-temperature MAS was not described up to now in the literature. Preliminary time-dependent density functional theory calculations of the SrCl structure were carried out in order to obtain reasonable estimates of the absorption spectrum of the target molecule. The calculations, which were carried out at BHandHLyp/def2-QZVP level of theory, proved a very accurate and inexpensive way to get information about the spectrum of the SrCl molecule, which enabled us to perform the Cl determination with good sensitivity and specificity. The molecular absorption of the SrCl molecule has been measured using the wavelength at 635.862nm, and zirconium and palladium have been evaluated as the chemical modifiers in order to increase the sensitivity of the gaseous SrCl molecule generated in the graphite furnace. The pyrolysis and vaporization temperatures were 600°C and 2300°C, respectively. Accuracy and precision of the method have been evaluated using biological certified reference materials of both animal and plant origins, showing good agreement with the informed and certified values. Limit of detection and characteristic mass were 1.0 and 2.2ng, respectively. The results found using HR-CS GF MAS were in agreement (95% confidence level) compared to those obtained by electrothermal vaporization-inductively coupled plasma mass spectrometry.

Simultaneous determination of bromine and chlorine in coal using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis

A new method for the direct analysis of coal using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis was developed, aiming at the determination of Br and Cl. The procedure does not require any significant sample pretreatment and allows simultaneous determination of both elements to be carried out, requiring small mass aliquots of sample (about 0.5mg). All operating parameters, including carrier gas flow-rate and RF power, were optimized for maximum sensitivity. The use of modifiers/aerosol carriers (Pd, Pd+Al and Pd+Ca) was evaluated, and the mixture of Pd and Ca was chosen, allowing pyrolysis and vaporization temperatures of 700°C and 1900°C, respectively. Chlorine was accurately determined using calibration against solid standards, whereas Br could also be determined using calibration against aqueous standard solutions. The limits of quantification were 0.03μgg−1 for Br and 7μgg−1 for Cl, and no spectral interferences were observed.

Plasma-based ambient desorption/ionization mass spectrometry: state-of-the-art in qualitative and quantitative analysis.

Ambient desorption/ionization mass spectrometry (ADI-MS) aims to enable direct analysis of gaseous, liquid, and/or solid samples under ambient conditions. In ADI-MS, different types of desorption/ionization sources are classified according to their basic method of operation, namely spray-based, laser-based, or plasma-based. This review discusses many of the plasma-based techniques coupled to mass spectrometry in terms of their current performance in fast qualitative screening and quantitative analysis. Critical aspects, for example sample preparation and introduction, quantification, and matrix effects, are addressed. Furthermore, the applicability of plasma-based sources to portable mass spectrometers and their capabilities in imaging experiments are summarized. The applications discussed are of two types. In one, direct screening is performed without any or with minimal sample pretreatment. Samples with low matrix content are qualitatively analyzed without interferences. The other, more challenging applications, namely samples with high matrix content and most quantitative analysis, typically require sample preparation ranging from simple dilution to extensive multi-step procedures.

Fundamental properties of a touchable high-power pulsed microplasma jet and its application as a desorption/ionization source for ambient mass spectrometry.

Plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) has attracted considerable attention in many fields because of its capacity for direct sample analyses. In this study, a high-power pulsed microplasma jet (HPPMJ) was developed and investigated as a new plasma desorption/ionization source. In an HPPMJ, a microhollow cathode discharge is generated in a small hole (500 µm in diameter) using a pulsed high-power supply. This system can realize a maximum power density of 5 × 10(8) W/cm(3). The measured electron number density, excitation temperature and afterglow gas temperature of the HPPMJ were 3.7 × 10(15) cm(-3), 7000 K at maximum and less than 60 °C, respectively, which demonstrate that the HPPMJ is a high-energy, high-density plasma source that is comparable with an argon inductively coupled plasma while maintaining a low gas temperature. The HPPMJ causes no observable damage to the target because of its low gas temperature and electrode configuration; thus, we can apply it directly to human skin. To demonstrate the analytical capacity of ADI-MS using an HPPMJ, the plasma was applied to direct solid sample analysis of the active ingredients in pharmaceutical tablets. Caffeine, acetaminophen, ethenzamide, isopropylantipyrine and ibuprofen were successfully detected. Application to living tissue was also demonstrated, and isopropylantipyrine on a finger was successfully analyzed without damaging the skin. The limits of detection (LODs) for caffeine, isopropylantipyrine and ethenzamide were calculated, and LODs at the picogram level were achieved. These results indicate the applicability of the HPPMJ for high-sensitivity analysis of materials on a heat-sensitive surface.

Method development for the determination of bromine in coal using high-resolution continuum source graphite furnace molecular absorption spectrometry and direct solid sample analysis

This work reports a simple approach for Br determination in coal using direct solid sample analysis in a graphite tube furnace and high-resolution continuum source molecular absorption spectrometry. The molecular absorbance of the calcium mono-bromide (CaBr) molecule has been measured using the rotational line at 625.315nm. Different chemical modifiers (zirconium, ruthenium, palladium and a mixture of palladium and magnesium nitrates) have been evaluated in order to increase the sensitivity of the CaBr absorption, and Zr showed the best overall performance. The pyrolysis and vaporization temperatures were 800°C and 2200°C, respectively. Accuracy and precision of the method have been evaluated using certified coal reference materials (BCR 181, BCR 182, NIST 1630a, and NIST 1632b) with good agreement (between 98 and 103%) with the informed values for Br. The detection limit was around 4ng Br, which corresponds to about 1.5μgg−1 Br in coal, based on a sample mass of 3mg. In addition, the results were in agreement with those obtained using electrothermal vaporization inductively coupled plasma mass spectrometry, based on a Student t-test at a 95% confidence level. A mechanism for the formation of the CaBr molecule is proposed, which might be considered for other diatomic molecules as well.

High-resolution continuum source graphite furnace atomic absorption spectrometry for direct analysis of solid samples and complex materials: a tutorial review

This work tries to provide guidance for the development of new methods aiming at the direct analysis of solid samples or complex liquid materials using HR CS GFAAS.

Determination of selenium in soil samples using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

Least squares background correction (LSBC) for spectral interference of the NO and PO molecules in the determination of Se.

Direct analysis of herbal powders by pipette-tip electrospray ionization mass spectrometry

Conventional electrospray ionization mass spectrometry (ESI-MS) is widely used for analysis of solution samples. The development of solid-substrate ESI-MS allows direct ionization analysis of bulky solid samples. In this study, we developed pipette-tip ESI-MS, a technique that combines pipette tips with syringe and syringe pump, for direct analysis of herbal powders, another common form of samples. We demonstrated that various herbal powder samples, including herbal medicines and food samples, could be readily online extracted and analyzed using this technique. Various powder samples, such as Rhizoma coptidis, lotus plumule, great burdock achene, black pepper, Panax ginseng, roasted coffee beans, Fructus Schisandrae Chinensis and Fructus Schisandrae Sphenantherae, were analyzed using pipette-tip ESI-MS and quality mass spectra with stable and durable signals could be obtained. Both positive and negative ion modes were attempted and various compounds including amino acids, oligosaccharides, glycosides, alkaloids, organic acids, ginosensides, flavonoids and lignans could be detected. Principal component analysis (PCA) based on the acquired mass spectra allowed rapid differentiation of closely related herbal species.

Determinations of Sb and Mo in Cairo's dust using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

The present work describes the determination of Sb and Mo in dust deposited on tree leaves using direct solid sample analysis. Nineteen air particulate samples were collected from different districts of Cairo and surrounding cities. Since some samples have been taken from places less exposed to the pollution factors, the present study allows the comparison of air quality between high and low polluted areas. High-resolution continuum source graphite furnace atomic absorption spectrometry has been investigated, using direct solid sample analysis. The optimum pyrolysis and atomization temperatures for Sb were found to be 800 °C and 1900 °C, and 1200 °C and 2650 °C, respectively for Mo. The limits of detection and quantification for both, Sb and Mo, were 15 μg g−1 and 50 ng g−1, respectively. The characteristic mass at was found to be m0 = 38 pg for Sb (217.582 nm) and m0 = 28 pg for Mo (313.259 nm). The results obtained for three certified reference materials of urban particulate matter confirmed the validity of the investigated method. The content of Sb varied between 213 ± 1.3 μg g−1 and 1117 ± 230 μg g−1 with an average of 667 ± 339 μg g−1. On the other hand, the Mo content varied from 113 ± 2.3 μg g−1 to 361 ± 51 μg g−1 and its average value equals 190 ± 62 μg g−1.

Determination of the total mercury in contaminated soils by direct solid sampling atomic absorption spectrometry using an AMA-254 device and radiochemical neutron activation analysis

High total mercury (T-Hg) contents in soils, up to 25mgkg−1, were determined by two independent methods: a one-purpose atomic absorption spectrometer AMA-254 (Advanced Mercury Analyser) with direct solid sampling and radiochemical neutron activation analysis (RNAA), using sample masses of 10mg to 25mg and about 150mg, respectively. An excellent agreement between results of both methods was obtained. For quality control (QC) purposes, NIST SRM 2711 Montana Soil and NIST SRM 2711a were analyzed by both methods using the above sample masses. The results obtained compared with the NIST certified values within the uncertainty margins, thus proving the accuracy of the procedures employed. A new mercury value of 1.42mgkg−1±0.12mgkg−1 was determined in NIST SRM 1648a Urban Particulate Matter by RNAA. For achieving accurate results by the AMA-254 spectrometer, optimizing of the analytical procedure was necessary, consisting of analyzing small (10mg to 25mg) sample masses. It has been found that the cryogenic grinding used provided sufficiently representative and homogeneous samples. In view of the decomposition procedures employed in AMA-254 and RNAA procedures, it can be inferred that the mercury contained in QC samples was presumably bound in an organic fraction. A test in which HgS was analyzed by RNAA showed that even mercury present in sulfide form would be fully recovered using the procedures employed.

Application of tandem calibration for the direct analysis of copper by inductively coupled plasma atomic emission spectrometry (ICP-AES)

A procedure has been proposed for the direct ICP-AES analysis of solid copper samples using spark sampling. Calibration curves have been obtained using multi-element reference solutions of analytes (MES). The internal standards are spectral lines of copper with the energy parameters (excitation and ionization potentials) similar to those of analytes. Standard Reference Material (SRM) of copper have been used for the estimation of performance characteristics. The absence of significant differences between the found and certified concentrations of analytes has been shown. The developed procedure of ICP-AES analysis of solid copper samples with spark sampling and calibration using MES provides the determination of up to 14 elements: Ag, As, Au, Cd, Fe, Mn, Ni, P, Pb, Pt, Sb, Se, Sn, Te, and Zn in the concentration range from n × 10−3 to n × 10−1 wt %.

Sequential determination of Cd and Cr in biomass samples and their ashes using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

High-resolution continuum source graphite furnace atomic absorption spectrometry, because of the use of only one radiation source for all elements, offers the possibility of sequential determination of two or more elements from the same sample aliquot if their volatilities are significantly different. Cd and Cr were determined sequentially in samples of biomass and biomass ashes employing direct solid sample analysis. The use of a chemical modifier was found to be not necessary, and calibration could be carried out using aqueous standard solutions. A pyrolysis temperature of 400°C and an atomization temperature of 1500°C were used for the determination of Cd; no losses of Cr were observed at this temperature. After the atomization of Cd the wavelength was changed and Cr atomized at 2600°C. The limits of detection (LOD) and quantification (LOQ) were 1.1μgkg−1 and 3.7μgkg−1, respectively, for Cd and 21μgkg−1 and 70μgkg−1, respectively, for Cr using the most sensitive line at 357.869nm, or 90μgkg−1 and 300μgkg−1, respectively, using the less sensitive line at 428.972nm. The precision, expressed as relative standard deviation was around 10%, which is typical for direct solid sample analysis. The values found for Cd in biomass samples were between <1.1µgkg−1 and 789µgkg−1, whereas those for Cr were between 7.9mgkg−1 and 89mgkg−1; the values found in the ashes were significantly lower for Cd, between <1.1µgkg−1 and 6.3µgkg−1, whereas the trend was not so clear for Cr, where the values were between 3.4mgkg−1 and 28mgkg−1.