Morgana B. Dessuy

Method development for the determination of lead in wine using electrothermal atomic absorption spectrometry comparing platform and filter furnace atomizers and different chemical modifiers

A method has been developed for the determination of lead in wine by electrothermal atomic absorption spectrometry without any sample preparation and calibration against aqueous standards, using 7.5 microg Pd as a chemical modifier. The results obtained for seven wines using the proposed method and an acid digestion procedure did not show any significant difference using a Students t-test. Atomization in a transversally heated filter atomizer (THFA) was compared with atomization in a conventional transversally heated platform furnace. The former provided a 2.6-fold higher sensitivity, improving the characteristic mass from 34 to 12 pg and a 1.6-fold better limit of detection (0.3 microg L(-1) compared to 0.5 microg L(-1)) for aqueous solutions using the same injection volume of 20 microL. However, the average precision, expressed as the relative standard deviation for the determination of lead in wine under routine conditions was improved from 4.6% with platform atomization to 0.6% in the THFA. The lead content found in seven arbitrarily chosen white and red wines, five from Brazil, one from Chile and one from Spain, ranged from 6 to 60 microg L(-1) Pb with an average content of 11.4 microg L(-1) Pb for the wines from South America.

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 1.1 μg kg(-1) and 3.7 μg kg(-1), respectively, for Cd and 21 μg kg(-1) and 70 μg kg(-1), respectively, for Cr using the most sensitive line at 357.869 nm, or 90 μg kg(-1) and 300 μg kg(-1), respectively, using the less sensitive line at 428.972 nm. 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 <1.1 µg kg(-1) and 789 µg kg(-1), whereas those for Cr were between 7.9 mg kg(-1) and 89 mg kg(-1); the values found in the ashes were significantly lower for Cd, between <1.1 µg kg(-1) and 6.3 µg kg(-1), whereas the trend was not so clear for Cr, where the values were between 3.4 mg kg(-1) and 28 mg kg(-1).

Detection of the origin of Brazilian wines based on the determination of only four elements using high-resolution continuum source flame AAS.

A method has been developed to determine 10 elements in Brazilian red wines using high-resolution continuum source flame atomic absorption spectrometry, a technique that allows the fast sequential determination of an essentially unlimited number of elements per sample, each one under previously optimized conditions. All measurements were made without sample preparation, using aqueous standard solutions for calibration. The results were in agreement within 99% of confidence (t-test) with those obtained by inductively coupled plasma optical emission spectrometry. The same grape, Cabernet sauvignon, was used in all experiments, and the wines from each region were prepared especially for this investigation in order to avoid any confusion due to grapes from other regions, which are often used in commercial wines. The elements K, Mn, Rb and Sr were found to be the best indicators for the origin of the wines, based on a Principal Component Analysis.

A flow-batch analyzer with piston propulsion applied to automatic preparation of calibration solutions for Mn determination in mineral waters by ET AAS

The increasing development of miniaturized flow systems and the continuous monitoring of chemical processes require dramatically simplified and cheap flow schemes and instrumentation with large potential for miniaturization and consequent portability. For these purposes, the development of systems based on flow and batch technologies may be a good alternative. Flow-batch analyzers (FBA) have been successfully applied to implement analytical procedures, such as: titrations, sample pre-treatment, analyte addition and screening analysis. In spite of its favourable characteristics, the previously proposed FBA uses peristaltic pumps to propel the fluids and this kind of propulsion presents high cost and large dimension, making unfeasible its miniaturization and portability. To overcome these drawbacks, a low cost, robust, compact and non-propelled by peristaltic pump FBA is proposed. It makes use of a lab-made piston coupled to a mixing chamber and a step motor controlled by a microcomputer. The piston-propelled FBA (PFBA) was applied for automatic preparation of calibration solutions for manganese determination in mineral waters by electrothermal atomic-absorption spectrometry (ET AAS). Comparing the results obtained with two sets of calibration curves (five by manual and five by PFBA preparations), no significant statistical differences at a 95% confidence level were observed by applying the paired t-test. The standard deviation of manual and PFBA procedures were always smaller than 0.2 and 0.1mugL(-1), respectively. By using PFBA it was possible to prepare about 80 calibration solutions per hour.

Determination of lead in biomass and products of the pyrolysis process by direct solid or liquid sample analysis using HR-CS GF AAS

A method has been developed for the determination of lead in biomass, bio-oil, pyrolysis aqueous phase, and biomass ashes by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) and direct solid or liquid sample analysis. All measurements were performed without chemical modifier and calibration could be carried out using aqueous standard solutions. A pyrolysis temperature of 800°C and an atomization temperature of 2200°C were applied. The limits of detection and quantification were, respectively, 0.5 µg kg(-1) and 2 µg kg(-1) using the analytical line at 217.001 nm and 6 µg kg(-1) and 19 µg kg(-1) at 283.306 nm. The precision, expressed as relative standard deviation, was between 3% and 10%, which is suitable for direct analysis. The lead concentrations found for the solid samples varied between 0.28 and 1.4 mg kg(-1) for biomass and between 0.25 and 2.3 mg kg(-1) for ashes, these values were much higher than those found for bio-oil (2.2-16.8 µg kg(-1)) and pyrolysis aqueous phase (3.2-18.5 µg kg(-1)). After the determination of lead in the samples, it was possible to estimate the relative distribution of this element in the fractions of the pyrolysis products, and it was observed that most of the lead present in the biomass was eliminated to the environment during the pyrolysis process, with a significant portion retained in the ashes.

Sequential and simultaneous determination of four elements in soil samples using high-resolution continuum source graphite furnace atomic and molecular absorption spectrometry

An analytical method has been developed for the sequential and simultaneous determination of Cd, Cr, Fe and Al (via the AlH molecule) in soil samples using high-resolution continuum source graphite furnace atomic and molecular absorption spectrometry and direct solid sample analysis. First, Cd (228.802 nm) was determined using 800 °C and 1700 °C as the pyrolysis and atomization temperatures, respectively. Subsequently, after changing the wavelength, Cr (425.433 nm), Fe (425.076 nm) and Al (425.315 nm) were determined simultaneously from the same sample aliquot using 2600 °C as the atomization (Cr and Fe) or vaporization (AlH) temperature. Al determination was carried out using the diatomic molecule AlH without adding a molecule-forming reagent. The interference caused by Al in Cd determination was minimized by using 10 μL of a 10% v/v H2SO4 solution in all measurements. Aqueous standard solutions were used for calibration and the limits of detection and quantification obtained were 7.3 and 24 pg mg−1 for Cd, 0.13 and 0.45 ng mg−1 for Cr, 0.07 and 0.23 μg mg−1 for Fe and 0.42 and 1.4 μg mg−1 for Al, respectively. The concentration values for Cd, Cr, Fe and Al obtained from the soil certified reference material (CRM) Montana Soil I (NIST SRM 2710a) analysis were in agreement with the reported ones. The precision of the measurements, expressed as the relative standard deviation, was better than 10%. Six soil samples from a vineyard field were investigated and the results are in accordance with the Brazilian legislation.

Fast sequential determination of antimony and lead in pewter alloys using high-resolution continuum source flame atomic absorption spectrometry

A simple method has been developed to determine antimony and lead in pewter alloy cups produced in Brazil, using fast sequential determination by high-resolution continuum source flame atomic absorption spectrometry. The samples were dissolved in HCl and H2O2, employing a cold finger system in order to avoid analyte losses. The main resonance line of lead at 217.001 nm and a secondary line of antimony at 212.739 nm were used. The limits of detection for lead and antimony were 0.02 and 5.7 mg L−1, respectively. The trueness of the method was established by recovery tests and comparing the results obtained by the proposed method with those obtained by inductively coupled plasma optical emission spectrometry. The results were compared using a students t-test and there was no significant difference at a 95% confidence interval. With the developed methods, it was possible to determine accurately antimony and lead in pewter samples. The lead concentration found in the analysed samples was around 1 mg g−1, which means that they are not lead free; however, the content was below the maximum allowed level of 5 mg g−1. The antimony content, which was found to be between 40 and 46 mg g−1, is actually of greater concern, as antimony is known to be potentially toxic already at very low concentrations, although there is no legislation yet for this element.

Multivariate optimization and validation of an analytical method for the determination of cadmium in wines employing ET AAS

, respectively, were obtained using a sample volume of 20 µL. The precision expressed as relative standard deviation (RSD %) was 0.30, 0.37 and 0.49% for wines with cadmium concentrations of 1.286, 0.266 and 0.356 µg L −1 , respectively. The accuracy of the new direct determination methodology applying ET AAS was assessed by comparison with an acid digestion methodology, also with determination by ET AAS, using five wine samples. The proposed method was applied for the determination of cadmium in 30 Brazilian wine samples. The cadmium content varied from 0.146 to 1.563 µg L −1 ; all these values are lower than the permissible maximum level stipulated by the International Organization of Vine and Wine (OIV) and also by Brazilian legislation, which is 10 µg L −1 .

Simultaneous determination of Mo and Ni in wine and soil amendments by HR-CS GF AAS

The use of high-resolution continuum-source graphite furnace atomic absorption spectrometry (HR-CS GF AAS), equipped with a linear charge-coupled device (CCD) array detector, makes simultaneous determination of more than one element possible. In this work, HR-CS GF AAS was used for the simultaneous determination of Mo (313.259 nm) and Ni (313.410 nm), for which two analytical methods were developed: direct solid sample analysis for soil amendments and direct sample injection for wine samples. For both these methods, a pyrolysis temperature of 1200 °C and an atomization temperature of 2650 °C were used. Aqueous standard solutions were used for calibration. The linear correlation coefficient was higher than 0.997 for the two analytes. Detection limits of 0.05 and 0.8 μg L−1 for wine samples and 0.04 and 0.60 mg kg−1 for soil amendments were found for Mo and Ni, respectively. To investigate the accuracy of the developed method, digested and undigested wine samples were evaluated with spike recovery values between 94% and 106%. For solid samples, three CRM were evaluated, and the values found for Mo were not significantly different from the certified ones; however, those for Ni were always too high. It was found that this was due to a direct line overlap of the Ni line with the Fe line. This effect was overcome by determining Fe using the unresolved analytical line doublet at 312.565/312.568 nm and subtracting this value from the total concentration (Ni + Fe) determined at 313.410 nm. Note that this interference was not observed in wine samples because of their low Fe concentration.

Determination of chromium and antimony in polymers from electrical and electronic equipment using high-resolution continuum source graphite furnace atomic absorption spectrometry

In the last few years, the European Union adopted two directives: the Waste Electrical and Electronic Equipment (WEEE) directive and the Restriction of Hazardous Substances (RoHS) directive. The RoHS directive had a major impact on the routine control of hazardous substances, including toxic trace metals in all kind of materials that are used in electrical and electronic equipment. This work proposes an analytical method for the determination of Cr and Sb in polymers from different electrical and electronic equipment using direct analysis of solid samples and high-resolution continuum source graphite furnace atomic absorption spectrometry with calibration against aqueous standards. Additional strategies are presented for reducing the sensitivity in order to cope with high analyte concentrations. The limit of detection was found to be 0.06 mg kg−1 for both analytes, Cr and Sb, and the characteristic mass was 62 pg for Cr and 35 pg for Sb. The trueness of the method has been assessed by analyzing a certified reference material of low-density polyethylene, and a good agreement with the certified values has been obtained. The precision of the method, expressed as relative standard deviation (RSD), was between 4 and 13% for chromium and 4 and 10% for antimony. The method is sensitive, and fast, and it does not require any sample preparation except grinding.