Álvaro T. Duarte

Slurry Sampling—An Analytical Strategy for the Determination of Metals and Metalloids by Spectroanalytical Techniques

Abstract This article critically overviews the state-of-the-art of slurry sampling as an approach for the minimization of sample preparation prior to the determination of metals and metalloids in complex matrices by spectroanalytical techniques. Relevant factors involved in the optimization of slurry-based analytical procedures and the dependence of the quality of the results on the calibration method selected are discussed in detail. The advantages and limitations compared to solid sampling for the analysis of solid matrices are highlighted and discussed. Analytical applications of slurry sampling reported in the literature emphasizing publications between 2004 and 2009 are comprehensively compiled covering detection by flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ET-AAS), cold vapor atomic absorption spectrometry (CV-AAS), hydride generation atomic absorption spectrometry (HG-AAS), hydride generation atomic fluorescence spectrometry (HG-AFS), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS).

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).

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.

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.

Development of analytical methods for the determination of copper and manganese in infant formula using high resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

Two fast, simple and reliable methods for the determination of Cu and Mn in infant formula composed of different types of raw materials (rice, oats, bovine milk and soybean) were developed using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) and direct solid sample analysis. All measurements were carried out without any chemical modifier and with aqueous standard solutions for calibration. The optimum pyrolysis temperature was 1300 °C for both analytes, and atomization temperatures were 2300 °C and 2100 °C for Cu and Mn, respectively. The characteristic mass was 8.0 pg for both analytes; the limits of detection and quantification were 0.003 μg g−1 and 0.01 μg g−1, respectively, for Cu, based on a sample mass of 3.0 mg, and 0.01 μg g−1 and 0.04 μg g−1, respectively, for Mn, based on a sample mass of 1.0 mg. The concentrations obtained ranged from 1.3 to 6.8 μg g−1 for Cu and 0.7 to 17.2 μg g−1 for Mn. The accuracy of the methods was evaluated using the certified reference material NIST SRM 1568a (rice flour) and the results presented no significant difference between the certified and found concentrations. The methods are sensitive, simple and do not require any sample pretreatment besides milling and homogenization of samples.