Determination of cadmium in sediments and in sewage sludge by slurry sampling electrothermal atomic absorption spectrometry using iridium as permanent modifier

Abstract

É proposto um procedimento para a determinação de Cd em sedimentos e em lodo de esgoto doméstico sob a forma de suspensões por espectrometria de absorção atômica com atomização eletrotérmica. As suspensões, 1 mg mL -1 , foram preparadas pela adição de solução 5% v/v de ácido nítrico à amostra moída com tamanho de partícula ≤ 50 µm, em banho de ultra-som. A homogeneidade das suspensões foi assegurada pela passagem de fluxo constante de argônio no recipiente do amostrador automático, antes da transferência de alíquota da suspensão para o interior do forno de grafite. Dois modificadores permanentes depositados sobre a plataforma de grafite pirolítico foram testados: Ru e Ir. Modificadores em solução foram também testados: Pd + Mg e fosfato, separadamente ou em conjunto com Mg. O tubo tratado com Ir foi utilizado devido a sua boa performance como modificador e também por razões práticas. Cerca de 80% do Cd é extraído para a fase aquosa da suspensão. Para testar a exatidão do método, três materiais certificados foram analisados: um sedimento marinho, um sedimento fluvial e lodo de esgoto de origem doméstica. As concentrações obtidas, usando-se calibração com soluções padrão aquosas preparadas no mesmo meio das suspensões, estão em concordância com os valores certificados para intervalo de confiança de 95%, após aplicação do teste Student-t. O limite de detecção (3σ) foi de 43 ng g -1 na amostra sólida e o desvio padrão relativo para o sedimento MESS-2 foi de 2,3% (n = 10).A procedure for the determination of Cd in sediment and sewage sludge as slurries by electrothermal atomic absorption spectrometry is proposed. The slurry, 1 mg mL -1 , was prepared by mixing sample ground to a particle size ≤ 50 µm with 5% v/v nitric acid in an ultrasonic bath. The homogeneity of the slurries was assured by passing a constant flow of argon into the autosampler cup, just before transferring an aliquot to the graphite furnace. Two permanent modifiers deposited on the platform were tested: Ru and Ir. Modifiers in solution were also tested: Pd plus Mg and phosphate alone or plus Mg. The Ir-treated tube was adopted due to its good performance as modifier and also for practical reasons. About 80% of Cd is extracted to the water phase of the slurry. To test the accuracy of the method, three certified materials were analyzed: a marine sediment, a river sediment and a domestic sewage sludge. The concentrations obtained, using calibration against aqueous standards prepared in the same medium as the slurries, are in agreement with the certified values, at a confidence level of 95%, according to the Student-t test. The limit of detection (3σ) was 43 ng g -1 in the solid sample and the relative standard deviation for the sediment MESS-2 was 2.3% (n = 10).Keywords: cadmium, slurry, ET AAS, modifier, sediment, sewage sludge IntroductionCadmium is a heavy metal, relatively rare and without known vital biological functions for human beings.However, it is quite toxic and its concentration in the environment, even if low, requires periodic control. C...

Atomic spectrometry update. Environmental analysis

“…A characteristic mass of 13.8 pg was obtained and the LOD for the proposed method was around 0.06 mg g 21 . Borges and co-workers 159 proposed an ETAAS procedure for the determination of Cd in sediment and sewage sludge slurries. Two permanent modifiers deposited on the platform were tested, Ru and Ir.…”

“…Using batch processing and iridium-treated graphite tubes, Moreda-Pineiro and co-workers reported methods for the determination of As, Bi and Se, 160 As, Bi, Ge, Hg and Se IV , 282 Hg 283 and Sn 284 in a variety of geological and environmental matrices. A similar analytical arrangement was used by a Brazilian research group to determine Cd 159 and As 150 in slurries of sediments, coal and fly ash by HG-ETAAS. Other studies employing slurry sampling measured Tl in soils and sediments, 158 Cr in fly ash 285 and Cr, Mo and V in soils and sediments.…”

“…142 On-line flow-injection methods for the separation and preconcentration of analytes in microcolumns coupled to FAAS have been proposed recently for the determination of Ag in ore samples 314 and Cr in sediments. 315 As noted in Section 4.2.1.2, there is much active interest in the introduction of solid samples as slurries directly into graphite furnaces 157,159,166,285,316 or via cold vapour/hydride generation systems. 150,160,[282][283][284] The use of solid sample graphite furnace AAS has also been proposed for determining the amount of As 297 and Hg 114 remaining in the solid residues left after sequential leaching of sediments using the BCR threestep extraction procedure.…”

Determination of As, Cd, Pb and Tl in coal by electrothermal vaporization inductively coupled plasma mass spectrometry using slurry sampling and external calibration against aqueous standards

“…A few problems were, however, associated with these procedures, such as the adherence of particulate matter on the capillary tip of the autosampler when using stabilizing agents [13], adherence of particles to the magnetic stirring bar [19] and the difficulties associated to the use of autosamplers with vortex mixing [13], resulting mainly in repeatability problems. More efficient methods involve the use of argon [20,21] and ultrasound probes [22][23][24]. A limited number of publications dealt with the analysis of coal slurries by ETV-ICP-MS [23,25] and graphite furnace atomic absorption spectrometry (GF AAS) [26][27][28].…”