Determination of trace elements by inductively coupled plasma mass spectrometry of biomass and fuel oil reference materials using milligram sample sizes

Abstract

Most of the analytical techniques used to quantify elements associated with solid samples suffer from high detection limits and cannot be used for trace elements in biomass samples, particularly when only 20 mg are available for analysis. Inductively coupled plasma mass spectrometry (ICP-MS) can achieve detection limits of parts-per-trillion with liquid sample introduction by solution nebulisation. This technique was therefore tested with two standard biomass reference materials: oriental tobacco leaves and cabbage leaves. Two preparations successfully used on coal standards were used to digest the solid samples: a total digestion method (wet ashing digestion) and a partial leaching (microwave extraction). The concentrations of up to seventeen elements (As, Ba, Be, Cd, Co, Cr, Cu, Ga, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn) were measured after the two preparations. The accuracy and sensitivity of the measurements improved when the dilution factor decreased from 5000 to 1000 and to 500. Since the proportion of mineral matter in biomass samples is small (5%), the microwave digestion extracted elements that are generally not completely extracted from coal samples (e.g. Sb). However, some trace element concentrations were below the limit of quantification after microwave extraction, even with a reduced dilution factor (As, Se and Mo) and could not be quantified. A fuel oil was also digested. The trace element concentrations were very low (between 28 and 0.1 microgram g(-1)) but acceptable results were obtained by applying a dilution factor of 100. Only six elements in the fuel oil (As, Ba, Co, Ni, Se and V) had certified or indicated values. Factors affecting the accuracy and sensitivity of the analyses are discussed. The reproducibility of analysis of the tobacco leaf standard was checked over a period of nine months by both digestion methods. The wet ashing method gave acceptable reproducibility for Ba, Cd, Co, Cu, Ga, Mn, Mo, Ni, Pb, V and Zn but poor precision for Cr, Se and Sn and showed evidence of residual chloride interference for As. The microwave extraction gave good reproducibility for As, Ba, Cd, Co, Cr, Cu, Mo, Ni and Zn but poor precision for Se and low recoveries for Ga, Mn, Sn and V. In spite of the small quantities of material analysed, it proved possible to determine the trace elements at levels down to 0.1 microgram g(-1) in the reference materials.

The nutrient content of three edible plants of the Republic of Niger

“…With regard to minerals and trace elements, the cabbage leaves from Niger had levels of copper, manganese, lead, arsenic, cadmium, chromium and zinc that were comparable to those reported by Lachas et al (2000); however, the amount of molybdenum we found in B. oleracea was 10-20 times higher than they reported. Likewise, the calcium content of B. oleracea we report herein (27.4 mg/g dry weight) is also 10-20 times higher than the calcium value reported recently by Barta and Tibbitts (2000) (1.0-2.1 mg/g dry weight).…”

Identification of organically associated trace elements in wood and coal by inductively coupled plasma mass spectrometry

“…The operating parameters of the instrument were as described previously 36,. 42 Quantification was obtained for all the elements by external standard calibration curves drawn through the origin and three calibration points (10, 20 and 30 µgL −1 ,) using multielement 2 M HNO 3 aqueous standard solutions. Isotopes used in this work were: 75 As, 137 Ba, 9 Be, 111 Cd, 52 Cr, 59 Co, 63 Cu, 71 Ga, 55 Mn, 95 Mo, 60 Ni, 208 Pb, 121 Sb, 82 Se, 51 V and 66 Zn.…”

Analyse de métaux traces dans les produits pétroliers, état de l'art

“…La destruction en système ouvert a le désavantage de ne pas être quantitatif pour certains éléments pouvant être perdus au cours de la minéralisation. Lachas et al (2000) compare les résultats obtenus sur une huile certifiée après une minéralisa-tion par voie humide à l'acide sulfurique et une extraction par micro-onde sur des quantités de matière de 20 mg. Bien que l'extraction ne permette pas de s'assurer que la totalité des métaux présents soit disponible, les résultats obtenus par cette voie sont meilleurs que ceux obtenus en mode humide, surtout pour les éléments Cr, Cu, Mo et Sn sous-dosés en mode humide et donc partiellement perdus lors de la minéra-lisation. Une dernière alternative pour passer les éléments d'intérêt en phase aqueuse consiste en la minéralisation en bombe de combustion et récupération des produits de combustion dans une solution basique.…”

“…Cette limitation peut s'avérer être un avantage lorsque le produit à analyser n'est disponible qu'en très faible quantité. Ainsi, Lachas et al (2000), Richaud et al (2000) et Wondimu et al (2000) ont utilisé la méthode sur différents produits organiques de la chaîne pétrolière et avec des masses oscillant entre 3 et 250 mg.…”