An Evaluation of the Effects of Primary and Cross-Contamination during the Preparation of Rock Powders for Chemical Determinations

Autor(es)

Sertek, Jose P. ^[1] ; Andrade, Sandra ^[1] ; Ulbrich, Horstpeter H. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: GEOSTANDARDS AND GEOANALYTICAL RESEARCH; v. 39, n. 3, p. 381-397, SEP 2015.
• Citações Web of Science: 2

Resumo

Quartz crystals from the Batatal site, Minas Gerais, southern Brazil, were used to determine quantitatively primary contamination when submitting the samples to milling processes. Crushing devices used were a primary steel jaw crusher (br1), a secondary tungsten carbide (WC) crusher (br2) and a hydraulic press with stainless steel plates (pr). Fragments with suitable sizes were then ground in different Fritsch planetary mills, equipped with agate, WC and chromium-steel rings for 7, 4 and 3min, respectively. Solutions of the powders were analysed initially with the TotalQuant method in a quadrupole ICP-MS instrument, providing semi-quantitative results for seventy-five elements. Contamination from crushers and mills was visible in major and minor elements such as Fe, Mn and Ti, and noticeable in trace elements such as Cr, Co, Ni, Cu and also V, Zr, Sc; significant contamination was observed from W, Mo, Co, Ta and Nb (mainly by use of the WC devices). Little or no contamination was observed for Pb, REE, Sr and Rb, elements that are important in routine isotopic determinations. Cross-contamination was tested by grinding either a granite or a basalt sample, followed by conventional cleaning with mica-free quartz sand, before the working quartz powder was prepared. Les cristaux de quartz du site de Batatal, Minas Gerais (sud du Bresil), ont ete utilises pour determiner quantitativement la contamination primaire lorsque des echantillons sont soumis a des procedes de broyage. Les dispositifs de broyage utilises ont ete un concasseur primaire a machoires d'acier (br1), un concasseur (br2) secondaire en carburede tungstene (WC) et une presse hydraulique avec des plaques d'acier inoxydable (pr). Les fragments ayant des tailles appropriees ont ensuite ete broyes dans differents broyeurs planetaires Fritsch, equipes d'anneaux en agate, en WC et en acier chrome pendant respectivement 7, 4 et 3 min. Des solutions derivees de ces poudres ont ete initialement analysees avec la methodeTotalQuant(TM) en utilisant un instrument quadripole ICP-MS, offrant des resultats semi-quantitatifs pour soixante-quinze elements. La contamination par les concasseurs et broyeurs est notable pour les elements majeurs et mineurs tels que Fe, Mn et Ti, et appreciable pour les elements traces tels que Cr, Co, Ni, Cu et aussi V, Zr, et Sc; une contamination significative a ete observee pour W, Mo, Co, Ta et Nb (principalement avec l'utilisation des dispositifs en WC). Peu ou pas de contamination a ete observee pour Pb, REE, Sr et Rb, des elements qui sont importants pour les determinations isotopiques de routine. La contamination croisee a ete testee par le broyage d'un echantillon soit de granite soit de basalte, suivi par un nettoyage classique avec du sable de quartz depourvu de mica, avant que la poudre de quartz utilisee pour ce travail ne soit preparee. (AU)

• Processo FAPESP: 12/06082-6 - A província magmática Paraná-Etendeka no Brasil: relações temporais e petrológicas entre o magmatismo toleítico e alcalino e suas implicações geodinâmicas
• Beneficiário: Excelso Ruberti
• Modalidade de apoio: Auxílio à Pesquisa - Temático