Evaluation of sample preparation focusing on the quantification of Cd and Pb through laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to tree rings and speleothems

• Grant number: 18/18648-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2018
• End date: January 31, 2019
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Analytical Chemistry
• Agreement: NSF and NSF's Partnership for International Research and Education (PIRE)
• Principal Investigator: Marco Aurelio Zezzi Arruda
• Grantee: Caio Henrique dos Santos Alves
• Host Institution: Instituto de Química (IQ). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Associated research grant: 17/50085-3 - PIRE: climate research education in the Americas using tree-ring speleothem examples (PIRE-CREATE), AP.TEM

Abstract

This Scientific Initiation project emphasizes the potentialities of the LA-ICP-MS focusing on the sample preparation for quantitative analysis of Cd and Pb from tree rings and speleothems with the aim of characterizing evidence of past extreme flooding events. Briefly, the LA-ICP-MS technique is based on the use of a laser delivering enough energy to the surface of the sample, being able to ablate the material. The Nd:YAG laser wavelengths (at 213 or 266 nm) have enough energy for ablating and vaporizing the samples, being the gaseous phase transported from the ablation chamber to the ICP torch through argon gas (or others. Then, the LA-ICP-MS is a powerful technique, which can be applied for sort of samples, if accurately optimized sample preparation process and the laser and ICP-MS parameters. Additionally, when employed quantitative approaches, the concentrations can also be estimated at ¼m scale, allowing in loco quantitative analysis. Regarding the experimental, the conditions pointed out here will be generals, and proposed through our expertise and the literature. It is obvious that though the development of such project, they can be modified, in order to adequate our work with the proposed studies. After drying, the samples will be prepared by breaking the particles into a fine powder through different mills (pestle and mortar, ball mill and cryogenic mill). After homogenizing the samples, a pressure machine will be used for producing the sample pellets. All variable involved in the sample milling will be optimized, such as time, speed and temperature of milling. Additionally, the ICP-MS conditions will be evaluated as well as those involved in the ablation process, such as plasma radiofrequency power (900 - 1400 W), nebulization gas (0.9 - 1.2 L/min) and auxiliary gas (1.4 - 2.0 L/min), gases used in the reaction and collision cells (O2, CH4 or H2), which is analyte-dependent as well as the interferences observed, laser intensity (30-60%), frequency (10-20 Hz), spot size (55-80 µm). The 12C will be used as internal standard, for compensating possible instrumental oscillations, which affect the precision of the results. In terms of quantitative analysis, to the pellets obtained previously, a spiked solution will be added to perform the calibration curve. This kind of strategy minimizes the interferences arising from the sample matrix. Two aspects are still important to note: (I) the validation of the results by ICP-MS after microwave decomposition is mandatory in this case, and (II) standards and samples should be placed together in the ablation chamber.