Quantitative mapping of trace elements in agate using LA-ICP-MS

Chan-Soo Park,Hyung Seon Shin,Hana Cho,Keewook Yi,Yoonsup Kim

doi:10.1186/s40543-015-0078-x

Abstract

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an optimized technique for the quantitative mapping of trace elements on geological materials. Agate is an aggregate of microcrystalline silica showing a variety of colorful bands due to the species and concentrations of transition metals and is thus an appropriate sample to test the availability, efficiency, and detection limit of LA-ICP-MS trace element mapping. Two fortification agate samples selected for elemental mapping are characterized by the colorful and bluish banding layers, respectively. The colorful agate sample consists mainly of two growth zones varying in color from pale orange-red brown to gray tones, whereas the blue agate sample simply shows alternating blue and white bands. Two different types of mineral inclusions, Fe oxide/hydroxide and hollandite (Ba(Mn4+ 6Mn3+ 2)O16), were identified in the inner and outer halves of the former sample, respectively. The distribution patterns of eight trace elements in these samples, including Al, Co, Cr, Cu, Fe, Mn, Ni, and Ti, were investigated, using both electron microprobe and LA-ICP-MS. Aluminum and Fe are the most abundant trace elements in both agate samples up to 5000 ppm although their concentrations in the colorful agate sample are an order of magnitude higher than those in the blue agate sample. The concentrations of other elements in the agate samples are several parts per million levels. The quantitative maps of the colorful agate sample have shown that Fe was mainly distributed in the inner half, but Al, Cu, and Mn in the outer half. In particular, Fe and Mn were primarily concentrated as small spots. On the other hand, the oscillatory zoning patterns are apparent in the quantitative maps of the blue agate sample, showing a correlative relationship between Al and Ti but an antithetic relationship between Al and Fe. The Al and Fe distribution patterns of the colorful agate sample are reproduced in the Al Kα and Fe Kα X-ray maps, but not clear in blue agate. Quantitative elemental maps using LA-ICP-MS are privileged to visualize trace elements distributions.

Highlights

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an optimized technique for the quantitative mapping of trace elements on geological materials
Qualitative mapping was carried out, using a Shimadzu 1600 electron microprobe equipped with wavelengthdispersive spectrometers (WDS) at the Jeonju branch of Korea Basic Science Institute (KBSI), by measuring intensities of the Al Kα, Co Kα, Cr Kα, Cu Kα, Fe Kα, Mn Kα, Ti Kα, and Ni Kα characteristic X-ray lines considered as potential chromophores in agate (Table 1)
The quantitative distribution maps of trace elements in two agate samples were acquired by a series of long line scan and a subsequent merging of line scans with Iolite software

Summary

Introduction

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an optimized technique for the quantitative mapping of trace elements on geological materials. Coupled plasma mass spectrometry (ICPMS) has become the most widely accepted analytical technique for simultaneously measuring a range of trace elements at variable concentration levels (Durrant 1999; Günther and Heinrich 1999; Günther et al 2000; Sylvester 2001a; Heinrich et al 2003). In addition to LA-ICP-MS, both ion and electron microprobes are commonly used for in situ analysis of trace elements (Müller et al 2003). LA-ICP-MS analyses combine the strength of the above techniques: relatively straightforward calibration procedures with a low detection limit. LAICP-MS has relatively poorer spatial resolution and requires relatively larger sampling volumes than both electron and ion microprobes (Woodhead et al 2007)

Methods

Results

Discussion

Conclusion