LA-ICP-MS for Trace Element Mapping of Agate

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Inductively coupled plasma mass spectrometry (ICP-MS) is a widely used method for quantifying trace elements at variable concentrations.

Laser ablation (LA) is a powerful technique for the solid sampling of geological materials, particularly when an LA system is attached to ICP-MS (LA-ICP-MS).

LA-ICP-MS therefore represents an optimized method for quantitatively mapping trace elements on geological samples.

The quantitative mapping of these elements is possible with other techniques, but LA-ICP-MS is the only method that performs at low detection limits across a wide range of elements and with an acquisition time that is relatively short.

At the Korea Basic Science Institute and Chungbuk National University, researchers have used two agate samples to evaluate the use of LA-ICP-MS in trace element mapping. One of the samples was a colorful agate sample and the other was a blue sample.

Agate, which is a cryptocrystalline form of silica, was chosen because it displays rhythmic color banding as a result of the transition metals incorporated during its formation by chemical precipitation. The shade of colors is also altered when the elements work in combination.

Colorful agate is mainly made up of two growth zones; an inner half with colors ranging from a pale orange through to red-brown and an outer half mainly made up of gray bands. The blue sample basically consists of blue and white bands.

Figure 1. Two fortification agate samples. They are oval in shape with approximately 50-mm-long major axes and are characterized by a colorful and b bluish banding layers, respectively. The former varies in color, from gray through orange and red to brown towards the center. On the other hand, the latter consists of bluish chalcedony alternating with white microcrystalline quartz. Open rectangles represent the areas of ablation

As reported in the Journal of Analytical Science and Technology, Chan-Soo Park and team used Iolite software to generate quantitative distribution maps of the trace elements. The maps showed trace element fluctuations and concentrations in the samples that could not be seen using conventional spot analysis.

In the colorful sample, aluminium and iron were the most abundant elements, present in up to 5000 parts per million (ppm) and 4000 ppm, respectively, whereas only minor amounts of copper, cobalt and manganese were present, in 200, 5 and 3 ppm, respectively. Quantitative maps showed that the presence of aluminium, characterized by grayish-colored bands, was particularly concentrated in the outer half and generally not present in the inner half. Iron-rich bands and small concentrated iron spots were seen in the inner half. The distribution of copper and manganese was similar to aluminium, although mainly concentrated as small, spot-shaped inclusions.

In the blue sample, aluminium and iron were again the most abundant elements, present at up to 400 and 100 ppm, respectively. Manganese and titanium were also present, but in much smaller amounts, at less than 15 ppm and 1 ppm, respectively. Quantitative maps showed oscillatory zoning patterns for the elements and that aluminium distribution was consistent with that of titanium, but antithetic to that of iron.

For the colorful sample, qualitative Al Kα and Fe Kα X-ray maps reproduced trace element distribution patterns that were similar to the quantitative maps, but they were not clear for the blue sample.

Park and colleagues say that the findings “clearly demonstrate that LA-ICP-MS can provide valuable data for interpretations of compositional variations in association with microstructures, chemical/physical phase boundaries, and geological and environmental heterogeneous samples.”

You can read the entire article here.

This information has been sourced, reviewed and adapted from materials provided by SpingerOpen.